scroller.ts

import { CommonModule, DOCUMENT, isPlatformBrowser } from '@angular/common';
import {
    AfterContentInit,
    AfterViewChecked,
    ChangeDetectionStrategy,
    ChangeDetectorRef,
    Component,
    ContentChildren,
    ElementRef,
    EventEmitter,
    Inject,
    Input,
    NgModule,
    NgZone,
    OnDestroy,
    OnInit,
    Output,
    PLATFORM_ID,
    QueryList,
    Renderer2,
    SimpleChanges,
    TemplateRef,
    ViewChild,
    ViewEncapsulation
} from '@angular/core';
import { PrimeTemplate, SharedModule } from 'primeng/api';
import { DomHandler } from 'primeng/dom';
import { SpinnerIcon } from 'primeng/icons/spinner';
import { ScrollerLazyLoadEvent, ScrollerScrollEvent, ScrollerScrollIndexChangeEvent, ScrollerToType } from './scroller.interface';
import { ScrollerOptions } from 'primeng/api';
import { Nullable, VoidListener } from 'primeng/ts-helpers';
/**
 * Scroller is a performance-approach to handle huge data efficiently.
 * @group Components
 */
@Component({
    selector: 'p-scroller',
    template: `
        <ng-container *ngIf="!_disabled; else disabledContainer">
            <div
                #element
                [attr.id]="_id"
                [attr.tabindex]="tabindex"
                [ngStyle]="_style"
                [class]="_styleClass"
                [ngClass]="{ 'p-scroller': true, 'p-scroller-inline': inline, 'p-both-scroll': both, 'p-horizontal-scroll': horizontal }"
                (scroll)="onContainerScroll($event)"
            >
                <ng-container *ngIf="contentTemplate; else buildInContent">
                    <ng-container *ngTemplateOutlet="contentTemplate; context: { $implicit: loadedItems, options: getContentOptions() }"></ng-container>
                </ng-container>
                <ng-template #buildInContent>
                    <div #content class="p-scroller-content" [ngClass]="{ 'p-scroller-loading': d_loading }" [ngStyle]="contentStyle">
                        <ng-container *ngFor="let item of loadedItems; let index = index; trackBy: _trackBy || index">
                            <ng-container *ngTemplateOutlet="itemTemplate; context: { $implicit: item, options: getOptions(index) }"></ng-container>
                        </ng-container>
                    </div>
                </ng-template>
                <div *ngIf="_showSpacer" class="p-scroller-spacer" [ngStyle]="spacerStyle"></div>
                <div *ngIf="!loaderDisabled && _showLoader && d_loading" class="p-scroller-loader" [ngClass]="{ 'p-component-overlay': !loaderTemplate }">
                    <ng-container *ngIf="loaderTemplate; else buildInLoader">
                        <ng-container *ngFor="let item of loaderArr; let index = index">
                            <ng-container *ngTemplateOutlet="loaderTemplate; context: { options: getLoaderOptions(index, both && { numCols: _numItemsInViewport.cols }) }"></ng-container>
                        </ng-container>
                    </ng-container>
                    <ng-template #buildInLoader>
                        <ng-container *ngIf="loaderIconTemplate; else buildInLoaderIcon">
                            <ng-container *ngTemplateOutlet="loaderIconTemplate; context: { options: { styleClass: 'p-scroller-loading-icon' } }"></ng-container>
                        </ng-container>
                        <ng-template #buildInLoaderIcon>
                            <SpinnerIcon [styleClass]="'p-scroller-loading-icon'" />
                        </ng-template>
                    </ng-template>
                </div>
            </div>
        </ng-container>
        <ng-template #disabledContainer>
            <ng-content></ng-content>
            <ng-container *ngIf="contentTemplate">
                <ng-container *ngTemplateOutlet="contentTemplate; context: { $implicit: items, options: { rows: _items, columns: loadedColumns } }"></ng-container>
            </ng-container>
        </ng-template>
    `,
    changeDetection: ChangeDetectionStrategy.Default,
    encapsulation: ViewEncapsulation.None,
    styleUrls: ['./scroller.css'],
    host: {
        class: 'p-scroller-viewport p-element'
    }
})
export class Scroller implements OnInit, AfterContentInit, AfterViewChecked, OnDestroy {
    /**
     * Unique identifier of the element.
     * @group Props
     */
    @Input() get id(): string | undefined {
        return this._id;
    }
    set id(val: string | undefined) {
        this._id = val;
    }
    /**
     * Inline style of the component.
     * @group Props
     */
    @Input() get style(): any {
        return this._style;
    }
    set style(val: any) {
        this._style = val;
    }
    /**
     * Style class of the element.
     * @group Props
     */
    @Input() get styleClass(): string | undefined {
        return this._styleClass;
    }
    set styleClass(val: string | undefined) {
        this._styleClass = val;
    }
    /**
     * Index of the element in tabbing order.
     * @group Props
     */
    @Input() get tabindex() {
        return this._tabindex;
    }
    set tabindex(val: number) {
        this._tabindex = val;
    }
    /**
     * An array of objects to display.
     * @group Props
     */
    @Input() get items(): any[] | undefined | null {
        return this._items;
    }
    set items(val: any[] | undefined | null) {
        this._items = val;
    }
    /**
