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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 | @Input() containerHeight: number | |
10 | @Input() pageHeight: number | |
11 | @Input() firstLoadedPage = 1 | |
12 | @Input() percentLimit = 70 | |
13 | @Input() autoInit = false | |
14 | ||
15 | @Output() nearOfBottom = new EventEmitter<void>() | |
16 | @Output() nearOfTop = new EventEmitter<void>() | |
17 | @Output() pageChanged = new EventEmitter<number>() | |
18 | ||
19 | private decimalLimit = 0 | |
20 | private lastCurrentBottom = -1 | |
21 | private lastCurrentTop = 0 | |
22 | private scrollDownSub: Subscription | |
23 | private scrollUpSub: Subscription | |
24 | private pageChangeSub: Subscription | |
25 | private middleScreen: number | |
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 | this.middleScreen = window.innerHeight / 2 | |
43 | ||
44 | // Emit the last value | |
45 | const throttleOptions = { leading: true, trailing: true } | |
46 | ||
47 | const scrollObservable = fromEvent(window, 'scroll') | |
48 | .pipe( | |
49 | startWith(null), | |
50 | throttleTime(200, undefined, throttleOptions), | |
51 | map(() => ({ current: window.scrollY, maximumScroll: document.body.clientHeight - window.innerHeight })), | |
52 | distinctUntilChanged((o1, o2) => o1.current === o2.current), | |
53 | share() | |
54 | ) | |
55 | ||
56 | // Scroll Down | |
57 | this.scrollDownSub = scrollObservable | |
58 | .pipe( | |
59 | // Check we scroll down | |
60 | filter(({ current }) => { | |
61 | const res = this.lastCurrentBottom < current | |
62 | ||
63 | this.lastCurrentBottom = current | |
64 | return res | |
65 | }), | |
66 | filter(({ current, maximumScroll }) => maximumScroll <= 0 || (current / maximumScroll) > this.decimalLimit) | |
67 | ) | |
68 | .subscribe(() => this.nearOfBottom.emit()) | |
69 | ||
70 | // Scroll up | |
71 | this.scrollUpSub = scrollObservable | |
72 | .pipe( | |
73 | // Check we scroll up | |
74 | filter(({ current }) => { | |
75 | const res = this.lastCurrentTop > current | |
76 | ||
77 | this.lastCurrentTop = current | |
78 | return res | |
79 | }), | |
80 | filter(({ current, maximumScroll }) => { | |
81 | return current !== 0 && (1 - (current / maximumScroll)) > this.decimalLimit | |
82 | }) | |
83 | ) | |
84 | .subscribe(() => this.nearOfTop.emit()) | |
85 | ||
86 | // Page change | |
87 | this.pageChangeSub = scrollObservable | |
88 | .pipe( | |
89 | distinct(), | |
90 | map(({ current }) => this.calculateCurrentPage(current)), | |
91 | distinctUntilChanged() | |
92 | ) | |
93 | .subscribe(res => this.pageChanged.emit(res)) | |
94 | } | |
95 | ||
96 | private calculateCurrentPage (current: number) { | |
97 | const scrollY = current + this.middleScreen | |
98 | ||
99 | const page = Math.max(1, Math.ceil(scrollY / this.pageHeight)) | |
100 | ||
101 | // Offset page | |
102 | return page + (this.firstLoadedPage - 1) | |
103 | } | |
104 | } |