org-mime.el

;;; org-mime.el --- org html export for text/html MIME emails  -*- lexical-binding: t; -*-

;; Copyright (C) 2010-2015 Eric Schulte, 2016-2021 Chen Bin

;; Author: Eric Schulte
;; Maintainer: Chen Bin <chenbin.sh@gmail.com>
;; Keywords: mime, mail, email, html
;; Homepage: http://github.com/org-mime/org-mime
;; Version: 0.3.2
;; Package-Requires: ((emacs "25.1"))

;; This file is not part of GNU Emacs.

;;; 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.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; WYSIWYG, html mime composition using org-mode
;;
;; For mail composed using the orgstruct-mode minor mode, this
;; provides a function for converting all or part of your mail buffer
;; to embedded html as exported by org-mode.  Call `org-mime-htmlize'
;; in a message buffer to convert either the active region or the
;; entire buffer to html.
;;
;; Similarly the `org-mime-org-buffer-htmlize' function can be called
;; from within an org-mode buffer to convert the buffer to html, and
;; package the results into an email handling with appropriate MIME
;; encoding.
;;
;; `org-mime-org-subtree-htmlize' is similar to `org-mime-org-buffer-htmlize'
;; but works on current subtree.  It can read following subtree properties:
;; MAIL_SUBJECT, MAIL_TO, MAIL_FROM, MAIL_CC, and MAIL_BCC. MAIL_IN_REPLY_TO
;;
;; Here is the sample of a subtree:
;; * mail one
;;   :PROPERTIES:
;;   :MAIL_SUBJECT: mail title
;;   :MAIL_TO: person1@gmail.com
;;   :MAIL_FROM: sender@gmail.com
;;   :MAIL_CC: person2@gmail.com
;;   :MAIL_BCC: person3@gmail.com
;;   :MAIL_IN_REPLY_TO: <MESSAGE_ID>
;;   :END:
;;
;; To avoid exporting the table of contents, you can setup
;; `org-mime-export-options' as below,
;;   (setq org-mime-export-options '(:with-latex dvipng
;;                                   :section-numbers nil
;;                                   :with-author nil
;;                                   :with-toc nil))
;; It overrides Org default settings, but still inferior to file-local settings.
;;
;; Or just setup your export options in the org buffer/subtree.  These are
;; overridden by `org-mime-export-options' when it is non-nil.
;;
;;
;; Quick start:
;; Write a message in message-mode, make sure the mail body follows
;; org format.  Run `org-mime-edit-mail-in-org-mode' to edit mail
;; in a special edit with `org-mode'.
;; Run `org-mime-htmlize' to convert the plain text mail to html mail.
;; Run `org-mime-revert-to-plain-text-mail' if you want to restore to
;; plain text mail.
;;
;; Setup (OPTIONAL):
;; You might want to bind this to a key with something like the
;; following message-mode binding
;;
;;   (add-hook 'message-mode-hook
;;             (lambda ()
;;               (local-set-key (kbd "C-c M-o") 'org-mime-htmlize)))
;;
;; and the following org-mode binding
;;
;;   (add-hook 'org-mode-hook
;;             (lambda ()
;;               (local-set-key (kbd "C-c M-o") 'org-mime-org-buffer-htmlize)))
;;
;; Extra Tips:
;; 1. In order to embed images into your mail, use the syntax below,
;;
;;    [[/full/path/to/your.jpg]]
;;
;; 2. It's easy to define your hack the exported plain text and html.
;; For example, below code removes "\\" from plain text,
;;
;;   (add-hook 'org-mime-plain-text-hook
;;             (lambda ()
;;               (while (re-search-forward "\\\\" nil t)
;;                 (replace-match ""))))
;;
;; For example, below code renders text between "#" in red color from html,
;;
;;   (add-hook 'org-mime-html-hook
;;             (lambda ()
;;               (while (re-search-forward "#\\([^#]*\\)#" nil t)
;;                 (replace-match "<span style=\"color:red\">\\1</span>"))))
;;
;; 3. The quoted mail uses Gmail's style, so reply looks clean and modern.
;;
;; 4. Please note this program can only embed exported HTML into mail.
;;    Org-mode is responsible for rendering HTML.
;;
;;    For example, see https://github.com/org-mime/org-mime/issues/38
;;    The solution is patching org-mode,
;;    https://lists.gnu.org/archive/html/emacs-orgmode/2019-11/msg00016.html
;;
;; 5. See https://github.com/org-mime/org-mime for more tips
;;

