[gnu-emacs-elpa] / packages / gnugo / gnugo.el

;;; gnugo.el --- play GNU Go in a buffer

;; Copyright (C) 2014  Free Software Foundation, Inc.

;; Author: Thien-Thi Nguyen <ttn@gnu.org>
;; Version: 2.3.1
;; Package-Requires: ((ascii-art-to-unicode "1.5"))

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; Playing
;; -------
;;
;; This file provides the command `gnugo' which allows you to play the game of
;; go against the external program "gnugo" (http://www.gnu.org/software/gnugo)
;; in a dedicated Emacs buffer, or to resume a game in progress.  NOTE: In
;; this file, to avoid confusion w/ elisp vars and funcs, we use the term "GNU
;; Go" to refer to the process object created by running the external program.
;;
;; At the start of a new game, you can pass additional command-line arguments
;; to GNU Go to specify level, board size, color, komi, handicap, etc.  By
;; default GNU Go plays at level 10, board size 19, color white, and zero for
;; both komi and handicap.
;;
;; To play a stone, move the cursor to the desired vertice and type `SPC' or
;; `RET'; to pass, `P' (note: uppercase); to quit, `q'; to undo one of your
;; moves (as well as a possibly intervening move by GNU Go), `u'.  To undo
;; back through an arbitrary stone that you played, place the cursor on a
;; stone and type `U' (note: uppercase).  Other keybindings are described in
;; the `gnugo-board-mode' documentation, which you may view with the command
;; `describe-mode' (normally `C-h m') in that buffer.  The buffer name shows
;; the last move and who is currently to play.  Capture counts and other info
;; are shown on the mode line immediately following the major mode name.
;;
;; While GNU Go is pondering its next move, certain commands that rely on its
;; assistence will result in a "still waiting" error.  Do not be alarmed; that
;; is normal.  When it is your turn again you may retry the command.  In the
;; meantime, you can use Emacs for other tasks, or start an entirely new game
;; with `C-u M-x gnugo'.  (NOTE: A new game will slow down all games. :-)
;;
;; If GNU Go should crash during a game the mode line will show "no process".
;; Please report the event to the GNU Go maintainers so that they can improve
;; the program.
;;
;;
;; Meta-Playing (aka Customizing)
;; ------------------------------
;;
;; Customization is presently limited to
;;   vars:            `gnugo-program'
;;                    `gnugo-animation-string'
;;                    `gnugo-mode-line'
;;                    `gnugo-X-face' `gnugo-O-face' `gnugo-grid-face'
;;                    `gnugo-xpms'
;;   normal hooks:    `gnugo-board-mode-hook'
;;                    `gnugo-post-move-hook'
;;   and the keymap:  `gnugo-board-mode-map'
;;
;; The variable `gnugo-xpms' is a special case.  To set it you need to load
;; gnugo-xpms.el (http://www.emacswiki.org) or some other library w/ congruent
;; interface.

;;; Code:

(eval-when-compile (require 'cl))       ; use the source luke!
(require 'ascii-art-to-unicode)         ; for `aa2u'
(require 'time-date)                    ; for `time-subtract'

;;;---------------------------------------------------------------------------
;;; Political arts

(defconst gnugo-version "2.3.1"
  "Version of gnugo.el currently loaded.
This follows a MAJOR.MINOR.PATCH scheme.")

;;;---------------------------------------------------------------------------
;;; Variables for the uninquisitive programmer

(defvar gnugo-program "gnugo"
  "Command to start an external program that speaks GTP, such as \"gnugo\".
The value may also be in the form \"PROGRAM OPTIONS...\" in which case the
the command `gnugo' will prefix OPTIONS in its default offering when it
queries you for additional options.  It is an error for \"--mode\" to appear
in OPTIONS.

For more information on GTP and GNU Go, feel free to visit:
http://www.gnu.org/software/gnugo")

(defvar gnugo-board-mode-map nil
  "Keymap for GNUGO Board mode.")

(defvar gnugo-frolic-mode-map nil
  "Keymap for GNUGO Frolic mode.")

(defvar gnugo-board-mode-hook nil
  "Hook run when entering GNUGO Board mode.")

(defvar gnugo-inhibit-refresh nil
  "Used in `gnugo-post-move-hook'.")

(defvar gnugo-post-move-hook nil
  "Normal hook run after a move and before the board is refreshed.
Hook functions can prevent the call to `gnugo-refresh' by evaluating:
  (setq gnugo-inhibit-refresh t)
Initially, when `run-hooks' is called, the current buffer is the GNUGO
Board buffer of the game.  Hook functions that switch buffers must take
care not to call (directly or indirectly through some other function)
`gnugo-put' or `gnugo-get' after the switch.")

(defvar gnugo-animation-string
  (let ((jam "*#") (blink " #") (spin "-\\|/") (yada "*-*!"))
    (concat jam jam jam jam jam
            ;; "SECRET MESSAGE HERE"
            blink blink blink blink blink blink blink blink
            ;; Playing go is like fighting ignorance: when you think you have
            ;; surrounded something by knowing it very well it often turns
            ;; out that in the time you spent deepening this understanding,
            ;; other areas of ignorance have surrounded you.
            spin spin spin spin spin spin spin spin spin
            ;; Playing go is not like fighting ignorance: what one person
            ;; knows many people may come to know; knowledge does not build
            ;; solely move by move.  Wisdom, on the other hand...
            yada yada yada))
  "String whose individual characters are used for animation.
Specifically, the commands `gnugo-worm-stones' and `gnugo-dragon-stones'
render the stones in their respective result groups as the first character
in the string, then the next, and so on.")

(defvar gnugo-mode-line "~b ~w :~m :~u"
  "A `mode-line-format'-compliant value for GNUGO Board mode.
If a single string, the following special escape sequences are
replaced with their associated information:
  ~b,~w  black,white captures (a number)
  ~p     current player (black or white)
  ~m     move number
  ~t     time waiting for the current move
  ~u     time taken for the Ultimate (most recent) move
The times are in seconds, or \"-\" if that information is not available.
For ~t, the value is a snapshot, use `gnugo-refresh' to update it.")

(defvar gnugo-X-face 'font-lock-string-face
  "Name of face to use for X (black) stones.")

(defvar gnugo-O-face 'font-lock-builtin-face
  "Name of face to use for O (white) stones.")

(defvar gnugo-grid-face 'default
  "Name of face to use for the grid (A B C ... 1 2 3 ...).")

;;;---------------------------------------------------------------------------
;;; Variables for the inquisitive programmer

(defconst gnugo-font-lock-keywords
  '(("X" . gnugo-X-face)
    ("O" . gnugo-O-face))
  "Font lock keywords for `gnugo-board-mode'.")

(defvar gnugo-option-history nil)

(defvar gnugo-state nil)                ; hint: C-c C-p

(eval-when-compile
  (defvar gnugo-xpms nil))

(defvar gnugo-frolic-parent-buffer nil)
(defvar gnugo-frolic-origin nil)

;;;---------------------------------------------------------------------------
;;; Support functions

(defsubst gnugo--mkht (&rest etc)
  (apply 'make-hash-table :test 'eq etc))

(defsubst gnugo--compare-strings (s1 beg1 s2 beg2)
  (compare-strings s1 beg1 nil s2 beg2 nil))

(defun gnugo-put (key value)
  "Associate move/game/board-specific property KEY with VALUE.

There are many properties, each named by a keyword, that record and control
how gnugo.el manages each game.  Each GNUGO Board buffer has its own set
of properties, stored in the hash table `gnugo-state'.  Here we document
some of the more stable properties.  You may wish to use them as part of
a `gnugo-post-move-hook' function, for example.  Be careful to preserve
the current buffer as `gnugo-state' is made into a buffer-local variable.
NOTE: In the following, \"see foo\" actually means \"see foo source or
you may never really understand to any degree of personal satisfaction\".

 :proc -- subprocess named \"gnugo\", \"gnugo<1>\" and so forth

 :diamond -- the part of the subprocess name after \"gnugo\", may be \"\"

 :game-over -- nil until game over at which time its value is set to
               the alist `((live GROUP ...) (dead GROUP ...))'

 :sgf-collection -- after a `loadsgf' command, entire parse tree of file,
                    a simple list of one or more gametrees, updated in
                    conjunction w/ :sgf-gametree and :monkey

 :sgf-gametree -- one of the gametrees in :sgf-collection

 :monkey -- vector of two elements:
            MEM, a pointer to one of the branches in the gametree;
            BIDX, the index of the \"current branch\"

 :gnugo-color -- either \"black\" or \"white\"
 :user-color
 :last-mover

 :last-waiting  -- seconds and time value, respectively; see `gnugo-push-move'
 :waiting-start

 :black-captures -- these are strings since gnugo.el doesn't do anything
 :white-captures    w/ the information besides display it in the mode line;
                    gory details in functions `gnugo-propertize-board-buffer'
                    and `gnugo-merge-showboard-results' (almost more effort
                    than they are worth!)

 :display-using-images -- XPMs, to be precise; see functions `gnugo-yy',
                          `gnugo-toggle-image-display' and `gnugo-refresh',
                          as well as gnugo-xpms.el (available elsewhere)

 :all-yy -- list of 46 keywords used as the `category' text property
            (so that their plists, typically w/ property `display' or
            `do-not-display') are consulted by the Emacs display engine;
            46 = 9 places * (4 moku + 1 empty) + 1 hoshi; see functions
            `gnugo-toggle-image-display', `gnugo-yy' and `gnugo-yang'

 :lparen-ov -- overlays shuffled about to indicate the last move; only
 :rparen-ov    one is used when displaying using images

 :last-user-bpos -- board position; keep the hapless human happy

As things stabilize probably more info will be added to this docstring."
  (declare (indent 1))
  (puthash key value gnugo-state))

(defun gnugo-get (key)
  "Return the move/game/board-specific value for KEY.
See `gnugo-put'."
  (gethash key gnugo-state))

(defsubst gnugo--tree-mnum (tree)
  (aref tree 1))

(defsubst gnugo--tree-ends (tree)
  (aref tree 0))

(defsubst gnugo--set-tree-ends (tree ls)
  (aset tree 0 (apply 'vector ls))
  (gnugo--tree-ends tree))

(defun gnugo--root-node (&optional tree)
  (aref (or tree (gnugo-get :sgf-gametree))
        2))

(defun gnugo-describe-internal-properties ()
  "Pretty-print `gnugo-state' properties in another buffer.
Handle the big, slow-to-render, and/or uninteresting ones specially."
  (interactive)
  (let ((buf (current-buffer))
        (d (gnugo-get :diamond))
        acc)
    (loop for key being the hash-keys of gnugo-state
          using (hash-values val)
          do (push (cons key
                         (case key
                           ((:xpms :local-xpms)
                            (format "hash: %X (%d images)"
                                    (sxhash val)
                                    (length val)))
                           (:sgf-collection
                            (length val))
                           (:sgf-gametree
                            (list (hash-table-count
                                   (gnugo--tree-mnum val))
                                  (gnugo--root-node val)
                                  (gnugo--tree-ends val)))
                           (:monkey
                            (let ((mem (aref val 0)))
                              (list (aref val 1)
                                    (car mem))))
                           (t val)))
                   acc))
    (switch-to-buffer (get-buffer-create
                       (format "%s*GNUGO Board Properties*"
                               (gnugo-get :diamond))))
    (erase-buffer)
    (emacs-lisp-mode)
    (setq truncate-lines t)
    (save-excursion
      (pp acc
          (current-buffer))
      (goto-char (point-min))
      (let ((rx (format "overlay from \\([0-9]+\\).+\n%s\\s-+"
                        (if (string= "" d)
                            ".+\n"
                          ""))))
        (while (re-search-forward rx (point-max) t)
          (let ((pos (get-text-property (string-to-number (match-string 1))
                                        'gnugo-position buf)))
            (delete-region (+ 2 (match-beginning 0)) (point))
            (insert (format " %S" pos))))))
    (message "%d properties" (length acc))))

(defun gnugo-board-buffer-p (&optional buffer)
  "Return non-nil if BUFFER is a GNUGO Board buffer."
  (eq 'gnugo-board-mode
      (buffer-local-value
       'major-mode
       (or buffer (current-buffer)))))

(defun gnugo-board-user-play-ok-p (&optional buffer)
  "Return non-nil if BUFFER is a GNUGO Board buffer ready for a user move."
  (with-current-buffer (or buffer (current-buffer))
    (and gnugo-state (not (gnugo-get :waitingp)))))

(defsubst gnugo--blackp (string)
  (string= "black" string))

(defun gnugo-other (color)
  (if (gnugo--blackp color) "white" "black"))

(defun gnugo-gate (&optional in-progress-p)
  (unless (gnugo-board-buffer-p)
    (user-error "Wrong buffer -- try M-x gnugo"))
  (unless (gnugo-get :proc)
    (user-error "No \"gnugo\" process!"))
  (when (gnugo-get :waitingp)
    (user-error "Not your turn yet -- please wait for \"\(%s to play\)\""
                (gnugo-get :user-color)))
  (when (and in-progress-p (gnugo-get :game-over))
    (user-error "Sorry, game over")))

(defun gnugo-sentinel (proc string)
  (let ((status (process-status proc)))
    (when (memq status '(exit signal))
      (let ((buf (process-buffer proc)))
        (when (buffer-live-p buf)
          (with-current-buffer buf
            (setq mode-line-process
                  (list " [%s ("
                        (propertize (car (split-string string))
                                    'face 'font-lock-warning-face)
                        ")]"))
            (when (eq proc (gnugo-get :proc))
              (gnugo-put :proc nil))))))))

(defun gnugo--begin-exchange (proc filter line)
  (declare (indent 2))                  ; good time, for a rime
                                        ; nice style, for a wile...
  (set-process-filter proc filter)
  (process-send-string proc line)
  (process-send-string proc "\n"))

