add parser for begin_image_row blocks

config.el

@@ -158,6 +158,7 @@
 
 ;; --- ronny core ---
 (load! "ronny/core")
+(load! "ronny/parser")
 
 ;; Doom keybindings under SPC m C
 (map! :map org-mode-map

ronny/parser.el

@@ -0,0 +1,109 @@
+;;; ronny/parser.el -*- lexical-binding: t; -*-
+
+;; extract links from HTML
+;; take exported HTML like
+;;    <a href="url1">some text</a>
+;;    <a href="url2">other text</a>
+;;
+;; turn it to Lisp data
+;;    (("url1"  .  "some text")
+;;     ("url2"  .  "other text"))
+;;
+;; arguments
+;;    html
+;;
+;; 1a create a local variable items, initiall empty (nil)
+;; 2a create a temporary scratch buffer to search through the HTML text safely
+;; 2b put the HTML string into that temporary buffer
+;; 2c go to the start of the buffer
+;; 3a loop through links
+;; 3b search for links of the form
+;;       <a href="URL">CAPTION</a>
+;; 4a store each link and build a pair ("url" . "caption") and push it into 'items'
+;; 5a reverse the order because push built the list backwards, so restore original order
+(defun ronny-parser--extract-html-links (html)
+  "Extract (url . caption) pairs from exported HTML links."
+  (let (items)                         ;; 1a
+    (with-temp-buffer                  ;; 2a
+      (insert html)                    ;; 2b
+      (goto-char (point-min))          ;; 2c
+      (while (re-search-forward                               ;; 3a
+              "<a href=\"\\([^\"]+\\)\">\\([^<]+\\)</a>"      ;; 3b
+              nil t)
+        (push (cons (match-string 1) (match-string 2)) items)))   ;; 4a
+    (nreverse items)))                                            ;; 5a
+
+
+;; convert parsed links into final HTML
+;;
+;; take list data of the form
+;;    (("url1" . "caption1")
+;;     ("url2" . "caption2"))
+;;
+;; and turn it into
+;;   <div class="image-row">
+;;     <div class="image-item"><a href="url1"><img src="url1" width="150"><div class="caption">shy cat</div></a></div>
+;;     <div class="image-item"><a href="url2"><img src="url2" width="150"><div class="caption">happy cat</div></a></div>
+;;   </div>
+;;
+;; arguments:
+;;   items  -> list of (url . caption) pairs
+;;
+;; 1a create the row container leave %s as the place whre all image items go
+;;
+;; 2a build all items
+;;       map over each item
+;;       convert it to a string
+;;       join them together
+;;
+;; 2b  for each item process one pair at a time
+;; 2c split pair into url and caption
+;;
+;; 2d build image block
+;; 2e join with newlines
+
+(defun ronny-parser--build-image-row-html (items)
+  "Build custom image row HTML from ITEMS."
+  (format                                       ;; 1a
+   "<div class=\"image-row\">\n%s\n</div>"      ;; 1a
+   (mapconcat                        ;; 2a
+    (lambda (item)                   ;; 2b
+      (let ((url (car item))                ;; 2c
+            (caption (cdr item)))           ;; 2c
+        (format                      ;; 2d
+         "<div class=\"image-item\"><a href=\"%s\"><img src=\"%s\" width=\"150\"><div class=\"caption\">%s</div></a></div>"
+         url url caption)))
+    items                        ;; 2e
+    "\n")))                      ;; 2e
+
+;; filter the exported special block
+;; this is the function Org calls during export
+;; if HTML export, transform it.  otherwise leave it alone
+;;
+;; arguments:
+;;   text    - exported text for the special block
+;;   backend - export target (html, latex, etc)
+;;   info    - export metadata
+;;
+;; 1a check backend and only do custom logic for HTML
+;; 2a extra links.  parse the block's HTML and get (url . caption) list
+;; 2b if links found rebuild block as custom image row
+;;         otherwise return original text
+(defun ronny-parser-filter-image-row (text backend info)
+  "Replace an exported image_row special block with custom HTML."
+
+  (if (org-export-derived-backend-p backend 'html)                ;; 1a
+      (let ((items (ronny-parser--extract-html-links text)))      ;; 2a
+        (if items                                                    ;; 2b
+            (ronny-parser--build-image-row-html items)               ;; 2b
+          text))                                                     ;; 2b
+    text))
+
+;; register the filter with Org
+;; after export machinery is loaded use this function for special blocks
+;;
+;; 1a ox is Org export.  prevents errors if export code is not loaded yet
+;; 1b add the function to the list of special-block filters
+(with-eval-after-load 'ox                                          ;; 1a
+  (add-to-list 'org-export-filter-special-block-functions          ;; 1b
+               #'ronny-parser-filter-image-row))                   ;; 1b