;;; Code:
(require 'cl-lib)
(require 'outline)
(require 'org)
(require 'ox-org)
(require 'ox-html)
(require 'message)

(defcustom org-mime-beautify-quoted-mail-p t
  "Beautify quoted mail in more clean HTML, like Gmail."
  :group 'org-mime
  :type 'boolean)

(defcustom org-mime-use-property-inheritance nil
  "Non-nil means al MAIL_ properties apply also for sub-levels."
  :group 'org-mime
  :type 'boolean)

(defcustom org-mime-library 'mml
  "Library to use for marking up MIME elements."
  :group 'org-mime
  :type '(choice 'mml 'semi 'vm))

(defcustom org-mime-export-ascii nil
  "ASCII export options for text/plain.
Default (nil) selects the original org file."
  :group 'org-mime
  :type '(choice 'ascii 'latin1 'utf-8))

(defcustom org-mime-preserve-breaks t
  "Temporary value of `org-export-preserve-breaks' during mime encoding."
  :group 'org-mime
  :type 'boolean)

(defcustom org-mime-fixed-width-wrap
  "<pre style=\"font-family: courier, monospace;\">\n%s</pre>\n"
  "Format string used to wrap a fixed width HTML email."
  :group 'org-mime
  :type 'string)

(defcustom org-mime-find-html-start 'identity
  "Call back to search the new HTML start for htmlize in message buffer."
  :group 'org-mime
  :type 'sexp)

(defcustom org-mime-org-html-with-latex-default 'dvipng
  "Default value of `org-html-with-latex'."
  :group 'org-mime
  :type 'sexp)

(defcustom org-mime-mail-signature-separator
  (or message-signature-separator "^--\s?$")
  "Default mail signature separator."
  :group 'org-mime
  :type 'string)

(defvar org-mime-export-options '(:with-latex dvipng)
  "Default export options which may override org buffer/subtree options.
You could avoid exporting section-number/author/toc.
It overrides Org default settings, but still inferior to file-local settings.")

(defvar org-mime-plain-text-hook nil
  "Hook to run over the plain text buffer before adding it to email.
This is used to process plain text part of email .")

(defvar org-mime-html-hook nil
  "Hook to run over the html buffer before adding it to email.
This is used to process html part of email.")

(defvar org-mime-pre-html-hook nil
  "Hook to run before html export.
Functions should take no arguments and will be run in a
buffer holding the text to be exported.")

(defvar org-mime-send-buffer-hook nil
  "Hook to run in the Org-mode file before export.")

(defvar org-mime-debug nil
  "Enable debug logger.")

;; internal variables
(defvar org-mime-src--overlay nil)
(defvar org-mime-src--beg-marker nil)
(defvar org-mime-src--end-marker nil)
(defvar org-mime--saved-temp-window-config nil)
(defconst org-mime-src--hint "## org-mime hint: Press C-c C-c to commit change.\n")

(defun org-mime-get-buffer-export-options ()
  "Get export options in buffer."
  (or org-mime-export-options
      (and (fboundp 'org-export--get-inbuffer-options)
           (org-export--get-inbuffer-options))))

(defun org-mime-get-export-options (subtreep)
  "SUBTREEP is t if current node is subtree."
  (cond
   (subtreep
    (or org-mime-export-options
        (and (fboundp 'org-export--get-subtree-options)
             (org-export--get-subtree-options))))
   (t
    (org-mime-get-buffer-export-options))))

(defun org-mime-current-line ()
  "Get current line."
  (buffer-substring-no-properties (line-beginning-position)
                                  (line-end-position)))

(defun org-mime-use-ascii-charset ()
  "Return nil unless `org-mime-export-ascii' is set to a valid value."
  (car (memq org-mime-export-ascii '(ascii utf-8 latin1))))

(defun org-mime-export-ascii-maybe (text &optional opts)
  "Export TEXT to ascii format with OPTS."
  (let* ((ascii-charset (org-mime-use-ascii-charset))
         (plain-text (cond
                      (ascii-charset
                       (setq org-ascii-charset ascii-charset)
                       (org-export-string-as text 'ascii nil opts))
                      (t
                       text))))
    plain-text))