(defun gnugo--q (fmt &rest args)
  "Send formatted command \"FMT ARGS...\"; wait for / return response.
The response is a string whose first two characters indicate the
status of the command.  See also `gnugo-query'."
  (when (gnugo-get :waitingp)
    (user-error "Sorry, still waiting for %s to play"
                (gnugo-get :gnugo-color)))
  (let ((proc (gnugo-get :proc)))
    (process-put proc :incomplete t)
    (process-put proc :srs "")          ; synchronous return stash
    (gnugo--begin-exchange
        proc (lambda (proc string)
               (let ((full (concat (process-get proc :srs)
                                   string)))
                 (process-put proc :srs full)
                 (unless (numberp (gnugo--compare-strings
                                   full (max 0 (- (length full)
                                                  2))
                                   "\n\n" nil))
                   (process-put proc :incomplete nil))))
      (if (null args)
          fmt
        (apply #'format fmt args)))
    (while (process-get proc :incomplete)
      (accept-process-output proc 30))
    (prog1 (substring (process-get proc :srs) 0 -2)
      (process-put proc :srs ""))))

(defun gnugo-query (message-format &rest args)
  "Send GNU Go a command formatted with MESSAGE-FORMAT and ARGS.
Return a string that omits the first two characters (corresponding
to the status indicator in the Go Text Protocol).  Use this function
when you are sure the command cannot fail."
  (substring (apply 'gnugo--q message-format args)
             2))

(defun gnugo-lsquery (message-format &rest args)
  (split-string (apply 'gnugo-query message-format args)))

(defsubst gnugo--count-query (fmt &rest args)
  (length (apply 'gnugo-lsquery fmt args)))

(defsubst gnugo--root-prop (prop &optional tree)
  (cdr (assq prop (gnugo--root-node tree))))

(defun gnugo--set-root-prop (prop value &optional tree)
  (let* ((root (gnugo--root-node tree))
         (cur (assq prop root)))
    (if cur
        (setcdr cur value)
      (push (cons prop value)
            (cdr (last root))))))

(defun gnugo--play-stone (color pos-or-PASS)
  (let ((accept (gnugo--q (format "play %s %s" color pos-or-PASS))))
    (unless (= ?= (aref accept 0))
      (user-error "%s" accept))))

(defsubst gnugo--user-play-stone (pos-or-PASS)
  (gnugo--play-stone (gnugo-get :user-color) pos-or-PASS))

(defun gnugo-goto-pos (pos)
  "Move point to board position POS, a letter-number string."
  (goto-char (point-min))
  (forward-line (- (1+ (gnugo-get :SZ))
                   (string-to-number (substring pos 1))))
  (forward-char 1)
  (forward-char (+ (if (= 32 (following-char)) 1 2)
                   (* 2 (- (let ((letter (aref pos 0)))
                             (if (> ?I letter)
                                 letter
                               (1- letter)))
                           ?A)))))

(defun gnugo-f (frag)
  (intern (format ":gnugo-%s%s-props" (gnugo-get :diamond) frag)))

(defun gnugo-yang (c)
  (cdr (assq c '((?+ . hoshi)
                 (?. . empty)
                 (?X . (bmoku . bpmoku))
                 (?O . (wmoku . wpmoku))))))

(defun gnugo-yy (yin yang &optional momentaryp)
  (gnugo-f (format "%d-%s"
                   yin (cond ((and (consp yang) momentaryp) (cdr yang))
                             ((consp yang) (car yang))
                             (t yang)))))

(defun gnugo-toggle-image-display ()
  (unless (and (fboundp 'display-images-p) (display-images-p))
    (user-error "Display does not support images, sorry"))
  (require 'gnugo-xpms)
  (unless (and (boundp 'gnugo-xpms) gnugo-xpms)
    (user-error "Could not load `gnugo-xpms', sorry"))
  (let ((fresh (or (gnugo-get :local-xpms) gnugo-xpms)))
    (unless (eq fresh (gnugo-get :xpms))
      (gnugo-put :xpms fresh)
      (gnugo-put :all-yy nil)))
  (let* ((new (not (gnugo-get :display-using-images)))
         (act (if new 'display 'do-not-display)))
    (mapc (lambda (yy)
            (setcar (symbol-plist yy) act))
          (or (gnugo-get :all-yy)
              (gnugo-put :all-yy
                (prog1 (mapcar (lambda (ent)
                                 (let* ((k (car ent))
                                        (yy (gnugo-yy (cdr k) (car k))))
                                   (setplist yy `(not-yet ,(cdr ent)))
                                   yy))
                               (gnugo-get :xpms))
                  (let ((imul (image-size (get (gnugo-yy 5 (gnugo-yang ?+))
                                               'not-yet))))
                    (gnugo-put :w-imul (car imul))
                    (gnugo-put :h-imul (cdr imul)))))))
    (setplist (gnugo-f 'ispc) (and new '(display (space :width 0))))
    (gnugo-put :highlight-last-move-spec
      (if new
          '((lambda (p)
              (get (gnugo-yy (get-text-property p 'gnugo-yin)
                             (get-text-property p 'gnugo-yang)
                             t)
                   'display))
            0 delete-overlay)
        (gnugo-get :default-highlight-last-move-spec)))
    ;; a kludge to be reworked another time perhaps by another gnugo.el lover
    (dolist (group (cdr (assq 'dead (gnugo-get :game-over))))
      (mapc 'delete-overlay (cdar group))
      (setcdr (car group) nil))
    (gnugo-put :wmul (if new (gnugo-get :w-imul) 1))
    (gnugo-put :hmul (if new (gnugo-get :h-imul) 1))
    (gnugo-put :display-using-images new)))

(defun gnugo-toggle-grid ()
  "Turn the grid around the board on or off."
  (interactive)
  (funcall (if (memq :nogrid buffer-invisibility-spec)
               'remove-from-invisibility-spec
             'add-to-invisibility-spec)
           :nogrid)
  (save-excursion (gnugo-refresh)))

(defun gnugo-propertize-board-buffer ()
  (erase-buffer)
  (insert (substring (gnugo--q "showboard") 3))
  (let* ((grid-props (list 'invisible :nogrid
                           'font-lock-face gnugo-grid-face))
         (%gpad (gnugo-f 'gpad))
         (%gspc (gnugo-f 'gspc))
         (%lpad (gnugo-f 'lpad))
         (%rpad (gnugo-f 'rpad))
         (ispc-props (list 'category (gnugo-f 'ispc) 'rear-nonsticky t))
         (size (gnugo-get :SZ))
         (size-string (number-to-string size)))
    (goto-char (point-min))
    (put-text-property (point) (1+ (point)) 'category (gnugo-f 'tpad))
    (skip-chars-forward " ")
    (put-text-property (1- (point)) (point) 'category %gpad)
    (put-text-property (point) (progn (end-of-line) (point)) 'category %gspc)
    (forward-char 1)
    (add-text-properties (1+ (point-min)) (1- (point)) grid-props)
    (while (looking-at "\\s-*\\([0-9]+\\)[ ]")
      (let* ((row (match-string-no-properties 1))
             (edge (match-end 0))
             (other-edge (+ edge (* 2 size) -1))
             (right-empty (+ other-edge (length row) 1))
             (top-p (string= size-string row))
             (bot-p (string= "1" row)))
        (let* ((nL (- edge 1 (length size-string)))
               (nR (- edge 1))
               (ov (make-overlay nL nR (current-buffer) t)))
          (add-text-properties nL nR grid-props)
          ;; We redundantly set `invisible' in the overlay to workaround
          ;; a display bug whereby text *following* the overlaid text is
          ;; displayed with the face of the overlaid text, but only when
          ;; that text is invisible (i.e., `:nogrid' in invisibility spec).
          ;; This has something to do w/ the bletcherous `before-string'.
          (overlay-put ov 'invisible :nogrid)
          (overlay-put ov 'category %lpad))
        (do ((p edge (+ 2 p)) (ival 'even (if (eq 'even ival) 'odd 'even)))
            ((< other-edge p))
          (let* ((position (format "%c%s" (aref "ABCDEFGHJKLMNOPQRST"
                                                (truncate (- p edge) 2))
                                   row))
                 (yin (let ((A-p (= edge p))
                            (Z-p (= (1- other-edge) p)))
                        (cond ((and top-p A-p) 1)
                              ((and top-p Z-p) 3)
                              ((and bot-p A-p) 7)
                              ((and bot-p Z-p) 9)
                              (top-p 2)
                              (bot-p 8)
                              (A-p 4)
                              (Z-p 6)
                              (t 5))))
                 (yang (gnugo-yang (char-after p))))
            (add-text-properties p (1+ p)
                                 `(gnugo-position
                                   ,position
                                   gnugo-yin
                                   ,yin
                                   gnugo-yang
                                   ,yang
                                   category
                                   ,(gnugo-yy yin yang)
                                   front-sticky
                                   (gnugo-position gnugo-yin))))
          (unless (= (1- other-edge) p)
            (add-text-properties (1+ p) (+ 2 p) ispc-props)
            (put-text-property p (+ 2 p) 'intangible ival)))
        (add-text-properties (1+ other-edge) right-empty grid-props)
        (goto-char right-empty)
        (when (looking-at "\\s-+\\(WH\\|BL\\).*capt.* \\([0-9]+\\).*$")
          (let ((prop (if (string= "WH" (match-string 1))
                          :white-captures
                        :black-captures))
                (beg (match-beginning 2))
                (end (match-end 2)))
            (put-text-property beg end :gnugo-cf (cons (- end beg) prop))
            (gnugo-put prop (match-string-no-properties 2))))
        (end-of-line)
        (put-text-property right-empty (point) 'category %rpad)
        (forward-char 1)))
    (add-text-properties (1- (point)) (point-max) grid-props)
    (skip-chars-forward " ")
    (put-text-property (1- (point)) (point) 'category %gpad)
    (put-text-property (point) (progn (end-of-line) (point))
                       'category %gspc)))

(defun gnugo-merge-showboard-results ()
  (let ((aft (substring (gnugo--q "showboard") 3))
        (adj 1)                         ; string to buffer position adjustment

        (sync "[0-9]* stones$")
        ;; Note: `sync' used to start w/ "[0-9]+", but that is too
        ;; restrictive a condition that fails in the case of:
        ;;
        ;; (before)
        ;;   ... WHITE has captured 1 stones
        ;;                           ^
        ;; (after)
        ;;   ... WHITE has captured 14 stones
        ;;                           ^
        ;;
        ;; where the after count has more digits than the before count,
        ;; but shares the same leading digits.  In this case, the result
        ;; of `compare-strings' points to the SPC following the before
        ;; count (indicated by caret in this example).

        (bef (buffer-substring-no-properties (point-min) (point-max)))
        (bef-start 0) (bef-idx 0)
        (aft-start 0) (aft-idx 0)
        aft-sync-backtrack mis inc cut new very-strange)
    (while (numberp (setq mis (gnugo--compare-strings
                               bef bef-start
                               aft aft-start)))
      (setq aft-sync-backtrack nil
            inc (if (cl-minusp mis)
                    (- (+ 1 mis))
                  (- mis 1))
            bef-idx (+ bef-start inc)
            aft-idx (+ aft-start inc)
            bef-start (if (eq bef-idx (string-match sync bef bef-idx))
                          (match-end 0)
                        (1+ bef-idx))
            aft-start (if (and (eq aft-idx (string-match sync aft aft-idx))
                               (let ((peek (1- aft-idx)))
                                 (while (not (= 32 (aref aft peek)))
                                   (setq peek (1- peek)))
                                 (setq aft-sync-backtrack (1+ peek))))
                          (match-end 0)
                        (1+ aft-idx))
            cut (+ bef-idx adj
                   (if aft-sync-backtrack
                       (- aft-sync-backtrack aft-idx)
                     0)))
      (goto-char cut)
      (if aft-sync-backtrack
          (let* ((asb aft-sync-backtrack)
                 (l-p (get-text-property cut :gnugo-cf))
                 (old-len (car l-p))
                 (capprop (cdr l-p))
                 (keep (text-properties-at cut)))
            (setq new (substring aft asb (string-match " " aft asb)))
            (plist-put keep :gnugo-cf (cons (length new) capprop))
            (gnugo-put capprop new)
            (delete-char old-len)
            (insert (apply 'propertize new keep))
            (incf adj (- (length new) old-len)))
        (setq new (aref aft aft-idx))
        (insert-and-inherit (char-to-string new))
        (let ((yin (get-text-property cut 'gnugo-yin))
              (yang (gnugo-yang new)))
          (add-text-properties cut (1+ cut)
                               `(gnugo-yang
                                 ,yang
                                 category
                                 ,(gnugo-yy yin yang))))
        (delete-char 1)
        ;; do this last to avoid complications w/ font lock
        ;; (this also means we cannot include `intangible' in `front-sticky')
        (when (setq very-strange (get-text-property (1+ cut) 'intangible))
          (put-text-property cut (1+ cut) 'intangible very-strange))))))

(defsubst gnugo--move-prop (node)
  (or (assq :B node)
      (assq :W node)))

(defun gnugo--as-pos-func ()
  (lexical-let ((size (gnugo-get :SZ)))
    ;; rv
    (lambda (cc)
      (if (string= "" cc)
          "PASS"
        (let ((col (aref cc 0)))
          (format "%c%d"
                  (+ ?A (- (if (> ?i col) col (1+ col)) ?a))
                  (- size (- (aref cc 1) ?a))))))))

(defun gnugo-move-history (&optional rsel)
  "Determine and return the game's move history.
Optional arg RSEL controls side effects and return value.
If nil, display the history in the echo area as \"(N moves)\"
followed by the space-separated list of moves.  When called
interactively with a prefix arg (i.e., RSEL is `(4)'), display
similarly, but suffix with the mover (either \":B\" or \":W\").
If RSEL is the symbol `car' return the most-recent move; if
`cadr', the next-to-most-recent move; if `count' the number of
moves thus far; if `two' the last two moves as a list, oldest last.

