;;; org-auto-id.el --- Add custom id to all org entries, useful for html exporting. -*- lexical-binding: t; -*-

;; Copyright (C) 2019 Yann Esposito

;; Author: Yann Esposito <yann@esposito.host>
;; Maintainer: Yann Esposito <yann@esposito.host>
;; Created: 28 Jul 2019
;; Version: 0.1
;; Keywords: org
;; Homepage: https://gitlab.esy.fun/yogsototh/org-auto-id
;; Package-Requires: ((emacs "24.4") org)

;; This file is not part of GNU Emacs

;;; Commentary:
;; Will warn you if you have duplicate CUSTOM_ID.

;;; License:

;; Licensed under the same terms as Emacs.

;;; Code:

(require 'org)

(defvar org-auto-id--all-ids '()
  "List as set of all ids of the current org-file")

(defun org-auto-id-format (title)
  "Generate a new org-id using TITLE."
  (concat (downcase (replace-regexp-in-string "\\W" "-" title))))

(defun org-auto-id-add-id (id &optional new?)
  "Add the id to the set of existing ids, warn if not a generation of new id."
  (if (member id org-auto-id--all-ids)
      (progn (unless new?
               (message "Duplicate CUSTOM_ID found: %s" id))
             (org-auto-id-add-id (format "%s-%04x" id (random (expt 16 4))) new?))
    (progn
      (add-to-list 'org-auto-id--all-ids id)
      id)))

(defun org-auto-id-custom-id-get (&optional pom create)
  "Get the CUSTOM_ID property of the entry at point-or-marker POM.
If POM is nil, refer to the entry at point.
If the entry does not have an CUSTOM_ID, the function returns nil.
However, when CREATE is non nil, create a CUSTOM_ID if none is present already.
In any case, the CUSTOM_ID of the entry is returned."
  (interactive)
  (org-with-point-at pom
    (let ((id (org-entry-get nil "CUSTOM_ID")))
      (cond
       ((and id (stringp id) (string-match "\\S-" id))
        (progn
          (org-auto-id-add-id id)
          id))
       (create
        (let ((id (org-auto-id-format (org-entry-get nil "ITEM"))))
          (let ((new-id (org-auto-id-add-id id t)))
            (org-entry-put pom "CUSTOM_ID" new-id)
            new-id)))))))

(defun org-auto-id-add-ids-to-headlines-in-file ()
  "Add CUSTOM_ID properties to all headlines.
In the current file, all headlines which do not already have a CUSTOM_ID.
Only adds ids if the `auto-id' option is set to `t' in the file somewhere.
ie, #+OPTIONS: auto-id:t"
  (interactive)
  (save-excursion
    (widen)
    (goto-char (point-min))
    (let ((add-suffix (re-search-forward "^#\\+OPTIONS:.* auto-id-add-suffix:t" (point-max) t)))
      (when (re-search-forward "^#\\+OPTIONS:.* auto-id:t" (point-max) t)
        (setq org-auto-id--all-ids '())
        (org-map-entries (lambda () (org-auto-id-custom-id-get (point) 'create)))))))

(add-hook 'org-mode-hook
          (lambda ()
            (add-hook 'before-save-hook
                      (lambda ()
                        (when (and (eq major-mode 'org-mode)
                                   (eq buffer-read-only nil))
                          (org-auto-id-add-ids-to-headlines-in-file))))))

(provide 'org-auto-id)

;;; org-auto-id.el ends here