(defun org-mime-export-buffer-or-subtree (subtreep)
  "Similar to `org-html-export-as-html' and `org-org-export-as-org'.
SUBTREEP is t if current node is subtree."
  (let* ((opts (org-mime-get-export-options subtreep))
         (plain (org-mime-export-ascii-maybe (buffer-string) opts))
         (buf (org-export-to-buffer 'html "*Org Mime Export*" nil subtreep nil t opts))
         (body (prog1
                   (with-current-buffer buf
                     (buffer-string))
                 (kill-buffer buf))))
    (cons body plain)))

(defun org-mime-export-string (string &optional options)
  "Export STRING into html with OPTIONS."
  ;; Emacs 25+ prefer exporting drawer by default
  ;; obviously not acceptable in exporting to mail body
  (let* ((org-export-with-drawers nil))

    (when org-mime-export-options
      (setq options org-mime-export-options))

    ;; we won't export title from org file anyway
    (if options (setq options (plist-put options 'title nil)))

    ;; emacs24.4+
    (org-export-string-as string 'html t options)))

;; example hook, for setting a dark background in
;; <pre style="background-color: #EEE;"> elements
(defun org-mime-change-element-style (element style)
  "Set <ELEMENT> elements in exported html with new default html STYLE."
  (while (re-search-forward (format "<%s" element) nil t)
    (replace-match (format "<%s style=\"%s\"" element style))))

(defun org-mime-change-class-style (class style)
  "CLASS is used for new default html STYLE in exported html."
  (while (re-search-forward (format "class=\"%s\"" class) nil t)
    (replace-match (format "class=\"%s\" style=\"%s\"" class style))))

(defun org-mime-file (ext path id)
  "Markup a file with EXT, PATH and ID for attachment."
  (when org-mime-debug (message "org-mime-file called => %s %s %s" ext path id))
  (cl-case org-mime-library
    (mml (format "<#part type=\"%s\" filename=\"%s\" disposition=inline id=\"<%s>\">\n<#/part>\n"
                 ext path id))
    (semi (concat
           (format "--[[%s\nContent-Disposition: inline;\nContent-ID: <%s>][base64]]\n"
                   ext id)
           (base64-encode-string
            (with-temp-buffer
              (set-buffer-multibyte nil)
              (insert-file-contents-literally path)
              (buffer-string)))))
    (vm "?")))

(defun org-mime-beautify-quoted (html)
  "Beautify quoted mail in modern UI style.
HTML is the body of the message."
  (when org-mime-debug
    (message "org-mime-beautify-quoted called => %s" html))
  (let ((quote-depth 0)
        (line-depth 0)
        (in-quote-p nil)
        (quote-opening "<blockquote class=\"gmail_quote\" style=\"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex\">\n\n<div>")
        (quote-closing "\n</div></blockquote>\n"))
    (with-temp-buffer
      ;; clean title of quoted
      (insert (replace-regexp-in-string
               "<p>[\n\r]*&gt;&gt;&gt;&gt;&gt; .* == \\([^\r\n]*\\)[\r\n]*</p>"
               "<div class=\"gmail_quote\">\\1</div>"
               html))
      (goto-char (point-min))
      (while (not (eobp))
        (setq line-depth 0)
        (setq in-quote-p nil)
        (while (looking-at "&gt;[ \t]*")
          (setq in-quote-p t)
          (replace-match "")
          (cl-incf line-depth))
        (cond
         ((< quote-depth line-depth)
          (while (< quote-depth line-depth)
            (insert quote-opening)
            (cl-incf quote-depth)))
         ((> quote-depth line-depth)
          (while (> quote-depth line-depth)
            (insert quote-closing)
            (cl-decf quote-depth))))
        (if (and in-quote-p (looking-at "^[ \t]*$"))
            (progn
              (insert "</div>\n<div>")
              (forward-line)
              (insert "<br /></div>\n<div>"))
          (forward-line)))
      (buffer-substring (point-min) (point-max)))))

(defun org-mime-multipart (plain html &optional images)
  "Markup PLAIN body a multipart/alternative with HTML alternatives.
If html portion of message includes IMAGES they are wrapped in
multipart/related part."
  (cl-case org-mime-library
    (mml (concat "<#multipart type=alternative>\n<#part type=text/plain>\n"
                 plain
                 (when images "<#multipart type=related>")
                 "<#part type=text/html>\n"
                 (if org-mime-beautify-quoted-mail-p
                     (org-mime-beautify-quoted html)
                   html)
                 images
                 (when images "<#/multipart>\n")
                 "<#/multipart>\n"))
    (semi (concat
           "--" "<<alternative>>-{\n"
           "--" "[[text/plain]]\n" plain
           (when images (concat "--" "<<alternative>>-{\n"))
           "--" "[[text/html]]\n"  html
           images
           (when images (concat "--" "}-<<alternative>>\n"))
           "--" "}-<<alternative>>\n"))
    (vm "?")))