For all other values of RSEL, do nothing and return nil."
  (interactive "P")
  (let* ((monkey (gnugo-get :monkey))
         (mem (aref monkey 0))
         (as-pos (gnugo--as-pos-func))
         acc node mprop move)
    (cl-flet*
        ((as-pos-maybe (x) (if (string= "resign" x)
                               x
                             (funcall as-pos x)))
         (next (byp) (when (setq node (pop mem)
                                 mprop (gnugo--move-prop node))
                       (setq move (as-pos-maybe (cdr mprop)))
                       (push (if byp
                                 (format "%s%s" move (car mprop))
                               move)
                             acc)))
         (nn () (next nil))
         (tell () (message "(%d moves) %s"
                           (length acc)
                           (mapconcat 'identity (nreverse acc) " ")))
         (finish (byp) (while mem (next byp)) (tell)))
      (pcase rsel
        (`(4) (finish t))
        (`nil (finish nil))
        (`car        (car (nn)))
        (`cadr  (nn) (car (nn)))
        (`count (gethash (car mem) (gnugo--tree-mnum
                                    (gnugo-get :sgf-gametree))))
        (`two (nn) (nn) acc)
        (_ nil)))))

(define-derived-mode gnugo-frolic-mode special-mode "GNUGO Frolic"
  "A special mode for manipulating a GNUGO gametree.

\\{gnugo-frolic-mode-map}"
  (setq truncate-lines t)
  (buffer-disable-undo))

(defun gnugo-frolic-quit ()
  "Kill GNUGO Frolic buffer and switch to its parent buffer."
  (interactive)
  (let ((bye (current-buffer)))
    (switch-to-buffer (when (buffer-live-p gnugo-frolic-parent-buffer)
                        gnugo-frolic-parent-buffer))
    (kill-buffer bye)))

(defun gnugo-frolic-return-to-origin ()
  "Move point to the board's current position."
  (interactive)
  (if (not gnugo-frolic-origin)
      (message "No origin")
    (goto-char gnugo-frolic-origin)
    (recenter (- (count-lines (line-beginning-position)
                              (point-max))))))

(defun gnugo-frolic-in-the-leaves ()
  "Display the game tree in a *GNUGO Frolic* buffer.
This looks something like:

  1 B  --  E7    E7    E7    E7
  2 W  --  K10   K10   K10   K10
  3 B  --  E2    E2    E2    E2
  4 W  --  J3    J3    J3    J3
  5 B  --  A6    A6    A6    A6
  6 W  --  C9    C9    C9    C9
           │
           ├─────┬─────┐
           │     │     │
  7 B  --  H7    B8    C8    C8
                       │
                       ├─────┐
                       │     │
  8 W  --  D9    D9    D9    E9
  9 B  --              H8    H8
 10 W  --              PASS  PASS
 11 B  --              H5    PASS
 12 W  --              PASS
 13 B  --             *PASS

with 0, 1, ... N (in this case N is 3) in the header line
to indicate the branches.  Branch 0 is the \"main line\".
Point (* in this example) indicates the current position,
and moves not actually on the game tree (e.g., E7, branch 3)
are dimmed.  Type \\[describe-mode] in that buffer for details."
  (interactive)
  (let* ((buf (get-buffer-create (concat (gnugo-get :diamond)
                                         "*GNUGO Frolic*")))
         (from (or gnugo-frolic-parent-buffer
                   (current-buffer)))
         ;; todo: use defface once we finally succumb to ‘customize’
         (dimmed-node-face (list :inherit 'default
                                 :foreground "gray50"))
         (tree (gnugo-get :sgf-gametree))
         (ends (copy-sequence (gnugo--tree-ends tree)))
         (mnum (gnugo--tree-mnum tree))
         (seen (gnugo--mkht))
         (soil (gnugo--mkht))
         (width (length ends))
         (lanes (number-sequence 0 (1- width)))
         (monkey (gnugo-get :monkey))
         (as-pos (gnugo--as-pos-func))
         (at (car (aref monkey 0)))
         (bidx (aref monkey 1))
         (valid (map 'vector (lambda (end)
                               (gethash (car end) mnum))
                     ends))
         (max-move-num (apply 'max (append valid nil)))
         (inhibit-read-only t)
         finish)
    (cl-flet
        ((on (node)
             (gethash node seen))
         (emph (s face)
               (propertize s 'face face))
         (fsi (properties fmt &rest args)
              (insert (apply 'propertize
                             (apply 'format fmt args)
                             properties))))
      ;; breathe in
      (loop
       for bx below width
       do (loop
           with fork
           for node in (aref ends bx)
           do (if (setq fork (on node))
                  (cl-flet
                      ((tip-p (bix)
                              ;; todo: ignore non-"move" nodes
                              (eq node (car (aref ends bix))))
                       (link (other)
                             (pushnew other (gethash node soil))))
                    (unless (tip-p bx)
                      (unless (tip-p fork)
                        (link fork))
                      (link bx)))
                (puthash node bx seen))
           until fork))
      ;; breathe out
      (switch-to-buffer buf)
      (gnugo-frolic-mode)
      (erase-buffer)
      (setq header-line-format
            (lexical-let ((full (concat
                                 (make-string 11 ?\s)
                                 (mapconcat (lambda (n)
                                              (format "%-5s" n))
                                            lanes
                                            " "))))
              `((:eval
                 (funcall
                  ,(lambda ()
                     (cl-flet
                         ((sp (w) (propertize
                                   " " 'display
                                   `(space :width ,w))))
                       (concat
                        (when (eq 'left scroll-bar-mode)
                          (let ((w (or scroll-bar-width
                                       (frame-parameter
                                        nil 'scroll-bar-width)))
                                (cw (frame-char-width)))
                            (sp (if w
                                    (/ w cw)
                                  2))))
                        (let ((fc (fringe-columns 'left t)))
                          (unless (zerop fc)
                            (sp fc)))
                        (condition-case nil
                            (substring full (window-hscroll))
                          (error ""))))))))))
      (set (make-local-variable 'gnugo-frolic-parent-buffer) from)
      (set (make-local-variable 'gnugo-state)
           (buffer-local-value 'gnugo-state from))
      (loop
       with props
       for n                            ; move number
       from max-move-num downto 1
       do (setq props (list 'n n))
       do
       (loop
        with (move forks br)
        initially (progn
                    (goto-char (point-min))
                    (fsi props
                         "%3d %s  -- "
                         n (aref ["W" "B"] (logand 1 n))))
        for bx below width
        do (let* ((node (unless (< (aref valid bx) n)
                          ;; todo: ignore non-"move" nodes
                          (pop (aref ends bx))))
                  (ok (when node
                        (= bx (on node))))
                  (s (cond ((not node) "")
                           ((not (setq move (gnugo--move-prop node))) "-")
                           (t (funcall as-pos (cdr move))))))
             (when (and ok (setq br (gethash node soil)))
               (push (cons bx (sort br '<))
                     forks))
             (fsi (list* 'bx bx props)
                  " %-5s"
                  (cond ((and (eq at node)
                              (or ok (= bx bidx)))
                         (when (= bx bidx)
                           (setq finish (point-marker)))
                         (emph s (list :inherit 'default
                                       :foreground (frame-parameter
                                                    nil 'cursor-color))))
                        ((not ok)
                         (emph s dimmed-node-face))
                        (t s))))
        finally do
        (when (progn (fsi props "\n")
                     (setq forks (nreverse forks)))
          (let* ((margin (make-string 11 ?\s))
                 (heads (mapcar #'car forks))
                 (tails (mapcar #'cdr forks)))
            (cl-flet*
                ((spaced (lanes func)
                         (mapconcat func lanes "     "))
                 ;;  live to play               ~   ~              ()
                 ;;  play to learn             (+) (-)       . o O
                 ;;  learn to live  --ttn        .M.   _____U
                 (dashed (lanes func) ;;;       _____ ^^^^
                         (mapconcat func lanes "-----"))
                 (cnxn (lanes set)
                       (spaced lanes (lambda (bx)
                                       (if (memq bx set)
                                           "|"
                                         " "))))
                 (pad-unless (condition)
                             (if condition
                                 ""
                               "     "))
                 (edge (set)
                       (insert margin
                               (cnxn lanes set)
                               "\n")))
              (edge heads)
              (loop with bef
                    for ls on forks
                    do (let* ((one (car ls))
                              (yes (append
                                    ;; "aft" heads
                                    (mapcar 'car (cdr ls))
                                    ;; ‘bef’ tails
                                    (apply 'append (mapcar 'cdr bef))))
                              (ord (sort one '<))
                              (beg (car ord))
                              (end (car (last ord))))
                         (cl-flet
                             ((also (b e) (cnxn (number-sequence b e)
                                                yes)))
                           (insert
                            margin
                            (also 0 (1- beg))
                            (pad-unless (zerop beg))
                            (dashed (number-sequence beg end)
                                    (lambda (bx)
                                      (cond ((memq bx ord) "+")
                                            ((memq bx yes) "|")
                                            (t             "-"))))
                            (pad-unless (>= end width))
                            (also (1+ end) (1- width))
                            "\n"))
                         (push one bef)))
              (edge (apply 'append tails))
              (aa2u (line-beginning-position
                     (- (1+ (length forks))))
                    (point))))))))
    (when finish
      (set (make-local-variable 'gnugo-frolic-origin) finish)
      (gnugo-frolic-return-to-origin))))

(defun gnugo--awake (how)
  ;; Valid HOW elements:
  ;;   require-valid-branch
  ;;   (line . numeric)
  ;;   (line . move-string)
  ;; Invalid elements blissfully ignored.  :-D
  (let* ((tree (gnugo-get :sgf-gametree))
         (ends (gnugo--tree-ends tree))
         (width (length ends))
         (monkey (gnugo-get :monkey))
         (line (case (cdr (assq 'line how))
                 (numeric
                  (count-lines (point-min) (line-beginning-position)))
                 (move-string
                  (save-excursion
                    (when (re-search-backward "^ *[0-9]+ [BW]" nil t)
                      (match-string 0))))
                 (t nil)))
         (col (current-column))
         (a (unless (> 10 col)
              (let ((try (/ (- col 10)
                            6)))
                (unless (<= width try)
                  try))))
         (rv (list a)))
    (when (memq 'require-valid-branch how)
      (unless a
        (user-error "No branch here")))
    (loop with omit = (cdr (assq 'omit how))
          for (name . value) in `((line   . ,line)
                                  (bidx   . ,(aref monkey 1))
                                  (monkey . ,monkey)
                                  (width  . ,width)
                                  (ends   . ,ends)
                                  (tree   . ,tree))
          do (unless (memq name omit)
               (push value rv)))
    rv))

(defmacro gnugo--awakened (how &rest body)
  (declare (indent 1))
  `(destructuring-bind ,(loop with omit = (cdr (assq 'omit how))
                              with ls   = (list 'a)
                              for name in '(line bidx monkey
                                                 width ends
                                                 tree)
                              do (unless (memq name omit)
                                   (push name ls))
                              finally return ls)
       (gnugo--awake ',how)
     ,@body))

(defsubst gnugo--move-to-bcol (bidx)
  (move-to-column (+ 10 (* 6 bidx))))

(defun gnugo--swiz (direction &optional blunt)
  (gnugo--awakened (require-valid-branch
                    (omit tree)
                    (line . numeric))
    (let* ((b (cond ((numberp blunt)
                     (unless (and (< -1 blunt)
                                  (< blunt width))
                       (user-error "No such branch: %s" blunt))
                     blunt)
                    (t (mod (+ direction a) width))))
           (flit (if blunt (lambda (n)
                             (cond ((= n a) b)
                                   ((= n b) a)
                                   (t n)))
                   (lambda (n)
                     (mod (+ direction n) width))))
           (was (copy-sequence ends))
           (new-bidx (funcall flit bidx)))
      (loop for bx below width
            do (aset ends (funcall flit bx)
                     (aref was bx)))
      (unless (= new-bidx bidx)
        (aset monkey 1 new-bidx))
      (gnugo-frolic-in-the-leaves)
      (goto-char (point-min))
      (forward-line line)
      (gnugo--move-to-bcol b))))

(defun gnugo-frolic-exchange-left ()
  "Exchange the current branch with the one to its left."
  (interactive)
  (gnugo--swiz -1 t))

(defun gnugo-frolic-rotate-left ()
  "Rotate all branches left."
  (interactive)
  (gnugo--swiz -1))

(defun gnugo-frolic-exchange-right ()
  "Exchange the current branch with the one to its right."
  (interactive)
  (gnugo--swiz 1 t))

(defun gnugo-frolic-rotate-right ()
  "Rotate all branches right."
  (interactive)
  (gnugo--swiz 1))

(defun gnugo-frolic-set-as-main-line ()
  "Make the current branch the main line."
  (interactive)
  (gnugo--swiz nil 0))

(defun gnugo-frolic-prune-branch ()
  "Remove the current branch from the gametree.
This fails if there is only one branch in the tree.
This fails if the monkey is on the current branch
\(a restriction that will probably be lifted Real Soon Now\)."
  (interactive)
  (gnugo--awakened (require-valid-branch
                    (line . move-string))
    ;; todo: define meaningful eviction semantics; remove restriction
    (when (= a bidx)
      (user-error "Cannot prune with monkey on branch"))
    (when (= 1 width)
      (user-error "Cannot prune last remaining branch"))
    (let ((new (append ends nil)))
      ;; Explicit ignorance avoids byte-compiler warning.
      (ignore (pop (nthcdr a new)))
      (gnugo--set-tree-ends tree new))
    (when (< a bidx)
      (aset monkey 1 (decf bidx)))
    (gnugo-frolic-in-the-leaves)
    (when line
      (goto-char (point-min))
      (search-forward line)
      (gnugo--move-to-bcol (min a (- width 2))))))

(defun gnugo--sideways (backwards n)
  (gnugo--awakened ((omit tree ends monkey bidx line))
    (gnugo--move-to-bcol (mod (if backwards
                                  (- (or a width) n)
                                (+ (or a -1) n))
                              width))))

(defun gnugo-frolic-backward-branch (&optional n)
  "Move backward N (default 1) branches."
  (interactive "p")
  (gnugo--sideways t n))

(defun gnugo-frolic-forward-branch (&optional n)
  "Move forward N (default 1) branches."
  (interactive "p")
  (gnugo--sideways nil n))