     * The height/width of item according to orientation.
     * @group Props
     */
    @Input() get itemSize(): number[] | number {
        return this._itemSize;
    }
    set itemSize(val: number[] | number) {
        this._itemSize = val;
    }
    /**
     * Height of the scroll viewport.
     * @group Props
     */
    @Input() get scrollHeight(): string | undefined {
        return this._scrollHeight;
    }
    set scrollHeight(val: string | undefined) {
        this._scrollHeight = val;
    }
    /**
     * Width of the scroll viewport.
     * @group Props
     */
    @Input() get scrollWidth(): string | undefined {
        return this._scrollWidth;
    }
    set scrollWidth(val: string | undefined) {
        this._scrollWidth = val;
    }
    /**
     * The orientation of scrollbar.
     * @group Props
     */
    @Input() get orientation(): 'vertical' | 'horizontal' | 'both' {
        return this._orientation;
    }
    set orientation(val: 'vertical' | 'horizontal' | 'both') {
        this._orientation = val;
    }
    /**
     * Used to specify how many items to load in each load method in lazy mode.
     * @group Props
     */
    @Input() get step(): number {
        return this._step;
    }
    set step(val: number) {
        this._step = val;
    }
    /**
     * Delay in scroll before new data is loaded.
     * @group Props
     */
    @Input() get delay() {
        return this._delay;
    }
    set delay(val: number) {
        this._delay = val;
    }
    /**
     * Delay after window's resize finishes.
     * @group Props
     */
    @Input() get resizeDelay() {
        return this._resizeDelay;
    }
    set resizeDelay(val: number) {
        this._resizeDelay = val;
    }
    /**
     * Used to append each loaded item to top without removing any items from the DOM. Using very large data may cause the browser to crash.
     * @group Props
     */
    @Input() get appendOnly(): boolean {
        return this._appendOnly;
    }
    set appendOnly(val: boolean) {
        this._appendOnly = val;
    }
    /**
     * Specifies whether the scroller should be displayed inline or not.
     * @group Props
     */
    @Input() get inline() {
        return this._inline;
    }
    set inline(val: boolean) {
        this._inline = val;
    }
    /**
     * Defines if data is loaded and interacted with in lazy manner.
     * @group Props
     */
    @Input() get lazy() {
        return this._lazy;
    }
    set lazy(val: boolean) {
        this._lazy = val;
    }
    /**
     * If disabled, the scroller feature is eliminated and the content is displayed directly.
     * @group Props
     */
    @Input() get disabled() {
        return this._disabled;
    }
    set disabled(val: boolean) {
        this._disabled = val;
    }
    /**
     * Used to implement a custom loader instead of using the loader feature in the scroller.
     * @group Props
     */
    @Input() get loaderDisabled() {
        return this._loaderDisabled;
    }
    set loaderDisabled(val: boolean) {
        this._loaderDisabled = val;
    }
    /**
     * Columns to display.
     * @group Props
     */
    @Input() get columns(): any[] | undefined | null {
        return this._columns;
    }
    set columns(val: any[] | undefined | null) {
        this._columns = val;
    }
    /**
     * Used to implement a custom spacer instead of using the spacer feature in the scroller.
     * @group Props
     */
    @Input() get showSpacer() {
        return this._showSpacer;
    }
    set showSpacer(val: boolean) {
        this._showSpacer = val;
    }
    /**
     * Defines whether to show loader.
     * @group Props
     */
    @Input() get showLoader() {
        return this._showLoader;
    }
    set showLoader(val: boolean) {
        this._showLoader = val;
    }
    /**
     * Determines how many additional elements to add to the DOM outside of the view. According to the scrolls made up and down, extra items are added in a certain algorithm in the form of multiples of this number. Default value is half the number of items shown in the view.
     * @group Props
     */
    @Input() get numToleratedItems() {
        return this._numToleratedItems;
    }
    set numToleratedItems(val: number) {
        this._numToleratedItems = val;
    }
    /**
     * Defines whether the data is loaded.
     * @group Props
     */
    @Input() get loading(): boolean | undefined {
        return this._loading;
    }
    set loading(val: boolean | undefined) {
        this._loading = val;
    }
    /**
     * Defines whether to dynamically change the height or width of scrollable container.
     * @group Props
     */
    @Input() get autoSize(): boolean {
        return this._autoSize;
    }
    set autoSize(val: boolean) {
        this._autoSize = val;
    }
    /**
     * Function to optimize the dom operations by delegating to ngForTrackBy, default algoritm checks for object identity.
     * @group Props
     */
    @Input() get trackBy(): Function {
        return this._trackBy;
    }
    set trackBy(val: Function) {
        this._trackBy = val;
    }
    /**
     * Defines whether to use the scroller feature. The properties of scroller component can be used like an object in it.
     * @group Props
     */
    @Input() get options(): ScrollerOptions | undefined {
        return this._options;
    }
    set options(val: ScrollerOptions | undefined) {
        this._options = val;

