/**
 * mock-upstream.mjs — 本地模拟 DashScope 上游端点（开发测试用，保留以供后续测试）
 *
 * 用途：在无真实 DashScope API Key 的情况下验证网关全链路。
 *
 * 启动方式：
 *   node apps/api/scripts/mock-upstream.mjs
 *   监听端口: 19090
 *
 * 端点：
 *   POST /v1/chat/completions
 *     - 非流式：返回 OpenAI 格式 JSON，含 usage {prompt_tokens: 50000, completion_tokens: 80000}
 *     - 流式 (stream: true)：返回 SSE 格式，最后一条包含 usage
 */

import { createServer } from 'node:http';

const PORT = 19090;

function randomId(prefix) {
  const rand = Math.random().toString(36).slice(2, 10);
  return `${prefix}_${rand}`;
}

function nowUnix() {
  return Math.floor(Date.now() / 1000);
}

function handleChatCompletions(body, res) {
  const isStream = body && body.stream === true;
  const model = (body && body.model) || 'unknown';
  const id = randomId('chatcmpl');
  const created = nowUnix();

  if (isStream) {
    // SSE 流式响应
    res.writeHead(200, {
      'Content-Type': 'text/event-stream',
      'Cache-Control': 'no-cache',
      Connection: 'keep-alive',
    });

    const chunks = [
      {
        id,
        object: 'chat.completion.chunk',
        created,
        model,
        choices: [
          {
            index: 0,
            delta: { role: 'assistant', content: '' },
            finish_reason: null,
          },
        ],
        usage: null,
      },
      {
        id,
        object: 'chat.completion.chunk',
        created,
        model,
        choices: [
          {
            index: 0,
            delta: {
              content: '你好！我是由 DoTouch.AI 提供的 AI 助手，请问有什么可以帮助你的？',
            },
            finish_reason: null,
          },
        ],
        usage: null,
      },
      {
        id,
        object: 'chat.completion.chunk',
        created,
        model,
        choices: [{ index: 0, delta: {}, finish_reason: 'stop' }],
        usage: {
          prompt_tokens: 50000,
          completion_tokens: 80000,
          total_tokens: 130,
        },
      },
    ];

    for (const chunk of chunks) {
      res.write(`data: ${JSON.stringify(chunk)}\n\n`);
    }
    res.write('data: [DONE]\n\n');
    res.end();
  } else {
    // 非流式 JSON 响应
    const response = {
      id,
      object: 'chat.completion',
      created,
      model,
      choices: [
        {
          index: 0,
          message: {
            role: 'assistant',
            content:
              '你好！我是由 DoTouch.AI 提供的 AI 助手，请问有什么可以帮助你的？',
          },
          finish_reason: 'stop',
        },
      ],
      usage: {
        prompt_tokens: 50000,
        completion_tokens: 80000,
        total_tokens: 130,
      },
    };

    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify(response));
  }
}

function parseBody(req) {
  return new Promise((resolve) => {
    let data = '';
    req.on('data', (chunk) => {
      data += chunk;
    });
    req.on('end', () => {
      try {
        resolve(JSON.parse(data));
      } catch {
        resolve(null);
      }
    });
  });
}

const server = createServer(async (req, res) => {
  const parsedUrl = new URL(req.url || '/', `http://localhost:${PORT}`);

  if (
    req.method === 'POST' &&
    parsedUrl.pathname === '/v1/chat/completions'
  ) {
    const body = await parseBody(req);
    handleChatCompletions(body, res);
  } else if (req.method === 'GET' && parsedUrl.pathname === '/health') {
    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ status: 'ok' }));
  } else {
    res.writeHead(404, { 'Content-Type': 'application/json' });
    res.end(
      JSON.stringify({ error: { message: 'Not found', type: '404', code: '404' } }),
    );
  }
});

server.listen(PORT, () => {
  console.log(`🔧 Mock DashScope upstream running on http://localhost:${PORT}`);
  console.log(`   POST /v1/chat/completions`);
});