const fs = require('fs');
const http = require('http');
const https = require('https');

function getProtocol(url) {
  return url.startsWith('https') ? https : http;
}

function fetchJSON(url) {
  return new Promise((resolve, reject) => {
    getProtocol(url).get(url, (res) => {
      let data = '';
      res.on('data', chunk => data += chunk);
      res.on('end', () => {
        try { resolve(JSON.parse(data)); }
        catch { reject(new Error(`JSON 解析失败: ${data.slice(0, 200)}`)); }
      });
    }).on('error', reject);
  });
}

function downloadFile(url, dest, showProgress = true) {
  return new Promise((resolve, reject) => {
    getProtocol(url).get(url, (res) => {
      if (res.statusCode >= 300 && res.statusCode < 400 && res.headers.location) {
        return downloadFile(res.headers.location, dest, showProgress).then(resolve).catch(reject);
      }
      if (res.statusCode !== 200) return reject(new Error(`HTTP ${res.statusCode}`));

      const total = parseInt(res.headers['content-length'], 10);
      let downloaded = 0;
      let lastTime = Date.now();
      let lastBytes = 0;
      const file = fs.createWriteStream(dest);

      res.on('data', (chunk) => {
        downloaded += chunk.length;
        if (!showProgress) return;
        const now = Date.now();
        const elapsed = (now - lastTime) / 1000;
        if (elapsed < 0.3) return;

        const speed = (downloaded - lastBytes) / elapsed;
        lastTime = now;
        lastBytes = downloaded;
        const speedStr = speed >= 1048576
          ? `${(speed / 1048576).toFixed(1)} MB/s`
          : `${(speed / 1024).toFixed(0)} KB/s`;

        if (total) {
          const pct = downloaded / total;
          const barWidth = 30;
          const filled = Math.round(pct * barWidth);
          const bar = '█'.repeat(filled) + '░'.repeat(barWidth - filled);
          const eta = speed > 0 ? Math.ceil((total - downloaded) / speed) : 0;
          const etaStr = eta > 60 ? `${Math.floor(eta / 60)}m${eta % 60}s` : `${eta}s`;
          process.stdout.write(`\r  ⬇️  [${bar}] ${(pct * 100).toFixed(1)}%  ${(downloaded / 1048576).toFixed(1)}/${(total / 1048576).toFixed(1)} MB  ${speedStr}  ETA ${etaStr}   `);
        } else {
          process.stdout.write(`\r  ⬇️  ${(downloaded / 1048576).toFixed(1)} MB  ${speedStr}   `);
        }
      });

      res.pipe(file);
      file.on('finish', () => { file.close(); if (showProgress) console.log(); resolve(); });
      file.on('error', (err) => { fs.unlink(dest, () => {}); reject(err); });
    }).on('error', reject);
  });
}

function downloadBuffer(url) {
  return new Promise((resolve, reject) => {
    getProtocol(url).get(url, (res) => {
      if (res.statusCode >= 300 && res.statusCode < 400 && res.headers.location) {
        return downloadBuffer(res.headers.location).then(resolve).catch(reject);
      }
      if (res.statusCode !== 200) return reject(new Error(`HTTP ${res.statusCode}`));
      const chunks = [];
      res.on('data', chunk => chunks.push(chunk));
      res.on('end', () => resolve(Buffer.concat(chunks)));
    }).on('error', reject);
  });
}

module.exports = { fetchJSON, downloadFile, downloadBuffer };