/**
 * Split a chat answer into the spoken layer (before the first H2) and the
 * report skeleton (from that H2 onward). The cut is any ATX H2, so a drifted
 * first heading still folds instead of dumping the whole body.
 *
 * Fenced `##` lines are not cuts. The fence rule matches `chat-markdown-split`.
 */

export type SpokenAndReportSplit = Readonly<{
  spoken: string;
  report: string;
  headings: readonly string[];
}>;

const FENCE = /^\s{0,3}(`{3,}|~{3,})/;
const H2 = /^##\s+\S/;

function extractHeadings(report: string): string[] {
  const lines = report.split("\n");
  let insideFence = false;
  const headings: string[] = [];
  for (const line of lines) {
    if (FENCE.test(line)) insideFence = !insideFence;
    if (!insideFence && H2.test(line)) {
      headings.push(line.replace(/^##\s+/, "").trim());
    }
  }
  return headings;
}

export function splitSpokenAndReport(text: string): SpokenAndReportSplit {
  const lines = text.split("\n");
  let insideFence = false;
  let cut = -1;
  for (let index = 0; index < lines.length; index += 1) {
    const line = lines[index] ?? "";
    if (FENCE.test(line)) insideFence = !insideFence;
    if (!insideFence && H2.test(line)) {
      cut = index;
      break;
    }
  }
  if (cut < 0) return { spoken: text, report: "", headings: [] };
  const spoken = lines.slice(0, cut).join("\n").replace(/\s+$/u, "");
  const report = lines.slice(cut).join("\n");
  return { spoken, report, headings: extractHeadings(report) };
}

export function shortenAnswerHeading(heading: string): string {
  if (heading === "统一参数与原始结构") return "统一参数";
  if (heading === "技法审计表") return "技法审计";
  return heading;
}

export function answerDetailCaption(headings: readonly string[]): string {
  if (headings.length === 0) return "";
  const labels = headings.slice(0, 3).map(shortenAnswerHeading);
  if (headings.length <= 3) return labels.join("、");
  return `${labels.join("、")} 等 ${headings.length} 节`;
}