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

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