(defun gnugo--vertical (n direction)
  (when (> 0 n)
    (setq n (- n)
          direction (- direction)))
  (gnugo--awakened ((line . numeric)
                    (omit tree ends width monkey bidx))
    (let ((stop (if (> 0 direction)
                    0
                  (max 0 (1- (count-lines (point-min)
                                          (point-max))))))
          (col (unless a
                 (current-column))))
      (loop while (not (= line stop))
            do (loop do (progn
                          (forward-line direction)
                          (incf line direction))
                     until (get-text-property (point) 'n))
            until (zerop (decf n)))
      (if a
          (gnugo--move-to-bcol a)
        (move-to-column col)))))

(defun gnugo-frolic-previous-move (&optional n)
  "Move to the Nth (default 1) previous move."
  (interactive "p")
  (gnugo--vertical n -1))

(defun gnugo-frolic-next-move (&optional n)
  "Move to the Nth (default 1) next move."
  (interactive "p")
  (gnugo--vertical n 1))

(defun gnugo-boss-is-near ()
  "Do `bury-buffer' until the current one is not a GNU Board."
  (interactive)
  (while (gnugo-board-buffer-p)
    (bury-buffer)))

(defsubst gnugo--passp (string)
  (string= "PASS" string))

(defsubst gnugo--no-regrets (monkey ends)
  (eq (aref ends (aref monkey 1))
      (aref monkey 0)))

(defun gnugo--as-cc-func ()
  (lexical-let ((size (gnugo-get :SZ)))
    (lambda (pos)
      (let* ((col (aref pos 0))
             (one (+ ?a (- col (if (< ?H col) 1 0) ?A)))
             (two (+ ?a (- size (string-to-number
                                 (substring pos 1))))))
        (format "%c%c" one two)))))

(defsubst gnugo--decorate (node alist)
  ;; NB: ALIST should not have :B or :W keys.
  (setcdr (last node) alist))

(defun gnugo-note (property value &optional mogrifyp)
  (when mogrifyp
    (let ((as-cc (gnugo--as-cc-func)))
      (cl-flet
          ((mog (pos) (if (gnugo--passp pos)
                          ""
                        (funcall as-cc pos))))
        (setq value (if (consp value)
                        (mapcar #'mog value)
                      (mog value))))))
  (let* ((pair (cons property value))
         (fruit (list pair))
         (monkey (gnugo-get :monkey))
         (mem (aref monkey 0))
         (tip (car mem)))
    (if (memq property '(:B :W))
        (let* ((tree (gnugo-get :sgf-gametree))
               (ends (gnugo--tree-ends tree))
               (mnum (gnugo--tree-mnum tree))
               (count (length ends))
               (tip-move-num (gethash tip mnum))
               (bidx (aref monkey 1)))
          ;; Detect déjà-vu.  That is, when placing "A", avoid:
          ;;
          ;;   X---Y---A         new
          ;;        \
          ;;         --A---B     old
          ;;
          ;; (such "variations" do not actually vary!) in favor of:
          ;;
          ;;   X---Y---A         new
          ;;            \
          ;;             --B     old
          ;;
          ;; This linear search loses for multiple ‘old’ w/ "A",
          ;; a very unusual (but not invalid, sigh) situation.
          (loop
           with (bx previous)
           for i
           ;; Start with latest / highest likelihood for hit.
           ;; (See "to the right" comment, below.)
           from (if (gnugo--no-regrets monkey ends)
                    1
                  0)
           below count
           if (setq bx (mod (+ bidx i) count)
                    previous
                    (loop with node
                          for m on (aref ends bx)
                          while (< tip-move-num
                                   (gethash (setq node (car m))
                                            mnum))
                          if (eq mem (cdr m))
                          return
                          (when (equal pair (assoc property node))
                            m)
                          finally return
                          nil))
           ;; yes => follow
           return
           (progn
             (unless (= bidx bx)
               (rotatef (aref ends bidx)
                        (aref ends bx)))
             (setq mem previous))
           ;; no => construct
           finally do
           (progn
             (unless (gnugo--no-regrets monkey ends)
               (setq ends (gnugo--set-tree-ends
                           tree (let ((ls (append ends nil)))
                                  ;; copy old to the right of new
                                  (push mem (nthcdr bidx ls))
                                  ls))))
             (puthash fruit (1+ (gethash tip mnum)) mnum)
             (push fruit mem)
             (aset ends bidx mem)))
          (setf (aref monkey 0) mem))
      (gnugo--decorate tip fruit))))

(defun gnugo-close-game (end-time resign)
  (gnugo-put :game-end-time end-time)
  (let ((now (or end-time (current-time))))
    (gnugo-put :scoring-seed (logior (ash (logand (car now) 255) 16)
                                     (cadr now))))
  (gnugo-put :game-over
    (if (or (eq t resign)
            (and (stringp resign)
                 (string-match "[BW][+][Rr]esign" resign)))
        (cl-flet
            ((ls (color) (mapcar
                          (lambda (x)
                            (cons (list color)
                                  (split-string x)))
                          (split-string
                           (gnugo-query "worm_stones %s" color)
                           "\n"))))
          (let ((live (append (ls "black") (ls "white"))))
            `((live ,@live)
              (dead))))
      (let ((dd (gnugo-query "dragon_data"))
            (start 0) mem color ent live dead)
        (while (string-match "\\(.+\\):\n[^ ]+[ ]+\\(black\\|white\\)\n"
                             dd start)
          (setq mem (match-string 1 dd)
                color (match-string 2 dd)
                start (match-end 0)
                ent (cons (list color)
                          (sort (gnugo-lsquery "dragon_stones %s" mem)
                                'string<)))
          (string-match "\nstatus[ ]+\\(\\(ALIVE\\)\\|[A-Z]+\\)\n"
                        dd start)
          (if (match-string 2 dd)
              (push ent live)
            (push ent dead))
          (setq start (match-end 0)))
        `((live ,@live)
          (dead ,@dead))))))

(defun gnugo--unclose-game ()
  (dolist (prop '(:game-over            ; all those in -close-game
                  :scoring-seed
                  :game-end-time))
    (gnugo-put prop nil))
  (let* ((root (gnugo--root-node))
         (cur (assq :RE root)))
    (when cur
      (assert (not (eq cur (car root))) nil
              ":RE at head of root node: %S"
              root)
      (delq cur root))))

(defun gnugo-push-move (userp move)
  (let* ((color (gnugo-get (if userp :user-color :gnugo-color)))
         (start (gnugo-get :waiting-start))
         (now (current-time))
         (resignp (string= "resign" move))
         (passp (gnugo--passp move))
         (head (gnugo-move-history 'car))
         (onep (and head (gnugo--passp head)))
         (donep (or resignp (and onep passp))))
    (unless passp
      (gnugo-merge-showboard-results))
    (gnugo-put :last-mover color)
    (when userp
      (gnugo-put :last-user-bpos (and (not passp) (not resignp) move)))
    (gnugo-note (if (gnugo--blackp color) :B :W) move (not resignp))
    (when start
      (gnugo-put :last-waiting (cadr (time-subtract now start))))
    (when donep
      (gnugo-close-game now resignp))
    (gnugo-put :waiting-start (and (not donep) now))
    donep))

(defun gnugo-venerate (yin yang)
  (let* ((fg-yy (gnugo-yy yin yang))
         (fg-disp (or (get fg-yy 'display)
                      (get fg-yy 'do-not-display)))
         (fg-data (plist-get (cdr fg-disp) :data))
         (bg-yy (gnugo-yy yin (gnugo-yang ?.)))
         (bg-disp (or (get bg-yy 'display)
                      (get bg-yy 'do-not-display)))
         (bg-data (plist-get (cdr bg-disp) :data))
         (bop (lambda (s)
                (let* ((start 0)
                       (ncolors
                        (when (string-match "\\([0-9]+\\)\\s-+[0-9]+\"," s)
                          (setq start (match-end 0))
                          (string-to-number (match-string 1 s)))))
                  (while (and (not (cl-minusp ncolors))
                              (string-match ",\n" s start))
                    (setq start (match-end 0)
                          ncolors (1- ncolors)))
                  (string-match "\"" s start)
                  (match-end 0))))
         (new (copy-sequence fg-data))
         (lx (length fg-data))
         (sx (funcall bop fg-data))
         (sb (funcall bop bg-data))
         (color-key (aref new sx)))     ; blech, heuristic
    (while (< sx lx)
      (when (and (not (= color-key (aref new sx)))
                 (cl-plusp (random 4)))
        (aset new sx (aref bg-data sb)))
      (incf sx)
      (incf sb))
    (create-image new 'xpm t :ascent 'center)))

(defun gnugo-refresh (&optional nocache)
  "Update GNUGO Board buffer display.
While a game is in progress, parenthesize the last-played stone (no parens
for pass).  If the buffer is currently displayed in the selected window,
recenter the board (presuming there is extra space in the window).  Update
the mode line.  Lastly, move point to the last position played by the user,
if that move was not a pass.

Prefix arg NOCACHE requests complete reconstruction of the display, which may
be slow.  (This should normally be unnecessary; specify it only if the display
seems corrupted.)  NOCACHE is silently ignored when GNU Go is thinking about
its move."
  (interactive "P")
  (when (and nocache (not (gnugo-get :waitingp)))
    (gnugo-propertize-board-buffer))
  (let* ((last-mover (gnugo-get :last-mover))
         (other (gnugo-other last-mover))
         (move (gnugo-move-history 'car))
         (game-over (gnugo-get :game-over))
         window last)
    ;; last move
    (when move
      (let ((l-ov (gnugo-get :lparen-ov))
            (r-ov (gnugo-get :rparen-ov)))
        (if (member move '("PASS" "resign"))
            (mapc 'delete-overlay (list l-ov r-ov))
          (gnugo-goto-pos move)
          (let* ((p (point))
                 (hspec (gnugo-get :highlight-last-move-spec))
                 (display-value (nth 0 hspec))
                 (l-offset (nth 1 hspec))
                 (l-new-pos (+ p l-offset))
                 (r-action (nth 2 hspec)))
            (overlay-put l-ov 'display
                         (if (functionp display-value)
                             (funcall display-value p)
                           display-value))
            (move-overlay l-ov l-new-pos (1+ l-new-pos))
            (if r-action
                (funcall r-action r-ov)
              (move-overlay r-ov (+ l-new-pos 2) (+ l-new-pos 3)))))))
    ;; buffer name
    (rename-buffer (concat (gnugo-get :diamond)
                           (if game-over
                               (format "%s(game over)"
                                       (if (string= move "resign")
                                           (concat move "ation ")
                                         ""))
                             (format "%s(%s to play)"
                                     (if move (concat move " ") "")
                                     other))))
    ;; pall of death
    (when game-over
      (let ((live (cdr (assq 'live game-over)))
            (dead (cdr (assq 'dead game-over)))
            p pall)
        (unless (eq game-over (get-text-property 1 'game-over))
          (dolist (group (append live dead))
            (dolist (pos (cdr group))
              (gnugo-goto-pos pos)
              (setq p (point))
              (put-text-property p (1+ p) 'group group)))
          (put-text-property 1 2 'game-over game-over))
        (dolist (group live)
          (when (setq pall (cdar group))
            (mapc 'delete-overlay pall)
            (setcdr (car group) nil)))
        (dolist (group dead)
          (unless (cdar group)
            (let (ov pall c (color (caar group)))
              (setq c (if (gnugo--blackp color) "x" "o"))
              (dolist (pos (cdr group))
                (gnugo-goto-pos pos)
                (setq p (point) ov (make-overlay p (1+ p)))
                (overlay-put
                 ov 'display
                 (if (gnugo-get :display-using-images)
                     ;; respect the dead individually; it takes more time
                     ;; but that's not a problem (for them)
                     (gnugo-venerate (get-text-property p 'gnugo-yin)
                                     (gnugo-yang (aref (upcase c) 0)))
                   (propertize c 'face 'font-lock-warning-face)))
                (push ov pall))
              (setcdr (car group) pall))))))
    ;; window update
    (when (setq window (get-buffer-window (current-buffer)))
      (let* ((gridp (not (memq :nogrid buffer-invisibility-spec)))
             (size (gnugo-get :SZ))
             (under10p (< size 10))
             (h (- (truncate (- (window-height window)
                                (* size (gnugo-get :hmul))
                                (if gridp 2 0))
                             2)
                   (if gridp 0 1)))
             (edges (window-edges window))
             (right-w-edge (nth 2 edges))
             (avail-width (- right-w-edge (nth 0 edges)))
             (wmul (gnugo-get :wmul))
             (imagesp (symbol-plist (gnugo-f 'ispc)))
             (w (/ (- avail-width
                      (* size wmul)
                      (if imagesp
                          0
                        (1- size))
                      2                 ; between board and grid
                      (if gridp
                          (if under10p 2 4)
                        0))
                   2.0)))
        (dolist (pair `((tpad . ,(if (and h (cl-plusp h))
                                     `(display ,(make-string h 10))
                                   '(invisible :nogrid)))
                        (gpad . (display
                                 (space :align-to
                                        ,(+ w
                                            2.0
                                            (cond (imagesp (+ (* 0.5 wmul)
                                                              (if under10p
                                                                  -0.5
                                                                0.5)))
                                                  (under10p 0)
                                                  (t 1))))))
                        (gspc . ,(when imagesp
                                   `(display
                                     (space-width
                                      ,(-
                                        ;; DWR: image width alone => OBOE!
                                        ;;- wmul
                                        ;; NB: ‘(* wmul cw)’ is the same
                                        ;; as ‘(car (image-size ... t))’.
                                        (let ((cw (frame-char-width)))
                                          (/ (+ 1.0 (* wmul cw))
                                             cw))
                                        1.0)))))
                        (lpad . ,(let ((d `(display (space :align-to ,w))))
                                   ;; We distinguish between these cases to
                                   ;; workaround a display bug whereby the
                                   ;; `before-string' is omitted entirely (not
                                   ;; rendered) when interacting w/ the text
                                   ;; mode last-move left-paren for moves in
                                   ;; column A.
                                   (if gridp
                                       `(before-string
                                         ,(apply 'propertize " " d))
                                     d)))
                        (rpad . (display
                                 (space :align-to ,(1- avail-width))))))
          (setplist (gnugo-f (car pair)) (cdr pair)))))
    ;; mode line update
    (let ((cur (gnugo-get :mode-line)))
      (unless (equal cur gnugo-mode-line)
        (setq cur gnugo-mode-line)
        (gnugo-put :mode-line cur)
        (gnugo-put :mode-line-form
          (cond ((stringp cur)
                 (setq cur (copy-sequence cur))
                 (let (acc cut c)
                   (while (setq cut (string-match "~[bwpmtu]" cur))
                     (aset cur cut ?%)
                     (setq c (aref cur (incf cut)))
                     (aset cur cut ?s)
                     (push
                      `(,(intern (format "squig-%c" c))
                        ,(case c
                           (?b '(or (gnugo-get :black-captures) 0))
                           (?w '(or (gnugo-get :white-captures) 0))
                           (?p '(gnugo-other (gnugo-get :last-mover)))
                           (?t '(let ((ws (gnugo-get :waiting-start)))
                                  (if ws
                                      (cadr (time-since ws))
                                    "-")))
                           (?u '(or (gnugo-get :last-waiting) "-"))
                           (?m '(gnugo-move-history 'count))))
                      acc))
                   `(let ,(delete-dups (copy-sequence acc))
                      (format ,cur ,@(reverse (mapcar 'car acc))))))
                (t cur))))
      (let ((form (gnugo-get :mode-line-form)))
        (setq mode-line-process
              (and form
                   ;; this dynamicism is nice but excessive in its wantonness
                   ;;- `(" [" (:eval ,form) "]")
                   ;; this dynamicism is ok because the user triggers it
                   (list (format " [%s]" (eval form))))))
      (force-mode-line-update))
    ;; last user move
    (when (setq last (gnugo-get :last-user-bpos))
      (gnugo-goto-pos last))))

