/**
 * 根据 url 下载文件到 savePath（支持 http/https）
 * 入参：url, savePath（相对路径时基于 folderPath）
 */
const path = require('path')
const fs = require('fs')
const https = require('https')
const http = require('http')

function buildSavePath(savePath, folderPath) {
  if (!savePath || typeof savePath !== 'string') return null
  const trimmed = savePath.trim()
  if (path.isAbsolute(trimmed) || trimmed.match(/^[A-Za-z]:/)) return trimmed
  return folderPath ? path.join(folderPath, trimmed) : path.resolve(trimmed)
}

function downloadToFile(url, filePath) {
  return new Promise((resolve, reject) => {
    const protocol = url.startsWith('https') ? https : http
    const request = protocol.get(url, { timeout: 60000 }, (response) => {
      if (response.statusCode === 301 || response.statusCode === 302) {
        const redirect = response.headers.location
        if (redirect) return downloadToFile(redirect, filePath).then(resolve).catch(reject)
      }
      if (response.statusCode !== 200) {
        reject(new Error(`HTTP ${response.statusCode}`))
        return
      }
      const dir = path.dirname(filePath)
      if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true })
      const file = fs.createWriteStream(filePath)
      response.pipe(file)
      file.on('finish', () => { file.close(); resolve({ success: true, path: filePath }) })
      file.on('error', (err) => { fs.unlink(filePath, () => {}); reject(err) })
    })
    request.on('error', reject)
    request.setTimeout(60000, () => { request.destroy(); reject(new Error('timeout')) })
  })
}

async function executeDownload({ url, savePath, folderPath }) {
  if (!url || typeof url !== 'string' || !url.trim()) return { success: false, error: 'download 缺少 url 参数' }
  if (!savePath && savePath !== '') return { success: false, error: 'download 缺少 savePath 参数' }
  const absolutePath = buildSavePath(String(savePath).trim(), folderPath)
  if (!absolutePath) return { success: false, error: 'download 缺少 savePath 参数' }
  try {
    await downloadToFile(url.trim(), absolutePath)
    return { success: true, path: absolutePath }
  } catch (e) {
    return { success: false, error: e && (e.message || String(e)) || 'download failed' }
  }
}

module.exports = { executeDownload }