Add Atom feed from my source control system to each page

publish.el

@@ -30,6 +30,12 @@
 (require 'rainbow-delimiters)
 (require 'subr-x)
 
+(defconst publish-root
+  (file-name-directory
+   (or load-file-name
+       (buffer-file-name)))
+  "The directory where ‘oni-org’ was loaded from.")
+
 (add-hook 'prog-mode-hook 'rainbow-delimiters-mode)
 
 (defun publish-calculate-reading-time (buffer)
@@ -89,5 +95,21 @@
          :publishing-directory "public/")
         ("all" :components ("index" "posts" "assets"))))
 
+(defvar publish-feed-url-format
+  ;"https://gitlab.com/ryuslash/ryuslash.org/-/commits/master/%s?feed_token=Rf8otgpS8YEiYakJN4NR&format=atom"
+  "https://code.ryuslash.org/new-ryuslash.org/atom/%s?h=master"
+  "Format string for the URL to the page’s atom feed.")
+
+(add-hook 'org-export-before-processing-hook
+          (lambda (backend)
+            (when (eq backend 'html)
+              (let ((file-name (if (string= (buffer-file-name)
+                                            (expand-file-name "index.org"))
+                                   ""
+                                 (file-relative-name (buffer-file-name) publish-root))))
+               (insert "#+HTML_HEAD: <link rel=\"alternate\" type=\"application/atom+xml\" href=\""
+                       (format publish-feed-url-format file-name)
+                       "\" title=\"Atom Feed\"/>\n")))))
+
 (provide 'publish)
 ;;; publish.el ends here