import { fn } from '../helper'
import { isUndef } from '../lib'

async function useConcurrency(tasks: Array<fn>, maxConcurrency: number) {
  if (isUndef(maxConcurrency)) {
    console.warn('maxConcurrency is undefined')
    return null
  }
  const ret: Array<any> = []
  const excluding: any[] = []
  for (let i = 0; i < tasks.length; i++) {
    const res = tasks[i]()
    ret.push(res)

    if (maxConcurrency < tasks.length) {
      const p = res.then(() => excluding.splice(excluding.indexOf(p), 1))
      excluding.push(p)

      if (excluding.length >= maxConcurrency) {
        await Promise.race(excluding)
      }
    }
  }
  return Promise.all(ret)
}

export { useConcurrency }