#!/usr/bin/env node
/**
 * 乘法口诀 —— 本地离线语音识别后端（零 npm 依赖）
 *   GET  /            → 返回 index.html
 *   POST /stt         → 上传录音(webm/mp4/…)，用 ffmpeg 转码 + whisper.cpp 离线识别，返回 { text }
 *
 * 依赖的系统命令（已用 brew 安装）：ffmpeg、whisper-cli
 * 模型：./models/ggml-small.bin（默认，较准）或 ggml-base.bin（较快，用 WHISPER_MODEL 切换）
 */
const http = require('http');
const fs = require('fs');
const os = require('os');
const path = require('path');
const { spawn } = require('child_process');
const crypto = require('crypto');

const ROOT = __dirname;
const PORT = process.env.PORT || 8000;
const THREADS = String(Math.min(8, os.cpus().length || 4));
const WHISPER = process.env.WHISPER_BIN || 'whisper-cli';
const FFMPEG = process.env.FFMPEG_BIN || 'ffmpeg';

// 选模型：环境变量优先；否则有 small 用 small，没有就用 base
function resolveModel() {
  if (process.env.WHISPER_MODEL && fs.existsSync(process.env.WHISPER_MODEL)) return process.env.WHISPER_MODEL;
  const small = path.join(ROOT, 'models', 'ggml-small.bin');
  const base = path.join(ROOT, 'models', 'ggml-base.bin');
  if (fs.existsSync(small)) return small;
  if (fs.existsSync(base)) return base;
  return small; // 交给运行时报错提示
}
const MODEL = resolveModel();
const GRAMMAR = process.env.WHISPER_GRAMMAR || path.join(ROOT, 'grammar', 'number.gbnf');
const HAS_GRAMMAR = fs.existsSync(GRAMMAR);
// 备用初始提示（无语法文件时才用），偏向中文数字
const PROMPT = '以下是小学生背诵乘法口诀说出的答案，通常是一个中文数字，例如：一、二、六、九、十二、二十一、四十九、八十一。';

// ---- 按题动态生成 grammar：前缀锁死为本题因数，得数保持全开放（不会把答错扶正）----
// 只允许中文数字输出：阿拉伯数字会把「十四/七十四」压扁成 14/74，丢掉「十」的信息
const CN = ['零', '一', '二', '三', '四', '五', '六', '七', '八', '九'];
const GRAMMAR_NUM = [
  'product ::= tens | teen | unit | "十"',
  'unit    ::= "零" | "一" | "二" | "三" | "四" | "五" | "六" | "七" | "八" | "九" | alias',
  // 发音兼容别名：n/l 不分（六→牛/流/柳/溜）、口语“两”、同音变调（九→酒）。
  // 若不给别名，方言发音会被语法硬扭到“错误的”数字（如 niú 更接近 jiǔ「九」）；
  // 给出别名让解码器输出真实听到的音，前端 DIG 表再映射回数字。
  'alias   ::= "牛" | "流" | "柳" | "溜" | "两" | "酒"',
  'teen    ::= "十" unit',
  'tens    ::= unit "十" unit?',
].join('\n');
const dynGrammarCache = new Map();
function dynGrammar(a, b) {
  const key = a + 'x' + b;
  if (dynGrammarCache.has(key)) return dynGrammarCache.get(key);
  const g = [
    'root    ::= prefix? product',
    `prefix  ::= ("${CN[a]}${CN[b]}"${a !== b ? ` | "${CN[b]}${CN[a]}"` : ''}) "得"?`,
    GRAMMAR_NUM,
  ].join('\n');
  const file = path.join(os.tmpdir(), 'calx-grammar-' + key + '.gbnf');
  fs.writeFileSync(file, g);
  dynGrammarCache.set(key, file);
  return file;
}

const MIME_EXT = {
  'audio/webm': 'webm', 'audio/ogg': 'ogg', 'audio/mp4': 'mp4',
  'audio/aac': 'aac', 'audio/x-m4a': 'm4a', 'audio/mpeg': 'mp3', 'audio/wav': 'wav',
};

function tmp(ext) {
  return path.join(os.tmpdir(), 'calx-' + process.pid + '-' + crypto.randomBytes(4).toString('hex') + '.' + ext);
}
function run(cmd, args) {
  return new Promise((resolve) => {
    const p = spawn(cmd, args);
    let err = '';
    p.stderr.on('data', d => { err += d; });
    p.on('error', e => resolve({ code: -1, err: String(e) }));
    p.on('close', code => resolve({ code, err }));
  });
}