        if (val && typeof val === 'object') {
            //@ts-ignore
            Object.entries(val).forEach(([k, v]) => this[`_${k}`] !== v && (this[`_${k}`] = v));
        }
    }
    /**
     * Callback to invoke in lazy mode to load new data.
     * @param {ScrollerLazyLoadEvent} event - Custom lazy load event.
     * @group Emits
     */
    @Output() onLazyLoad: EventEmitter<ScrollerLazyLoadEvent> = new EventEmitter<ScrollerLazyLoadEvent>();
    /**
     * Callback to invoke when scroll position changes.
     * @param {ScrollerScrollEvent} event - Custom scroll event.
     * @group Emits
     */
    @Output() onScroll: EventEmitter<ScrollerScrollEvent> = new EventEmitter<ScrollerScrollEvent>();
    /**
     * Callback to invoke when scroll position and item's range in view changes.
     * @param {ScrollerScrollEvent} event - Custom scroll index change event.
     * @group Emits
     */
    @Output() onScrollIndexChange: EventEmitter<ScrollerScrollIndexChangeEvent> = new EventEmitter<ScrollerScrollIndexChangeEvent>();

    @ViewChild('element') elementViewChild: Nullable<ElementRef>;

    @ViewChild('content') contentViewChild: Nullable<ElementRef>;

    @ContentChildren(PrimeTemplate) templates: Nullable<QueryList<PrimeTemplate>>;

    _id: string | undefined;

    _style: { [klass: string]: any } | null | undefined;

    _styleClass: string | undefined;

    _tabindex: number = 0;

    _items: any[] | undefined | null;

    _itemSize: number | number[] = 0;

    _scrollHeight: string | undefined;

    _scrollWidth: string | undefined;

    _orientation: 'vertical' | 'horizontal' | 'both' = 'vertical';

    _step: number = 0;

    _delay: number = 0;

    _resizeDelay: number = 10;

    _appendOnly: boolean = false;

    _inline: boolean = false;

    _lazy: boolean = false;

    _disabled: boolean = false;

    _loaderDisabled: boolean = false;

    _columns: any[] | undefined | null;

    _showSpacer: boolean = true;

    _showLoader: boolean = false;

    _numToleratedItems: any;

    _loading: boolean | undefined;

    _autoSize: boolean = false;

    _trackBy: any;

    _options: ScrollerOptions | undefined;

    d_loading: boolean = false;

    d_numToleratedItems: any;

    contentEl: any;

    contentTemplate: Nullable<TemplateRef<any>>;

    itemTemplate: Nullable<TemplateRef<any>>;

    loaderTemplate: Nullable<TemplateRef<any>>;

    loaderIconTemplate: Nullable<TemplateRef<any>>;

    first: any = 0;

    last: any = 0;

    page: number = 0;

    isRangeChanged: boolean = false;

    numItemsInViewport: any = 0;

    lastScrollPos: any = 0;

    lazyLoadState: any = {};

    loaderArr: any[] = [];

    spacerStyle: { [klass: string]: any } | null | undefined = {};

    contentStyle: { [klass: string]: any } | null | undefined = {};

    scrollTimeout: any;

    resizeTimeout: any;

    initialized: boolean = false;

    windowResizeListener: VoidListener;

    defaultWidth: number | undefined;

    defaultHeight: number | undefined;

    defaultContentWidth: number | undefined;

    defaultContentHeight: number | undefined;

    get vertical() {
        return this._orientation === 'vertical';
    }

    get horizontal() {
        return this._orientation === 'horizontal';
    }

    get both() {
        return this._orientation === 'both';
    }

    get loadedItems() {
        if (this._items && !this.d_loading) {
            if (this.both) return this._items.slice(this._appendOnly ? 0 : this.first.rows, this.last.rows).map((item) => (this._columns ? item : item.slice(this._appendOnly ? 0 : this.first.cols, this.last.cols)));
            else if (this.horizontal && this._columns) return this._items;
            else return this._items.slice(this._appendOnly ? 0 : this.first, this.last);
        }

        return [];
    }

    get loadedRows() {
        return this.d_loading ? (this._loaderDisabled ? this.loaderArr : []) : this.loadedItems;
    }

    get loadedColumns() {
        if (this._columns && (this.both || this.horizontal)) {
            return this.d_loading && this._loaderDisabled ? (this.both ? this.loaderArr[0] : this.loaderArr) : this._columns.slice(this.both ? this.first.cols : this.first, this.both ? this.last.cols : this.last);
        }

        return this._columns;
    }

    get isPageChanged() {
        return this._step ? this.page !== this.getPageByFirst() : true;
    }

    constructor(@Inject(DOCUMENT) private document: Document, @Inject(PLATFORM_ID) private platformId: any, private renderer: Renderer2, private cd: ChangeDetectorRef, private zone: NgZone) {}

    ngOnInit() {
        this.setInitialState();
    }

    ngOnChanges(simpleChanges: SimpleChanges) {
        let isLoadingChanged = false;

        if (simpleChanges.loading) {
            const { previousValue, currentValue } = simpleChanges.loading;

            if (this.lazy && previousValue !== currentValue && currentValue !== this.d_loading) {
                this.d_loading = currentValue;
                isLoadingChanged = true;
            }
        }

        if (simpleChanges.orientation) {
            this.lastScrollPos = this.both ? { top: 0, left: 0 } : 0;
        }

