// Pure, LLM-free formatting for the intro/body of a gate widget.
// The body arrives as a plain string with blank-line-separated paragraphs and
// bullet lines prefixed by "•", "-" or "*". We fold it into structured blocks
// so the renderer can draw a real list (hanging indent) and emphasise the
// leading term of each bullet.

export type IntroBlock =
  | { kind: "para"; text: string }
  | { kind: "list"; items: string[] };

const BULLET_RE = /^\s*[•\-*]\s+/;

/** Fold raw intro text into paragraph and list blocks. */
export function parseIntroBlocks(intro: string): IntroBlock[] {
  const lines = intro.replace(/\r\n/g, "\n").split("\n");
  const blocks: IntroBlock[] = [];
  let para: string[] = [];
  let list: string[] = [];

  const flushPara = () => {
    if (para.length) {
      blocks.push({ kind: "para", text: para.join(" ").trim() });
      para = [];
    }
  };
  const flushList = () => {
    if (list.length) {
      blocks.push({ kind: "list", items: list });
      list = [];
    }
  };

  for (const raw of lines) {
    const line = raw.trimEnd();
    if (BULLET_RE.test(line)) {
      flushPara();
      list.push(line.replace(BULLET_RE, "").trim());
    } else if (line.trim() === "") {
      flushPara();
      flushList();
    } else {
      flushList();
      para.push(line.trim());
    }
  }
  flushPara();
  flushList();
  return blocks;
}

// Separators that mark the end of a leading term ("term → definition",
// "term: definition"). Ordered longest-first is not needed since indexOf picks
// the earliest match across all of them.
const LEAD_SEPARATORS = [" → ", " -> ", " — ", " – ", ": "];

/**
 * Split a bullet into its leading term (to emphasise) and the remainder,
 * or return null when there is no clear short lead worth bolding.
 */
export function splitLead(item: string): { lead: string; rest: string } | null {
  let at = -1;
  for (const sep of LEAD_SEPARATORS) {
    const idx = item.indexOf(sep);
    if (idx > 0 && (at === -1 || idx < at)) at = idx;
  }
  if (at === -1) return null;
  const lead = item.slice(0, at);
  // Only emphasise a genuinely short lead: a label, not half a sentence.
  if (lead.length > 60 || lead.trim().split(/\s+/).length > 6) return null;
  return { lead, rest: item.slice(at) };
}