379 lines
11 KiB
JavaScript
379 lines
11 KiB
JavaScript
/**
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* Lazy Image Loader with Retry Logic
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* Implements Intersection Observer for viewport-based lazy loading
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* and exponential backoff retry for failed thumbnail requests
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*/
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import { loadThumbnail } from './imageLoader.js';
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/**
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* Configuration for lazy loading and retry behavior
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*/
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const CONFIG = {
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// Intersection Observer options
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rootMargin: '50px', // Load images 50px before they enter viewport
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threshold: 0.01, // Trigger when 1% of image is visible
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// Retry configuration
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maxRetries: 3,
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initialRetryDelay: 1000, // 1 second
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maxRetryDelay: 10000, // 10 seconds
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retryBackoffMultiplier: 2, // Exponential backoff
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// Batch loading
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batchSize: 10, // Load 10 images at a time
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batchDelay: 100, // 100ms delay between batches
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};
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/**
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* Manages lazy loading of thumbnails with retry logic
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*/
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export class LazyImageLoader {
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constructor() {
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this.observer = null;
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// Key by element identity to avoid collisions when multiple elements share the same image path.
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this.pendingLoads = new Map(); // imgElement -> {imagePath, retries, retryTimeout}
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this.loadingQueue = [];
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this.isProcessingQueue = false;
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this.loadStats = {
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total: 0,
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loaded: 0,
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failed: 0,
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retrying: 0
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};
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this.onProgressCallback = null;
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}
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/**
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* Initialize the Intersection Observer
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*/
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init() {
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if (this.observer) {
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return; // Already initialized
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}
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this.observer = new IntersectionObserver((entries) => {
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entries.forEach(entry => {
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if (entry.isIntersecting) {
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const img = entry.target;
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const imagePath = img.dataset.imagePath;
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// Check dataset values as strings (dataset always stores strings)
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if (imagePath && img.dataset.loaded !== 'true' && img.dataset.loading !== 'true') {
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this.queueImageLoad(img, imagePath);
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}
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}
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});
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}, {
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rootMargin: CONFIG.rootMargin,
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threshold: CONFIG.threshold
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});
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}
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/**
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* Observe an image element for lazy loading
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* @param {HTMLImageElement} img - Image element to observe
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* @param {string} imagePath - Path to the image
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* @param {string} thumbnailSize - Size of thumbnail to load
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*/
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observe(img, imagePath, thumbnailSize = 'large') {
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if (!this.observer) {
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this.init();
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}
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// Store metadata on element
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img.dataset.imagePath = imagePath;
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img.dataset.thumbnailSize = thumbnailSize;
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img.dataset.loaded = 'false';
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img.dataset.loading = 'false';
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// Start observing
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this.observer.observe(img);
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this.loadStats.total++;
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this.updateProgress();
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}
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/**
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* Queue an image for loading (batch processing)
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* @param {HTMLImageElement} img - Image element
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* @param {string} imagePath - Path to the image
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*/
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queueImageLoad(img, imagePath) {
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img.dataset.loading = 'true';
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this.loadingQueue.push({ img, imagePath });
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if (!this.isProcessingQueue) {
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this.processQueue();
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}
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}
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/**
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* Process the loading queue in batches
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*/
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async processQueue() {
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if (this.isProcessingQueue || this.loadingQueue.length === 0) {
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return;
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}
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this.isProcessingQueue = true;
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while (this.loadingQueue.length > 0) {
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// Take a batch from the queue
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const batch = this.loadingQueue.splice(0, CONFIG.batchSize);
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// Load all images in the batch concurrently
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await Promise.allSettled(
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batch.map(({ img, imagePath }) => this.loadImage(img, imagePath, 0))
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);
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// Small delay before next batch to avoid overwhelming the server
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if (this.loadingQueue.length > 0) {
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await this.delay(CONFIG.batchDelay);
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}
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}
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this.isProcessingQueue = false;
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}
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/**
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* Load a single image with retry logic
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* @param {HTMLImageElement} img - Image element
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* @param {string} imagePath - Path to the image
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* @param {number} retryCount - Current retry attempt
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*/
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async loadImage(img, imagePath, retryCount = 0) {
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const thumbnailSize = img.dataset.thumbnailSize || 'large';
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try {
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// Attempt to load thumbnail
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const thumbnailUrl = await loadThumbnail({ path: imagePath }, thumbnailSize);
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// Set the image source
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img.src = thumbnailUrl;
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img.dataset.loaded = 'true';
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img.dataset.loading = 'false';
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// Update stats
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this.loadStats.loaded++;
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if (retryCount > 0) {
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this.loadStats.retrying--;
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}
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this.updateProgress();
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// Remove from pending loads
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this.pendingLoads.delete(img);
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} catch (error) {
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console.warn(`Failed to load thumbnail for ${imagePath} (attempt ${retryCount + 1}):`, error);
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// Check if we should retry
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if (retryCount < CONFIG.maxRetries) {
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// Calculate retry delay with exponential backoff
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const retryDelay = Math.min(
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CONFIG.initialRetryDelay * Math.pow(CONFIG.retryBackoffMultiplier, retryCount),
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CONFIG.maxRetryDelay
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);
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console.log(`Retrying in ${retryDelay}ms...`);
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// Update stats
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if (retryCount === 0) {
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this.loadStats.retrying++;
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}
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this.updateProgress();
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// Replace any existing pending retry for this element.
