'use strict';

/**
 * 多 LLM 路由 v2 — 稳定性增强版
 *
 * 改进点:
 * 1. SSE 心跳 (每 15s :ping, 防止 Nginx 超时断连)
 * 2. backpressure 处理 (暂停上游 when 客户端消费慢)
 * 3. 非流式请求瞬态重试 (429/502/503 + ECONNRESET)
 * 4. 流式错误发送 SSE error event 而非静默断开
 * 5. 连接/读取超时分离 (15s/180s)
 *
 * @module src/llm-router
 */

const https = require('https');
const http = require('http');
const { URL } = require('url');

// ─── DNS 预解析缓存 (B2 修复: 最大 100 条, 防内存泄露) ───
const dns = require('dns');
const _dnsCache = new Map();
const DNS_CACHE_TTL = 300000; // 5 分钟
const DNS_MAX_ENTRIES = 100;

function cachedLookup(hostname, options, callback) {
  if (typeof options === 'function') { callback = options; options = {}; }
  const cached = _dnsCache.get(hostname);
  if (cached && Date.now() - cached.ts < DNS_CACHE_TTL) {
    return process.nextTick(() => callback(null, cached.address, cached.family));
  }
  dns.lookup(hostname, options, (err, address, family) => {
    if (!err) {
      // 超限时淘汰最旧条目
      if (_dnsCache.size >= DNS_MAX_ENTRIES) {
        const oldest = _dnsCache.keys().next().value; // Map 保持插入顺序
        _dnsCache.delete(oldest);
      }
      _dnsCache.set(hostname, { address, family, ts: Date.now() });
    }
    callback(err, address, family);
  });
}

// ─── SSRF 防护 (B1 修复: 从 proxy.js 同步) ───
const ALLOWED_LLM_HOSTS = new Set([
  'api.anthropic.com', 'api.openai.com',
  'dashscope.aliyuncs.com', 'api.deepseek.com', 'api.moonshot.cn',
  'open.bigmodel.cn', 'ark.cn-beijing.volces.com',
  'api.hunyuan.cloud.tencent.com', 'qianfan.baidubce.com',
  'openrouter.ai',
]);
if (process.env.ALLOWED_API_HOSTS) {
  for (const h of process.env.ALLOWED_API_HOSTS.split(',')) {
    if (h.trim()) ALLOWED_LLM_HOSTS.add(h.trim());
  }
}

function _isPrivateHost(hostname) {
  const lower = hostname.replace(/^\[|\]$/g, '').toLowerCase();
  if (/^f[cd][0-9a-f]{2}:/.test(lower)) return true;
  if (/^fe[89ab][0-9a-f]:/.test(lower)) return true;
  if (lower === '::1' || lower === '::') return true;
  if (hostname.startsWith('[::ffff:')) return _isPrivateHost(hostname.slice(8, -1));
  const parts = hostname.split('.');
  if (parts.length === 4 && parts.every(p => /^\d+$/.test(p))) {
    const [a, b] = parts.map(Number);
    if (a === 10 || a === 127 || a === 0) return true;
    if (a === 172 && b >= 16 && b <= 31) return true;
    if (a === 192 && b === 168) return true;
    if (a === 169 && b === 254) return true;
  }
  return hostname === 'localhost';
}

function _validateLLMBaseUrl(baseUrl) {
  if (!baseUrl) return;
  let url;
  try { url = new URL(baseUrl); } catch { throw { status: 400, message: 'base_url 格式无效' }; }
  if (ALLOWED_LLM_HOSTS.has(url.hostname)) return;
  if (_isPrivateHost(url.hostname)) throw { status: 403, message: '不允许访问内网地址' };
  throw { status: 403, message: '不允许的 LLM API 地址' };
}

// 启动预热
for (const h of ['dashscope.aliyuncs.com', 'api.deepseek.com', 'api.moonshot.cn', 'open.bigmodel.cn', 'ark.cn-beijing.volces.com', 'api.hunyuan.cloud.tencent.com', 'qianfan.baidubce.com']) {
  dns.lookup(h, () => {});
}

// ─── HTTP Agent: keepAlive 连接池 + DNS 缓存 ───
const httpsAgent = new https.Agent({
  keepAlive: true, maxSockets: 10, maxFreeSockets: 5,
  keepAliveMsecs: 30000, lookup: cachedLookup,
});
const httpAgent = new http.Agent({
  keepAlive: true, maxSockets: 10, maxFreeSockets: 5,
  keepAliveMsecs: 30000, lookup: cachedLookup,
});