;;;---------------------------------------------------------------------------
;;; Game play actions

(defun gnugo-get-move-insertion-filter (proc string)
  (with-current-buffer (process-buffer proc)
    (let* ((so-far (gnugo-get :get-move-string))
           (full   (gnugo-put :get-move-string (concat so-far string))))
      (when (string-match "^= \\(.+\\)\n\n" full)
        (let ((pos-or-pass (match-string 1 full)))
          (gnugo-put :get-move-string nil)
          (gnugo-put :waitingp nil)
          (gnugo-push-move nil pos-or-pass)
          (let ((buf (current-buffer)))
            (let (gnugo-inhibit-refresh)
              (run-hooks 'gnugo-post-move-hook)
              (unless gnugo-inhibit-refresh
                (with-current-buffer buf
                  (gnugo-refresh))))))))))

(defun gnugo-get-move (color)
  (gnugo-put :waitingp t)
  (gnugo--begin-exchange
      (gnugo-get :proc) 'gnugo-get-move-insertion-filter
    (concat "genmove " color))
  (accept-process-output))

(defun gnugo-cleanup ()
  (when (gnugo-board-buffer-p)
    (unless (zerop (buffer-size))
      (message "Thank you for playing GNU Go."))
    (mapc (lambda (sym)
            (setplist sym nil)          ; "...is next to fordliness." --Huxley
            ;; Sigh, "2nd arg optional" obsolete as of Emacs 23.3.
            ;; No worries, things will be Much Better w/ structs, RSN...
            (unintern sym nil))
          (append (gnugo-get :all-yy)
                  (mapcar 'gnugo-f
                          '(anim
                            tpad
                            gpad
                            gspc
                            lpad
                            rpad
                            ispc))))
    (setq gnugo-state nil)))

(defun gnugo-position ()
  (or (get-text-property (point) 'gnugo-position)
      (user-error "Not a proper position point")))

(defun gnugo-move ()
  "Make a move on the GNUGO Board buffer.
The position is computed from current point.
Signal error if done out-of-turn or if game-over.
To start a game try M-x gnugo."
  (interactive)
  (gnugo-gate t)
  (let* ((buf (current-buffer))
         (pos (gnugo-position)))
    (gnugo--user-play-stone pos)
    (gnugo-push-move t pos)             ; value always nil for non-pass move
    (let (gnugo-inhibit-refresh)
      (run-hooks 'gnugo-post-move-hook)
      (unless gnugo-inhibit-refresh
        (with-current-buffer buf
          (gnugo-refresh))))
    (with-current-buffer buf
      (gnugo-get-move (gnugo-get :gnugo-color)))))

(defun gnugo-mouse-move (e)
  "Do `gnugo-move' at mouse location."
  (interactive "@e")
  (mouse-set-point e)
  (when (looking-at "[.+]")
    (gnugo-move)))

(defun gnugo-pass ()
  "Make a pass on the GNUGO Board buffer.
Signal error if done out-of-turn or if game-over.
To start a game try M-x gnugo."
  (interactive)
  (gnugo-gate t)
  (gnugo--user-play-stone "PASS")
  (let ((donep (gnugo-push-move t "PASS"))
        (buf (current-buffer)))
    (let (gnugo-inhibit-refresh)
      (run-hooks 'gnugo-post-move-hook)
      (unless gnugo-inhibit-refresh
        (with-current-buffer buf
          (gnugo-refresh))))
    (unless donep
      (with-current-buffer buf
        (gnugo-get-move (gnugo-get :gnugo-color))))))

(defun gnugo-mouse-pass (e)
  "Do `gnugo-pass' at mouse location."
  (interactive "@e")
  (mouse-set-point e)
  (gnugo-pass))

(defun gnugo-resign ()
  (interactive)
  (gnugo-gate t)
  (if (not (y-or-n-p "Resign? "))
      (message "(not resigning)")
    (gnugo-push-move t "resign")
    (gnugo-refresh)))

(defun gnugo-animate-group (w/d)
  ;; W/D is a symbol, either ‘worm’ or ‘dragon’.
  (let* ((pos (gnugo-position))
         (orig-b-m-p (buffer-modified-p))
         blurb stones)
    (unless (memq (following-char) '(?X ?O))
      (user-error "No stone at %s" pos))
    (setq blurb (message "Computing %s stones ..." w/d)
          stones (gnugo-lsquery "%s_stones %s" w/d pos))
    (message "%s %s in group." blurb (length stones))
    (setplist (gnugo-f 'anim) nil)
    (let* ((spec (if (gnugo-get :display-using-images)
                     (loop with yin  = (get-text-property (point) 'gnugo-yin)
                           with yang = (gnugo-yang (following-char))
                           with up   = (get (gnugo-yy yin yang t) 'display)
                           with dn   = (get (gnugo-yy yin yang) 'display)
                           for n below (length gnugo-animation-string)
                           collect (if (zerop (logand 1 n))
                                       dn up))
                   (split-string gnugo-animation-string "" t)))
           (cell (list spec))
           (ovs (save-excursion
                  (mapcar (lambda (pos)
                            (gnugo-goto-pos pos)
                            (let* ((p (point))
                                   (ov (make-overlay p (1+ p))))
                              (overlay-put ov 'category (gnugo-f 'anim))
                              (overlay-put ov 'priority most-positive-fixnum)
                              ov))
                          stones))))
      (setplist (gnugo-f 'anim) (cons 'display cell))
      (while (and (cdr spec)            ; let last linger lest levity lost
                  (sit-for 0.08675309)) ; jenny jenny i got your number...
        (setcar cell (setq spec (cdr spec)))
        ;; Force redisplay of overlays.
        (set-buffer-modified-p orig-b-m-p))
      (sit-for 5)
      (mapc 'delete-overlay ovs)
      t)))

(defun gnugo-display-group-data (command buffer-name)
  (message "Computing %s ..." command)
  (let ((data (gnugo--q "%s %s" command (gnugo-position))))
    (switch-to-buffer buffer-name)
    (erase-buffer)
    (insert data))
  (message "Computing %s ... done." command))

(defun gnugo-worm-stones ()
  "In the GNUGO Board buffer, animate \"worm\" at current position.
Signal error if done out-of-turn or if game-over.
See variable `gnugo-animation-string' for customization."
  (interactive)
  (gnugo-gate)
  (gnugo-animate-group 'worm))

(defun gnugo-worm-data ()
  "Display in another buffer data from \"worm\" at current position.
Signal error if done out-of-turn or if game-over."
  (interactive)
  (gnugo-gate)
  (gnugo-display-group-data "worm_data" "*gnugo worm data*"))

(defun gnugo-dragon-stones ()
  "In the GNUGO Board buffer, animate \"dragon\" at current position.
Signal error if done out-of-turn or if game-over.
See variable `gnugo-animation-string' for customization."
  (interactive)
  (gnugo-gate)
  (gnugo-animate-group 'dragon))

(defun gnugo-dragon-data ()
  "Display in another buffer data from \"dragon\" at current position.
Signal error if done out-of-turn or if game-over."
  (interactive)
  (gnugo-gate)
  (gnugo-display-group-data "dragon_data" "*gnugo dragon data*"))

(defun gnugo-toggle-dead-group ()
  "In a GNUGO Board buffer, during game-over, toggle a group as dead.
The group is selected from current position (point).  Signal error if
not in game-over or if there is no group at that position.

In the context of GNU Go, a group is called a \"dragon\" and may be
composed of more than one \"worm\" (set of directly-connected stones).
It is unclear to the gnugo.el author whether or not GNU Go supports
 - considering worms as groups in their own right; and
 - toggling group aliveness via GTP.
Due to these uncertainties, this command is only half complete; the
changes you may see in Emacs are not propagated to the gnugo subprocess.
Thus, GTP commands like `final_score' may give unexpected results.

If you are able to expose via GTP `change_dragon_status' in utils.c,
you may consider modifying the `gnugo-toggle-dead-group' source code
to enable full functionality."
  (interactive)
  (let ((game-over (or (gnugo-get :game-over)
                       (user-error "Sorry, game still in play")))
        (group (or (get-text-property (point) 'group)
                   (user-error "No stone at that position")))
        (now (current-time)))
    (gnugo-put :scoring-seed (logior (ash (logand (car now) 255) 16)
                                     (cadr now)))
    (let ((live (assq 'live game-over))
          (dead (assq 'dead game-over))
          bef now)
      (if (memq group live)
          (setq bef live now dead)
        (setq bef dead now live))
      (setcdr bef (delq group (cdr bef)))
      (setcdr now (cons group (cdr now)))
      ;; disabled permanently -- too wrong
      (when nil
        (cl-flet
            ((populate (group)
                       (let ((color (caar group)))
                         (dolist (stone (cdr group))
                           (gnugo--play-stone color stone)))))
          (if (eq now live)
              (populate group)
            ;; drastic (and wrong -- clobbers capture info, etc)
            (gnugo-query "clear_board")
            (mapc #'populate (cdr live)))))
      ;; here is the desired interface (to be enabled Some Day)
      (when nil
        (gnugo-query "change_dragon_status %s %s"
                     (cadr group) (if (eq now live)
                                      'alive
                                    'dead)))))
  (save-excursion
    (gnugo-refresh)))

(defun gnugo-estimate-score ()
  "Display estimated score of a game of GNU Go.
Output includes number of stones on the board and number of stones
captured by each player, and the estimate of who has the advantage (and
by how many stones)."
  (interactive)
  (message "Est.score ...")
  (let ((black (gnugo--count-query "list_stones black"))
        (white (gnugo--count-query "list_stones white"))
        (black-captures (gnugo-query "captures black"))
        (white-captures (gnugo-query "captures white"))
        (est (gnugo-query "estimate_score")))
    ;; might as well update this
    (gnugo-put :black-captures black-captures)
    (gnugo-put :white-captures white-captures)
    (message "Est.score ... B %s %s | W %s %s | %s"
             black black-captures white white-captures est)))

(defun gnugo-write-sgf-file (filename)
  "Save the game history to FILENAME (even if unfinished).
If FILENAME already exists, Emacs confirms that you wish to overwrite it."
  (interactive "FWrite game as SGF file: ")
  (when (and (file-exists-p filename)
             (not (y-or-n-p "File exists. Continue? ")))
    (user-error "Not writing %s" filename))
  (gnugo/sgf-write-file (gnugo-get :sgf-collection) filename)
  (set-buffer-modified-p nil))

(defun gnugo--who-is-who (wait play samep)
  (message "GNU Go %splays as %s, you as %s (%s)"
           (if samep "" "now ")
           wait play (if samep
                         "as before"
                       "NOTE: this is a switch!")))

(defsubst gnugo--nodep (x)
  (keywordp (caar x)))

(defsubst gnugo--SZ! (size)
  (gnugo-put :SZ size))

(defun gnugo-read-sgf-file (filename)
  "Load the first game tree from FILENAME, a file in SGF format."
  (interactive "fSGF file to load: ")
  (when (file-directory-p filename)
    (user-error "Cannot load a directory (try a filename with extension .sgf)"))
  (let (ans play wait samep coll tree)
    ;; problem: requiring GTP `loadsgf' complicates network subproc support;
    ;; todo: skip it altogether when confident about `gnugo/sgf-create'
    (unless (= ?= (aref (setq ans (gnugo--q "loadsgf %s"
                                            (expand-file-name filename)))
                        0))
      (user-error "%s" ans))
    (setq play (substring ans 2)
          wait (gnugo-other play)
          samep (string= (gnugo-get :user-color) play))
    (gnugo-put :last-mover wait)
    (unless samep
      (gnugo-put :gnugo-color wait)
      (gnugo-put :user-color play))
    (setq coll (gnugo/sgf-create filename)
          tree (nth (let ((n (length coll)))
                      ;; This is better:
                      ;; (if (= 1 n)
                      ;;     0
                      ;;   (let* ((q (format "Which game? (1-%d)" n))
                      ;;          (choice (1- (read-number q 1))))
                      ;;     (if (and (< -1 choice) (< choice n))
                      ;;         choice
                      ;;       (message "(Selecting the first game)")
                      ;;       0)))
                      ;; but this is what we use (for now) to accomodate
                      ;; (aka faithfully mimic) GTP `loadsgf' limitations:
                      (unless (= 1 n)
                        (message "(Selecting the first game)"))
                      0)
                    coll))
    (gnugo-put :sgf-collection coll)
    (gnugo-put :sgf-gametree tree)
    (gnugo-put :monkey (vector (aref (gnugo--tree-ends tree) 0) 0))
    ;; This is deliberately undocumented for now.
    (gnugo--SZ! (gnugo--root-prop :SZ tree))
    (let (game-over)
      (gnugo-put :game-over
        (setq game-over
              (or (gnugo--root-prop :RE tree)
                  (and (equal '("PASS" "PASS") (gnugo-move-history 'two))
                       'two-passes))))
      (when (and game-over
                 ;; (maybe) todo: user var to inhibit (can be slow)
                 t)
        (gnugo-close-game nil game-over)))
    (gnugo-refresh t)
    (set-buffer-modified-p nil)
    (gnugo--who-is-who wait play samep)))

(defun gnugo-magic-undo (spec &optional noalt keep)
  "Undo moves on the GNUGO Board, based on SPEC, a string or number.
If SPEC is a string in the form of a board position (e.g., \"T19\"),
check that the position is occupied by a stone of the user's color,
and if so, remove moves from the history until that position is clear.
If SPEC is a positive number, remove exactly that many moves from the
history, signaling an error if the history is exhausted before finishing.
If SPEC Is 0 (zero), remove either one or two moves,
so that you are to play next.
If SPEC is not recognized, signal \"bad spec\" error.

