'use strict';

const fs = require('fs');

function escapeRe(value) {
  return String(value).replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}

function normalizeQuestion(value) {
  return String(value || '').toLowerCase().replace(/[^\p{L}\p{N}]+/gu, ' ').trim();
}

// 用官网 FAQ 更新本地 markdown：保留 frontmatter、章节标题和 Q 顺序，
// 只替换已有问题的答案，新问题追加到文件末尾。
function updateMarkdownFile(filePath, questions) {
  if (!fs.existsSync(filePath)) return { changed: false, reason: 'file_missing', added: 0, updated: 0 };
  let content = fs.readFileSync(filePath, 'utf8');
  const bodyStart = (content.match(/^---\n[\s\S]*?\n---\n/) || [''])[0].length;
  const body = content.slice(bodyStart);

  const existing = new Map();
  let currentQ = null;
  let answer = [];
  const flush = () => {
    if (currentQ) existing.set(normalizeQuestion(currentQ), { question: currentQ, answer: answer.join('\n').trim() });
  };
  for (const line of body.split('\n')) {
    const q = line.match(/^###\s+Q:\s*(.*)$/);
    if (q) {
      flush();
      currentQ = q[1].trim();
      answer = [];
    } else if (currentQ) {
      answer.push(line);
    }
  }
  flush();

  let changed = false;
  let added = 0;
  let updated = 0;
  const additions = [];
  for (const item of questions) {
    if (!item.q || !item.a) continue;
    const key = normalizeQuestion(item.q);
    if (existing.has(key)) {
      const prev = existing.get(key);
      if (prev.answer !== item.a) {
        const re = new RegExp(`(### Q: ${escapeRe(prev.question)}\\n)([\\s\\S]*?)(?=\\n### Q:|$)`, 'm');
        if (re.test(content)) {
          content = content.replace(re, (_m, prefix) => `${prefix}${item.a}\n`);
          prev.answer = item.a;
          changed = true;
          updated += 1;
        }
      }
    } else {
      existing.set(key, { question: item.q, answer: item.a });
      additions.push(`### Q: ${item.q}\n${item.a}\n`);
      added += 1;
      changed = true;
    }
  }

  if (additions.length) {
    content = content.replace(/\s+$/, '') + '\n\n' + additions.join('\n');
  }
  if (changed) fs.writeFileSync(filePath, content, 'utf8');
  return { changed, added, updated };
}

module.exports = { updateMarkdownFile };