// ─── 重试配置 ───
const RETRYABLE_STATUS = new Set([429, 502, 503, 504]);
const RETRYABLE_ERRORS = new Set(['ECONNRESET', 'ETIMEDOUT', 'ECONNREFUSED', 'EPIPE', 'EAI_AGAIN']);
const MAX_RETRIES = 2;

function isRetryable(err, statusCode) {
  if (statusCode && RETRYABLE_STATUS.has(statusCode)) return true;
  if (err && RETRYABLE_ERRORS.has(err.code)) return true;
  if (err && /socket hang up|ECONNRESET|ETIMEDOUT/i.test(err.message)) return true;
  return false;
}

function retryDelay(attempt) {
  return 1000 * Math.pow(2, attempt) + Math.random() * 500;
}

function sleep(ms) { return new Promise(r => setTimeout(r, ms)); }

// ─── SSE 心跳 ───
const SSE_HEARTBEAT_MS = 15000;

function startSSEHeartbeat(res) {
  const timer = setInterval(() => {
    if (res.writableEnded || res.destroyed) { clearInterval(timer); return; }
    try { res.write(':ping\n\n'); } catch { clearInterval(timer); }
  }, SSE_HEARTBEAT_MS);
  if (timer.unref) timer.unref();
  return timer;
}

// ─── Provider 配置 ───
const PROVIDERS = {
  anthropic: {
    baseUrl: 'https://api.anthropic.com',
    pathPrefix: '/v1/messages',
    authHeader: 'x-api-key',
    versionHeader: { 'anthropic-version': process.env.ANTHROPIC_API_VERSION || '2023-06-01' },
    modelPrefixes: ['claude-'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: opts.messages,
      max_tokens: opts.maxTokens || 8192,
      stream: opts.stream || false,
      ...(opts.systemPrompt ? { system: opts.systemPrompt } : {}),
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.input_tokens || 0,
      output_tokens: data?.usage?.output_tokens || 0,
    }),
  },
  openai: {
    baseUrl: 'https://api.openai.com',
    pathPrefix: '/v1/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['gpt-', 'o1-', 'o3-', 'o4-', 'chatgpt-'],
    buildBody: (opts) => {
      const isReasoningModel = /^(o1|o3|o4)-/i.test(opts.model);
      const tokenParam = isReasoningModel
        ? { max_completion_tokens: opts.maxTokens || 8192 }
        : { max_tokens: opts.maxTokens || 8192 };
      return {
        model: opts.model,
        messages: [
          ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
          ...opts.messages,
        ],
        ...tokenParam,
        stream: opts.stream || false,
      };
    },
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
  qwen: {
    baseUrl: 'https://dashscope.aliyuncs.com/compatible-mode',
    pathPrefix: '/v1/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['qwen'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      max_tokens: opts.maxTokens || 8192,
      stream: opts.stream || false,
      enable_thinking: false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
  deepseek: {
    baseUrl: 'https://api.deepseek.com',
    pathPrefix: '/v1/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['deepseek-'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      max_tokens: opts.maxTokens || 8192,
      stream: opts.stream || false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.output_tokens || 0,
    }),
  },
  kimi: {
    baseUrl: 'https://api.moonshot.cn',
    pathPrefix: '/v1/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['moonshot-', 'kimi'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      max_tokens: opts.maxTokens || 8192,
      stream: opts.stream || false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
  zhipu: {
    baseUrl: 'https://open.bigmodel.cn/api/paas',
    pathPrefix: '/v4/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['glm-'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      max_tokens: opts.maxTokens || 4096,
      stream: opts.stream || false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
  volcengine: {
    baseUrl: 'https://ark.cn-beijing.volces.com/api/v3',
    pathPrefix: '/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['doubao-', 'ep-'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      max_tokens: opts.maxTokens || 4096,
      stream: opts.stream || false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
  hunyuan: {
    baseUrl: 'https://api.hunyuan.cloud.tencent.com',
    pathPrefix: '/v1/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['hunyuan-'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      ...(opts.maxTokens ? { max_tokens: opts.maxTokens } : {}),
      stream: opts.stream || false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
  baidu: {
    baseUrl: 'https://qianfan.baidubce.com',
    pathPrefix: '/v2/chat/completions',
    authHeader: 'Authorization',
    authPrefix: 'Bearer ',
    versionHeader: {},
    modelPrefixes: ['ernie-'],
    buildBody: (opts) => ({
      model: opts.model,
      messages: [
        ...(opts.systemPrompt ? [{ role: 'system', content: opts.systemPrompt }] : []),
        ...opts.messages,
      ],
      max_tokens: opts.maxTokens || 4096,
      stream: opts.stream || false,
    }),
    parseUsage: (data) => ({
      input_tokens: data?.usage?.prompt_tokens || 0,
      output_tokens: data?.usage?.completion_tokens || 0,
    }),
  },
};

function detectProvider(model) {
  if (!model) return 'qwen';
  const lower = model.toLowerCase();
  for (const [name, config] of Object.entries(PROVIDERS)) {
    if (config.modelPrefixes.some(prefix => lower.startsWith(prefix))) {
      return name;
    }
  }
  return 'qwen';
}

function getProviderConfig(providerName, overrideBaseUrl) {
  const config = PROVIDERS[providerName];
  if (!config) throw { status: 400, message: `不支持的 provider: ${providerName}` };
  // B1 修复: SSRF 防护
  if (overrideBaseUrl) _validateLLMBaseUrl(overrideBaseUrl);
  return { ...config, baseUrl: overrideBaseUrl || config.baseUrl };
}

function listProviders() {
  return Object.entries(PROVIDERS).map(([name, config]) => ({
    name, models: config.modelPrefixes, baseUrl: config.baseUrl,
  }));
}

