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

   1 import { distinct, distinctUntilChanged, filter, map, share, startWith, throttleTime } from 'rxjs/operators'
   2 import { Directive, ElementRef, 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   @Input() containerHeight: number
  10   @Input() pageHeight: number
  11   @Input() firstLoadedPage = 1
  12   @Input() percentLimit = 70
  13   @Input() autoInit = false
  14   @Input() onItself = 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   private middleScreen: number
  27   private container: HTMLElement
  28
  29   constructor (private el: ElementRef) {
  30     this.decimalLimit = this.percentLimit / 100
  31   }
  32
  33   ngOnInit () {
  34     if (this.autoInit === true) return this.initialize()
  35   }
  36
  37   ngOnDestroy () {
  38     if (this.scrollDownSub) this.scrollDownSub.unsubscribe()
  39     if (this.scrollUpSub) this.scrollUpSub.unsubscribe()
  40     if (this.pageChangeSub) this.pageChangeSub.unsubscribe()
  41   }
  42
  43   initialize () {
  44     if (this.onItself) {
  45       this.container = this.el.nativeElement
  46     }
  47
  48     this.middleScreen = window.innerHeight / 2
  49
  50     // Emit the last value
  51     const throttleOptions = { leading: true, trailing: true }
  52
  53     const scrollObservable = fromEvent(this.container || window, 'scroll')
  54       .pipe(
  55         startWith(null),
  56         throttleTime(200, undefined, throttleOptions),
  57         map(() => this.getScrollInfo()),
  58         distinctUntilChanged((o1, o2) => o1.current === o2.current),
  59         share()
  60       )
  61
  62     // Scroll Down
  63     this.scrollDownSub = scrollObservable
  64       .pipe(
  65         // Check we scroll down
  66         filter(({ current }) => {
  67           const res = this.lastCurrentBottom < current
  68
  69           this.lastCurrentBottom = current
  70           return res
  71         }),
  72         filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit)
  73       )
  74       .subscribe(() => this.nearOfBottom.emit())
  75
  76     // Scroll up
  77     this.scrollUpSub = scrollObservable
  78       .pipe(
  79         // Check we scroll up
  80         filter(({ current }) => {
  81           const res = this.lastCurrentTop > current
  82
  83           this.lastCurrentTop = current
  84           return res
  85         }),
  86         filter(({ current, maximumScroll }) => {
  87           return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit
  88         })
  89       )
  90       .subscribe(() => this.nearOfTop.emit())
  91
  92     // Page change
  93     this.pageChangeSub = scrollObservable
  94       .pipe(
  95         distinct(),
  96         map(({ current }) => this.calculateCurrentPage(current)),
  97         distinctUntilChanged()
  98       )
  99       .subscribe(res => this.pageChanged.emit(res))
 100   }
 101
 102   private calculateCurrentPage (current: number) {
 103     const scrollY = current + this.middleScreen
 104
 105     const page = Math.max(1, Math.ceil(scrollY / this.pageHeight))
 106
 107     // Offset page
 108     return page + (this.firstLoadedPage - 1)
 109   }
 110
 111   private getScrollInfo () {
 112     if (this.container) {
 113       return { current: this.container.scrollTop, maximumScroll: this.container.scrollHeight }
 114     }
 115
 116     return { current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight }
 117   }
 118 }