/**
 * Mock LLM 服务器 — OpenAI 兼容格式，用于 E2E 测试。
 *
 * 启动后监听 MOCK_LLM_PORT（默认 3600），提供：
 * - POST /v1/chat/completions  流式聊天补全（SSE）
 *
 * 响应内容固定为 "你好！这是一个测试回复。" 分段流式输出，
 * 保证 agent chat 的 streamText 能正常消费。
 */
import { createServer, type Server } from "node:http";

const PORT = Number(process.env.MOCK_LLM_PORT) || 3600;
const REPLY = "你好！这是一个测试回复。";

function splitChunks(text: string): string[] {
  const chunks: string[] = [];
  for (const ch of text) {
    chunks.push(ch);
  }
  return chunks;
}

function handleChatCompletions(req: any, res: any) {
  let body = "";
  req.on("data", (chunk: Buffer) => {
    body += chunk.toString();
  });
  req.on("end", () => {
    let parsed: any = {};
    try {
      parsed = JSON.parse(body);
    } catch {
      parsed = {};
    }

    const model = parsed.model || "mock-model";
    const chunks = splitChunks(REPLY);

    res.writeHead(200, {
      "Content-Type": "text/event-stream",
      "Cache-Control": "no-cache",
      Connection: "keep-alive",
    });

    let idx = 0;
    const timer = setInterval(() => {
      if (idx < chunks.length) {
        const delta = chunks[idx];
        const sseData = JSON.stringify({
          id: "chatcmpl-mock",
          object: "chat.completion.chunk",
          created: Math.floor(Date.now() / 1000),
          model,
          choices: [
            {
              index: 0,
              delta: { content: delta },
              finish_reason: null,
            },
          ],
        });
        res.write(`data: ${sseData}\n\n`);
        idx++;
      } else {
        const doneData = JSON.stringify({
          id: "chatcmpl-mock",
          object: "chat.completion.chunk",
          created: Math.floor(Date.now() / 1000),
          model,
          choices: [
            {
              index: 0,
              delta: {},
              finish_reason: "stop",
            },
          ],
        });
        res.write(`data: ${doneData}\n\n`);
        res.write("data: [DONE]\n\n");
        res.end();
        clearInterval(timer);
      }
    }, 20);
  });
}

let server: Server;

function start(): Promise<Server> {
  return new Promise((resolve) => {
    server = createServer((req, res) => {
      res.setHeader("Access-Control-Allow-Origin", "*");
      res.setHeader("Access-Control-Allow-Headers", "*");
      res.setHeader("Access-Control-Allow-Methods", "*");
      if (req.method === "OPTIONS") {
        res.writeHead(204);
        res.end();
        return;
      }
      const url = req.url || "";
      if (url.startsWith("/v1/chat/completions") && req.method === "POST") {
        handleChatCompletions(req, res);
        return;
      }
      res.writeHead(404, { "Content-Type": "application/json" });
      res.end(JSON.stringify({ error: "not found" }));
    });
    server.listen(PORT, () => {
      console.log(`[mock-llm] listening on http://localhost:${PORT}`);
      resolve(server);
    });
  });
}

function stop(): Promise<void> {
  return new Promise((resolve) => {
    if (server) {
      server.close(() => resolve());
    } else {
      resolve();
    }
  });
}

export { start, stop };