;;; org-attach-embedded-images.el --- Transmute images to attachments
;;
;; Copyright 2018-2021 Free Software Foundation, Inc.
;;
;; Author: Marco Wahl
;; Version: 0.1
;; Keywords: org, media
;;
;; This file is not part of GNU Emacs.
;;
;; 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 <https://www.gnu.org/licenses/>.

;;; Commentary:
;;
;; There are occasions when images are displayed in a subtree which
;; are not org attachments.  For example if you copy and paste a part
;; of a web page (containing images) from eww to an org subtree.

;; This module provides command `org-attach-embedded-images-in-subtree'
;; to save such images as attachments and insert org links to them.

;; Install:

;; To use this module insert it to `org-modules'.  The insert can be
;; performed via {M-x customize-variable RET org-modules RET} followed
;; by insertion of `org-attach-embedded-images' to the external
;; modules section.

;; Alternatively you can add the line

;; (require 'org-attach-embedded-images)

;; to your emacs configuration.

;; Use

;;     M-x org-attach-embedded-images-in-subtree

;; in a subtree with embedded images.  The images get attached and can
;; later be reviewed.

;; Note: Possibly

;;     M-x org-toggle-inline-images

;; is needed to see the images in the Org mode window.


;; Code:

(require 'org)
(require 'org-attach)


;; Auxiliary functions

(defun org-attach-embedded-images--next-property-display-data (position limit)
  "Return position of the next property-display location with image data.
Return nil if there is no next display property.
POSITION and LIMIT as in `next-single-property-change'."
  (let ((pos (next-single-property-change position 'display nil limit)))
    (while (and (< pos limit)
		(let ((display-prop
		       (plist-get (text-properties-at pos) 'display)))
		  (or (not display-prop)
		      (not (plist-get (cdr display-prop) :data)))))
      (setq pos (next-single-property-change pos 'display nil limit)))
    pos))

(defun org-attach-embedded-images--attach-with-sha1-name (data)
  "Save the image given as DATA as org attachment with its sha1 as name.
Return the filename."
  (let* ((extension (symbol-name (image-type-from-data data)))
         (basename (concat (sha1 data) "." extension))
	 (dir (org-attach-dir t))
         (filename (concat dir "/" basename)))
    (unless (file-exists-p filename)
      (with-temp-file filename
        (setq buffer-file-coding-system 'binary)
        (set-buffer-multibyte nil)
        (insert data)))
    (org-attach-sync)
    basename))


;; Command

;;;###autoload
(defun org-attach-embedded-images-in-subtree ()
  "Save the displayed images as attachments and insert links to them."
  (interactive)
  (when (org-before-first-heading-p)
    (user-error "Before first heading.  Nothing has been attached."))
  (save-excursion
    (org-attach-dir t)
    (let ((beg (progn (org-back-to-heading) (point)))
          (end (progn (org-end-of-subtree) (point)))
	  names)
      ;; pass 1
      (goto-char beg)
      (while (< (goto-char (org-attach-embedded-images--next-property-display-data (point) end)) end)
	(let ((data (plist-get (cdr (plist-get (text-properties-at (point)) 'display)) :data)))
	  (assert data)
	  (push (org-attach-embedded-images--attach-with-sha1-name data)
		names)))
      ;; pass 2
      (setq names (nreverse names))
      (goto-char beg)
      (while names
	(goto-char (org-attach-embedded-images--next-property-display-data (point) end))
        (while (get-text-property (point) 'display)
	  (goto-char (next-property-change (point) nil end)))
        (skip-chars-forward "]")
        (insert (concat "\n[[attachment:" (pop names) "]]"))))))


(provide 'org-attach-embedded-images)


;;; org-attach-embedded-images.el ends here