;; content-on-sx — nested block trees (section container).
;;
;; CtSection is a block whose ivar `children` is an ordered list of blocks (any
;; type, including nested sections → arbitrary depth). This turns the document
;; from a flat sequence into the ordered TREE of the architecture sketch.
;;
;; Self-contained: CtSection answers asHTML/asSx/asText/asMarkdown: by folding
;; its children's renderings — pure polymorphic recursion, so it composes with
;; the existing render boundary with no changes to block.sx or render.sx. (The
;; relevant per-block render bootstrap must be loaded for the children.)
;;
;; Requires (loaded by harness): block.sx, doc.sx, render.sx (asHTML/asSx);
;; markdown.sx / text.sx for those formats on children.

(define
  content-bootstrap-section!
  (fn
    ()
    (begin
      (st-class-define! "CtSection" "CtBlock" (list "children"))
      (ct-def-method! "CtSection" "children" "children ^ children")
      (ct-def-method! "CtSection" "type" "type ^ #section")
      (ct-def-method!
        "CtSection"
        "asHTML"
        "asHTML ^ '<section>' , (children inject: '' into: [:a :b | a , (b asHTML)]) , '</section>'")
      (ct-def-method!
        "CtSection"
        "asSx"
        "asSx ^ '(section ' , (children inject: '' into: [:a :b | a , (b asSx)]) , ')'")
      (ct-def-method!
        "CtSection"
        "asText"
        "asText ^ (children inject: '' into: [:a :b | (b asText = '') ifTrue: [a] ifFalse: [(a = '' ifTrue: [b asText] ifFalse: [a , ' ' , b asText])]])")
      (ct-def-method!
        "CtSection"
        "asMarkdown:"
        "asMarkdown: nl ^ (children inject: '' into: [:a :b | a , (a = '' ifTrue: [''] ifFalse: [nl , nl]) , (b asMarkdown: nl)])")
      true)))

(define
  mk-section
  (fn
    (id children)
    (st-iv-set!
      (st-iv-set! (st-make-instance "CtSection") "id" id)
      "children"
      children)))

(define
  section?
  (fn (b) (and (st-instance? b) (= (get b :class) "CtSection"))))

(define section-children (fn (sec) (st-send sec "children" (list))))

;; copy-on-write child edits (return a new section)
(define
  section-with-children
  (fn (sec children) (st-iv-set! sec "children" children)))
(define
  section-append
  (fn
    (sec block)
    (section-with-children sec (append (section-children sec) (list block)))))

;; ── tree traversal (descends into nested sections) ──
(define
  block-deep-find
  (fn
    (blocks id)
    (if
      (= (len blocks) 0)
      nil
      (let
        ((b (first blocks)))
        (if
          (= (blk-id b) id)
          b
          (let
            ((nested (if (section? b) (block-deep-find (section-children b) id) nil)))
            (if (= nested nil) (block-deep-find (rest blocks) id) nested)))))))

(define doc-deep-find (fn (doc id) (block-deep-find (doc-blocks doc) id)))

(define
  block-tree-ids
  (fn
    (blocks)
    (if
      (= (len blocks) 0)
      (list)
      (let
        ((b (first blocks)))
        (append
          (cons
            (blk-id b)
            (if (section? b) (block-tree-ids (section-children b)) (list)))
          (block-tree-ids (rest blocks)))))))

(define doc-tree-ids (fn (doc) (block-tree-ids (doc-blocks doc))))

(define block-tree-count (fn (blocks) (len (block-tree-ids blocks))))
(define doc-tree-count (fn (doc) (len (doc-tree-ids doc))))