export class ZQueue {
  functions = []
  autoRun = false
  running = false
  context = {}

  constructor (config = {}) {
    return this.options(config)
  }

  options (config = {}) {
    if (typeof config.autoRun !== 'undefined') this.autoRun = !!config.autoRun
    if (typeof config.context !== 'undefined') this.context = config.context
    return this
  }

  push (fn) {
    if (typeof fn !== 'function') throw new Error('Cannot add non-functions to the queue')
    this.functions.push(fn)
    if (this.autoRun) this.executeEach()
    return this
  }

  async executeAll (context) {
    if (this.running) return
    this.options({ context })
    this.running = true
    const results = []
    let i = -1
    while (++i < this.functions.length) {
      if (typeof this.functions[i] === 'function') results.push(Promise.resolve(this.functions[i].call(context)))
    }
    const all = await Promise.all(results)
    this.running = false
    return all
  }

  async executeEach (context) {
    if (this.running) return
    this.options({ context })
    this.running = true
    const results = []
    for (const fn of this.functions) {
      if (typeof fn === 'function') {
        results.push(await Promise.resolve(fn.call(context)))
      }
    }
    this.running = false
    return results
  }
}