/**
 * 核心 LLM 请求 — 非流式 (支持重试)
 */
function _sendNonStream(provider, apiKey, body, isHttps, requestOpts) {
  return new Promise((resolve, reject) => {
    const transport = isHttps ? https : http;
    const proxyReq = transport.request(requestOpts, (proxyRes) => {
      proxyReq.setTimeout(180_000);
      const chunks = [];
      proxyRes.on('data', c => chunks.push(c));
      proxyRes.on('end', () => {
        const raw = Buffer.concat(chunks).toString('utf8');
        try { resolve({ status: proxyRes.statusCode, data: JSON.parse(raw), headers: proxyRes.headers }); }
        catch { resolve({ status: proxyRes.statusCode, data: raw, headers: proxyRes.headers }); }
      });
      proxyRes.on('error', reject);
    });
    proxyReq.on('error', (err) => {
      err.message = `LLM 请求失败: ${err.message}`;
      reject(err);
    });
    proxyReq.on('timeout', () => {
      proxyReq.destroy(new Error('LLM API 连接超时 (30s)'));
    });
    proxyReq.write(JSON.stringify(body));
    proxyReq.end();
  });
}

/**
 * 核心 LLM 请求 — 流式 (不重试, 带心跳+backpressure)
 */
function _sendStream(provider, apiKey, body, res, isHttps, requestOpts) {
  return new Promise((resolve, reject) => {
    const transport = isHttps ? https : http;
    const proxyReq = transport.request(requestOpts, (proxyRes) => {
      proxyReq.setTimeout(300_000); // 流式读取 5 分钟

      if (proxyRes.statusCode !== 200) {
        const chunks = [];
        proxyRes.on('data', c => chunks.push(c));
        proxyRes.on('end', () => {
          const raw = Buffer.concat(chunks).toString('utf8');
          try { resolve({ status: proxyRes.statusCode, data: JSON.parse(raw), streamed: false }); }
          catch { resolve({ status: proxyRes.statusCode, data: { error: raw }, streamed: false }); }
        });
        proxyRes.on('error', reject);
        return;
      }

      // SSE headers
      res.writeHead(200, {
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        'Connection': 'keep-alive',
        'X-Accel-Buffering': 'no',
      });

      // 启动心跳
      const heartbeatTimer = startSSEHeartbeat(res);

      let lastDataLine = '';
      let inThink = false;
      let fullText = '';

      proxyRes.on('data', c => {
        const text = c.toString();
        const lines = text.split('\n');
        const outLines = [];

        for (const line of lines) {
          if (line.startsWith('data: ') && line !== 'data: [DONE]') {
            const jsonStr = line.slice(6);
            lastDataLine = jsonStr;
            try {
              const parsed = JSON.parse(jsonStr);
              const delta = parsed.choices?.[0]?.delta;
              if (delta) {
                if (delta.reasoning_content !== undefined) {
                  delete delta.reasoning_content;
                }
                if (delta.content) {
                  let content = delta.content;
                  if (inThink) {
                    const endIdx = content.indexOf('</think>');
                    if (endIdx !== -1) { inThink = false; content = content.slice(endIdx + 8); }
                    else content = '';
                  }
                  if (!inThink && content.includes('<think>')) {
                    const startIdx = content.indexOf('<think>');
                    const endIdx = content.indexOf('</think>', startIdx);
                    if (endIdx !== -1) { content = content.slice(0, startIdx) + content.slice(endIdx + 8); }
                    else { content = content.slice(0, startIdx); inThink = true; }
                  }
                  delta.content = content;
                  if (content) fullText += content;
                }
              }
              outLines.push('data: ' + JSON.stringify(parsed));
            } catch {
              outLines.push(line);
            }
          } else {
            outLines.push(line);
          }
        }