Refresh the board for each move undone.  If (in the case where SPEC is
a number) after finishing, the color to play is not the user's color,
schedule a move by GNU Go.

After undoing the move(s), schedule a move by GNU Go if it is GNU Go's
turn to play.  Optional second arg NOALT non-nil inhibits this.

Optional third arg KEEP non-nil means do not prune the undone moves
from the gametree, such that they become a sub-gametree (variation)
when play resumes."
  (gnugo-gate)
  (let* ((n 0)
         (user-color (gnugo-get :user-color))
         (monkey (gnugo-get :monkey))
         (tree (gnugo-get :sgf-gametree))
         (ends (gnugo--tree-ends tree))
         (remorseful (not (gnugo--no-regrets monkey ends)))
         done ans)
    (cond ((numberp spec)
           (setq n (if (zerop spec)
                       (if (string= user-color (gnugo-get :last-mover))
                           1
                         2)
                     spec)
                 done (lambda () (zerop n))))
          ((string-match "^[a-z]" spec)
           (let ((pos (upcase spec)))
             (setq done `(lambda ()
                           (gnugo-goto-pos ,pos)
                           (memq (following-char) '(?. ?+))))
             (when (funcall done)
               (user-error "%s already clear" pos))
             (when (= (save-excursion
                        (gnugo-goto-pos pos)
                        (following-char))
                      (if (gnugo--blackp user-color)
                          ?O
                        ?X))
               (user-error "%s not occupied by %s" pos user-color))))
          (t (user-error "Bad spec: %S" spec)))
    (when (gnugo-get :game-over)
      (gnugo--unclose-game))
    (while (not (funcall done))
      (setq ans (gnugo--q "undo"))
      (unless (= ?= (aref ans 0))
        (user-error "%s" ans))
      (pop (aref monkey 0))
      (gnugo-put :last-mover (gnugo-other (gnugo-get :last-mover)))
      (gnugo-merge-showboard-results)   ; all
      (gnugo-refresh)                   ; this
      (decf n)                          ; is
      (redisplay))                      ; eye candy
    (let* ((ulastp (string= (gnugo-get :last-mover) user-color))

           (ubpos (gnugo-move-history (if ulastp 'car 'cadr))))
      (gnugo-put :last-user-bpos (if (and ubpos (not (gnugo--passp ubpos)))
                                     ubpos
                                   (gnugo-get :center-position)))
      (gnugo-refresh t)
      (unless (or keep remorseful)
        (aset ends (aref monkey 1) (aref monkey 0)))
      (when (and ulastp (not noalt))
        (gnugo-get-move (gnugo-get :gnugo-color))))))

(defun gnugo-undo-one-move (&optional me-next)
  "Undo exactly one move (perhaps GNU Go's, perhaps yours).
Do not schedule a move by GNU Go even if it is GNU Go's turn to play.
Prefix arg ME-NEXT means to arrange for you to play
the color of the next move (and GNU Go the opposite).
This is useful after loading an SGF file whose last
move was done by the color you prefer to play:
 \\[gnugo-read-sgf-file] FILENAME RET
 C-u \\[gnugo-undo-one-move]

See also `gnugo-undo-two-moves'."
  (interactive "P")
  (gnugo-gate)
  (gnugo-magic-undo 1 t)
  (when me-next
    (let* ((wait (gnugo-get :last-mover))
           (play (gnugo-other wait)))
      (gnugo--who-is-who wait play (string= play (gnugo-get :user-color)))
      (gnugo-put :user-color play)
      (gnugo-put :gnugo-color wait))))

(defun gnugo-undo-two-moves ()
  "Undo a pair of moves (GNU Go's and yours).
However, if you are the last mover, undo only one move.
Regardless, after undoing, it is your turn to play again."
  (interactive)
  (gnugo-gate)
  (gnugo-magic-undo 0))

(defun gnugo-oops (&optional position)
  "Like `gnugo-undo-two-moves', but keep the undone moves.
The kept moves become a sub-gametree (variation) when play resumes.
Prefix arg means, instead, undo repeatedly up to and including
the move which placed the stone at point, like `\\[gnugo-fancy-undo]'."
  (interactive "P")
  (gnugo-gate)
  (gnugo-magic-undo (if position
                        (gnugo-position)
                      0)
                    nil t))

(defun gnugo-okay (&optional full)
  "Redo a pair of undone moves.
Prefix arg means to redo all the undone moves."
  (interactive "P")
  (gnugo-gate)
  (let* ((tree (gnugo-get :sgf-gametree))
         (ends (gnugo--tree-ends tree))
         (monkey (gnugo-get :monkey)))
    (if (gnugo--no-regrets monkey ends)
        (message "Oop ack!")
      (let* ((as-pos (gnugo--as-pos-func))
             (mnum (gnugo--tree-mnum tree))
             (mem (aref monkey 0))
             (bidx (aref monkey 1))
             (end (aref ends bidx))
             (ucolor (gnugo-get :user-color))
             (gcolor (gnugo-other ucolor))
             (uprop (if (gnugo--blackp ucolor)
                        :B :W)))
        (cl-flet ((mvno (node) (gethash node mnum)))
          (loop
           with ok = (if full
                         (mvno (car end))
                       (+ 2 (mvno (car mem))))
           with (node move todo)
           for ls on end
           do (progn
                (setq node (car ls)
                      move (gnugo--move-prop node))
                (when (and move (>= ok (mvno node)))
                  (let ((userp (eq uprop (car move))))
                    (push (list (if userp ucolor gcolor)
                                userp
                                (funcall as-pos (cdr move)))
                          todo))))
           until (eq mem (cdr ls))
           finally do
           (loop
            for (color userp pos) in todo
            do (progn
                 (gnugo--play-stone color pos)
                 (gnugo-push-move userp pos)
                 (gnugo-refresh)
                 (redisplay)))))))))

(defun gnugo-display-final-score ()
  "Display final score and other info in another buffer (when game over).
If the game is still ongoing, Emacs asks if you wish to stop play (by
making sure two \"pass\" moves are played consecutively, if necessary).
Also, add the `:RE' SGF property to the root node of the game tree."
  (interactive)
  (let ((game-over (gnugo-get :game-over)))
    (unless (or game-over
                (and (not (gnugo-get :waitingp))
                     (y-or-n-p "Game still in play. Stop play now? ")))
      (user-error "Sorry, game still in play"))
    (unless game-over
      (cl-flet
          ((pass (userp)
                 (message "Playing PASS for %s ..."
                          (gnugo-get (if userp :user-color :gnugo-color)))
                 (sit-for 1)
                 (gnugo-push-move userp "PASS")))
        (unless (pass t)
          (pass nil)))
      (gnugo-refresh)
      (sit-for 3)))
  (let ((b=  "   Black = ")
        (w=  "   White = ")
        (res (when (string= "resign" (gnugo-move-history 'car))
               (gnugo-get :last-mover)))
        blurb result)
    (if res
        (setq blurb (list
                     (format "%s wins.\n"
                             (substring (if (= ?b (aref res 0)) w= b=)
                                        3 8))
                     "The game is over.\n"
                     (format "Resignation by %s.\n" res))
              result (concat (upcase (substring (gnugo-other res) 0 1))
                             "+Resign"))
      (message "Computing final score ...")
      (let* ((g-over (gnugo-get :game-over))
             (live   (cdr (assq 'live g-over)))
             (dead   (cdr (assq 'dead g-over)))
             (seed   (gnugo-get :scoring-seed))
             (terr-q (format "final_status_list %%s_territory %d" seed))
             (terr   "territory")
             (capt   "captures")
             (b-terr (gnugo--count-query terr-q "black"))
             (w-terr (gnugo--count-query terr-q "white"))
             (b-capt (string-to-number (gnugo-get :black-captures)))
             (w-capt (string-to-number (gnugo-get :white-captures)))
             (komi   (gnugo--root-prop :KM)))
        (setq blurb (list "The game is over.  Final score:\n")
              result (gnugo-query "final_score %d" seed))
        (cond ((string= "Chinese" (gnugo--root-prop :RU))
               (dolist (group live)
                 (incf (if (gnugo--blackp (caar group))
                           b-terr
                         w-terr)
                       (length (cdr group))))
               (dolist (group dead)
                 (incf (if (gnugo--blackp (caar group))
                           w-terr
                         b-terr)
                       (length (cdr group))))
               (push (format "%s%d %s = %3.1f\n" b= b-terr terr b-terr) blurb)
               (push (format "%s%d %s + %3.1f %s = %3.1f\n" w=
                             w-terr terr komi 'komi (+ w-terr komi))
                     blurb))
              (t
               (dolist (group dead)
                 (incf (if (gnugo--blackp (caar group))
                           w-terr
                         b-terr)
                       (* 2 (length (cdr group)))))
               (push (format "%s%d %s + %s %s = %3.1f\n" b=
                             b-terr terr
                             b-capt capt
                             (+ b-terr b-capt))
                     blurb)
               (push (format "%s%d %s + %s %s + %3.1f %s = %3.1f\n" w=
                             w-terr terr
                             w-capt capt
                             komi 'komi
                             (+ w-terr w-capt komi))
                     blurb)))
        (push (if (string= "0" result)
                  "The game is a draw.\n"
                (format "%s wins by %s.\n"
                        (substring (if (= ?B (aref result 0)) b= w=) 3 8)
                        (substring result 2)))
              blurb)
        (message "Computing final score ... done")))
    ;; extra info
    (let ((beg (gnugo-get :game-start-time))
          (end (gnugo-get :game-end-time)))
      (when end
        (push "\n" blurb)
        (cl-flet
            ((yep (pretty moment)
                  (push (format-time-string
                         (concat pretty ": %Y-%m-%d %H:%M:%S %z\n")
                         moment)
                        blurb)))
          (yep "Game start" beg)
          (yep "       end" end))))
    (setq blurb (apply 'concat (nreverse blurb)))
    (gnugo--set-root-prop :RE result)
    (switch-to-buffer (format "%s*GNUGO Final Score*" (gnugo-get :diamond)))
    (erase-buffer)
    (insert blurb)))

(defun gnugo-quit ()
  "Kill the current buffer, assumed to be in GNUGO Board mode, maybe.
If the game is not over, ask for confirmation first."
  (interactive)
  (if (or (gnugo-get :game-over)
          (y-or-n-p "Quit? "))
      (kill-buffer nil)
    (message "(not quitting)")))

(defun gnugo-leave-me-alone ()
  "Kill the current buffer unconditionally."
  (interactive)
  (kill-buffer nil))

(defun gnugo-fancy-undo (count)
  "Rewind the game tree in various ways.
Prefix arg COUNT means to undo that many moves.
Otherwise, undo repeatedly up to and including the move
which placed the stone at point."
  (interactive "P")
  (gnugo-magic-undo
   ;; TODO: Move this into `gnugo-magic-undo' proper.
   (cond ((numberp count) count)
         ((consp count) (car count))
         (t (gnugo-position)))))

(defun gnugo-toggle-image-display-command () ; ugh
  "Toggle use of images to display the board, then refresh."
  (interactive)
  (gnugo-toggle-image-display)
  (save-excursion (gnugo-refresh)))

(defun gnugo-describe-position ()
  "Display the board position under cursor in the echo area.
If there a stone at that position, also display its move number."
  (interactive)
  (let ((pos (gnugo-position))          ; do first (can throw)
        (color (case (following-char)
                 (?X :B)
                 (?O :W))))
    (message
     "%s%s" pos
     (or (when color
           (loop
            with monkey = (gnugo-get :monkey)
            with tree   = (gnugo-get :sgf-gametree)
            with mnum   = (gnugo--tree-mnum tree)
            with as-cc  = (gnugo--as-cc-func)
            with fruit  = (cons color (funcall as-cc pos))
            for node in (aref monkey 0)
            if (member fruit node)
            return
            (format " (move %d)"
                    (gethash node mnum))
            finally return
            nil))
         ""))))

(defun gnugo-switch-to-another ()
  "Switch to another GNU Go game buffer (if any)."
  (interactive)
  (loop for buf in (cdr (buffer-list))
        if (gnugo-board-buffer-p buf)
        return (progn
                 (bury-buffer)
                 (switch-to-buffer buf))
        finally do (message "(only one)")))

;;;---------------------------------------------------------------------------
;;; Command properties and gnugo-command

;; GTP commands entered by the user are never issued directly to GNU Go;
;; instead, their behavior and output are controlled by the property
;; `:gnugo-gtp-command-spec' hung off of each (interned/symbolic) command.
;; The value of this property is a sub-plist, w/ sub-properties as follows:
;;
;; :full -- completely interpret the command string; the value is a
;;          func that takes the list of words derived from splitting the
;;          command string (minus the command) and handles everything.
;;
;; :output -- either a keyword specifying the preferred output method:
;;              :message -- show output in minibuffer
;;              :discard -- sometimes you just don't care;
;;            or a function that takes one arg, the output string, and
;;            handles it completely.   default is to switch to buffer
;;            "*gnugo command output*" if the output has a newline,
;;            otherwise use `message'.
;;
;; :post-thunk -- run after output processing (at the very end).

