console.clear()

class RealDealObserver {
  constructor(destination) {
    this.destination = destination
  }

  next(value) {
    const destination = this.destination
    if (destination.next && !this.isUnsubscribed) {
      destination.next && this.destination.next(value)
    }
  }

  error(err) {
    const destination = this.destination
    if (!this.isUnsubscribed) {
      if (destination.error) {
        destination.error(err)
      }
      this.unsubscribe()
    }
  }

  complete() {
    const destination = this.destination
    if (!this.isUnsubscribed) {
      if (destination.complete) {
        destination.complete()
      }
      this.unsubscribe()
    }
  }

  unsubscribe() {
    this.isUnsubscribed = true
    if (this._unsubscribe) {
      this._unsubscribe()
    }
  }
}

class Observable {
  constructor(_subscribe) {
    this._subscribe = _subscribe
  }

  subscribe(observer) {
    const realDealObserver = new RealDealObserver(observer)
    realDealObserver._unsubscribe = this._subscribe(realDealObserver)
    return () => realDealObserver.unsubscribe()
  }
}

const a = [
  'Fred',
  'Quentin',
  'idiot',
  'Doug',
  'tr0n',
  'James',
  'Bitchface',
  'Maude',
  'Gladys',
  'Ploppy',
  'Manuel',
  'Greg'
]

const observable$ = new Observable((observer) => {
  let i = 0
  const id = setInterval(() => {
    if (i < a.length) {
      observer.next(`Sup ${a[i]}`)
      i++
    } else {
      observer.complete()
    }
  }, 100)

  return () => {
    console.log('Are you sure you want to unsubscribe? Kidding, unsubscribed.')
    clearInterval(id)
  }
})

const observer = {
  next(x) { console.log('next -> ' + x)},
  error(err) {},
  complete() { console.log('We are done diddly done!')}
}

const subscription$ = observable$.subscribe(observer)