(defun org-mime-url-to-path (url current-file)
  "If URL is file path, convert to valid path.
Or else use CURRENT-FILE to calculate path."
  (let* ((dir (file-name-directory current-file))
         (path (expand-file-name url dir)))
    (cond
     ((string-match-p "^file:///" url)
      (let* ((str (replace-regexp-in-string "^file://" "" url)))
        (when (and (eq system-type 'windows-nt)
                   (string-match "^/[a-zA-Z]:" str))
          ;; remove the first character from "/C:/Windows/File.txt"
          (setq str (substring str 1)))
        str))

     ((file-exists-p path)
      path)

     (t
      (expand-file-name url default-directory)))))

(defun org-mime-replace-images (str current-file)
  "Replace images in STR with cid links.
CURRENT-FILE is used to calculate full path of images."
  (when org-mime-debug (message "org-mime-replace-images called => %s" current-file))
  (let* (html-images)
    (cons
     (replace-regexp-in-string ;; replace images in html
      "src=\"\\([^\"]+\\)\""
      (lambda (text)
        (format
         "src=\"cid:%s\""
         (let* ((url (and (string-match "src=\"\\([^\"]+\\)\"" text)
                          (match-string 1 text)))
                (path (org-mime-url-to-path url current-file))
                (ext (file-name-extension path))
                (id (replace-regexp-in-string "[\/\\\\]" "_" path)))

           ;; Catch non-existent files here. Otherwise users get an error on sending.
           (unless (file-exists-p path)
             (user-error "Path: %s does not exist" path))

           ;; Do it
           (add-to-list 'html-images
                        (org-mime-file (concat "image/" ext) path id))
           id)))
      str)
     html-images)))

(defun org-mime-extract-non-image-files ()
  "Extract non-image links in current buffer."
  (cond
   ((>= (org-mime-org-major-version) 9)
    (org-element-map (org-element-parse-buffer) 'link
      (lambda (link)
        (when (and (string= (org-element-property :type link) "file")
                   (not (string-match
                         (cdr (assoc "file" org-html-inline-image-rules))
                         (org-element-property :path link))))
          (org-element-property :path link)))))
   (t
    (message "Warning: org-element-map is not available. File links will not be attached.")
    nil)))

(defun org-mime-apply-plain-text-hook (text)
  "Apply TEXT hook."
  (if org-mime-plain-text-hook
      (with-temp-buffer
        (insert text)
        (goto-char (point-min))
        (run-hooks 'org-mime-plain-text-hook)
        (buffer-string))
    text))

(defun org-mime-apply-html-hook (html)
  "Apply HTML hook."
  (if org-mime-html-hook
      (with-temp-buffer
        (insert html)
        (goto-char (point-min))
        (run-hooks 'org-mime-html-hook)
        (buffer-string))
    html))

(defun org-mime-insert-html-content (plain file html)
  "Insert PLAIN into FILE with HTML content."
  (let* ((files (org-mime-extract-non-image-files))
         ;; dvipng for inline latex because MathJax doesn't work in mail
         ;; Also @see https://github.com/org-mime/org-mime/issues/16
         ;; (setq org-html-with-latex nil) sometimes useful
         (org-html-with-latex org-mime-org-html-with-latex-default)
         ;; we don't want to convert org file links to html
         (org-html-link-org-files-as-html nil)
         (org-link-file-path-type 'absolute)
         ;; prettify reply with ">"
         (org-export-preserve-breaks org-mime-preserve-breaks)
         ;; org 9
         (org-html-htmlize-output-type 'inline-css)
         ;; org 8
         (org-export-htmlize-output-type 'inline-css)
         (html-and-images (org-mime-replace-images html file))
         (images (cdr html-and-images))
         (html (org-mime-apply-html-hook (car html-and-images))))

