/**
 * Mine the first unchecked task-checklist item from plan markdown.
 */

/**
 * Return the text of the first `- [ ]` item under `## Task checklist`.
 * If that section is missing, fall back to the first unchecked checkbox anywhere.
 * Returns null when none found.
 */
export function nextUncheckedStep(planMarkdown: string): string | null {
  const md = planMarkdown.replace(/\r\n/g, "\n");

  const sectionMatch = /^##\s+Task checklist\s*$/im.exec(md);
  if (sectionMatch && sectionMatch.index !== undefined) {
    const start = sectionMatch.index + sectionMatch[0].length;
    const rest = md.slice(start);
    const nextHeading = /^##\s+/im.exec(rest);
    const body = nextHeading ? rest.slice(0, nextHeading.index) : rest;
    const fromSection = firstUnchecked(body);
    if (fromSection) return fromSection;
  }

  return firstUnchecked(md);
}

function firstUnchecked(text: string): string | null {
  const re = /^\s*[-*]\s+\[\s\]\s+(.+?)\s*$/gm;
  const m = re.exec(text);
  if (!m) return null;
  const item = m[1]!.trim();
  if (!item || item === "(none)") return null;
  return item;
}