Allow specifying field values from org-mode properties (#22)

* Allow specifying field values from org-mode properties

* Update documentation and fine-tune the diff

* Refactor, fix indentation, and other minor fixes

Renamed all-fields to named-fields since the heading and content
before first subheading can also be a field.

---------

Co-authored-by: Renat Galimov <renat@Renats-MacBook-Pro.local>
Co-authored-by: orgtre <orgtre@posteo.net>

README.org

@@ -84,6 +84,19 @@ If you're using [[https://github.com/radian-software/straight.el][straight.el]]
         This works for all note types, just make the first 2 fields absent and
         ~anki-editor~ will use note heading as first field and the text below the heading as second field.
 
+     ,* You can extract a field value from an org-property
+        :PROPERTIES:
+        :ANKI_NOTE_TYPE: Basic
+        :ANKI_FIELD_FRONT: Can one define an anki-field inside an org-mode property?
+        :ANKI_PREPEND_HEADING: nil
+        :END:
+
+        Yes. In this example, =anki-editor=  will use the =ANKI_FIELD_FRONT= property value as
+        a front side of the Anki card and the body of the card as its back.
+
+     ,** Front
+        Notice that property fields will override subheading fields.
+        This block will be skipped
    #+END_SRC
 
    - Anki deck is provided by ~ANKI_DECK~ property.  This property is

anki-editor.el

@@ -442,6 +442,8 @@ The implementation is borrowed and simplified from ox-html."
 (defconst anki-editor-prop-deck "ANKI_DECK")
 (defconst anki-editor-prop-format "ANKI_FORMAT")
 (defconst anki-editor-prop-prepend-heading "ANKI_PREPEND_HEADING")
+(defconst anki-editor-prop-field-prefix "ANKI_FIELD_"
+  "Anki fields with names got from an org-node property.")
 (defconst anki-editor-prop-tags "ANKI_TAGS")
 (defconst anki-editor-prop-tags-plus (concat anki-editor-prop-tags "+"))
 (defconst anki-editor-prop-failure-reason "ANKI_FAILURE_REASON")
@@ -806,6 +808,14 @@ Return a list of cons of (FIELD-NAME . FIELD-CONTENT)."
              do (org-forward-heading-same-level nil t)
              until (= last-pt (point)))))
 
+(defun anki-editor--property-fields (fields)
+  "Extract Anki FIELDS from entry properties."
+  (cl-loop for field in fields
+           for property = (concat anki-editor-prop-field-prefix (upcase field))
+           for property-value = (org-entry-get-with-inheritance property)
+           when property-value
+           collect (cons field property-value)))
+
 (defun anki-editor--note-contents-before-subheading ()
   "Get content between heading at point and next sub/heading.
 
@@ -857,32 +867,30 @@ When the `subheading-fields' don't match the `note-type's fields,
 map missing fields to the `heading' and/or `content-before-subheading'.
 Return a list of cons of (FIELD-NAME . FIELD-CONTENT)."
   (anki-editor--with-collection-data-updated
-    (let* ((fields-matching (cl-intersection
+   (let* ((model-fields (alist-get
-			     (alist-get note-type
+                         note-type anki-editor--model-fields
-					anki-editor--model-fields
+                         nil nil #'string=))
-					nil nil #'string=)
+          (property-fields (anki-editor--property-fields model-fields))
-			     (mapcar #'car subheading-fields)
+          (named-fields (seq-uniq (append subheading-fields property-fields)
+                                  (lambda (left right)
+                                    (string= (car left) (car right)))))
+          (fields-matching (cl-intersection
+                            model-fields (mapcar #'car named-fields)
                             :test #'string=))
 	  (fields-missing (cl-set-difference
-			    (alist-get note-type
+                           model-fields (mapcar #'car named-fields)
-				       anki-editor--model-fields
-				       nil nil #'string=)
-			    (mapcar #'car subheading-fields)
 			   :test #'string=))
 	  (fields-extra (cl-set-difference
-			  (mapcar #'car subheading-fields)
+			 (mapcar #'car named-fields) model-fields
-			  (alist-get note-type
-				     anki-editor--model-fields
-				     nil nil #'string=)
 			 :test #'string=))
 	  (fields (cl-loop for f in fields-matching
 			   collect (cons f (alist-get
-					     f subheading-fields
+					    f named-fields
 					    nil nil #'string=))))
 	  (heading-format anki-editor-prepend-heading-format))
      (cond ((equal 0 (length fields-missing))
 	    (when (< 0 (length fields-extra))
-	       (user-error "Failed to map all subheadings to a field")))
+	      (user-error "Failed to map all named fields")))
 	   ((equal 1 (length fields-missing))
 	    (if (equal 0 (length fields-extra))
 		(if (equal "" (string-trim content-before-subheading))