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const existingPending = this.pendingLoads.get(img);
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if (existingPending?.retryTimeout) {
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clearTimeout(existingPending.retryTimeout);
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}
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// Store pending retry
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const retryTimeout = setTimeout(() => {
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this.loadImage(img, imagePath, retryCount + 1);
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}, retryDelay);
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this.pendingLoads.set(img, {
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imagePath,
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retries: retryCount + 1,
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retryTimeout
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});
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} else {
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// Max retries exceeded, show error state
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img.dataset.loaded = 'error';
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img.dataset.loading = 'false';
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// Update stats
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this.loadStats.failed++;
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if (retryCount > 0) {
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this.loadStats.retrying--;
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}
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this.updateProgress();
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// Show error placeholder
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this.showErrorState(img, imagePath);
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// Remove from pending loads
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this.pendingLoads.delete(img);
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}
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}
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}
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/**
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* Show error state for failed image
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* @param {HTMLImageElement} img - Image element
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* @param {string} imagePath - Path to the image
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*/
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showErrorState(img, imagePath) {
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// Create error placeholder
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const errorDiv = document.createElement('div');
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errorDiv.style.cssText = `
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width: 100%;
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height: 150px;
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display: flex;
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flex-direction: column;
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align-items: center;
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justify-content: center;
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background: #333;
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color: #999;
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font-size: 11px;
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padding: 10px;
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text-align: center;
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gap: 8px;
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`;
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const iconDiv = document.createElement('div');
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iconDiv.textContent = '⚠️';
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iconDiv.style.fontSize = '24px';
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const messageDiv = document.createElement('div');
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messageDiv.textContent = 'Failed to load';
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const retryButton = document.createElement('button');
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retryButton.textContent = '🔄 Retry';
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retryButton.style.cssText = `
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padding: 4px 8px;
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background: #4CAF50;
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color: white;
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border: none;
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border-radius: 4px;
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cursor: pointer;
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font-size: 11px;
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`;
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retryButton.addEventListener('click', (e) => {
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e.stopPropagation();
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errorDiv.remove();
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img.style.display = 'block';
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img.dataset.loaded = 'false';
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img.dataset.loading = 'false';
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this.queueImageLoad(img, imagePath);
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});
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errorDiv.appendChild(iconDiv);
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errorDiv.appendChild(messageDiv);
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errorDiv.appendChild(retryButton);
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// Hide image and show error
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img.style.display = 'none';
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img.parentNode.insertBefore(errorDiv, img.nextSibling);
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}
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/**
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* Set progress callback
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* @param {Function} callback - Called with {total, loaded, failed, retrying}
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*/
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onProgress(callback) {
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this.onProgressCallback = callback;
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}
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/**
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* Update and emit progress
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*/
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updateProgress() {
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if (this.onProgressCallback) {
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this.onProgressCallback({ ...this.loadStats });
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}
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}
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/**
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* Get current loading statistics
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* @returns {Object} Stats object with total, loaded, failed, retrying counts
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*/
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getStats() {
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return { ...this.loadStats };
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}
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/**
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* Reset statistics
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*/
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resetStats() {
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this.loadStats = {
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total: 0,
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loaded: 0,
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failed: 0,
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retrying: 0
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};
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this.updateProgress();
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}
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/**
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* Unobserve an image element
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* @param {HTMLImageElement} img - Image element to stop observing
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*/
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unobserve(img) {
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if (this.observer) {
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this.observer.unobserve(img);
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}
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const pending = this.pendingLoads.get(img);
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if (pending?.retryTimeout) {
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clearTimeout(pending.retryTimeout);
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}
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this.pendingLoads.delete(img);
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}
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/**
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* Disconnect observer and cleanup
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*/
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cleanup() {
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if (this.observer) {
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this.observer.disconnect();
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this.observer = null;
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}
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// Cancel all pending retries
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this.pendingLoads.forEach(pending => {
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if (pending.retryTimeout) {
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clearTimeout(pending.retryTimeout);
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}
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});
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this.pendingLoads.clear();
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this.loadingQueue = [];
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this.resetStats();
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}
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/**
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* Utility delay function
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* @param {number} ms - Milliseconds to delay
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* @returns {Promise}
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*/
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delay(ms) {
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return new Promise(resolve => setTimeout(resolve, ms));
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}
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}
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// Singleton instance
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let lazyLoaderInstance = null;
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/**
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* Get or create the global lazy loader instance
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* @returns {LazyImageLoader}
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*/
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export function getLazyLoader() {
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if (!lazyLoaderInstance) {
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lazyLoaderInstance = new LazyImageLoader();
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}
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return lazyLoaderInstance;
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}
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