(defun gnugo-command (command)
  "Send the Go Text Protocol COMMAND (a string) to GNU Go.
Output and Emacs behavior depend on which command is given (some
commands are handled completely by Emacs w/o using the subprocess;
some commands have their output displayed in specially prepared
buffers or in the echo area; some commands are instrumented to do
gnugo.el-specific housekeeping).

For example, for the command \"help\", Emacs visits the
GTP command reference info page.

NOTE: At this time, GTP command handling specification is still
      incomplete.  Thus, some commands WILL confuse gnugo.el."
  (interactive "sCommand: ")
  (if (string= "" command)
      (message "(no command given)")
    (let* ((split (split-string command))
           (cmd (intern (car split)))
           (spec (get cmd :gnugo-gtp-command-spec))
           (full (plist-get spec :full)))
      (if full
          (funcall full (cdr split))
        (message "Doing %s ..." command)
        (let* ((ans (gnugo--q command))
               (where (plist-get spec :output)))
          (if (string-match "unknown.command" ans)
              (message "%s" ans)
            (cond ((functionp where) (funcall where ans))
                  ((eq :discard where) (message ""))
                  ((or (eq :message where)
                       (not (string-match "\n" ans)))
                   (message "%s" ans))
                  (t (switch-to-buffer "*gnugo command output*")
                     (erase-buffer)
                     (insert ans)
                     (message "Doing %s ... done." command)))
            (let ((thunk (plist-get spec :post-thunk)))
              (when thunk (funcall thunk)))))))))

;;;---------------------------------------------------------------------------
;;; Major mode for interacting with a GNUGO subprocess

(put 'gnugo-board-mode 'mode-class 'special)
(defun gnugo-board-mode ()
  "Major mode for playing GNU Go.
Entering this mode runs the normal hook `gnugo-board-mode-hook'.
In this mode, keys do not self insert.

\\{gnugo-board-mode-map}"
  (switch-to-buffer (generate-new-buffer "(Uninitialized GNUGO Board)"))
  (buffer-disable-undo)                 ; todo: undo undo undoing
  (kill-all-local-variables)
  (use-local-map gnugo-board-mode-map)
  (set (make-local-variable 'font-lock-defaults)
       '(gnugo-font-lock-keywords t))
  (setq major-mode 'gnugo-board-mode
        mode-name "GNUGO Board"
        truncate-lines t)
  (add-hook 'kill-buffer-hook 'gnugo-cleanup nil t)
  (set (make-local-variable 'gnugo-state)
       (gnugo--mkht :size (1- 42)))
  (add-to-invisibility-spec :nogrid)
  (mapc (lambda (prop)
          (gnugo-put prop nil))         ; todo: separate display/game aspects;
        '(:game-over                    ;       move latter to func `gnugo'
          :waitingp
          :last-waiting
          :black-captures
          :white-captures
          :mode-line
          :mode-line-form
          :display-using-images
          :xpms
          :local-xpms
          :all-yy))
  (let ((name (if (string-match "[ ]" gnugo-program)
                  (let ((p (substring gnugo-program 0 (match-beginning 0)))
                        (o (substring gnugo-program (match-end 0)))
                        (h (or (car gnugo-option-history) "")))
                    (when (string-match "--mode" o)
                      (user-error "Found \"--mode\" in `gnugo-program'"))
                    (when (and o (cl-plusp (length o))
                               h (cl-plusp (length o))
                               (or (< (length h) (length o))
                                   (not (string= (substring h 0 (length o))
                                                 o))))
                      (push (concat o " " h) gnugo-option-history))
                    p)
                gnugo-program))
        (args (read-string "GNU Go options: "
                           (car gnugo-option-history)
                           'gnugo-option-history))
        proc
        board-size user-color handicap komi minus-l infile)
    (loop for (var default opt rx)
          in '((board-size      19 "--boardsize")
               (user-color "black" "--color" "\\(black\\|white\\)")
               (handicap         0 "--handicap")
               (komi           0.0 "--komi")
               (minus-l        nil "\\([^-]\\|^\\)-l[ ]*" "[^ ]+")
               (infile         nil "--infile" "[ ]*[^ ]+"))
          do (set var
                  (or (when (string-match opt args)
                        (let ((start (match-end 0)) s)
                          (string-match (or rx "[0-9.]+") args start)
                          (setq s (match-string 0 args))
                          (if rx s (string-to-number s))))
                      default)))
    (gnugo-put :user-color user-color)
    (let ((proc-args (split-string args)))
      (gnugo-put :proc-args proc-args)
      (gnugo-put :proc (setq proc (apply 'start-process "gnugo"
                                         (current-buffer) name
                                         "--mode" "gtp" "--quiet"
                                         proc-args))))
    (set-process-sentinel proc 'gnugo-sentinel)
    ;; Emacs is too protective sometimes, blech.
    (set-process-query-on-exit-flag proc nil)
    (when (or minus-l infile)
      (loop for (prop q)
            in '((board-size "query_boardsize")
                 (komi       "get_komi")
                 (handicap   "get_handicap"))
            do (set prop (string-to-number (gnugo-query q)))))
    (gnugo-put :diamond (substring (process-name proc) 5))
    (gnugo-put :gnugo-color (gnugo-other user-color))
    (gnugo-put :highlight-last-move-spec
      (gnugo-put :default-highlight-last-move-spec '("(" -1 nil)))
    (gnugo-put :lparen-ov (make-overlay 1 1))
    (gnugo-put :rparen-ov (let ((ov (make-overlay 1 1)))
                            (overlay-put ov 'display ")")
                            ov))
    (let* ((coll (gnugo/sgf-create "(;FF[4]GM[1])" t))
           (tree (car coll)))
      (gnugo-put :sgf-gametree tree)
      (gnugo-put :sgf-collection coll)
      (gnugo-put :monkey (vector (aref (gnugo--tree-ends tree) 0) 0)))
    (gnugo--SZ! board-size)
    (loop with gb = (gnugo--blackp (gnugo-other user-color))
          for (property value mogrifyp) in
          `((:SZ ,board-size)
            (:DT ,(format-time-string "%Y-%m-%d"))
            (:RU ,(if (string-match "--chinese-rules" args)
                      "Chinese"
                    "Japanese"))
            (:AP ("gnugo.el" . ,gnugo-version))
            (:KM ,komi)
            (,(if gb :PW :PB) ,(user-full-name))
            (,(if gb :PB :PW) ,(concat "GNU Go " (gnugo-query "version")))
            ,@(when (not (zerop handicap))
                `((:HA ,handicap)
                  (:AB ,(gnugo-lsquery "fixed_handicap %d" handicap)
                       t))))
          do (gnugo-note property value mogrifyp)))
  (gnugo-put :waiting-start (current-time))
  (gnugo-put :hmul 1)
  (gnugo-put :wmul 1)
  (run-hooks 'gnugo-board-mode-hook)
  (gnugo-refresh t))

;;;---------------------------------------------------------------------------
;;; Entry point

;;;###autoload
(defun gnugo (&optional new-game)
  "Run gnugo in a buffer, or resume a game in progress.
Prefix arg means skip the game-in-progress check and start a new
game straight away.
\\<gnugo-board-mode-map>
To play, use \\[gnugo-move] to place a stone or \\[gnugo-pass] to pass.

You are queried for additional command-line options (Emacs supplies
\"--mode gtp --quiet\" automatically).  Here is a list of options
that gnugo.el understands and handles specially:

    --boardsize num   Set the board size to use (5--19)
    --color <color>   Choose your color ('black' or 'white')
    --handicap <num>  Set the number of handicap stones (0--9)

If there is already a game in progress you may resume it instead of
starting a new one.  See `gnugo-board-mode' documentation for more info."
  (interactive "P")
  (let* ((all (let (acc)
                (dolist (buf (buffer-list))
                  (when (gnugo-board-buffer-p buf)
                    (push (cons (buffer-name buf) buf) acc)))
                acc))
         (n (length all)))
    (if (and (not new-game)
             (cl-plusp n)
             (y-or-n-p (format "GNU Go game%s in progress, resume play? "
                               (if (= 1 n) "" "s"))))
        ;; resume
        (switch-to-buffer
         (cdr (if (= 1 n)
                  (car all)
                (let ((sel (completing-read "Which one? " all nil t)))
                  (if (string= "" sel)
                      (car all)
                    (assoc sel all))))))
      ;; set up a new board
      (gnugo-board-mode)
      (let ((half (truncate (1+ (gnugo-get :SZ)) 2)))
        (gnugo-goto-pos (format "A%d" half))
        (forward-char (* 2 (1- half)))
        (gnugo-put :last-user-bpos
          (gnugo-put :center-position
            (get-text-property (point) 'gnugo-position))))
      ;; first move
      (gnugo-put :game-start-time (current-time))
      (let ((g (gnugo-get :gnugo-color))
            (n (or (gnugo--root-prop :HA) 0))
            (u (gnugo-get :user-color)))
        (gnugo-put :last-mover g)
        (when (or (and (gnugo--blackp u) (< 1 n))
                  (and (gnugo--blackp g) (< n 2)))
          (gnugo-put :last-mover u)
          (gnugo-refresh t)
          (gnugo-get-move g))))))

;;;---------------------------------------------------------------------------
;;; Load-time actions

(unless gnugo-frolic-mode-map
  (setq gnugo-frolic-mode-map (make-sparse-keymap))
  (suppress-keymap gnugo-frolic-mode-map)
  (mapc (lambda (pair)
          (define-key gnugo-frolic-mode-map (car pair) (cdr pair)))
        '(("q"          . gnugo-frolic-quit)
          ("C"          . gnugo-frolic-quit) ; like ‘View-kill-and-leave’
          ("\C-b"       . gnugo-frolic-backward-branch)
          ("\C-f"       . gnugo-frolic-forward-branch)
          ("\C-p"       . gnugo-frolic-previous-move)
          ("\C-n"       . gnugo-frolic-next-move)
          ("j"          . gnugo-frolic-exchange-left)
          ("J"          . gnugo-frolic-rotate-left)
          ("k"          . gnugo-frolic-exchange-right)
          ("K"          . gnugo-frolic-rotate-right)
          ("\C-m"       . gnugo-frolic-set-as-main-line)
          ("\C-\M-p"    . gnugo-frolic-prune-branch)
          ("o"          . gnugo-frolic-return-to-origin))))

(unless gnugo-board-mode-map
  (setq gnugo-board-mode-map (make-sparse-keymap))
  (suppress-keymap gnugo-board-mode-map)
  (mapc (lambda (pair)
          (define-key gnugo-board-mode-map (car pair) (cdr pair)))
        '(("?"        . describe-mode)
          ("\C-m"     . gnugo-move)
          (" "        . gnugo-move)
          ("P"        . gnugo-pass)
          ("R"        . gnugo-resign)
          ("q"        . gnugo-quit)
          ("Q"        . gnugo-leave-me-alone)
          ("U"        . gnugo-fancy-undo)
          ("\M-u"     . gnugo-undo-one-move)
          ("u"        . gnugo-undo-two-moves)
          ("\C-?"     . gnugo-undo-two-moves)
          ("o"        . gnugo-oops)
          ("O"        . gnugo-okay)
          ("\C-l"     . gnugo-refresh)
          ("\M-_"     . gnugo-boss-is-near)
          ("_"        . gnugo-boss-is-near)
          ("h"        . gnugo-move-history)
          ("L"        . gnugo-frolic-in-the-leaves)
          ("i"        . gnugo-toggle-image-display-command)
          ("w"        . gnugo-worm-stones)
          ("W"        . gnugo-worm-data)
          ("d"        . gnugo-dragon-stones)
          ("D"        . gnugo-dragon-data)
          ("t"        . gnugo-toggle-dead-group)
          ("g"        . gnugo-toggle-grid)
          ("!"        . gnugo-estimate-score)
          (":"        . gnugo-command)
          (";"        . gnugo-command)
          ("="        . gnugo-describe-position)
          ("s"        . gnugo-write-sgf-file)
          ("\C-x\C-s" . gnugo-write-sgf-file)
          ("\C-x\C-w" . gnugo-write-sgf-file)
          ("l"        . gnugo-read-sgf-file)
          ("F"        . gnugo-display-final-score)
          ("A"        . gnugo-switch-to-another)
          ;; mouse
          ([(down-mouse-1)] . gnugo-mouse-move)
          ([(down-mouse-2)] . gnugo-mouse-move) ; mitigate accidents
          ([(down-mouse-3)] . gnugo-mouse-pass)
          ;; delving into the curiosities
          ("\C-c\C-p" . gnugo-describe-internal-properties))))

(unless (get 'help :gnugo-gtp-command-spec)
  (cl-flet*
      ((sget (x) (get x :gnugo-gtp-command-spec))
       (jam (cmd prop val) (put cmd :gnugo-gtp-command-spec
                                (plist-put (sget cmd) prop val)))
       (defgtp (x &rest props) (dolist (cmd (if (symbolp x) (list x) x))
                                 (let ((ls props))
                                   (while ls
                                     (jam cmd (car ls) (cadr ls))
                                     (setq ls (cddr ls)))))))
    (cl-macrolet ((deffull (who &body body)
                    (declare (indent 1))
                    `(defgtp ',who :full (lambda (sel)
                                           ,@body))))

      (deffull help
        (info "(gnugo)GTP command reference")
        (when sel (setq sel (intern (car sel))))
        (let (buffer-read-only pad cur spec output found)
          (cl-flet
              ((note (s) (insert pad "[NOTE: gnugo.el " s ".]\n")))
            (goto-char (point-min))
            (save-excursion
              (while (re-search-forward "^ *[*] \\([a-zA-Z_]+\\)\\(:.*\\)*\n"
                                        (point-max) t)
                (unless pad
                  (setq pad (make-string (- (match-beginning 1)
                                            (match-beginning 0))
                                         32)))
                (when (plist-get
                       (setq spec
                             (get (setq cur (intern (match-string 1)))
                                  :gnugo-gtp-command-spec))
                       :full)
                  (note "handles this command completely"))
                (when (setq output (plist-get spec :output))
                  (if (functionp output)
                      (note "handles the output specially")
                    (case output
                      (:discard (note "discards the output"))
                      (:message (note "displays the output in the echo area")))))
                (when (eq sel cur)
                  (setq found (match-beginning 0))))))
          (cond (found (goto-char found))
                ((not sel))
                (t (message "(no such command: %s)" sel)))))

      (deffull final_score
        ;; Explicit ignorance avoids byte-compiler warning.
        (ignore sel)
        (gnugo-display-final-score))

      (defgtp '(boardsize
                clear_board
                fixed_handicap)
        :output :discard
        :post-thunk (lambda ()
                      (gnugo--unclose-game)
                      (gnugo-put :last-mover nil)
                      ;; ugh
                      (gnugo--SZ! (string-to-number
                                   (gnugo-query
                                    "query_boardsize")))
                      (gnugo-refresh t)))

      (deffull loadsgf
        (gnugo-read-sgf-file (car sel)))

      (deffull (undo gg-undo)
        (gnugo-magic-undo
         (let (n)
           (cond ((not sel) 1)
                 ((cl-plusp (setq n (string-to-number (car sel)))) n)
                 (t (car sel)))))))))

(provide 'gnugo)

\f
;;;---------------------------------------------------------------------------
;;; The remainder of this file defines a simplified SGF-handling library.
;;; When/if it should start to attain generality, it should be split off into
;;; a separate file (probably named sgf.el) w/ funcs and vars renamed sans the
;;; "gnugo/" prefix.

