/**
 * 假上游：实现够用的 OpenAI 兼容端点，把收到的原始请求体原样落盘。
 *
 * 用法：
 *   node capture-server.mjs --label st --port 8801
 *
 * 落盘目录默认 ./captures（相对本文件）。
 * 每个请求一个 <label>-<序号>.json，内容 { label, receivedAt, method, url, headers, body }。
 * body 是原始字符串，diff 工具再解析 —— 保留原文便于核对是否有我们没建模的字段。
 */
import { createServer } from "node:http";
import { mkdirSync, writeFileSync } from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";

const HERE = path.dirname(fileURLToPath(import.meta.url));

function readArgs(argv) {
  const out = { label: "unknown", port: 8800, out: path.join(HERE, "captures") };
  for (let i = 0; i < argv.length; i++) {
    const key = argv[i];
    const next = argv[i + 1];
    if (key === "--label") out.label = String(next);
    else if (key === "--port") out.port = Number(next);
    else if (key === "--out") out.out = path.resolve(String(next));
  }
  return out;
}

const args = readArgs(process.argv.slice(2));
mkdirSync(args.out, { recursive: true });

const REPLY_TEXT = "[[mock-reply]] 收到。";
const REPLY_REASONING = "[[mock-reasoning]] 想一下。";

function capture(req, url, raw) {
  const stamp = new Date().toISOString().replace(/[:.]/g, "-");
  const seq = String(globalThis.__captureSeq = (globalThis.__captureSeq ?? 0) + 1).padStart(3, "0");
  const file = path.join(args.out, `${args.label}-${seq}-${stamp}.json`);
  const payload = {
    label: args.label,
    receivedAt: new Date().toISOString(),
    method: req.method,
    url,
    headers: {
      "content-type": req.headers["content-type"] ?? null,
      authorization: req.headers.authorization ? "<redacted>" : null,
    },
    body: raw,
  };
  writeFileSync(file, JSON.stringify(payload, null, 2), "utf8");
  // 只写一行摘要，不把正文打到控制台
  let charCount = raw.length;
  try {
    const parsed = JSON.parse(raw);
    charCount = Array.isArray(parsed.messages)
      ? parsed.messages.reduce((n, m) => n + String(m.content ?? "").length, 0)
      : charCount;
  } catch {
    /* 非 JSON 就按原长度记 */
  }
  console.log(`[capture:${args.label}] ${req.method} ${url} -> ${path.basename(file)} (messages 正文 ${charCount} 字)`);
  return file;
}

function readBody(req) {
  return new Promise((resolve, reject) => {
    const chunks = [];
    req.on("data", (c) => chunks.push(c));
    req.on("end", () => resolve(Buffer.concat(chunks).toString("utf8")));
    req.on("error", reject);
  });
}

function sseHead(res) {
  res.writeHead(200, {
    "Content-Type": "text/event-stream; charset=utf-8",
    "Cache-Control": "no-cache",
    Connection: "keep-alive",
  });
}

function sseChunk(delta, finishReason = null) {
  return `data: ${JSON.stringify({
    id: "chatcmpl-mock",
    object: "chat.completion.chunk",
    created: Math.floor(Date.now() / 1000),
    model: "mock-model",
    choices: [{ index: 0, delta, finish_reason: finishReason }],
  })}\n\n`;
}

const server = createServer(async (req, res) => {
  const url = req.url ?? "/";
  if (req.method === "GET" && url.includes("/models")) {
    res.writeHead(200, { "Content-Type": "application/json; charset=utf-8" });
    res.end(
      JSON.stringify({
        object: "list",
        data: [{ id: "mock-model", object: "model", owned_by: "mock" }],
      }),
    );
    return;
  }

  const raw = await readBody(req);
  if (req.method !== "POST") {
    res.writeHead(404).end("not found");
    return;
  }

  let body = {};
  try {
    body = JSON.parse(raw);
  } catch {
    /* 保留原文，下面按默认处理 */
  }

  capture(req, url, raw);

  if (url.includes("/embeddings")) {
    res.writeHead(200, { "Content-Type": "application/json; charset=utf-8" });
    res.end(JSON.stringify({ object: "list", data: [{ embedding: [0] }] }));
    return;
  }

  if (url.includes("/completions")) {
    if (body.stream) {
      sseHead(res);
      const chunks = [];
      if (body.reasoning_effort && body.reasoning_effort !== "none") {
        chunks.push(sseChunk({ role: "assistant", reasoning_content: REPLY_REASONING }));
      }
      chunks.push(sseChunk({ role: "assistant", content: REPLY_TEXT }));
      chunks.push(sseChunk({}, "stop"));
      chunks.push("data: [DONE]\n\n");
      res.end(chunks.join(""));
      return;
    }
    res.writeHead(200, { "Content-Type": "application/json; charset=utf-8" });
    res.end(
      JSON.stringify({
        id: "chatcmpl-mock",
        object: "chat.completion",
        created: Math.floor(Date.now() / 1000),
        model: "mock-model",
        choices: [
          {
            index: 0,
            message: { role: "assistant", content: REPLY_TEXT },
            finish_reason: "stop",
          },
        ],
        usage: { prompt_tokens: 100, completion_tokens: 10, total_tokens: 110 },
      }),
    );
    return;
  }

  res.writeHead(200, { "Content-Type": "application/json; charset=utf-8" });
  res.end(JSON.stringify({ ok: true }));
});

server.listen(args.port, "127.0.0.1", () => {
  console.log(`[capture:${args.label}] listening on http://127.0.0.1:${args.port}/v1 -> ${args.out}`);
});