export default class RequestQuene {
  constructor(limits = 10, duration = 200) {
    this.duration = duration
    this.limits = limits
    this.q = []
    this.intervalId = null
    this.intervalDuration = duration
    this.numOfRunning = 0
  }

  check = () => {
    if (this.numOfRunning < this.limits) {
      this.q.splice(0, this.limits - this.numOfRunning).forEach(run => run())
      if (this.q.length === 0 && this.intervalId) {
        clearInterval(this.intervalId)
        this.intervalId = null
      }
    }
  }

  enquene(run) {
    this.q.push(run)
    if (!this.intervalId) {
      this.intervalId = setInterval(this.check, this.intervalDuration)
    }
  }

  add(request) {
    return new Promise((resolve, reject) => {
      const run = () => {
        this.numOfRunning++
        try {
          request()
            .then(res => {
              resolve(res)
            }, err => {
              reject(err)
            })
            .finally(() => {
              this.numOfRunning--
            })
        } catch (e) {
          this.numOfRunning--
          reject(e)
        }
      }
      if (this.numOfRunning < this.limits) {
        run()
      } else {
        this.enquene(run)
      }
    })
  }
}