;;; yasnippet.el --- Yet another snippet extension for Emacs.

;; Author: pluskid <pluskid@gmail.com>
;; Version: 0.1

;; This file 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 2, or (at your option)
;; any later version.

;; This file 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 GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; Nothing.

(require 'cl)

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;; User customizable variables
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(defvar yas/key-syntax "w"
  "Syntax of a key. This is used to determine the current key being 
expanded.")

(defvar yas/indent-line t
  "Each (except the 1st) line of the snippet template is indented to
current column if this variable is non-`nil'.")
(make-variable-buffer-local 'yas/indent-line)

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;; Internal variables
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(defvar yas/snippet-tables (make-hash-table)
  "A hash table of snippet tables corresponding to each major-mode.")

(defun yas/snippet-new ()
  "Create a new snippet."
  (cons nil nil))
(defun yas/snippet-field-groups (snippet)
  "Get field groups of SNIPPET."
  (car snippet))
(defun yas/snippet-field-groups-set (snippet groups)
  "Set field groups of SNIPPET."
  (setf (car snippet) groups))
(defun yas/snippet-exit-marker (snippet)
  "Get exit marker of SNIPPET."
  (cdr snippet))
(defun yas/snippet-add-field (snippet field)
  "Add FIELD to SNIPPET."
  (let ((group (find field
		     (yas/snippet-field-groups snippet)
		     :test
		     '(lambda (field group)
			(= (yas/snippet-field-number field)
			   (yas/snippet-field-group-number group))))))
    (if group
	(yas/snippet-field-group-add group field)
      (push (yas/snippet-field-group-new field)
	    (car snippet)))))

(defun yas/snippet-field-group-new (field)
  "Create a new field group."
  (list field             ; primary field
	(list field)      ; fields
	nil		  ; next field group
	nil))		  ; prev field group
(defun yas/snippet-field-group-primary (group)
  "Get the primary field of this group."
  (car group))
(defun yas/snippet-field-group-fields (group)
  "Get all fields belonging to this group."
  (cadr group))
(defun yas/snippet-field-group-set-next (group next)
  "Set next field group of GROUP."
  (setf (nth 2 group) next))
(defun yas/snippet-field-group-next (group)
  "Get next field group."
  (nth 2 group))
(defun yas/snippet-field-group-set-prev (group prev)
  "Set previous field group of GROUP."
  (setf (nth 2 group) prev))
(defun yas/snippet-field-group-prev (group)
  "Get previous field group."
  (nth 3 group))
(defun yas/snippet-field-group-value (group)
  "Get the default value of the field group."
  (or (yas/snippet-field-value
       (yas/snippet-field-group-primary group))
      ""))
(defun yas/snippet-field-group-number (group)
  "Get the number of the field group."
  (yas/snippet-field-number
   (yas/snippet-field-group-primary group)))
(defun yas/snippet-field-group-add (group field)
  "Add a field to the field group. If the value of the
field is not nil, it is set the primary field of the group."
  (push field (nth 1 group))
  (when (yas/snippet-field-value field)
    (setf (car group) field)))

(defun yas/snippet-field-new (overlay number value)
  "Create a new snippet-field."
  (cons overlay (cons number value)))
(defun yas/snippet-field-overlay (field)
  "Get the overlay of the field."
  (car field))
(defun yas/snippet-field-number (field)
  "Get the number of the field."
  (cadr field))
(defun yas/snippet-field-value (field)
  "Get the value of the field."
  (cddr field))
(defun yas/snippet-field-compare (field1 field2)
  "Compare two fields. The field with a number is sorted first.
If they both have a number, compare through the number. If neither
have, compare through the start point of the overlay."
  (let ((n1 (yas/snippet-field-number field1))
	(n2 (yas/snippet-field-number field2)))
    (if n1
	(if n2
	    (< n1 n2)
	  t)
      (if n2
	  nil
	(< (overlay-start (yas/snippet-field-overlay field1))
	   (overlay-start (yas/snippet-field-overlay field2)))))))

(defconst yas/escape-backslash
  (concat "YASESCAPE" "BACKSLASH" "PROTECTGUARD"))
(defconst yas/escape-dollar
  (concat "YASESCAPE" "DOLLAR" "PROTECTGUARD"))
(defconst yas/escape-backquote
  (concat "YASESCAPE" "BACKQUOTE" "PROTECTGUARD"))

