client/src/app/shared/video/infinite-scroller.directive.ts

   1 import { Directive, EventEmitter, Input, OnDestroy, OnInit, Output } from '@angular/core'
   2 import 'rxjs/add/operator/debounceTime'
   3 import 'rxjs/add/operator/distinct'
   4 import 'rxjs/add/operator/distinctUntilChanged'
   5 import 'rxjs/add/operator/filter'
   6 import 'rxjs/add/operator/map'
   7 import 'rxjs/add/operator/share'
   8 import 'rxjs/add/operator/startWith'
   9 import 'rxjs/add/operator/throttleTime'
  10 import { fromEvent } from 'rxjs/observable/fromEvent'
  11 import { Subscription } from 'rxjs/Subscription'
  12
  13 @Directive({
  14   selector: '[myInfiniteScroller]'
  15 })
  16 export class InfiniteScrollerDirective implements OnInit, OnDestroy {
  17   private static PAGE_VIEW_TOP_MARGIN = 500
  18
  19   @Input() containerHeight: number
  20   @Input() pageHeight: number
  21   @Input() percentLimit = 70
  22   @Input() autoLoading = false
  23
  24   @Output() nearOfBottom = new EventEmitter<void>()
  25   @Output() nearOfTop = new EventEmitter<void>()
  26   @Output() pageChanged = new EventEmitter<number>()
  27
  28   private decimalLimit = 0
  29   private lastCurrentBottom = -1
  30   private lastCurrentTop = 0
  31   private scrollDownSub: Subscription
  32   private scrollUpSub: Subscription
  33   private pageChangeSub: Subscription
  34
  35   constructor () {
  36     this.decimalLimit = this.percentLimit / 100
  37   }
  38
  39   ngOnInit () {
  40     if (this.autoLoading === true) return this.initialize()
  41   }
  42
  43   ngOnDestroy () {
  44     if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
  45     if (this.scrollUpSub) this.scrollUpSub.unsubscribe()
  46     if (this.pageChangeSub) this.pageChangeSub.unsubscribe()
  47   }
  48
  49   initialize () {
  50     // Emit the last value
  51     const throttleOptions = { leading: true, trailing: true }
  52
  53     const scrollObservable = fromEvent(window, 'scroll')
  54       .startWith(true)
  55       .throttleTime(200, undefined, throttleOptions)
  56       .map(() => ({ current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight }))
  57       .distinctUntilChanged((o1, o2) => o1.current === o2.current)
  58       .share()
  59
  60     // Scroll Down
  61     this.scrollDownSub = scrollObservable
  62       // Check we scroll down
  63       .filter(({ current }) => {
  64         const res = this.lastCurrentBottom < current
  65
  66         this.lastCurrentBottom = current
  67         return res
  68       })
  69       .filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
  70       .subscribe(() => this.nearOfBottom.emit())
  71
  72     // Scroll up
  73     this.scrollUpSub = scrollObservable
  74       // Check we scroll up
  75       .filter(({ current }) => {
  76         const res = this.lastCurrentTop > current
  77
  78         this.lastCurrentTop = current
  79         return res
  80       })
  81       .filter(({ current, maximumScroll }) => {
  82         return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit
  83       })
  84       .subscribe(() => this.nearOfTop.emit())
  85
  86     // Page change
  87     this.pageChangeSub = scrollObservable
  88       .distinct()
  89       .map(({ current }) => this.calculateCurrentPage(current))
  90       .distinctUntilChanged()
  91       .subscribe(res => this.pageChanged.emit(res))
  92   }
  93
  94   private calculateCurrentPage (current: number) {
  95     return Math.max(1, Math.round((current + InfiniteScrollerDirective.PAGE_VIEW_TOP_MARGIN) / this.pageHeight))
  96   }
  97 }