devexpress-reporting/viewer/internal/_pageLoader.js

DevExpress Reporting provides the capability to develop a reporting application to create and customize reports.

/**
* DevExpress HTML/JS Reporting (viewer\internal\_pageLoader.js)
* Version:  24.2.6
* Build date: Mar 18, 2025
* Copyright (c) 2012 - 2025 Developer Express Inc. ALL RIGHTS RESERVED
* License: https://www.devexpress.com/Support/EULAs/universal.xml
*/
import { DxDeferred } from '@devexpress/analytics-core/analytics-internal-native';
import { PreloadedPagesOffset } from '../settings';
export class PageLoader {
    get pages() {
        return this._preview.pages || [];
    }
    _getNextStartingIndex(currentIndex) {
        return this.pages.find(page => page?.pageIndex > currentIndex && !page.imageSrc)?.pageIndex;
    }
    _getPagesToUpdate(startIndex, endIndex, currentPageIndex) {
        return this.pages.slice(startIndex, endIndex).filter(page => {
            if (currentPageIndex !== undefined) {
                return page.pageIndex !== currentPageIndex;
            }
            return !page.imageSrc;
        });
    }
    _performPrefetch(pagesToUpdate, resolution, forcePng) {
        pagesToUpdate.forEach(page => this._preview.updatePage(page, resolution, forcePng));
    }
    _scheduleNextPrefetch(currentIndex, pendingPages) {
        this._loadTimeout = setTimeout(() => {
            const startIndex = this._getNextStartingIndex(currentIndex);
            if (!startIndex) {
                this.reset();
                return;
            }
            const promises = pendingPages.map(page => page.lastGetPageDeferred?.promise()).filter(x => !!x);
            DxDeferred.when(promises).done(() => {
                !this._disabled && this.prefetchPages(startIndex, startIndex + PreloadedPagesOffset(), undefined);
            });
        }, 700);
    }
    constructor(_preview) {
        this._preview = _preview;
        this._defaultResolution = 0.25;
        this._requestCyclesLimit = 5;
        this._currentPrefetchCycle = 0;
        this._disabled = true;
    }
    prefetchPages(startIndex, endIndex, currentPageIndex) {
        this._disabled = false;
        let zoom = this._preview.originalZoom;
        let forcePng = false;
        if (currentPageIndex === undefined) {
            zoom = this._defaultResolution;
            this._currentPrefetchCycle++;
            forcePng = true;
        }
        if (startIndex > this.pages.length - 1 || this._currentPrefetchCycle >= this._requestCyclesLimit) {
            this.reset();
            return;
        }
        const pendingPages = this._getPagesToUpdate(startIndex, endIndex, currentPageIndex);
        this._performPrefetch(pendingPages, zoom, forcePng);
        this._scheduleNextPrefetch(endIndex, pendingPages);
    }
    reset() {
        this._loadTimeout && clearTimeout(this._loadTimeout);
        this._loadTimeout = null;
        this._disabled = true;
        this._currentPrefetchCycle = 0;
    }
    isActive() {
        return !!this._loadTimeout;
    }
}