    ;; If there are files that were attached, we should remove the links,
    ;; and mark them as attachments. The links don't work in the html file.
    (when files
      (mapc (lambda (f)
              (setq html (replace-regexp-in-string
                          (format "<a href=\"%s\">%s</a>"
                                  (regexp-quote f) (regexp-quote f))
                          (format "%s (attached)" (file-name-nondirectory f))
                          html)))
            files))

    (insert (org-mime-multipart (org-mime-apply-plain-text-hook plain)
                                html
                                (if images (mapconcat 'identity images "\n"))))

    ;; Attach any residual files
    (when files
      (mapc (lambda (f)
              (when org-mime-debug (message "attaching: %s" f))
              (mml-attach-file f))
            files))

    ;; spacer
    (insert "\n\n")))

(defun org-mime-mail-body-begin ()
  "Get begin of mail body."
  (save-excursion
    (goto-char (point-min))
    (search-forward mail-header-separator)
    (+ (point) 1)))

(defun org-mime-mail-signature-begin ()
  "Find start of signature line in email."
  (save-excursion
    (goto-char (point-max))
    (re-search-backward org-mime-mail-signature-separator nil t nil)))


(defmacro org-mime-extract-tag-in-current-buffer (beginning end result)
  "Extract the text between BEGINNING and END and insert it into RESULT."
  `(when (and ,beginning ,end (< ,beginning ,end))
     (push (buffer-substring-no-properties ,beginning ,end) ,result)
     ;; delete old tag
     (delete-region ,beginning ,end)))

(defun org-mime-extract-non-org ()
  "Extract content not in org format (gpg signature, attachments ...)."
  (unless (org-region-active-p)
    (let* (secure-tags
           part-tags
           str
           b
           e
           (old-pos (point)))
      (goto-char (point-min))
      (while (re-search-forward "<#secure \\|<#part .* filename=" (point-max) t)
        (setq str (match-string 0))
        (setq b (match-beginning 0))
        (cond
         ;; one line gpg signature tag
         ((string-match "^<#secure " str)
          (setq e (line-end-position))
          (org-mime-extract-tag-in-current-buffer b e secure-tags))

         ;; multi-lines attachment
         ((string-match "^<#part .* filename=" str)
          (save-excursion
            (unless (re-search-forward "<#/part>" (point-max) t)
              (error (format "\"%s\" should have end tag." str)))
            (setq e (match-end 0))
            (org-mime-extract-tag-in-current-buffer b e part-tags))))

        ;; search next tag
        (goto-char (point-min)))

      ;; move cursor back to its original position
      (goto-char old-pos)

      (list :secure-tags (nreverse secure-tags)
            :part-tags (nreverse part-tags)))))

;;;###autoload
(defun org-mime-htmlize ()
  "Export a portion of an email to html using `org-mode'.
If called with an active region only export that region, otherwise entire body."
  (interactive)
  (when org-mime-debug (message "org-mime-htmlize called"))

  (let* ((region-p (org-region-active-p))
         (all-tags (org-mime-extract-non-org))
         (secure-tags (plist-get all-tags :secure-tags))
         (part-tags (plist-get all-tags :part-tags))
         (html-start (funcall org-mime-find-html-start
                              (or (and region-p (region-beginning))
                                  (org-mime-mail-body-begin))))
         (html-end (or (and region-p (region-end))
                       (or
                        (org-mime-mail-signature-begin)
                        (point-max))))
         (org-text (buffer-substring html-start html-end))
;; to hold attachments for inline html images
         (opts (org-mime-get-buffer-export-options))
         (plain (org-mime-export-ascii-maybe org-text opts))
         (html (org-mime-export-string org-text opts))
         (file (make-temp-name (expand-file-name
                                "mail" temporary-file-directory))))

    ;; delete current region
    (delete-region html-start html-end)
    (goto-char html-start)

    ;; restore secure tags
    (when secure-tags
      (insert (mapconcat #'identity secure-tags "\n"))
      ;; spacer
      (insert "\n\n"))

    ;; insert converted html
    (org-mime-insert-html-content plain file html)

    ;; restore part tags (attachments)
    (when part-tags
      (insert (mapconcat #'identity part-tags "\n"))
      (insert "\n\n"))))

