EnvelopeGenerator/EnvelopeGenerator.ReceiverUI/wwwroot/js/pdf-viewer.js

// PDF.js Viewer for Blazor WASM
window.pdfViewer = {
    pdfDoc: null,
    pageNum: 1,
    pageRendering: false,
    pageNumPending: null,
    scale: 1.5,
    canvas: null,
    ctx: null,
    totalPages: 0,
    currentRenderTask: null,
    dotNetReference: null,
    wheelEventAttached: false,

    async initialize(canvasId, pdfDataUrl, dotNetRef) {
        try {
            console.log('PDF.js initialization started for canvas:', canvasId);

            // Store .NET reference for callbacks
            this.dotNetReference = dotNetRef;

            // Wait for PDF.js to load
            if (typeof window.pdfjsLib === 'undefined') {
                console.error('PDF.js library not loaded, waiting...');
                await this.waitForPdfJs();
            }

            const pdfjsLib = window.pdfjsLib;
            pdfjsLib.GlobalWorkerOptions.workerSrc = 'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js';

            this.canvas = document.getElementById(canvasId);
            if (!this.canvas) {
                console.error('Canvas element not found:', canvasId);
                return false;
            }

            console.log('Canvas element found, loading PDF...');

            this.ctx = this.canvas.getContext('2d');

            // Attach mouse wheel event listener
            this.attachWheelEvent();

            // Load PDF from data URL
            const uint8Array = this.base64ToUint8Array(pdfDataUrl);
            console.log('PDF data converted to Uint8Array, size:', uint8Array.length);

            const loadingTask = pdfjsLib.getDocument({ data: uint8Array });
            this.pdfDoc = await loadingTask.promise;
            this.totalPages = this.pdfDoc.numPages;

            console.log('PDF loaded successfully, total pages:', this.totalPages);

            // Render first page
            await this.renderPage(this.pageNum);
            return true;
        } catch (error) {
            console.error('Error initializing PDF viewer:', error);
            return false;
        }
    },

    attachWheelEvent() {
        if (this.wheelEventAttached) return;
        
        // Attach to the entire document body for global zoom control
        document.body.addEventListener('wheel', (e) => {
            // Check if Ctrl key is pressed (zoom gesture)
            if (e.ctrlKey || e.metaKey) {
                e.preventDefault();
                
                if (e.deltaY < 0) {
                    // Scroll up = Zoom In
                    this.zoomIn();
                    if (this.dotNetReference) {
                        this.dotNetReference.invokeMethodAsync('OnZoomChanged', this.scale);
                    }
                } else {
                    // Scroll down = Zoom Out
                    this.zoomOut();
                    if (this.dotNetReference) {
                        this.dotNetReference.invokeMethodAsync('OnZoomChanged', this.scale);
                    }
                }
            }
        }, { passive: false });

        this.wheelEventAttached = true;
        console.log('Wheel event listener attached to document body');
    },

    async waitForPdfJs() {
        for (let i = 0; i < 50; i++) {
            if (typeof window.pdfjsLib !== 'undefined') {
                console.log('PDF.js loaded after', i * 100, 'ms');
                return;
            }
            await new Promise(resolve => setTimeout(resolve, 100));
        }
        throw new Error('PDF.js failed to load after 5 seconds');
    },

    base64ToUint8Array(base64) {
        // Remove data URL prefix if present
        const base64String = base64.includes(',') ? base64.split(',')[1] : base64;
        const raw = atob(base64String);
        const uint8Array = new Uint8Array(raw.length);
        for (let i = 0; i < raw.length; i++) {
            uint8Array[i] = raw.charCodeAt(i);
        }
        return uint8Array;
    },

    async renderPage(num) {
        this.pageRendering = true;

        try {
            // Get scroll container
            const container = this.canvas.closest('.pdf-frame');
            
            // Store scroll position and viewport center BEFORE rendering
            let scrollLeft = 0, scrollTop = 0;
            let centerX = 0, centerY = 0;
            let oldWidth = this.canvas.width;
            let oldHeight = this.canvas.height;
            
            if (container) {
                scrollLeft = container.scrollLeft;
                scrollTop = container.scrollTop;
                centerX = scrollLeft + container.clientWidth / 2;
                centerY = scrollTop + container.clientHeight / 2;
            }

            const page = await this.pdfDoc.getPage(num);
            const viewport = page.getViewport({ scale: this.scale });

            console.log('Rendering page:', num, 'Viewport:', viewport.width, 'x', viewport.height);

            this.canvas.height = viewport.height;
            this.canvas.width = viewport.width;

            const renderContext = {
                canvasContext: this.ctx,
                viewport: viewport
            };

            if (this.currentRenderTask) {
                console.log('Cancelling previous render task');
                this.currentRenderTask.cancel();
            }

            this.currentRenderTask = page.render(renderContext);
            await this.currentRenderTask.promise;

            console.log('Page rendered successfully');

            // Restore viewport center position AFTER rendering
            if (container && oldWidth > 0 && oldHeight > 0) {
                const scaleX = this.canvas.width / oldWidth;
                const scaleY = this.canvas.height / oldHeight;
                
                const newCenterX = centerX * scaleX;
                const newCenterY = centerY * scaleY;
                
                container.scrollLeft = newCenterX - container.clientWidth / 2;
                container.scrollTop = newCenterY - container.clientHeight / 2;
            }

            this.currentRenderTask = null;
            this.pageRendering = false;

            if (this.pageNumPending !== null) {
                this.renderPage(this.pageNumPending);
                this.pageNumPending = null;
            }
        } catch (error) {
            if (error.name === 'RenderingCancelledException') {
                console.log('Rendering cancelled, will render pending page');
            } else {
                console.error('Error rendering page:', error);
            }
            this.currentRenderTask = null;
            this.pageRendering = false;
        }
    },

    queueRenderPage(num) {
        if (this.pageRendering) {
            this.pageNumPending = num;
        } else {
            this.renderPage(num);
        }
    },

    nextPage() {
        if (this.pageNum >= this.totalPages) {
            return false;
        }
        this.pageNum++;
        this.queueRenderPage(this.pageNum);
        return true;
    },

    previousPage() {
        if (this.pageNum <= 1) {
            return false;
        }
        this.pageNum--;
        this.queueRenderPage(this.pageNum);
        return true;
    },

    goToPage(num) {
        if (num < 1 || num > this.totalPages) {
            return false;
        }
        this.pageNum = num;
        this.queueRenderPage(this.pageNum);
        return true;
    },

    zoomIn() {
        this.scale += 0.25;
        this.queueRenderPage(this.pageNum);
    },

    zoomOut() {
        if (this.scale > 0.5) {
            this.scale -= 0.25;
            this.queueRenderPage(this.pageNum);
        }
    },

    getCurrentPage() {
        return this.pageNum;
    },

    getTotalPages() {
        return this.totalPages;
    },

    getScale() {
        return this.scale;
    },

    dispose() {
        // Clean up event listeners
        if (this.wheelEventAttached) {
            // Note: We can't remove the exact listener without keeping a reference
            // but we can at least mark it as disposed
            this.wheelEventAttached = false;
            this.dotNetReference = null;
            console.log('PDF viewer disposed');
        }
    }
};