backend/libs/three/loaders/LoadingManager.js

class LoadingManager {
	constructor(onLoad, onProgress, onError) {
		const scope = this;

		let isLoading = false;
		let itemsLoaded = 0;
		let itemsTotal = 0;
		let urlModifier = undefined;
		const handlers = [];

		// Refer to #5689 for the reason why we don't set .onStart
		// in the constructor

		this.onStart = undefined;
		this.onLoad = onLoad;
		this.onProgress = onProgress;
		this.onError = onError;

		this.itemStart = function (url) {
			itemsTotal++;

			if (isLoading === false) {
				if (scope.onStart !== undefined) {
					scope.onStart(url, itemsLoaded, itemsTotal);
				}
			}

			isLoading = true;
		};

		this.itemEnd = function (url) {
			itemsLoaded++;

			if (scope.onProgress !== undefined) {
				scope.onProgress(url, itemsLoaded, itemsTotal);
			}

			if (itemsLoaded === itemsTotal) {
				isLoading = false;

				if (scope.onLoad !== undefined) {
					scope.onLoad();
				}
			}
		};

		this.itemError = function (url) {
			if (scope.onError !== undefined) {
				scope.onError(url);
			}
		};

		this.resolveURL = function (url) {
			if (urlModifier) {
				return urlModifier(url);
			}

			return url;
		};

		this.setURLModifier = function (transform) {
			urlModifier = transform;

			return this;
		};

		this.addHandler = function (regex, loader) {
			handlers.push(regex, loader);

			return this;
		};

		this.removeHandler = function (regex) {
			const index = handlers.indexOf(regex);

			if (index !== -1) {
				handlers.splice(index, 2);
			}

			return this;
		};

		this.getHandler = function (file) {
			for (let i = 0, l = handlers.length; i < l; i += 2) {
				const regex = handlers[i];
				const loader = handlers[i + 1];

				if (regex.global) regex.lastIndex = 0; // see #17920

				if (regex.test(file)) {
					return loader;
				}
			}

			return null;
		};
	}
}

const DefaultLoadingManager = new LoadingManager();

export { DefaultLoadingManager, LoadingManager };