        if (simpleChanges.numToleratedItems) {
            const { previousValue, currentValue } = simpleChanges.numToleratedItems;

            if (previousValue !== currentValue && currentValue !== this.d_numToleratedItems) {
                this.d_numToleratedItems = currentValue;
            }
        }

        if (simpleChanges.options) {
            const { previousValue, currentValue } = simpleChanges.options;

            if (this.lazy && previousValue?.loading !== currentValue?.loading && currentValue?.loading !== this.d_loading) {
                this.d_loading = currentValue.loading;
                isLoadingChanged = true;
            }

            if (previousValue?.numToleratedItems !== currentValue?.numToleratedItems && currentValue?.numToleratedItems !== this.d_numToleratedItems) {
                this.d_numToleratedItems = currentValue.numToleratedItems;
            }
        }

        if (this.initialized) {
            const isChanged = !isLoadingChanged && (simpleChanges.items?.previousValue?.length !== simpleChanges.items?.currentValue?.length || simpleChanges.itemSize || simpleChanges.scrollHeight || simpleChanges.scrollWidth);

            if (isChanged) {
                this.init();
                this.calculateAutoSize();
            }
        }
    }

    ngAfterContentInit() {
        (this.templates as QueryList<PrimeTemplate>).forEach((item) => {
            switch (item.getType()) {
                case 'content':
                    this.contentTemplate = item.template;
                    break;

                case 'item':
                    this.itemTemplate = item.template;
                    break;

                case 'loader':
                    this.loaderTemplate = item.template;
                    break;

                case 'loadericon':
                    this.loaderIconTemplate = item.template;
                    break;

                default:
                    this.itemTemplate = item.template;
                    break;
            }
        });
    }

    ngAfterViewInit() {
        Promise.resolve().then(() => {
            this.viewInit();
        });
    }

    ngAfterViewChecked() {
        if (!this.initialized) {
            this.viewInit();
        }
    }

    ngOnDestroy() {
        this.unbindResizeListener();

        this.contentEl = null;
        this.initialized = false;
    }

    viewInit() {
        if (isPlatformBrowser(this.platformId)) {
            if (DomHandler.isVisible(this.elementViewChild?.nativeElement)) {
                this.setInitialState();
                this.setContentEl(this.contentEl);
                this.init();

                this.defaultWidth = DomHandler.getWidth(this.elementViewChild?.nativeElement);
                this.defaultHeight = DomHandler.getHeight(this.elementViewChild?.nativeElement);
                this.defaultContentWidth = DomHandler.getWidth(this.contentEl);
                this.defaultContentHeight = DomHandler.getHeight(this.contentEl);
                this.initialized = true;
            }
        }
    }

    init() {
        if (!this._disabled) {
            this.setSize();
            this.calculateOptions();
            this.setSpacerSize();
            this.bindResizeListener();

            this.cd.detectChanges();
        }
    }

    setContentEl(el?: HTMLElement) {
        this.contentEl = el || this.contentViewChild?.nativeElement || DomHandler.findSingle(this.elementViewChild?.nativeElement, '.p-scroller-content');
    }

    setInitialState() {
        this.first = this.both ? { rows: 0, cols: 0 } : 0;
        this.last = this.both ? { rows: 0, cols: 0 } : 0;
        this.numItemsInViewport = this.both ? { rows: 0, cols: 0 } : 0;
        this.lastScrollPos = this.both ? { top: 0, left: 0 } : 0;
        this.d_loading = this._loading || false;
        this.d_numToleratedItems = this._numToleratedItems;
        this.loaderArr = [];
        this.spacerStyle = {};
        this.contentStyle = {};
    }

    getElementRef() {
        return this.elementViewChild;
    }

    getPageByFirst() {
        return Math.floor((this.first + this.d_numToleratedItems * 4) / (this._step || 1));
    }

    scrollTo(options: ScrollToOptions) {
        this.lastScrollPos = this.both ? { top: 0, left: 0 } : 0;
        this.elementViewChild?.nativeElement?.scrollTo(options);
    }

    scrollToIndex(index: number, behavior: ScrollBehavior = 'auto') {
        const { numToleratedItems } = this.calculateNumItems();
        const contentPos = this.getContentPosition();
        const calculateFirst = (_index = 0, _numT: number) => (_index <= _numT ? 0 : _index);
        const calculateCoord = (_first: number, _size: number, _cpos: number) => _first * _size + _cpos;
        const scrollTo = (left = 0, top = 0) => this.scrollTo({ left, top, behavior });
        let newFirst: any = 0;

        if (this.both) {
            newFirst = { rows: calculateFirst((<any>index)[0], numToleratedItems[0]), cols: calculateFirst((<any>index)[1], numToleratedItems[1]) };
            scrollTo(calculateCoord(newFirst.cols, (<number[]>this._itemSize)[1], contentPos.left), calculateCoord(newFirst.rows, (<number[]>this._itemSize)[0], contentPos.top));
        } else {
            newFirst = calculateFirst(index, numToleratedItems);
            this.horizontal ? scrollTo(calculateCoord(newFirst, <number>this._itemSize, contentPos.left), 0) : scrollTo(0, calculateCoord(newFirst, <number>this._itemSize, contentPos.top));
        }