(defun org-mime--get-buffer-title ()
  "Get buffer title."
  (let* ((options (org-mime-get-buffer-export-options))
         (tmp (and options (plist-get options :title))))
    (when tmp
      (let ((txt (car tmp)))
        (set-text-properties 0 (length txt) nil txt)
        txt))))

(defun org-mime-compose (exported file to subject headers)
  "Create mail body from EXPORTED in FILE with TO, SUBJECT, HEADERS."
  ;; start composing mail
  (let* ((html (car exported))
         (plain (cdr exported))
         patched-html)
    (compose-mail to subject headers nil)
    (message-goto-body)
    (setq patched-html (with-temp-buffer
                         (insert html)
                         (goto-char (point-min))
                         (run-hooks 'org-mime-pre-html-hook)
                         (buffer-string)))
    ;; insert text
    (org-mime-insert-html-content plain file patched-html)))

(defun org-mime-buffer-properties ()
  "Extract buffer properties."
  (let* (rlt value key)
    (org-element-map (org-element-parse-buffer) 'keyword
      (lambda (keyword)
        (when (and (string= (org-element-property :key keyword) "PROPERTY")
                   (string-match "^MAIL_\\(TO\\|SUBJECT\\|CC\\|BCC\\|IN_REPLY_TO\\|FROM\\) +"
                                 (setq value (org-element-property :value keyword)))
                   (setq key (concat "MAIL_" (match-string 1 value)))
                   (setq rlt
                         (plist-put rlt
                                    (intern (concat ":" key))
                                    (string-trim (replace-regexp-in-string key "" value))))))))
    rlt))

(defun org-mime-build-mail-other-headers (cc bcc from in-reply-to)
  "Build mail header from CC, BCC, IN_REPLY_TO and FROM."
  (let* ((arr (list (cons "Cc" cc) (cons "Bcc" bcc)  (cons "From" from ) (cons "In-Reply-To" in-reply-to )))
         rlt)
    (dolist (e arr)
      (when (cdr e)
        (push e rlt)))
    rlt))

;;;###autoload
(defun org-mime-org-buffer-htmlize ()
  "Create an email buffer of the current org buffer.
The email buffer will contain both html and in org formats as mime
alternatives.

The following file keywords can be used to control the headers:
#+MAIL_TO: some1@some.place
#+MAIL_SUBJECT: a subject line
#+MAIL_CC: some2@some.place
#+MAIL_BCC: some3@some.place
#+MAIL_FROM: sender@some.place
#+MAIL_FROM: sender@some.place
#+MAIL_IN_REPLY_TO: <MESSAGE_ID>

The cursor ends in the TO field."
  (interactive)
  (run-hooks 'org-mime-send-buffer-hook)
  (let* ((org-html-klipsify-src nil)
         (file (buffer-file-name (current-buffer)))
         (props (org-mime-buffer-properties))
         (subject (or (plist-get props :MAIL_SUBJECT)
                      (org-mime--get-buffer-title)
                      (if (not file) (buffer-name (buffer-base-buffer))
                        (file-name-sans-extension
                         (file-name-nondirectory file)))))
         (exported (org-mime-export-buffer-or-subtree nil))
         (to (plist-get props :MAIL_TO))
         (cc (plist-get props :MAIL_CC))
         (bcc (plist-get props :MAIL_BCC))
         (from (plist-get props :MAIL_FROM))
         (in-reply-to (plist-get props :MAIL_IN_REPLY_TO))
         (other-headers (org-mime-build-mail-other-headers cc
                                                           bcc
                                                           from
                                                           in-reply-to)))
    (org-mime-compose exported file to subject other-headers)
    (message-goto-to)))

(defun org-mime-org-major-version ()
  "Get Org major version."
  (string-to-number (car (split-string (org-release) "\\."))))

(defun org-mime-attr (property)
  "Get org mime PROPERTY."
  (org-entry-get nil property org-mime-use-property-inheritance))

;;;###autoload
(defun org-mime-org-subtree-htmlize (&optional htmlize-first-level)
  "Create an email buffer from current subtree.
If HTMLIZE-FIRST-LEVEL is t, first level subtree of current node is htmlized.

