const fs = require('fs')
const request = require('request')
const path = require('path')
const dirPath = path.join(__dirname, "baseMap");
const setting = require('./region')

function checkLocal(zoom, x, y) {
  return new Promise(resolve => {
    fs.exists(`${dirPath}/${zoom}_${x}_${y}.png`, resolve)
  })
}


const downImage = (function() {
  let count = 0
  const domains = [
    'http://a.tile.openstreetmap.org',
    'http://b.tile.openstreetmap.org',
    'http://c.tile.openstreetmap.org'
  ]
  const length = domains.length

  return async function downImage(zoom, x, y) {
    count++;

    let url = domains[count % length] + `/${zoom}/${x}/${y}.png`
    let local = `${dirPath}/${zoom}_${x}_${y}.png`

    console.log(url + '请求中')
    return new Promise(resolve => {
      try {
        // 如果30秒都还没完成则直接返回
        setTimeout(resolve, 30000)

        let readStream = request(url)
        let writeStream = fs.createWriteStream(local)

        readStream.on('error', errorHandle)

        function errorHandle(err) {
          resolve()
        }
 
        readStream.pipe(writeStream)
          .on('close', err => {
            if (err) {
              console.error(url + '文件下载失败')
            } else {
              console.log(url + '文件下载成功')
            }
            resolve()
          })
          .on('error', errorHandle)
      } catch (e) {
        resolve()
      }
    })
  }
})();

async function cache(...args) {
  if (!(await checkLocal(...args))) {
    await downImage(...args)
  }
}

process.on('message', async msg => {
  let zoom = Number(msg)
  // 多少个请求一并
  let parallel = 10

  console.log(zoom)
  let {minX, maxX, minY, maxY} = setting[zoom]
  // let min = parseInt(basic / 4)
  // let maxX = basic * 10
  // let maxY = maxX / 1.5
  let total = (maxX - minX) * (maxY - minY)
  let count = 0

  for (let x = maxX; x > minX; x--) {
    for (let y = minY; y < maxY && y < x;) {
      let run = y + parallel < maxY ? parallel : maxY - y
      let pros = []
      for (let h = 0; h < run; h++) {
        count++
        pros.push(cache(zoom, x, y + h))
      }
      await Promise.all(pros)
      y += run
      console.log('层级' + zoom + '总共' + total + '已下载' + count)
    }
  }


  fs.writeFileSync('./log.text', fs.readFileSync('./log.text') + '\r\n' + '层级' + zoom + '已下载完毕')
})