/* IMPORT */

import type { IObserver } from '~/types'
import { Stack } from '~/methods/debugger'

/* MAIN */

// This ensures that there's only one flushing of the queue happening at the same time

class Scheduler {

  /* VARIABLES */

  waiting: [IObserver, Stack?][] = [];

  counter: number = 0;
  locked: boolean = false;

  /* QUEING API */

  flush = (): void => {

    if (this.locked) return

    if (this.counter) return

    if (!this.waiting.length) return

    try {

      this.locked = true

      while (true) {

        const queue = this.waiting

        if (!queue.length) break

        this.waiting = []

        for (let i = 0, l = queue.length; i < l; i++) {

          queue[i][0].update(queue[i][1])

        }

      }

    } finally {

      this.locked = false

    }

  }

  wrap = (fn: () => void): void => {

    this.counter += 1

    fn()

    this.counter -= 1

    this.flush()

  }

  /* SCHEDULING API */

  schedule = (observer: IObserver, stack?: Stack): void => {

    this.waiting.push([observer, stack])

  }

}

/* EXPORT */

export default new Scheduler()