        this.isRangeChanged = this.first !== newFirst;
        this.first = newFirst;
    }

    scrollInView(index: number, to: ScrollerToType, behavior: ScrollBehavior = 'auto') {
        if (to) {
            const { first, viewport } = this.getRenderedRange();
            const scrollTo = (left = 0, top = 0) => this.scrollTo({ left, top, behavior });
            const isToStart = to === 'to-start';
            const isToEnd = to === 'to-end';

            if (isToStart) {
                if (this.both) {
                    if (viewport.first.rows - first.rows > (<any>index)[0]) {
                        scrollTo(viewport.first.cols * (<number[]>this._itemSize)[1], (viewport.first.rows - 1) * (<number[]>this._itemSize)[0]);
                    } else if (viewport.first.cols - first.cols > (<any>index)[1]) {
                        scrollTo((viewport.first.cols - 1) * (<number[]>this._itemSize)[1], viewport.first.rows * (<number[]>this._itemSize)[0]);
                    }
                } else {
                    if (viewport.first - first > index) {
                        const pos = (viewport.first - 1) * <number>this._itemSize;
                        this.horizontal ? scrollTo(pos, 0) : scrollTo(0, pos);
                    }
                }
            } else if (isToEnd) {
                if (this.both) {
                    if (viewport.last.rows - first.rows <= (<any>index)[0] + 1) {
                        scrollTo(viewport.first.cols * (<number[]>this._itemSize)[1], (viewport.first.rows + 1) * (<number[]>this._itemSize)[0]);
                    } else if (viewport.last.cols - first.cols <= (<any>index)[1] + 1) {
                        scrollTo((viewport.first.cols + 1) * (<number[]>this._itemSize)[1], viewport.first.rows * (<number[]>this._itemSize)[0]);
                    }
                } else {
                    if (viewport.last - first <= index + 1) {
                        const pos = (viewport.first + 1) * <number>this._itemSize;
                        this.horizontal ? scrollTo(pos, 0) : scrollTo(0, pos);
                    }
                }
            }
        } else {
            this.scrollToIndex(index, behavior);
        }
    }

    getRenderedRange() {
        const calculateFirstInViewport = (_pos: number, _size: number) => Math.floor(_pos / (_size || _pos));

        let firstInViewport = this.first;
        let lastInViewport: any = 0;

        if (this.elementViewChild?.nativeElement) {
            const { scrollTop, scrollLeft } = this.elementViewChild.nativeElement;

            if (this.both) {
                firstInViewport = { rows: calculateFirstInViewport(scrollTop, (<number[]>this._itemSize)[0]), cols: calculateFirstInViewport(scrollLeft, (<number[]>this._itemSize)[1]) };
                lastInViewport = { rows: firstInViewport.rows + this.numItemsInViewport.rows, cols: firstInViewport.cols + this.numItemsInViewport.cols };
            } else {
                const scrollPos = this.horizontal ? scrollLeft : scrollTop;
                firstInViewport = calculateFirstInViewport(scrollPos, <number>this._itemSize);
                lastInViewport = firstInViewport + this.numItemsInViewport;
            }
        }

        return {
            first: this.first,
            last: this.last,
            viewport: {
                first: firstInViewport,
                last: lastInViewport
            }
        };
    }

    calculateNumItems() {
        const contentPos = this.getContentPosition();
        const contentWidth = (this.elementViewChild?.nativeElement ? this.elementViewChild.nativeElement.offsetWidth - contentPos.left : 0) || 0;
        const contentHeight = (this.elementViewChild?.nativeElement ? this.elementViewChild.nativeElement.offsetHeight - contentPos.top : 0) || 0;
        const calculateNumItemsInViewport = (_contentSize: number, _itemSize: number) => Math.ceil(_contentSize / (_itemSize || _contentSize));
        const calculateNumToleratedItems = (_numItems: number) => Math.ceil(_numItems / 2);
        const numItemsInViewport: any = this.both
            ? { rows: calculateNumItemsInViewport(contentHeight, (<number[]>this._itemSize)[0]), cols: calculateNumItemsInViewport(contentWidth, (<number[]>this._itemSize)[1]) }
            : calculateNumItemsInViewport(this.horizontal ? contentWidth : contentHeight, <number>this._itemSize);

        const numToleratedItems = this.d_numToleratedItems || (this.both ? [calculateNumToleratedItems(numItemsInViewport.rows), calculateNumToleratedItems(numItemsInViewport.cols)] : calculateNumToleratedItems(numItemsInViewport));

        return { numItemsInViewport, numToleratedItems };
    }

    calculateOptions() {
        const { numItemsInViewport, numToleratedItems } = this.calculateNumItems();
        const calculateLast = (_first: number, _num: number, _numT: number, _isCols: boolean = false) => this.getLast(_first + _num + (_first < _numT ? 2 : 3) * _numT, _isCols);
        const first = this.first;
        const last = this.both
            ? { rows: calculateLast(this.first.rows, numItemsInViewport.rows, numToleratedItems[0]), cols: calculateLast(this.first.cols, numItemsInViewport.cols, numToleratedItems[1], true) }
            : calculateLast(this.first, numItemsInViewport, numToleratedItems);