        // backpressure 处理
        const canWrite = res.write(outLines.join('\n'));
        if (!canWrite) {
          proxyRes.pause();
          res.once('drain', () => proxyRes.resume());
        }
      });

      proxyRes.on('end', () => {
        clearInterval(heartbeatTimer);
        res.end();
        let usage = null;
        try {
          const parsed = JSON.parse(lastDataLine);
          if (parsed.usage) {
            usage = {
              input_tokens: parsed.usage.prompt_tokens || parsed.usage.input_tokens || 0,
              output_tokens: parsed.usage.completion_tokens || parsed.usage.output_tokens || 0,
            };
          }
        } catch { /* 无 usage */ }
        resolve({ streamed: true, status: 200, usage, fullText: fullText || undefined });
      });

      proxyRes.on('error', (err) => {
        clearInterval(heartbeatTimer);
        // 发送 SSE 错误事件
        try {
          res.write(`data: ${JSON.stringify({ error: { message: err.message, type: 'stream_error' } })}\n\n`);
        } catch { /* ignore */ }
        res.end();
        reject(err);
      });

      res.on('close', () => {
        clearInterval(heartbeatTimer);
        proxyReq.destroy();
      });
    });

    proxyReq.on('error', (err) => {
      err.message = `LLM 流式请求失败: ${err.message}`;
      reject(err);
    });
    proxyReq.on('timeout', () => {
      proxyReq.destroy(new Error('LLM API 连接超时 (30s)'));
    });
    proxyReq.write(JSON.stringify(body));
    proxyReq.end();
  });
}

/**
 * 通用 LLM 请求 — 自动选择流式/非流式, 非流式带重试
 */
async function sendLLMRequest(provider, apiKey, body, res, stream) {
  const config = PROVIDERS[provider.name || provider] || PROVIDERS.qwen;
  const base = provider.baseUrl || config.baseUrl;
  let baseUrl;
  try { baseUrl = new URL(base); }
  catch { throw { status: 400, message: `base_url 格式无效: ${base}` }; }

  const fullPath = baseUrl.pathname.replace(/\/$/, '') + config.pathPrefix;
  const url = new URL(fullPath, base);
  const isHttps = url.protocol === 'https:';

  const headers = {
    'Content-Type': 'application/json',
    'Content-Length': Buffer.byteLength(JSON.stringify(body)),
    ...config.versionHeader,
  };

  if (config.authHeader === 'Authorization') {
    headers['Authorization'] = (config.authPrefix || '') + apiKey;
  } else {
    headers[config.authHeader] = apiKey;
  }

  const requestOpts = {
    hostname: url.hostname,
    port: url.port || (isHttps ? 443 : 80),
    path: url.pathname,
    method: 'POST',
    headers,
    agent: isHttps ? httpsAgent : httpAgent,
    timeout: 30_000, // 连接超时 30s
  };

  if (stream && res) {
    return _sendStream(provider, apiKey, body, res, isHttps, requestOpts);
  }

  // 非流式: 带重试
  let lastError = null;
  for (let attempt = 0; attempt <= MAX_RETRIES; attempt++) {
    try {
      const result = await _sendNonStream(provider, apiKey, body, isHttps, requestOpts);
      if (RETRYABLE_STATUS.has(result.status) && attempt < MAX_RETRIES) {
        await sleep(retryDelay(attempt));
        continue;
      }
      return result;
    } catch (err) {
      lastError = err;
      if (isRetryable(err) && attempt < MAX_RETRIES) {
        await sleep(retryDelay(attempt));
        continue;
      }
      throw err;
    }
  }
  throw lastError;
}

// --- Circuit Breaker + EWMA hooks ---
let _circuitBreaker = null;
let _providerHealth = null;

function initPerformanceHooks(opts) {
  _circuitBreaker = opts.circuitBreaker || null;
  _providerHealth = opts.providerHealth || null;
}

function sendLLMRequestWithCB(provider, apiKey, body, res, stream) {
  const providerName = provider.name || provider;
  const startMs = Date.now();
  if (_circuitBreaker && !_circuitBreaker.canRequest(providerName)) {
    return Promise.reject(Object.assign(new Error('Circuit Breaker OPEN: ' + providerName), { status: 503 }));
  }
  return sendLLMRequest(provider, apiKey, body, res, stream).then(
    (result) => {
      const elapsed = Date.now() - startMs;
      const success = result.streamed ? true : (result.status >= 200 && result.status < 500);
      if (_circuitBreaker && success) _circuitBreaker.recordSuccess(providerName);
      if (_providerHealth && _providerHealth.recordRequestLatency) _providerHealth.recordRequestLatency(providerName, elapsed, success);
      return result;
    },
    (err) => {
      const elapsed = Date.now() - startMs;
      if (_circuitBreaker) _circuitBreaker.recordFailure(providerName);
      if (_providerHealth && _providerHealth.recordRequestLatency) _providerHealth.recordRequestLatency(providerName, elapsed, false);
      throw err;
    }
  );
}

module.exports = {
  detectProvider, getProviderConfig, listProviders,
  sendLLMRequest: sendLLMRequestWithCB,
  sendLLMRequestRaw: sendLLMRequest,
  initPerformanceHooks,
  PROVIDERS,
};