const fs = require("node:fs");
const path = require("node:path");
const { Readable } = require("node:stream");
const { pipeline } = require("node:stream/promises");

const DOWNLOAD_DIR = path.resolve(process.env.DOWNLOAD_DIR || "downloads");

function getServerCredentials(options = {}) {
  const apiUrl = options.apiUrl || process.env.REINLOOP_API_URL;
  const adminToken = options.adminToken || process.env.B_ADMIN_TOKEN;
  if (!apiUrl) throw new Error("缺少 server API URL");
  if (!adminToken) throw new Error("缺少 Admin Token");
  return { apiUrl, adminToken };
}

async function callServer(payload, options = {}) {
  const { apiUrl, adminToken } = getServerCredentials(options);
  const response = await fetch(apiUrl, {
    method: "POST",
    headers: { "content-type": "application/json" },
    body: JSON.stringify({ ...payload, adminToken })
  });
  let result = null;
  try {
    result = await response.json();
  } catch {
    result = null;
  }
  if (!response.ok) {
    const message = result && typeof result.errMsg === "string" && result.errMsg
      ? result.errMsg
      : `server 请求失败: HTTP ${response.status}`;
    throw new Error(message);
  }
  if (!result || typeof result !== "object") {
    throw new Error("server 返回格式无效");
  }
  if (!result.success) throw new Error(result.errMsg || "server 返回失败");
  return result;
}

async function downloadFromUrl(url, fileName, options = {}) {
  await fs.promises.mkdir(DOWNLOAD_DIR, { recursive: true });
  return downloadToPath(url, path.join(DOWNLOAD_DIR, path.basename(fileName)), options);
}

async function downloadToPath(url, destination, options = {}) {
  const response = await fetch(url);
  if (!response.ok || !response.body) {
    throw new Error(`下载失败: HTTP ${response.status}`);
  }

  await fs.promises.mkdir(path.dirname(destination), { recursive: true });
  const temporary = `${destination}.downloading`;

  try {
    await pipeline(Readable.fromWeb(response.body), fs.createWriteStream(temporary));
    await fs.promises.rename(temporary, destination);
  } catch (error) {
    await fs.promises.rm(temporary, { force: true });
    throw error;
  }

  console.log(`[${new Date().toISOString()}] 已下载: ${destination}`);
  return destination;
}

async function downloadFile(fileID, fileName, options = {}) {
  const { url } = await callServer({ type: "downloadModel", fileID }, options);
  return downloadFromUrl(url, fileName, options);
}

module.exports = { callServer, downloadFile, downloadFromUrl, downloadToPath, getServerCredentials };