const express = require("express");

const router = express.Router();

const VOLCENGINE_API_KEY = process.env.VOLCENGINE_API_KEY;
const VOLCENGINE_MODEL = process.env.VOLCENGINE_MODEL || "your_endpoint_id";
const VOLCENGINE_BASE_URL =
  process.env.VOLCENGINE_BASE_URL || "https://ark.cn-beijing.volces.com/api/v3";

router.post("/chat", async (req, res) => {
  try {
    if (!VOLCENGINE_API_KEY) {
      return res.status(500).json({
        error: "缺少 VOLCENGINE_API_KEY，请先在 .env 中配置",
      });
    }

    const { messages, model, temperature } = req.body || {};
    if (!Array.isArray(messages) || messages.length === 0) {
      return res.status(400).json({
        error: "请求体 messages 必须是非空数组",
      });
    }

    const response = await fetch(`${VOLCENGINE_BASE_URL}/chat/completions`, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${VOLCENGINE_API_KEY}`,
      },
      body: JSON.stringify({
        model: model || VOLCENGINE_MODEL,
        messages,
        temperature: typeof temperature === "number" ? temperature : 0.7,
      }),
    });

    const data = await response.json();
    if (!response.ok) {
      return res.status(response.status).json({
        error: "调用火山引擎 Chat 接口失败",
        detail: data,
      });
    }

    return res.json({
      id: data.id,
      model: data.model,
      content: data?.choices?.[0]?.message?.content || "",
      raw: data,
    });
  } catch (error) {
    return res.status(500).json({
      error: "服务内部错误",
      detail: error.message,
    });
  }
});

router.post("/chat/stream", async (req, res) => {
  try {
    if (!VOLCENGINE_API_KEY) {
      return res.status(500).json({
        error: "缺少 VOLCENGINE_API_KEY，请先在 .env 中配置",
      });
    }

    const { messages, model, temperature } = req.body || {};
    if (!Array.isArray(messages) || messages.length === 0) {
      return res.status(400).json({
        error: "请求体 messages 必须是非空数组",
      });
    }

    res.setHeader("Content-Type", "text/event-stream; charset=utf-8");
    res.setHeader("Cache-Control", "no-cache, no-transform");
    res.setHeader("Connection", "keep-alive");
    res.flushHeaders();

    const controller = new AbortController();
    req.on("close", () => {
      controller.abort();
    });

    const response = await fetch(`${VOLCENGINE_BASE_URL}/chat/completions`, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${VOLCENGINE_API_KEY}`,
      },
      body: JSON.stringify({
        model: model || VOLCENGINE_MODEL,
        messages,
        temperature: typeof temperature === "number" ? temperature : 0.7,
        stream: true,
      }),
      signal: controller.signal,
    });

    if (!response.ok) {
      const errorData = await response.json().catch(() => ({}));
      res.write(
        `data: ${JSON.stringify({
          error: "调用火山引擎流式接口失败",
          detail: errorData,
        })}\n\n`,
      );
      return res.end();
    }

    if (!response.body) {
      res.write(`data: ${JSON.stringify({ error: "未获取到流式响应体" })}\n\n`);
      return res.end();
    }

    const reader = response.body.getReader();
    const decoder = new TextDecoder("utf-8");
    let buffer = "";

    while (true) {
      const { done, value } = await reader.read();
      if (done) break;

      buffer += decoder.decode(value, { stream: true });
      const lines = buffer.split("\n");
      buffer = lines.pop() || "";

      for (const line of lines) {
        const trimmed = line.trim();
        if (!trimmed.startsWith("data:")) continue;

        const payload = trimmed.slice(5).trim();
        if (payload === "[DONE]") {
          res.write("data: [DONE]\n\n");
          res.end();
          return;
        }

        try {
          const parsed = JSON.parse(payload);
          const delta = parsed?.choices?.[0]?.delta?.content;
          if (delta) {
            res.write(`data: ${JSON.stringify({ delta })}\n\n`);
          }
        } catch (_error) {
          // 忽略非 JSON 片段，继续解析后续流内容
        }
      }
    }

    res.write("data: [DONE]\n\n");
    return res.end();
  } catch (error) {
    if (!res.headersSent) {
      return res.status(500).json({
        error: "服务内部错误",
        detail: error.message,
      });
    }

    res.write(`data: ${JSON.stringify({ error: error.message })}\n\n`);
    return res.end();
  }
});

module.exports = router;