        this.last = last;
        this.numItemsInViewport = numItemsInViewport;
        this.d_numToleratedItems = numToleratedItems;

        if (this.showLoader) {
            this.loaderArr = this.both ? Array.from({ length: numItemsInViewport.rows }).map(() => Array.from({ length: numItemsInViewport.cols })) : Array.from({ length: numItemsInViewport });
        }

        if (this._lazy) {
            Promise.resolve().then(() => {
                this.lazyLoadState = {
                    first: this._step ? (this.both ? { rows: 0, cols: first.cols } : 0) : first,
                    last: Math.min(this._step ? this._step : this.last, (<any[]>this.items).length)
                };

                this.handleEvents('onLazyLoad', this.lazyLoadState);
            });
        }
    }

    calculateAutoSize() {
        if (this._autoSize && !this.d_loading) {
            Promise.resolve().then(() => {
                if (this.contentEl) {
                    this.contentEl.style.minHeight = this.contentEl.style.minWidth = 'auto';
                    this.contentEl.style.position = 'relative';
                    (<ElementRef>this.elementViewChild).nativeElement.style.contain = 'none';

                    const [contentWidth, contentHeight] = [DomHandler.getWidth(this.contentEl), DomHandler.getHeight(this.contentEl)];
                    contentWidth !== this.defaultContentWidth && ((<ElementRef>this.elementViewChild).nativeElement.style.width = '');
                    contentHeight !== this.defaultContentHeight && ((<ElementRef>this.elementViewChild).nativeElement.style.height = '');

                    const [width, height] = [DomHandler.getWidth((<ElementRef>this.elementViewChild).nativeElement), DomHandler.getHeight((<ElementRef>this.elementViewChild).nativeElement)];
                    (this.both || this.horizontal) && ((<ElementRef>this.elementViewChild).nativeElement.style.width = width < <number>this.defaultWidth ? width + 'px' : this._scrollWidth || this.defaultWidth + 'px');
                    (this.both || this.vertical) && ((<ElementRef>this.elementViewChild).nativeElement.style.height = height < <number>this.defaultHeight ? height + 'px' : this._scrollHeight || this.defaultHeight + 'px');

                    this.contentEl.style.minHeight = this.contentEl.style.minWidth = '';
                    this.contentEl.style.position = '';
                    (<ElementRef>this.elementViewChild).nativeElement.style.contain = '';
                }
            });
        }
    }

    getLast(last = 0, isCols = false) {
        return this._items ? Math.min(isCols ? (this._columns || this._items[0]).length : this._items.length, last) : 0;
    }

    getContentPosition() {
        if (this.contentEl) {
            const style = getComputedStyle(this.contentEl);
            const left = parseFloat(style.paddingLeft) + Math.max(parseFloat(style.left) || 0, 0);
            const right = parseFloat(style.paddingRight) + Math.max(parseFloat(style.right) || 0, 0);
            const top = parseFloat(style.paddingTop) + Math.max(parseFloat(style.top) || 0, 0);
            const bottom = parseFloat(style.paddingBottom) + Math.max(parseFloat(style.bottom) || 0, 0);

            return { left, right, top, bottom, x: left + right, y: top + bottom };
        }

        return { left: 0, right: 0, top: 0, bottom: 0, x: 0, y: 0 };
    }

    setSize() {
        if (this.elementViewChild?.nativeElement) {
            const parentElement = this.elementViewChild.nativeElement.parentElement.parentElement;
            const width = this._scrollWidth || `${this.elementViewChild.nativeElement.offsetWidth || parentElement.offsetWidth}px`;
            const height = this._scrollHeight || `${this.elementViewChild.nativeElement.offsetHeight || parentElement.offsetHeight}px`;
            const setProp = (_name: string, _value: any) => ((<ElementRef>this.elementViewChild).nativeElement.style[_name] = _value);

            if (this.both || this.horizontal) {
                setProp('height', height);
                setProp('width', width);
            } else {
                setProp('height', height);
            }
        }
    }

    setSpacerSize() {
        if (this._items) {
            const contentPos = this.getContentPosition();
            const setProp = (_name: string, _value: any, _size: number, _cpos: number = 0) => (this.spacerStyle = { ...this.spacerStyle, ...{ [`${_name}`]: (_value || []).length * _size + _cpos + 'px' } });

            if (this.both) {
                setProp('height', this._items, (<number[]>this._itemSize)[0], contentPos.y);
                setProp('width', this._columns || this._items[1], (<number[]>this._itemSize)[1], contentPos.x);
            } else {
                this.horizontal ? setProp('width', this._columns || this._items, <number>this._itemSize, contentPos.x) : setProp('height', this._items, <number>this._itemSize, contentPos.y);
            }
        }
    }

    setContentPosition(pos: any) {
        if (this.contentEl && !this._appendOnly) {
            const first = pos ? pos.first : this.first;
            const calculateTranslateVal = (_first: number, _size: number) => _first * _size;
            const setTransform = (_x = 0, _y = 0) => (this.contentStyle = { ...this.contentStyle, ...{ transform: `translate3d(${_x}px, ${_y}px, 0)` } });

