const fs = require('fs')
const path = require('path')
const { randomUUID } = require('crypto')
const busboy = require('busboy')

const ALLOWED = { 'image/png': 'png', 'image/jpeg': 'jpg', 'image/webp': 'webp' }

function uploadFile(ctx, { dir }) {
  fs.mkdirSync(dir, { recursive: true }) // Node 10.12+ 自带递归创建

  return new Promise((resolve, reject) => {
    let bb
    try {
      bb = busboy({
        headers: ctx.req.headers,
        defParamCharset: 'utf8',
        limits: { fileSize: 5 * 1024 * 1024, files: 3, fields: 10 },
      })
    } catch (err) {
      return reject(Object.assign(err, { status: 415 }))
    }

    const fields = {}
    const tasks = []      // 每个文件一个 Promise，全部 finish 才算成功
    const written = []    // 出错时要删的文件

    bb.on('field', (name, val) => { fields[name] = val })

    bb.on('file', (name, file, { filename, mimeType }) => {
      const ext = ALLOWED[mimeType]
      if (!ext) return file.resume()           // 不要的也必须读掉
      const saveTo = path.join(dir, `${randomUUID()}.${ext}`)
      written.push(saveTo)
      const out = fs.createWriteStream(saveTo)

      tasks.push(new Promise((ok, fail) => {
        file.on('limit', () => fail(Object.assign(new Error('文件过大'), { status: 413 })))
        out.on('finish', () => ok({ field: name, originalName: filename, path: saveTo }))
        out.on('error', fail)
        file.on('error', fail)
      }))
      file.pipe(out)
    })

    bb.on('close', async () => {
      try {
        const files = await Promise.all(tasks)
        resolve({ success: true, fields, files })
      } catch (err) {
        written.forEach((p) => fs.rm(p, { force: true }, () => {}))
        reject(err)
      }
    })
    bb.on('error', reject)

    ctx.req.pipe(bb)
  })
}

module.exports = { uploadFile }