Add a helper function to migrate old notes

fix-notes-0.3.el

@@ -0,0 +1,45 @@
+(require 'seq)
+(require 'anki-editor)
+
+(defconst anki-editor-fix-prop-tags "ANKI_TAGS")
+(defconst anki-editor-fix-prop-deck "ANKI_DECK")
+(defconst anki-editor-fix-tag-note "note")
+(defconst anki-editor-fix-tag-deck "deck")
+
+
+(defun anki-editor-fix-notes (&optional list-of-files)
+  "Fix notes in LIST-OF-FILES, or in current buffer if it's nil.
+`anki-editor' has be to upgraded to `0.3' before using this
+command.  It should be noted that only letters, numbers, `_' and
+`@' are allowed in Org tags, and existing tags of headings will
+be considered as Anki tags now."
+
+  (interactive)
+  (when (yes-or-no-p "It's strongly recommended that you backup or version-control your old note files before running this command. Are you sure to continue ?")
+    (org-map-entries
+     (lambda ()
+       (message "Fixing in buffer \"%s\" at %d..." (buffer-name) (point))
+       (let* ((local-tags (org-get-local-tags))
+              (old-anki-tags (org-entry-get-multivalued-property nil anki-editor-fix-prop-tags))
+              (new-tags (cl-set-difference (append old-anki-tags (org-get-local-tags))
+                                           (list anki-editor-fix-tag-deck anki-editor-fix-tag-note)
+                                           :test #'string=)))
+
+         (unless (seq-every-p #'anki-editor-is-valid-org-tag new-tags)
+           (error "Fixing failed in buffer \"%s\" at point %d: only letters, numbers, `_', `@', `#' and `%%' are allowed in an Org tag"
+                  (buffer-name)
+                  (point)))
+         (org-set-tags-to new-tags)
+         (beginning-of-line)
+         (org-fix-tags-on-the-fly)
+         (org-entry-delete nil anki-editor-fix-prop-tags)
+         (cond
+          ((member anki-editor-fix-tag-deck local-tags)
+           (anki-editor-fix-deck)))))
+     nil
+     list-of-files)
+    (message "Fixing... DONE!")))
+
+(defun anki-editor-fix-deck ()
+  (interactive)
+  (org-set-property anki-editor-fix-prop-deck (nth 4 (org-heading-components))))