            if (this.both) {
                setTransform(calculateTranslateVal(first.cols, (<number[]>this._itemSize)[1]), calculateTranslateVal(first.rows, (<number[]>this._itemSize)[0]));
            } else {
                const translateVal = calculateTranslateVal(first, <number>this._itemSize);
                this.horizontal ? setTransform(translateVal, 0) : setTransform(0, translateVal);
            }
        }
    }

    onScrollPositionChange(event: Event) {
        const target = event.target;
        const contentPos = this.getContentPosition();
        const calculateScrollPos = (_pos: number, _cpos: number) => (_pos ? (_pos > _cpos ? _pos - _cpos : _pos) : 0);
        const calculateCurrentIndex = (_pos: number, _size: number) => Math.floor(_pos / (_size || _pos));
        const calculateTriggerIndex = (_currentIndex: number, _first: number, _last: number, _num: number, _numT: number, _isScrollDownOrRight: any) => {
            return _currentIndex <= _numT ? _numT : _isScrollDownOrRight ? _last - _num - _numT : _first + _numT - 1;
        };
        const calculateFirst = (_currentIndex: number, _triggerIndex: number, _first: number, _last: number, _num: number, _numT: number, _isScrollDownOrRight: any) => {
            if (_currentIndex <= _numT) return 0;
            else return Math.max(0, _isScrollDownOrRight ? (_currentIndex < _triggerIndex ? _first : _currentIndex - _numT) : _currentIndex > _triggerIndex ? _first : _currentIndex - 2 * _numT);
        };
        const calculateLast = (_currentIndex: number, _first: number, _last: number, _num: number, _numT: number, _isCols = false) => {
            let lastValue = _first + _num + 2 * _numT;

            if (_currentIndex >= _numT) {
                lastValue += _numT + 1;
            }

            return this.getLast(lastValue, _isCols);
        };

        const scrollTop = calculateScrollPos((<HTMLElement>target).scrollTop, contentPos.top);
        const scrollLeft = calculateScrollPos((<HTMLElement>target).scrollLeft, contentPos.left);

        let newFirst = this.both ? { rows: 0, cols: 0 } : 0;
        let newLast = this.last;
        let isRangeChanged = false;
        let newScrollPos = this.lastScrollPos;

        if (this.both) {
            const isScrollDown = this.lastScrollPos.top <= scrollTop;
            const isScrollRight = this.lastScrollPos.left <= scrollLeft;

            if (!this._appendOnly || (this._appendOnly && (isScrollDown || isScrollRight))) {
                const currentIndex = { rows: calculateCurrentIndex(scrollTop, (<number[]>this._itemSize)[0]), cols: calculateCurrentIndex(scrollLeft, (<number[]>this._itemSize)[1]) };
                const triggerIndex = {
                    rows: calculateTriggerIndex(currentIndex.rows, this.first.rows, this.last.rows, this.numItemsInViewport.rows, this.d_numToleratedItems[0], isScrollDown),
                    cols: calculateTriggerIndex(currentIndex.cols, this.first.cols, this.last.cols, this.numItemsInViewport.cols, this.d_numToleratedItems[1], isScrollRight)
                };

                newFirst = {
                    rows: calculateFirst(currentIndex.rows, triggerIndex.rows, this.first.rows, this.last.rows, this.numItemsInViewport.rows, this.d_numToleratedItems[0], isScrollDown),
                    cols: calculateFirst(currentIndex.cols, triggerIndex.cols, this.first.cols, this.last.cols, this.numItemsInViewport.cols, this.d_numToleratedItems[1], isScrollRight)
                };
                newLast = {
                    rows: calculateLast(currentIndex.rows, newFirst.rows, this.last.rows, this.numItemsInViewport.rows, this.d_numToleratedItems[0]),
                    cols: calculateLast(currentIndex.cols, newFirst.cols, this.last.cols, this.numItemsInViewport.cols, this.d_numToleratedItems[1], true)
                };

                isRangeChanged = newFirst.rows !== this.first.rows || newLast.rows !== this.last.rows || newFirst.cols !== this.first.cols || newLast.cols !== this.last.cols || this.isRangeChanged;
                newScrollPos = { top: scrollTop, left: scrollLeft };
            }
        } else {
            const scrollPos = this.horizontal ? scrollLeft : scrollTop;
            const isScrollDownOrRight = this.lastScrollPos <= scrollPos;

            if (!this._appendOnly || (this._appendOnly && isScrollDownOrRight)) {
                const currentIndex = calculateCurrentIndex(scrollPos, <number>this._itemSize);
                const triggerIndex = calculateTriggerIndex(currentIndex, this.first, this.last, this.numItemsInViewport, this.d_numToleratedItems, isScrollDownOrRight);

                newFirst = calculateFirst(currentIndex, triggerIndex, this.first, this.last, this.numItemsInViewport, this.d_numToleratedItems, isScrollDownOrRight);
                newLast = calculateLast(currentIndex, newFirst, this.last, this.numItemsInViewport, this.d_numToleratedItems);
                isRangeChanged = newFirst !== this.first || newLast !== this.last || this.isRangeChanged;
                newScrollPos = scrollPos;
            }
        }

        return {
            first: newFirst,
            last: newLast,
            isRangeChanged,
            scrollPos: newScrollPos
        };
    }