async function transcribe(buf, contentType, a, b) {
  const ext = MIME_EXT[(contentType || '').split(';')[0].trim()] || 'webm';
  const inFile = tmp(ext);
  const wavFile = tmp('wav');
  const outBase = wavFile.replace(/\.wav$/, '');
  const cleanup = () => [inFile, wavFile, outBase + '.txt'].forEach(f => { try { fs.unlinkSync(f); } catch (e) {} });
  try {
    fs.writeFileSync(inFile, buf);
    // 1) 转 16k 单声道 wav，并在前后各补 0.5s 静音
    //    （关键：短音节如“一/八”若无留白，whisper 常丢字或重复成“88”，补静音可修复）
    const ff = await run(FFMPEG, ['-y', '-loglevel', 'error', '-i', inFile,
      '-af', 'adelay=500ms:all=1,apad=pad_dur=0.5', '-ar', '16000', '-ac', '1', '-f', 'wav', wavFile]);
    if (ff.code !== 0 || !fs.existsSync(wavFile)) { cleanup(); return { text: '', error: 'ffmpeg failed: ' + ff.err.slice(0, 200) }; }
    // 2) whisper.cpp 离线识别：语法约束解码，强制输出成合法数字，杜绝英文/乱码幻听
    //    带题目参数时用按题定制的 grammar（前缀锁死为本题因数），进一步压缩解码错配空间
    const grammar = (a >= 1 && a <= 9 && b >= 1 && b <= 9) ? dynGrammar(a, b) : (HAS_GRAMMAR ? GRAMMAR : null);
    const args = ['-m', MODEL, '-l', 'zh', '-nt', '-np', '-mc', '0', '-t', THREADS, '-otxt', '-of', outBase, '-f', wavFile];
    if (grammar) args.splice(6, 0, '--grammar', grammar, '--grammar-rule', 'root');
    else args.splice(6, 0, '--prompt', PROMPT);
    const w = await run(WHISPER, args);
    let text = '';
    try { text = fs.readFileSync(outBase + '.txt', 'utf8'); } catch (e) {}
    text = text.replace(/\s+/g, '').replace(/[，。！？、,.!?]/g, '').trim();
    cleanup();
    if (w.code !== 0 && !text) return { text: '', error: 'whisper failed: ' + w.err.slice(0, 200) };
    return { text };
  } catch (e) {
    cleanup();
    return { text: '', error: String(e) };
  }
}

function handler(req, res) {
  const url = new URL(req.url, 'http://x');
  // ---- 静态页面 ----
  if (req.method === 'GET' && (url.pathname === '/' || url.pathname === '/index.html')) {
    fs.readFile(path.join(ROOT, 'index.html'), (e, data) => {
      if (e) { res.writeHead(404); res.end('index.html not found'); return; }
      res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8', 'Cache-Control': 'no-cache' });
      res.end(data);
    });
    return;
  }
  if (req.method === 'GET' && url.pathname === '/health') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ ok: true, model: path.basename(MODEL), modelExists: fs.existsSync(MODEL) }));
    return;
  }
  // ---- 语音识别 ----
  if (req.method === 'POST' && url.pathname === '/stt') {
    const chunks = [];
    let size = 0;
    req.on('data', d => { chunks.push(d); size += d.length; if (size > 12 * 1024 * 1024) req.destroy(); });
    req.on('end', async () => {
      const buf = Buffer.concat(chunks);
      const t0 = Date.now();
      const a = parseInt(url.searchParams.get('a'), 10), b = parseInt(url.searchParams.get('b'), 10);
      const out = await transcribe(buf, req.headers['content-type'], a, b);
      res.writeHead(200, { 'Content-Type': 'application/json; charset=utf-8' });
      res.end(JSON.stringify({ text: out.text || '', ms: Date.now() - t0, error: out.error || null }));
      console.log(`[stt] ${size}B  ${req.headers['content-type']}  -> "${out.text}"  ${Date.now() - t0}ms${out.error ? '  ERR:' + out.error : ''}`);
    });
    return;
  }
  res.writeHead(404); res.end('not found');
}

function lanIP() {
  const ifs = os.networkInterfaces();
  for (const name of Object.keys(ifs)) for (const i of ifs[name]) if (i.family === 'IPv4' && !i.internal) return i.address;
  return 'localhost';
}
const IP = lanIP();

http.createServer(handler).listen(PORT, '0.0.0.0', () => {
  console.log(`\n乘法口诀服务已启动`);
  console.log(`  HTTP : http://localhost:${PORT}   http://${IP}:${PORT}`);
  console.log(`识别引擎: ${WHISPER}   模型: ${path.basename(MODEL)}  ${fs.existsSync(MODEL) ? '✅' : '❌ 模型不存在'}   线程: ${THREADS}   语法约束: ${HAS_GRAMMAR ? '✅' : '❌(用prompt)'}`);
  console.log(`提示: 浏览器麦克风需要安全上下文——本机用 http://localhost:${PORT}；对外部署请挂在支持 HTTPS 的反向代理后面`);
});