;;; 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 ()
  "Extract the bodies of all source code blocks form the current
file into their own source-specific files."
  (interactive)
  (let ((base-name (file-name-sans-extension (buffer-file-name)))
        blocks)
    ;; blocks will be two nested association lists, first grouped by
    ;; language, then by session, the contents of the second a-list
    ;; will be source-code blocks
    (org-babel-map-source-blocks (buffer-file-name)
      (let* ((link (progn (org-store-link nil) (pop org-stored-links)))
             (source-name (intern (org-babel-get-src-block-name)))
             (info (org-babel-get-src-block-info))
             (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)
        ;; add the spec for this block to blocks under it's lang and session
        (setq by-lang (org-babel-alist-pop lang blocks))
        (setq by-session (org-babel-alist-pop session by-lang))
        (setq blocks (cons ;; by-language
                      (cons 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 "block = %S" blocks) ;; debugging
    (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 she-bang))
                           (comment-region (point) (progn (insert "generated by org-babel-tangle") (point)))
                           (message "specs=%s" specs)
                           (mapc #'org-babel-spec-to-string specs))))
           ;; (message "lang=%s lang-specs=%s ext=%s she-bang=%s by-session=%s" lang lang-specs ext she-bang by-session) ;; debugging
           ;; if there are multiple sessions then break out by session
           (if (> (length by-session) 1)
               (mapc (lambda (session-pair)
                       (to-file (format "%s-%s.%s" base-name (car session-pair) ext) (cdr session-pair)))
                     by-session)
             (message "by-session=%s" by-session)
             (to-file (format "%s.%s" base-name ext) (cdr (car by-session)))))))
     blocks)))

(defun org-babel-spec-to-string (spec)
  "Return the string version of spec suitable for inclusion in a
source code file.  SPEC has the form

  (link source-name params body)"
  (flet ((insert-comment (text)
                         (comment-region (point) (progn (insert text) (point)))))
    (insert-comment (format "\n\nlink: %s" (first spec)))
    (insert-comment (format "\nsource-name: %s" (second spec)))
    (insert (format "\n%s\n" (fourth spec)))))

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