    onScrollChange(event: Event) {
        const { first, last, isRangeChanged, scrollPos } = this.onScrollPositionChange(event);

        if (isRangeChanged) {
            const newState = { first, last };

            this.setContentPosition(newState);

            this.first = first;
            this.last = last;
            this.lastScrollPos = scrollPos;

            this.handleEvents('onScrollIndexChange', newState);

            if (this._lazy && this.isPageChanged) {
                const lazyLoadState = {
                    first: this._step ? Math.min(this.getPageByFirst() * this._step, (<any[]>this.items).length - this._step) : first,
                    last: Math.min(this._step ? (this.getPageByFirst() + 1) * this._step : last, (<any[]>this.items).length)
                };
                const isLazyStateChanged = this.lazyLoadState.first !== lazyLoadState.first || this.lazyLoadState.last !== lazyLoadState.last;

                isLazyStateChanged && this.handleEvents('onLazyLoad', lazyLoadState);
                this.lazyLoadState = lazyLoadState;
            }
        }
    }

    onContainerScroll(event: Event) {
        this.handleEvents('onScroll', { originalEvent: event });

        if (this._delay && this.isPageChanged) {
            if (this.scrollTimeout) {
                clearTimeout(this.scrollTimeout);
            }

            if (!this.d_loading && this.showLoader) {
                const { isRangeChanged } = this.onScrollPositionChange(event);
                const changed = isRangeChanged || (this._step ? this.isPageChanged : false);

                if (changed) {
                    this.d_loading = true;

                    this.cd.detectChanges();
                }
            }

            this.scrollTimeout = setTimeout(() => {
                this.onScrollChange(event);

                if (this.d_loading && this.showLoader && (!this._lazy || this._loading === undefined)) {
                    this.d_loading = false;
                    this.page = this.getPageByFirst();
                    this.cd.detectChanges();
                }
            }, this._delay);
        } else {
            !this.d_loading && this.onScrollChange(event);
        }
    }

    bindResizeListener() {
        if (isPlatformBrowser(this.platformId)) {
            if (!this.windowResizeListener) {
                this.zone.runOutsideAngular(() => {
                    const window = this.document.defaultView as Window;
                    const event = DomHandler.isTouchDevice() ? 'orientationchange' : 'resize';
                    this.windowResizeListener = this.renderer.listen(window, event, this.onWindowResize.bind(this));
                });
            }
        }
    }

    unbindResizeListener() {
        if (this.windowResizeListener) {
            this.windowResizeListener();
            this.windowResizeListener = null;
        }
    }

    onWindowResize() {
        if (this.resizeTimeout) {
            clearTimeout(this.resizeTimeout);
        }

        this.resizeTimeout = setTimeout(() => {
            if (DomHandler.isVisible(this.elementViewChild?.nativeElement)) {
                const [width, height] = [DomHandler.getWidth(this.elementViewChild?.nativeElement), DomHandler.getHeight(this.elementViewChild?.nativeElement)];
                const [isDiffWidth, isDiffHeight] = [width !== this.defaultWidth, height !== this.defaultHeight];
                const reinit = this.both ? isDiffWidth || isDiffHeight : this.horizontal ? isDiffWidth : this.vertical ? isDiffHeight : false;

                reinit &&
                    this.zone.run(() => {
                        this.d_numToleratedItems = this._numToleratedItems;
                        this.defaultWidth = width;
                        this.defaultHeight = height;
                        this.defaultContentWidth = DomHandler.getWidth(this.contentEl);
                        this.defaultContentHeight = DomHandler.getHeight(this.contentEl);

                        this.init();
                    });
            }
        }, this._resizeDelay);
    }

    handleEvents(name: string, params: any) {
        //@ts-ignore
        return this.options && (<any>this.options)[name] ? (<any>this.options)[name](params) : this[name].emit(params);
    }

    getContentOptions() {
        return {
            contentStyleClass: `p-scroller-content ${this.d_loading ? 'p-scroller-loading' : ''}`,
            items: this.loadedItems,
            getItemOptions: (index: number) => this.getOptions(index),
            loading: this.d_loading,
            getLoaderOptions: (index: number, options?: any) => this.getLoaderOptions(index, options),
            itemSize: this._itemSize,
            rows: this.loadedRows,
            columns: this.loadedColumns,
            spacerStyle: this.spacerStyle,
            contentStyle: this.contentStyle,
            vertical: this.vertical,
            horizontal: this.horizontal,
            both: this.both
        };
    }

    getOptions(renderedIndex: number) {
        const count = (this._items || []).length;
        const index = this.both ? this.first.rows + renderedIndex : this.first + renderedIndex;

        return {
            index,
            count,
            first: index === 0,
            last: index === count - 1,
            even: index % 2 === 0,
            odd: index % 2 !== 0
        };
    }

    getLoaderOptions(index: number, extOptions: any) {
        const count = this.loaderArr.length;

        return {
            index,
            count,
            first: index === 0,
            last: index === count - 1,
            even: index % 2 === 0,
            odd: index % 2 !== 0,
            ...extOptions
        };
    }
}

@NgModule({
    imports: [CommonModule, SharedModule, SpinnerIcon],
    exports: [Scroller, SharedModule],
    declarations: [Scroller]
})
export class ScrollerModule {}