(defconst gnugo/sgf-*r4-properties*
  '((AB "Add Black"       setup list stone)
    (AE "Add Empty"       game  list point)
    (AN "Annotation"      game  simpletext)
    (AP "Application"     root  (simpletext . simpletext))
    (AR "Arrow"           -     list (point . point))
    (AS "Who adds stones" -     simpletext) ; (LOA)
    (AW "Add White"       setup list stone)
    (B  "Black"           move  move)
    (BL "Black time left" move  real)
    (BM "Bad move"        move  double)
    (BR "Black rank"      game  simpletext)
    (BT "Black team"      game  simpletext)
    (C  "Comment"         -     text)
    (CA "Charset"         root  simpletext)
    (CP "Copyright"       game  simpletext)
    (CR "Circle"          -     list point)
    (DD "Dim points"      -     elist point) ; (inherit)
    (DM "Even position"   -     double)
    (DO "Doubtful"        move  none)
    (DT "Date"            game  simpletext)
    (EV "Event"           game  simpletext)
    (FF "Fileformat"      root  [number (1 . 4)])
    (FG "Figure"          -     (or none (number . simpletext)))
    (GB "Good for Black"  -     double)
    (GC "Game comment"    game  text)
    (GM "Game"            root  [number (1 . 20)])
    (GN "Game name"       game  simpletext)
    (GW "Good for White"  -     double)
    (HA "Handicap"        game  number) ; (Go)
    (HO "Hotspot"         -     double)
    (IP "Initial pos."    game  simpletext) ; (LOA)
    (IT "Interesting"     move  none)
    (IY "Invert Y-axis"   game  simpletext)          ; (LOA)
    (KM "Komi"            game  real)                ; (Go)
    (KO "Ko"              move  none)
    (LB "Label"           -     list (point . simpletext))
    (LN "Line"            -     list (point . point))
    (MA "Mark"            -     list point)
    (MN "set move number" move  number)
    (N  "Nodename"        -     simpletext)
    (OB "OtStones Black"  move  number)
    (ON "Opening"         game  text)
    (OT "Overtime"        game  simpletext)
    (OW "OtStones White"  move  number)
    (PB "Player Black"    game  simpletext)
    (PC "Place"           game  simpletext)
    (PL "Player to play"  setup color)
    (PM "Print move mode" -     number) ; (inherit)
    (PW "Player White"    game  simpletext)
    (RE "Result"          game  simpletext)
    (RO "Round"           game  simpletext)
    (RU "Rules"           game  simpletext)
    (SE "Markup"          -     point)  ; (LOA)
    (SL "Selected"        -     list point)
    (SO "Source"          game  simpletext)
    (SQ "Square"          -     list point)
    (ST "Style"           root  [number (0 . 3)])
    (SU "Setup type"      game  simpletext) ; (LOA)
    (SZ "Size"            root  (or number (number . number)))
    (TB "Territory Black" -     elist point) ; (Go)
    (TE "Tesuji"          move  double)
    (TM "Timelimit"       game  real)
    (TR "Triangle"        -     list point)
    (TW "Territory White" -     elist point) ; (Go)
    (UC "Unclear pos"     -     double)
    (US "User"            game  simpletext)
    (V  "Value"           -     real)
    (VW "View"            -     elist point) ; (inherit)
    (W  "White"           move  move)
    (WL "White time left" move  real)
    (WR "White rank"      game  simpletext)
    (WT "White team"      game  simpletext)
    (LT "Lose on time"    setup simpletext))
  ;; r4-specific notes
  ;; - changed: DT FG LB RE RU SZ
  ;; - added: AP AR AS DD IP IY LN OT PM SE SQ ST SU VW
  "List of SGF[4] properties, each of the form (PROP NAME CONTEXT SPEC...).")

(defun gnugo/sgf-create (file-or-data &optional data-p)
  "Return the SGF[4] collection parsed from FILE-OR-DATA.
FILE-OR-DATA is a file name or SGF[4] data.
Optional arg DATA-P non-nil means FILE-OR-DATA is
a string containing SGF[4] data.
A collection is a list of gametrees, each a vector of four elements:

 ENDS -- a vector of node lists, with shared tails
         (last element of all the lists is the root node)

 MNUM -- `eq' hash: node to move numbers; non-\"move\" nodes
         have a move number of the previous \"move\" node (or zero)

 ROOT -- the root node"
  ;; Arg names inspired by `create-image', despite -P being frowned upon.
  (let ((keywords (or (get 'gnugo/sgf-*r4-properties* :keywords)
                      (put 'gnugo/sgf-*r4-properties* :keywords
                           (mapcar (lambda (full)
                                     (cons (car full)
                                           (intern (format ":%s" (car full)))))
                                   gnugo/sgf-*r4-properties*))))
        (specs (or (get 'gnugo/sgf-*r4-properties* :specs)
                   (put 'gnugo/sgf-*r4-properties* :specs
                        (mapcar (lambda (full)
                                  (cons (car full) (cdddr full)))
                                gnugo/sgf-*r4-properties*))))
        SZ)
    (cl-labels
        ((sw () (skip-chars-forward " \t\n"))
         (x (end preserve-whitespace)
            (let ((beg (point))
                  (endp (case end
                          (:end (lambda (char) (= ?\] char)))
                          (:mid (lambda (char) (= ?\: char)))
                          (t (lambda (char) (or (= ?\: char)
                                                (= ?\] char))))))
                  c)
              (while (not (funcall endp (setq c (following-char))))
                (cond ((= ?\\ c)
                       (delete-char 1)
                       (if (eolp)
                           (kill-line 1)
                         (forward-char 1)))
                      ((unless preserve-whitespace
                         (looking-at "\\s-+"))
                       (delete-region (point) (match-end 0))
                       (insert " "))
                      (t (forward-char 1))))
              (buffer-substring-no-properties beg (point))))
         (one (type end) (let ((s (progn
                                    (forward-char 1)
                                    (x end (eq 'text type)))))
                           (case type
                             ((stone point move)
                              ;; blech, begone bu"tt"-ugly blatherings
                              ;; (but bide brobdingnagian boards)...
                              (if (and (string= "tt" s)
                                       SZ
                                       (>= 19 SZ))
                                  ""
                                s))
                             ((simpletext color) s)
                             ((number real double) (string-to-number s))
                             ((text) s)
                             ((none) "")
                             (t (error "Unhandled type: %S" type)))))
         (val (spec) (cond ((symbolp spec)
                            (one spec :end))
                           ((vectorp spec)
                            ;; todo: check range here.
                            (one (aref spec 0) :end))
                           ((eq 'or (car spec))
                            (let ((v (one (cadr spec) t)))
                              (if (= ?\] (following-char))
                                  v
                                (forward-char 1)
                                ;; todo: this assumes `spec' has the form
                                ;;         (or foo (foo . bar))
                                ;; i.e., foo is not rescanned.  e.g., `SZ'.
                                ;; probably this assumption is consistent
                                ;; w/ the SGF authors' desire to make the
                                ;; parsing easy, but you never know...
                                (cons v (one (cdaddr spec) :end)))))
                           (t (cons (one (car spec) :mid)
                                    (one (cdr spec) :end)))))
         (short (who) (when (eobp)
                        (error "Unexpected EOF while reading %s" who)))
         (atvalp () (= ?\[ (following-char)))
         (PROP () (let (name spec ltype)
                    (sw) (short 'property)
                    (when (looking-at "[A-Z]")
                      (setq name (read (current-buffer))
                            spec (cdr (assq name specs)))
                      (sw)
                      (cons
                       (cdr (assq name keywords))
                       (prog1 (if (= 1 (length spec))
                                  (val (car spec))
                                (unless (memq (setq ltype (car spec))
                                              '(elist list))
                                  (error "Bad spec: %S" spec))
                                (if (and (eq 'elist ltype) (sw)
                                         (not (atvalp)))
                                    nil
                                  (let ((type (cadr spec))
                                        mo ls)
                                    (while (and (sw) (atvalp)
                                                (setq mo (val type)))
                                      (push mo ls)
                                      (forward-char 1))
                                    (forward-char -1)
                                    (nreverse ls))))
                         (forward-char 1))))))
         (morep () (and (sw) (not (eobp))))
         (seek (c) (and (morep) (= c (following-char))))
         (seek-into (c) (when (seek c)
                          (forward-char 1)
                          t))
         (NODE () (when (seek-into ?\;)
                    (loop with prop
                          while (setq prop (PROP))
                          collect (progn
                                    (when (eq :SZ (car prop))
                                      (setq SZ (cdr prop)))
                                    prop))))
         (TREE (parent mnum)
               (let ((ls parent)
                     prev node)
                 (seek-into ?\()
                 (while (seek ?\;)
                   (setq prev (car ls)
                         node (NODE))
                   (puthash node (+ (if (gnugo--move-prop node)
                                        1
                                      0)
                                    (gethash prev mnum 0))
                            mnum)
                   (push node
                         ls))
                 (prog1
                     (if (not (seek ?\())
                         ;; singular
                         (list ls)
                       ;; multiple
                       (loop while (seek ?\()
                             append (TREE ls mnum)))
                   (seek-into ?\))))))
      (with-temp-buffer
        (if (not data-p)
            (insert-file-contents file-or-data)
          (insert file-or-data)
          (goto-char (point-min)))
        (loop while (morep)
              collect (let* ((mnum (gnugo--mkht :weakness 'key))
                             (ends (TREE nil mnum))
                             (root (car (last (car ends)))))
                        (vector (apply 'vector ends)
                                mnum
                                root)))))))

(defun gnugo/sgf-write-file (collection filename)
  (let ((aft-newline-appreciated '(:AP :GN :PB :PW :HA :KM :RU :RE))
        (me (cons "gnugo.el" gnugo-version))
        (specs (mapcar (lambda (full)
                         (cons (intern (format ":%s" (car full)))
                               (cdddr full)))
                       gnugo/sgf-*r4-properties*))
        p name v spec)
    (cl-labels
        ((esc (composed fmt arg)
              (mapconcat (lambda (c)
                           (case c
                             ;; ‘?\[’ is not strictly required
                             ;; but neither is it forbidden.
                             ((?\[ ?\] ?\\) (format "\\%c" c))
                             (?: (concat (if composed "\\" "") ":"))
                             (t (string c))))
                         (string-to-list (format fmt arg))
                         ""))
         (>>one (v) (insert "[" (esc nil "%s" v) "]"))
         (>>two (v) (insert "["
                            (esc t "%s" (car v))
                            ":"
                            (esc t "%s" (cdr v))
                            "]"))
         (>>nl () (cond ((memq name aft-newline-appreciated)
                         (insert "\n"))
                        ((< 60 (current-column))
                         (save-excursion
                           (goto-char p)
                           (insert "\n")))))
         (>>prop (prop)
                 (setq p (point)
                       name (car prop)
                       v (cdr prop))
                 (insert (substring (symbol-name name) 1))
                 (cond ((not v))
                       ((and (consp v)
                             (setq spec (cdr (assq name specs)))
                             (memq (car spec)
                                   '(list elist)))
                        (>>nl)
                        (let ((>> (if (consp (cadr spec))
                                      #'>>two
                                    #'>>one)))
                          (dolist (little-v v)
                            (setq p (point))
                            (funcall >> little-v)
                            (>>nl))))
                       ((consp v)
                        (>>two v) (>>nl))
                       (t
                        (>>one v) (>>nl))))
         (>>node (node)
                 (loop initially (insert ";")
                       for prop in node
                       do (>>prop prop)))
         (>>tree (tree)
                 (unless (zerop (current-column))
                   (newline))
                 (insert "(")
                 (dolist (x tree)
                   (funcall (if (gnugo--nodep x)
                                #'>>node
                              #'>>tree)
                            x))
                 (insert ")")))
      (with-temp-buffer
        (dolist (tree collection)
          ;; take responsibility for our actions
          (gnugo--set-root-prop :AP me tree)
          ;; write it out
          (let ((ht (gnugo--mkht))
                (leaves (append (gnugo--tree-ends tree) nil)))
            (cl-flet
                ((hang (stack)
                       (loop
                        with rh         ; rectified history
                        with bp         ; branch point
                        for node in stack
                        until (setq bp (gethash node ht))
                        do (puthash node
                                    (push node rh) ; good for now: ½τ
                                    ht)
                        finally return
                        (if (not bp)
                            ;; first run: main line
                            rh
                          ;; subsequent runs: grafts (value discarded)
                          (setcdr bp (nconc
                                      ;; Maintain order of ‘leaves’.
                                      (let ((was (cdr bp)))
                                        (if (gnugo--nodep (car was))
                                            (list was)
                                          was))
                                      (list rh)))))))
              (setq tree (hang (pop leaves)))
              (mapc #'hang leaves)
              (>>tree tree))))
        (newline)
        (write-file filename)))))

;;; gnugo.el ends here