(defconst yas/field-regexp
  (concat "$\\(?1:[0-9]+\\)" "\\|"
	  "${\\(?:\\(?1:[0-9]+\\):\\)?\\(?2:[^}]*\\)}"))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Internal functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defun yas/eval-string (string)
  "Evaluate STRING and convert the result to string."
  (condition-case err
      (format "%s" (eval (read string)))
    (error (format "(error in elisp evaluation: %s)" 
		   (error-message-string err)))))
(defsubst yas/replace-all (from to)
  "Replace all occurance from FROM to TO."
  (goto-char (point-min))
  (while (search-forward from nil t)
    (replace-match to t t)))
(defun yas/snippet-table (mode)
  "Get the snippet table corresponding to MODE."
  (let ((table (gethash mode yas/snippet-tables)))
    (unless table
      (setq table (make-hash-table :test 'equal))
      (puthash mode table yas/snippet-tables))
    table))
(defsubst yas/current-snippet-table ()
  "Get the snippet table for current major-mode."
  (yas/snippet-table major-mode))

(defsubst yas/template (key snippet-table)
  "Get template for KEY in SNIPPET-TABLE."
  (gethash key snippet-table))

(defun yas/current-key ()
  "Get the key under current position."
  (let ((start (point))
	(end (point)))
    (save-excursion
      (skip-syntax-backward yas/key-syntax)
      (setq start (point))
      (list (buffer-substring-no-properties start end)
	    start
	    end))))

(defun yas/expand-snippet (start end template)
  "Expand snippet at current point. Text between START and END
will be deleted before inserting template."
  (goto-char start)

  (let ((length (- end start))
	(column (current-column)))
  (save-restriction
    (narrow-to-region start start)

    (insert template)
    ;; Step 1: do necessary indent
    (when yas/indent-line
      (let* ((indent (if indent-tabs-mode
			 (concat (make-string (/ column tab-width) ?\t)
				 (make-string (% column tab-width) ?\ ))
		       (make-string column ?\ ))))
	(goto-char (point-min))
	(while (and (zerop (forward-line))
		    (= (current-column) 0))
	  (insert indent))))

    ;; Step 2: protect backslash and backquote
    (yas/replace-all "\\\\" yas/escape-backslash)
    (yas/replace-all "\\`" yas/escape-backquote)

    ;; Step 3: evaluate all backquotes
    (goto-char (point-min))
    (while (re-search-forward "`\\([^`]*\\)`" nil t)
      (replace-match (yas/eval-string (match-string-no-properties 1))
		     t t))

    ;; Step 4: protect all escapes, including backslash and backquot
    ;; which may be produced in Step 3
    (yas/replace-all "\\\\" yas/escape-backslash)
    (yas/replace-all "\\`" yas/escape-backquote)
    (yas/replace-all "\\$" yas/escape-dollar)

    (let ((snippet (yas/snippet-new)))
      ;; Step 5: Create fields
      (goto-char (point-min))
      (while (re-search-forward yas/field-regexp nil t)
	(yas/snippet-add-field
	 snippet
	 (yas/snippet-field-new
	  (make-overlay (match-beginning 0) (match-end 0))
	  (if (match-string-no-properties 1)
	      (string-to-number (match-string-no-properties 1))
	    nil)
	  (match-string-no-properties 2))))

      ;; Step 6: Sort and link each field group
      (yas/snippet-field-groups-set
       snippet
       (sort (yas/snippet-field-groups snippet)
	     '(lambda (group1 group2)
		(yas/snippet-field-compare
		 (yas/snippet-field-group-primary group1)
		 (yas/snippet-field-group-primary group2)))))
      (let ((prev nil))
	(dolist (group (yas/snippet-field-groups snippet))
	  (yas/snippet-field-group-set-prev group prev)
	  (when prev
	    (yas/snippet-field-group-set-next prev group))
	  (setq prev group)))

      ;; Step 7: Set up properties of overlays, including keymaps

      ;; Step 8: Replace fields with default values
      (dolist (group (yas/snippet-field-groups snippet))
	(let ((value (yas/snippet-field-group-value group)))
	  (dolist (field (yas/snippet-field-group-fields group))
	    (let* ((overlay (yas/snippet-field-overlay field))
		   (start (overlay-start overlay))
		   (end (overlay-end overlay))
		   (length (- end start)))
	      (goto-char start)
	      (insert value)
	      (delete-char length))))))

    ;; Step : restore all escape characters
    (yas/replace-all yas/escape-dollar "$")
    (yas/replace-all yas/escape-backquote "`")
    (yas/replace-all yas/escape-backslash "\\")

    (goto-char (point-max)))
  
  (delete-char length)))
  
  


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; User level functions
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(defun yas/define (mode key template)
  "Define a snippet. Expanding KEY into TEMPLATE."
  (puthash key template (yas/snippet-table mode)))

(defun yas/expand ()
  "Expand a snippet. When a snippet is expanded, t is returned,
otherwise, nil returned."
  (interactive)
  (multiple-value-bind (key start end) (yas/current-key)
    (let ((template (yas/template key (yas/current-snippet-table))))
      (if template
	  (progn
	    (yas/expand-snippet start end template)
	    t)
	nil))))

(provide 'yasnippet)