;; lib/host/htmlsx.sx — a pure-SX HTML → SX converter (the "radar migrator" core). Turns a
;; post's HTML content into an SX (article …) tree that host/blog--decompose! consumes: img,
;; p, figure/figcaption, iframe, headings, blockquote, lists, inline strong/em/a (kept nested;
;; decompose flattens them to text at the block level). Char-level tokenizer + a stack parser.
;; NOTE: substr is (string, start, LENGTH); index-of returns -1 when absent.

;; ── string helpers ──────────────────────────────────────────────────
(define host/html--at    (fn (s i) (if (< i (len s)) (substr s i 1) "")))
(define host/html--from  (fn (s i) (substr s i (- (len s) i))))     ;; s[i:]
(define host/html--slice (fn (s a b) (substr s a (- b a))))         ;; s[a:b)
(define host/html--replace-all
  (fn (s old new)
    (let ((i (index-of s old)))
      (if (< i 0) s
        (str (host/html--slice s 0 i) new
             (host/html--replace-all (host/html--from s (+ i (len old))) old new))))))

;; ── entity decode (the common named + a few numeric entities → UTF-8) ──
(define host/html--entities
  (list (list "&nbsp;" " ") (list "&amp;" "&") (list "&lt;" "<") (list "&gt;" ">")
        (list "&quot;" "\"") (list "&#39;" "'") (list "&apos;" "'") (list "&#x27;" "'")
        (list "&#x2019;" "’") (list "&#8217;" "’") (list "&#x2018;" "‘")
        (list "&hellip;" "…") (list "&#x2026;" "…") (list "&mdash;" "—") (list "&ndash;" "–")
        (list "&pound;" "£") (list "&#xA3;" "£") (list "&#163;" "£")))
(define host/html--decode
  (fn (s) (reduce (fn (acc pair) (host/html--replace-all acc (first pair) (first (rest pair)))) s host/html--entities)))

;; ── tag classification + name/attr parsing ──────────────────────────
(define host/html--void?
  (fn (n) (contains? (list "img" "br" "hr" "iframe" "input" "meta" "link" "source" "embed") n)))
;; the tag name from a tag's inner text ("img src=…" -> "img"): up to the first space or '/'.
(define host/html--tag-name
  (fn (inner)
    (let ((sp (index-of inner " ")))
      (lower (trim (host/html--replace-all (if (< sp 0) inner (host/html--slice inner 0 sp)) "/" ""))))))
;; parse the attrs of a tag's inner text into a dict (quoted or unquoted values).
(define host/html--attrs-loop
  (fn (rest acc)
    (let ((r (trim rest)))
      (if (or (= r "") (= r "/")) acc
        (let ((eq (index-of r "=")))
          (if (< eq 0) acc
            (let ((name (lower (trim (host/html--slice r 0 eq))))
                  (after (trim (host/html--from r (+ eq 1)))))
              (let ((q (host/html--at after 0)))
                (if (or (= q "\"") (= q "'"))
                  (let ((close (index-of (host/html--from after 1) q)))
                    (if (< close 0) acc
                      (host/html--attrs-loop (host/html--from after (+ close 2))
                        (assoc acc name (host/html--decode (host/html--slice after 1 (+ 1 close)))))))
                  (let ((sp2 (index-of after " ")))
                    (host/html--attrs-loop (if (< sp2 0) "" (host/html--from after sp2))
                      (assoc acc name (if (< sp2 0) after (host/html--slice after 0 sp2))))))))))))))
(define host/html--parse-attrs
  (fn (inner)
    (let ((sp (index-of inner " ")))
      (if (< sp 0) {} (host/html--attrs-loop (host/html--from inner (+ sp 1)) {})))))

;; ── tokenizer: HTML string → a list of {:t text|open|close|void …} tokens ──
(define host/html--tokens
  (fn (s)
    (let loop ((i 0) (acc (list)))
      (if (>= i (len s)) acc
        (if (= (host/html--at s i) "<")
          (let ((rel (index-of (host/html--from s i) ">")))
            (if (< rel 0) acc
              (let ((gt (+ i rel)) (inner (host/html--slice s (+ i 1) (+ i rel))))
                (cond
                  ((starts-with? inner "!") (loop (+ gt 1) acc))     ;; comment / doctype
                  ((starts-with? inner "/")
                   (loop (+ gt 1) (concat acc (list {:t "close" :name (host/html--tag-name (host/html--from inner 1))}))))
                  (else
                   (let ((name (host/html--tag-name inner)))
                     (loop (+ gt 1) (concat acc (list {:t (if (or (host/html--void? name) (ends-with? inner "/")) "void" "open")
                                                       :name name :attrs (host/html--parse-attrs inner)})))))))))
          (let ((rel (index-of (host/html--from s i) "<")))
            (let ((te (if (< rel 0) (len s) (+ i rel))))
              (let ((txt (host/html--decode (host/html--slice s i te))))
                (loop te (if (= (trim txt) "") acc (concat acc (list {:t "text" :text txt}))))))))))))

;; ── parser: tokens → a tree of {:name :attrs :kids} nodes (kids: node | string, in order).
;; A functional stack of open frames; a synthetic root frame collects the top-level nodes. ──
(define host/html--push-kid
  (fn (stack kid)
    (let ((top (first stack)))
      (cons (assoc top :kids (concat (get top :kids) (list kid))) (rest stack)))))
(define host/html--parse
  (fn (tokens)
    (let loop ((ts tokens) (stack (list {:name "article" :attrs {} :kids (list)})))
      (if (empty? ts) (get (first stack) :kids)
        (let ((tok (first ts)))
          (cond
            ((= (get tok :t) "text") (loop (rest ts) (host/html--push-kid stack (get tok :text))))
            ((= (get tok :t) "void") (loop (rest ts) (host/html--push-kid stack {:name (get tok :name) :attrs (get tok :attrs) :kids (list)})))
            ((= (get tok :t) "open") (loop (rest ts) (cons {:name (get tok :name) :attrs (get tok :attrs) :kids (list)} stack)))
            ((= (get tok :t) "close")
             (if (> (len stack) 1)
               (loop (rest ts) (host/html--push-kid (rest stack) (first stack)))
               (loop (rest ts) stack)))
            (else (loop (rest ts) stack))))))))

;; ── tree → SX. A node becomes (name :attr val … child …); text stays a string. Attr keys
;; become keywords via parse-safe (":src" -> the keyword :src) so decompose reads them. ──
(define host/html--attrs->sx
  (fn (attrs)
    (reduce (fn (acc k) (concat acc (list (parse-safe (str ":" k)) (get attrs k)))) (list) (keys attrs))))
(define host/html--node->sx
  (fn (node)
    (if (= (type-of node) "string") node
      (cons (string->symbol (get node :name))
        (concat (host/html--attrs->sx (get node :attrs))
                (map host/html--node->sx (get node :kids)))))))
;; HTML content string → an (article …) SX tree, ready for host/blog--decompose!.
(define host/html->sx
  (fn (html)
    (cons (quote article) (map host/html--node->sx (host/html--parse (host/html--tokens html))))))