'use strict';
// Telegram Bot API 薄封裝：零依賴，直接用內建 fetch。
// 含 Markdown→Telegram HTML 轉換（安全子集）、4000 字切分、HTML 解析失敗自動退回純文字。

function createTelegram(token) {
  const API = `https://api.telegram.org/bot${token}`;

  async function tg(method, params) {
    const res = await fetch(`${API}/${method}`, {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(params),
    });
    const data = await res.json();
    if (!data.ok) throw new Error(`${method} 失敗：${data.description}`);
    return data.result;
  }

  // Markdown → Telegram HTML（只轉安全子集：code block、inline code、連結、粗體、標題）。
  // 單星號斜體與底線刻意不轉：會誤傷清單符號 * 與 username 的底線。
  const SENTINEL = String.fromCharCode(0);
  function mdToTgHtml(md) {
    const esc = (s) => s.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;');
    const stash = [];
    const put = (html) => SENTINEL + (stash.push(html) - 1) + SENTINEL;
    let text = md.replace(/```\w*\n?([\s\S]*?)```/g, (_, code) => put(`<pre>${esc(code.replace(/\n$/, ''))}</pre>`));
    text = text.replace(/`([^`\n]+)`/g, (_, code) => put(`<code>${esc(code)}</code>`));
    text = esc(text);
    text = text.replace(/\[([^\]]+)\]\((https?:[^)\s]+)\)/g, '<a href="$2">$1</a>');
    text = text.replace(/\*\*([^*\n]+)\*\*/g, '<b>$1</b>');
    text = text.replace(/^#{1,6}\s+(.+)$/gm, '<b>$1</b>');
    return text.replace(new RegExp(`${SENTINEL}(\\d+)${SENTINEL}`, 'g'), (_, i) => stash[+i]);
  }

  // 送出訊息；HTML 解析失敗（切分把標籤切壞等）自動退回純文字。
  async function sendMessage(chatId, text, { replyTo, html = false } = {}) {
    const params = { chat_id: chatId, text };
    if (replyTo) params.reply_parameters = { message_id: replyTo, allow_sending_without_reply: true };
    if (html) {
      try {
        return await tg('sendMessage', { ...params, parse_mode: 'HTML' });
      } catch { /* fallback to plain */ }
    }
    return tg('sendMessage', params);
  }

  // 超過 4096 上限就切段（留餘裕切 4000）；只有第一段帶 reply。
  async function sendSplit(chatId, text, { replyTo, html = false } = {}) {
    const chunks = text.match(/[\s\S]{1,4000}/g) || ['（空回應）'];
    let first = null;
    for (const chunk of chunks) {
      const msg = await sendMessage(chatId, chunk, { replyTo, html });
      if (!first) first = msg;
      replyTo = undefined;
    }
    return first;
  }

  // 編輯既有訊息；過長則第一段 edit、其餘續傳新訊息。
  async function editOrSplit(chatId, messageId, text, { html = false } = {}) {
    const edit = async (t) => {
      const params = { chat_id: chatId, message_id: messageId, text: t };
      if (html) {
        try {
          return await tg('editMessageText', { ...params, parse_mode: 'HTML' });
        } catch (err) {
          // 「訊息沒變」不算錯；其他 HTML 失敗退回純文字
          if (String(err.message).includes('message is not modified')) return;
          return tg('editMessageText', params);
        }
      }
      return tg('editMessageText', params);
    };
    if (text.length <= 4000) return edit(text);
    const chunks = text.match(/[\s\S]{1,4000}/g) || [];
    await edit(chunks[0]);
    for (let i = 1; i < chunks.length; i++) await sendMessage(chatId, chunks[i], { html });
  }

  // 表情回應當狀態指示（👀 收到、👍 完成）；很多聊天型別不支援，失敗直接吞。
  function react(chatId, messageId, emoji) {
    return tg('setMessageReaction', {
      chat_id: chatId,
      message_id: messageId,
      reaction: emoji ? [{ type: 'emoji', emoji }] : [],
    }).catch(() => {});
  }

  // 上傳檔案到 Telegram：圖片走 sendPhoto，其餘（或 sendPhoto 失敗時）走 sendDocument
  async function sendFile(chatId, filePath, { caption, replyTo } = {}) {
    const fs = require('fs');
    const path = require('path');
    const name = path.basename(filePath);
    const isImage = /\.(png|jpe?g|gif|webp)$/i.test(name);
    const size = fs.statSync(filePath).size;

    const upload = async (method, field) => {
      const form = new FormData();
      form.append('chat_id', String(chatId));
      if (caption) form.append('caption', caption.slice(0, 1000));
      if (replyTo) form.append('reply_parameters', JSON.stringify({ message_id: replyTo, allow_sending_without_reply: true }));
      form.append(field, new Blob([fs.readFileSync(filePath)]), name);
      const res = await fetch(`${API}/${method}`, { method: 'POST', body: form });
      const data = await res.json();
      if (!data.ok) throw new Error(`${method} 失敗：${data.description}`);
      return data.result;
    };

    // sendPhoto 上限 10MB，且某些格式會被拒，失敗就退回用檔案傳
    if (isImage && size <= 9.5 * 1024 * 1024) {
      try {
        return await upload('sendPhoto', 'photo');
      } catch { /* fall through */ }
    }
    return upload('sendDocument', 'document');
  }

  async function downloadFile(fileId, destPath) {
    const fs = require('fs');
    const info = await tg('getFile', { file_id: fileId });
    const res = await fetch(`https://api.telegram.org/file/bot${token}/${info.file_path}`);
    if (!res.ok) throw new Error(`下載檔案失敗：HTTP ${res.status}`);
    const buf = Buffer.from(await res.arrayBuffer());
    fs.writeFileSync(destPath, buf);
    return destPath;
  }

  return { tg, mdToTgHtml, sendMessage, sendSplit, editOrSplit, react, downloadFile, sendFile };
}

module.exports = { createTelegram };