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+;;; ox-gfm.el --- Github Flavored Markdown Back-End for Org Export Engine
+
+;; Copyright (C) 2014 Lars Tveito
+
+;; Author: Lars Tveito
+;; Keywords: org, wp, markdown, github
+
+;; This file is not part of GNU Emacs.
+
+;; GNU Emacs 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.
+
+;; GNU Emacs 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.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This library implements a Markdown back-end (github flavor) for Org
+;; exporter, based on the `md' back-end.
+
+;;; Code:
+
+(require 'ox-md)
+
+
+
+;;; User-Configurable Variables
+
+(defgroup org-export-gfm nil
+  "Options specific to Markdown export back-end."
+  :tag "Org Github Flavored Markdown"
+  :group 'org-export
+  :version "24.4"
+  :package-version '(Org . "8.0"))
+
+(defcustom org-gfm-lang '(("emacs-lisp" . "lisp") ("elisp" . "lisp"))
+  "Alist of languages that are not recognized by Github, to
+  languages that are. Emacs lisp is a good example of this, where
+  we can use lisp as a nice replacement."
+  :group 'org-export-gfm)
+
+
+
+;;; Define Back-End
+
+(org-export-define-derived-backend 'gfm 'md
+  :export-block '("GFM" "GITHUB FLAVORED MARKDOWN")
+  :filters-alist '((:filter-parse-tree . org-md-separate-elements))
+  :menu-entry
+  '(?g "Export to Github Flavored Markdown"
+       ((?G "To temporary buffer"
+            (lambda (a s v b) (org-gfm-export-as-markdown a s v)))
+        (?g "To file" (lambda (a s v b) (org-gfm-export-to-markdown a s v)))
+        (?o "To file and open"
+            (lambda (a s v b)
+              (if a (org-gfm-export-to-markdown t s v)
+                (org-open-file (org-gfm-export-to-markdown nil s v)))))))
+  :translate-alist '((inner-template . org-gfm-inner-template)
+                     (strike-through . org-gfm-strike-through)
+                     (src-block . org-gfm-src-block)))
+
+
+
+;;; Transcode Functions
+
+;;;; Src Block
+
+(defun org-gfm-src-block (src-block contents info)
+  "Transcode SRC-BLOCK element into Github Flavored Markdown
+format. CONTENTS is nil.  INFO is a plist used as a communication
+channel."
+  (let* ((lang (org-element-property :language src-block))
+         (lang (or (assoc-default lang org-gfm-lang) lang))
+         (code (org-export-format-code-default src-block info))
+         (prefix (concat "```" lang "\n"))
+         (suffix "```"))
+    (concat prefix code suffix)))
+
+
+;;;; Strike-Through
+
+(defun org-html-strike-through (strike-through contents info)
+  "Transcode STRIKE-THROUGH from Org to Markdown (GFM).
+CONTENTS is the text with strike-through markup.  INFO is a plist
+holding contextual information."
+  (format "~~%s~~" contents))
+
+;;;; Table of contents
+
+(defun org-gfm-format-toc (headline)
+  "Return an appropriate table of contents entry for HEADLINE. INFO is a
+plist used as a communication channel."
+  (let* ((title (org-export-data
+                 (org-export-get-alt-title headline info) info))
+         (level (1- (org-element-property :level headline)))
+         (indent (concat (make-string (* level 2) ? )))
+         (ref-str (replace-regexp-in-string " " "-" (downcase title))))
+    (concat indent "- [" title "]" "(#" ref-str ")")))
+
+
+;;;; Template
+
+(defun org-gfm-inner-template (contents info)
+  "Return body of document after converting it to Markdown syntax.
+CONTENTS is the transcoded contents string.  INFO is a plist
+holding export options."
+  (let* ((depth (plist-get info :with-toc))
+         (headlines (and depth (org-export-collect-headlines info depth)))
+         (toc-string (or (mapconcat 'org-gfm-format-toc headlines "\n") ""))
+         (toc-tail (if headlines "\n\n" "")))
+    (concat toc-string toc-tail contents)))
+
+
+
+;;; Interactive function
+
+;;;###autoload
+(defun org-gfm-export-as-markdown (&optional async subtreep visible-only)
+  "Export current buffer to a Github Flavored Markdown buffer.
+
+If narrowing is active in the current buffer, only export its
+narrowed part.
+
+If a region is active, export that region.
+
+A non-nil optional argument ASYNC means the process should happen
+asynchronously.  The resulting buffer should be accessible
+through the `org-export-stack' interface.
+
+When optional argument SUBTREEP is non-nil, export the sub-tree
+at point, extracting information from the headline properties
+first.
+
+When optional argument VISIBLE-ONLY is non-nil, don't export
+contents of hidden elements.
+
+Export is done in a buffer named \"*Org GFM Export*\", which will
+be displayed when `org-export-show-temporary-export-buffer' is
+non-nil."
+  (interactive)
+  (org-export-to-buffer 'gfm "*Org GFM Export*"
+    async subtreep visible-only nil nil (lambda () (text-mode))))
+
+
+;;;###autoload
+(defun org-gfm-convert-region-to-md ()
+  "Assume the current region has org-mode syntax, and convert it
+to Github Flavored Markdown.  This can be used in any buffer.
+For example, you can write an itemized list in org-mode syntax in
+a Markdown buffer and use this command to convert it."
+  (interactive)
+  (org-export-replace-region-by 'gfm))
+
+
+;;;###autoload
+(defun org-gfm-export-to-markdown (&optional async subtreep visible-only)
+  "Export current buffer to a Github Flavored Markdown file.
+
+If narrowing is active in the current buffer, only export its
+narrowed part.
+
+If a region is active, export that region.
+
+A non-nil optional argument ASYNC means the process should happen
+asynchronously.  The resulting file should be accessible through
+the `org-export-stack' interface.
+
+When optional argument SUBTREEP is non-nil, export the sub-tree
+at point, extracting information from the headline properties
+first.
+
+When optional argument VISIBLE-ONLY is non-nil, don't export
+contents of hidden elements.
+
+Return output file's name."
+  (interactive)
+  (let ((outfile (org-export-output-file-name ".md" subtreep)))
+    (org-export-to-file 'gfm outfile async subtreep visible-only)))
+
+(provide 'ox-gfm)
+
+;; Local variables:
+;; generated-autoload-file: "org-loaddefs.el"
+;; End:
+
+;;; ox-gfm.el ends here