Following headline properties can determine the mail headers.
* subtree heading
  :PROPERTIES:
  :MAIL_SUBJECT: mail title
  :MAIL_TO: person1@gmail.com
  :MAIL_CC: person2@gmail.com
  :MAIL_BCC: person3@gmail.com
  :MAIL_FROM: sender@gmail.com
  :END:"
  (interactive "P")
  (save-excursion
    (org-back-to-heading)

    (when (and htmlize-first-level
               (not (string-match "^\\* " (org-mime-current-line))))
      ;; go back to the 1st level subtree
      (re-search-backward "^\\* ")
      (org-back-to-heading))

    (when (outline-on-heading-p nil)
      (let* ((file (buffer-file-name (current-buffer)))
             (props (org-mime-buffer-properties))
             (subject (or (org-mime-attr "MAIL_SUBJECT")
                          (plist-get props :MAIL_SUBJECT)
                          (nth 4 (org-heading-components))))
             (to (or (org-mime-attr "MAIL_TO")
                     (plist-get props :MAIL_TO)))
             (cc (or (org-mime-attr "MAIL_CC")
                     (plist-get props :MAIL_CC)))
             (bcc (or (org-mime-attr "MAIL_BCC")
                      (plist-get props :MAIL_BCC)))
             (in-reply-to (or (org-mime-attr "MAIL_IN_REPLY_TO")
                      (plist-get props :MAIL_BCC)))
             (from (or (org-mime-attr "MAIL_FROM")
                       (plist-get props :MAIL_FROM)))
             ;; Thanks to Matt Price improving handling of cc & bcc headers
             (other-headers (org-mime-build-mail-other-headers cc bcc from in-reply-to))
             (org-export-show-temporary-export-buffer nil)
             (org-export-show-temporary-export-buffer nil)
             ;; I wrap these bodies in export blocks because in org-mime-compose
             ;; they get exported again. This makes each block conditionally
             ;; exposed depending on the backend.
             (exported (save-restriction (org-narrow-to-subtree)
                                         (org-mime-export-buffer-or-subtree t))))
        (save-restriction
          (org-narrow-to-subtree)
          (org-mime-compose exported file to subject other-headers))
        (message-goto-to)))))

(defun org-mime-src--remove-overlay ()
  "Remove overlay from current source buffer."
  (when (overlayp org-mime-src--overlay)
    (delete-overlay org-mime-src--overlay)))

(defun org-mime-edited-code ()
  "Get edited code."
  (save-excursion
    (goto-char (point-min))
    (search-forward org-mime-src--hint (point-max) t)
    (goto-char (line-beginning-position))
    (buffer-substring-no-properties (point) (point-max))))

(defun org-mime-edit-src-save ()
  "Save parent buffer with current state source-code buffer."
  (interactive)
  (set-buffer-modified-p nil)
  (let* ((edited-code (org-mime-edited-code))
         (beg org-mime-src--beg-marker)
         (end org-mime-src--end-marker)
         (overlay org-mime-src--overlay))
    (with-current-buffer (marker-buffer org-mime-src--beg-marker)
      (undo-boundary)
      (goto-char beg)
      ;; Temporarily disable read-only features of OVERLAY in order to
      ;; insert new contents.
      (delete-overlay overlay)
      (delete-region beg end)
      (let* ((expecting-bol (bolp)))
        (insert edited-code)
        (when (and expecting-bol (not (bolp))) (insert "\n")))
      (save-buffer)
      (move-overlay overlay beg (point))))
  ;; `write-contents-functions' requires the function to return
  ;; a non-nil value so that other functions are not called.
  t)

(defun org-mime-src-mode-configure-edit-buffer ()
  "Set up clean up functions when editing source code."
  (add-hook 'kill-buffer-hook #'org-mime-src--remove-overlay nil 'local)
  (setq buffer-offer-save t)
  (setq-local write-contents-functions '(org-mime-edit-src-save)))

(defvar org-mime-src-mode-hook nil
  "Hook run after switching embedded org code to its `org-mode'.")

