[oni-org] Add dynamic block for org for linking together projects

This is similar to my backlinks dynamic block, but it supports links by id and
will print them as a checkbox so that the project can track progress by using
the progress cookies.

oni-org/oni-org.el

@@ -810,5 +810,49 @@ This is an around advice for ‘org-html--svg-image’ as FUN."
   (add-to-list 'org-duration-units `("p" . ,oni-org-pomodoro-duration))
   (org-duration-set-regexps))
 
+;;; Projects
+
+(defun oni-org-pick-project (property)
+  (when (string= property "PROJECT")
+    (org-map-entries (lambda () (concat (buffer-name) ":" (mapconcat (lambda (x) x) (org-get-outline-path t) ":"))) "CATEGORY=\"project\"")))
+
+(defun oni-org-link-project (value)
+  (let* ((split-value (split-string value ":"))
+         (marker (org-find-olp split-value)))
+    (save-excursion
+      (goto-char marker)
+      (format "[[id:%s][%s]]" (org-id-get-create) (car (last split-value))))))
+
+(add-to-list 'org-properties-postprocess-alist '("PROJECT" . oni-org-link-project))
+
+(add-hook 'org-property-allowed-value-functions #'oni-org-pick-project)
+
+(defun oni-org-dblock-write-project-steps (_params)
+  "Generate backlinks to org headings."
+  (let ((current-heading (nth 4 (org-heading-components)))
+        (current-heading-id
+         (let ((properties (org-entry-properties)))
+           (or (alist-get "CUSTOM_ID" properties nil nil #'string=)
+               (org-id-get-create))))
+        backlinks)
+    (when (not (null current-heading-id))
+      (save-excursion
+        (goto-char (point-min))
+        (while (re-search-forward (rx-to-string `(or (seq "[[id:" ,current-heading-id "]")
+                                                     (seq "#" ,current-heading-id "]"))) nil t)
+          (unless (or (oni-org-in-dblock-p)
+                      (oni-org-at-origin-property-p))
+            (let ((components (org-heading-components)))
+              (push (list (org-entry-is-done-p) (point) (nth 4 components)) backlinks))))))
+    (insert (string-join
+             (mapcar (lambda (link)
+                       (concat "- " (if (car link) "[X]" "[ ]") " [[*" (caddr link) "][" (caddr link) "]]"))
+                     (sort (seq-uniq backlinks (lambda (a b) (= (cadr a) (cadr b))))
+                           (lambda (a b) (< (cadr a) (cadr b)))))
+             "\n"))
+    (org-update-statistics-cookies nil)))
+
+(defalias 'org-dblock-write:oni-project-steps 'oni-org-dblock-write-project-steps)
+
 (provide 'oni-org)
 ;;; oni-org.el ends here