;;; org-babel-tangle.el --- Extract source code from org-mode files

;; Copyright (C) 2009 Dan Davison, Eric Schulte

;; Author: Dan Davison, Eric Schulte
;; Keywords: literate programming, reproducible research
;; Homepage: http://orgmode.org
;; Version: 0.01

;;; License:

;; 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, 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 GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; Extract the code from source blocks out into raw source-code files.

;;; Code:
(require 'org-babel)

(defvar org-babel-tangle-langs nil
  "Association list matching source-block languages.  The car of
each element should be a string indicating the source block
language, and the cdr should be a list containing the extension
and shebang(#!) line to use when writing out the language to
file.")

(defun org-babel-tangle-file (file &optional lang)
  "Extract the bodies of all source code blocks in FILE with
`org-babel-tangle'.  Optional argument LANG can be used to limit
the exported source code blocks by language."
  (save-window-excursion (find-file file) (org-babel-tangle lang)))

(defun org-babel-tangle (&optional lang)
  "Extract the bodies of all source code blocks from the current
file into their own source-specific files.  Optional argument
LANG can be used to limit the exported source code blocks by
language."
  (interactive)
  (save-excursion
    (let ((base-name (file-name-sans-extension (buffer-file-name)))
          (block-counter 0))
      (mapc ;; for every language create a file
       (lambda (by-lang)
         (let* ((lang (car by-lang))
                (lang-f (intern (concat lang "-mode")))
                (lang-specs (cdr (assoc lang org-babel-tangle-langs)))
                (ext (first lang-specs))
                (she-bang (second lang-specs))
                (by-session (cdr by-lang)))
           (flet ((to-file (filename specs)
                           (with-temp-file filename
                             (funcall lang-f)
                             (when she-bang (insert (concat she-bang "\n")))
                             (comment-region
			      (point) (progn (insert "generated by org-babel-tangle") (point)))
                             (mapc #'org-babel-spec-to-string (reverse specs)))))
             ;; if there are multiple sessions then break out by session
             (if (> (length by-session) 1)
                 (mapc (lambda (session-pair)
                         (setq block-counter (+ block-counter (length (cdr session-pair))))
                         (to-file (format
				   "%s-%s.%s" base-name (car session-pair) ext) (cdr session-pair)))
                       by-session)
               (setq block-counter (+ block-counter (length (cdr (car by-session)))))
               (to-file (format "%s.%s" base-name ext) (cdr (car by-session)))))))
       (org-babel-collect-blocks lang))
      (message "tangled %d source-code blocks" block-counter))))

(defun org-babel-collect-blocks (&optional lang)
  "Collect all source blocks in the current org-mode file.
Return two nested association lists, first grouped by language,
then by session, the contents will be source-code block
specifications of the form used by `org-babel-spec-to-string'.
Optional argument LANG can be used to limit the collected source
code blocks by language."
  (let ((block-counter 0) blocks)
    (org-babel-map-source-blocks (buffer-file-name)
      (setq block-counter (+ 1 block-counter))
      (let* ((link (progn (call-interactively 'org-store-link)
                          (org-babel-clean-text-properties (car (pop org-stored-links)))))
             (source-name (intern (or (org-babel-get-src-block-name)
                                      (format "block-%d" block-counter))))
             (info (org-babel-get-src-block-info))
             (src-lang (first info))
             (body (second info))
             (params (third info))
             (spec (list link source-name params body))
             (session (cdr (assoc :session params)))
             by-lang by-session)
        (unless (and lang (not (string= lang src-lang))) ;; maybe limit by language
          ;; add the spec for this block to blocks under it's language and session
          (setq by-lang (cdr (assoc src-lang blocks)))
          (setq blocks (delq (assoc src-lang blocks) blocks))
          (setq by-session (cdr (assoc session by-lang)))
          (setq by-lang (delq (assoc session by-lang) by-lang))
          (setq blocks (cons ;; by-language
                        (cons src-lang (cons ;; by-session
                                        (cons session (cons spec by-session)) by-lang))
                        blocks)))))
    ;; blocks should contain all source-blocks organized by language and session
    ;; (message "blocks=%S" blocks) ;; debugging
    blocks))

(defun org-babel-spec-to-string (spec)
  "Insert the source-code specified by SPEC into the current
source code file.  This function uses `comment-region' which
assumes that the appropriate major-mode is set.  SPEC has the
form

  (link source-name params body)"
  (flet ((insert-comment (text)
                         (comment-region (point) (progn (insert text) (point)))))
    (let ((link (first spec))
          (source-name (second spec))
          (body (fourth spec)))
      (insert "\n\n")
      (insert-comment (format "[[%s][%s]]" (org-link-escape link) source-name))
      (insert (format "\n%s\n" (org-babel-chomp body)))
      (insert-comment (format "%s ends here" source-name))
      (insert "\n"))))

(provide 'org-babel-tangle)
;;; org-babel-tangle.el ends here