(defun org-mime-edit-src-exit ()
  "Kill current sub-editing buffer and return to source buffer."
  (interactive)
  (let* ((beg org-mime-src--beg-marker)
         (end org-mime-src--end-marker)
         (edit-buffer (current-buffer))
         (source-buffer (marker-buffer beg)))
    (org-mime-edit-src-save)
    (unless source-buffer (error "Source buffer disappeared.  Aborting"))
    ;; Insert modified code.  Ensure it ends with a newline character.
    (kill-buffer edit-buffer)

    ;; to the beginning of the block opening line.
    (goto-char beg)

    ;; Clean up left-over markers and restore window configuration.
    (set-marker beg nil)
    (set-marker end nil)
    (when org-mime--saved-temp-window-config
      (set-window-configuration org-mime--saved-temp-window-config)
      (setq org-mime--saved-temp-window-config nil))))

(defvar org-mime-src-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map (kbd "C-c C-c") #'org-mime-edit-src-exit)
    (define-key map (kbd "C-x C-s") #'org-mime-edit-src-save)
    map))

(define-minor-mode org-mime-src-mode
  "Minor mode for org major mode buffers generated from mail body."
  :lighter " OrgMimeSrc")
(add-hook 'org-mime-src-mode-hook #'org-mime-src-mode-configure-edit-buffer)

(defun org-mime-src--make-source-overlay (beg end)
  "Create overlay between BEG and END positions and return it."
  (let* ((overlay (make-overlay beg end)))
    (overlay-put overlay 'face 'secondary-selection)
    (let ((read-only
           (list
            (lambda (&rest _)
              (user-error
               "Cannot modify an area being edited in a dedicated buffer")))))
      (overlay-put overlay 'modification-hooks read-only)
      (overlay-put overlay 'insert-in-front-hooks read-only)
      (overlay-put overlay 'insert-behind-hooks read-only))
    overlay))

(defun org-mime-edit-mail-in-org-mode ()
  "Call a special editor to edit the mail body in `org-mode'."
  (interactive)
  ;; see `org-src--edit-element'
  (cond
   ((eq major-mode 'org-mode)
    (message "This command is not for `org-mode'."))
   (t
    (setq org-mime--saved-temp-window-config (current-window-configuration))
    (let* ((beg (copy-marker (org-mime-mail-body-begin)))
           (end (copy-marker (or (org-mime-mail-signature-begin) (point-max))))
           (bufname "OrgMimeMailBody")
           (buffer (generate-new-buffer bufname))
           (overlay (org-mime-src--make-source-overlay beg end))
           (text (buffer-substring-no-properties beg end)))

      (setq org-mime-src--beg-marker beg)
      (setq org-mime-src--end-marker end)
      ;; don't use local-variable because only user can't edit multiple emails
      ;; or multiple embedded org code in one mail
      (setq org-mime-src--overlay overlay)

      (save-excursion
        (delete-other-windows)
        (org-switch-to-buffer-other-window buffer)
        (erase-buffer)
        (insert org-mime-src--hint)
        (insert text)
        (goto-char (point-min))
        (org-mode)
        (org-mime-src-mode))))))

(defun org-mime-revert-to-plain-text-mail ()
  "Revert mail body to plain text."
  (interactive)
  (let* ((txt-sep "<#part type=text/plain>")
         (html-sep "<#part type=text/html>")
         mail-beg
         mail-text
         txt-beg
         txt-end)
    (save-excursion
      (goto-char (point-min))
      (setq mail-beg (search-forward mail-header-separator (point-max) t))
      (setq txt-beg (search-forward txt-sep (point-max) t))
      (setq txt-end (search-forward html-sep (point-max) t)))
    (cond
     ((and mail-beg txt-beg txt-end (< mail-beg txt-beg txt-end))
      ;; extract text mail
      (setq mail-text (buffer-substring-no-properties txt-beg
                                                      (- txt-end (length html-sep))))
      ;; delete html mail
      (delete-region mail-beg (point-max))
      (when org-mime-debug
        (message "mail-beg=%s mail-text=%s" mail-beg mail-text))
      ;; restore text mail
      (insert mail-text))
     (t
      (message "Can not find plain text mail.")))))

(defun org-mime-confirm-when-no-multipart ()
  "Prompt whether to send email if the buffer is not htmlized."
  (let ((found-multipart (save-excursion
                           (save-restriction
                             (widen)
                             (goto-char (point-min))
                             (search-forward "<#multipart type=alternative>" nil t)))))
    (when (and (not found-multipart)
               (not (y-or-n-p "It seems `org-mime-htmlize' is NOT called; send anyway? ")))
      (setq quit-flag t))))


(provide 'org-mime)
;; Local Variables:
;; coding: utf-8
;; tab-width: 2
;; indent-tabs-mode: nil
;; End:
;;; org-mime.el ends here