import { Loader } from './Loader';

export const DefaultLoadingManager: LoadingManager;

/**
 * Handles and keeps track of loaded and pending data.
 */
export class LoadingManager {
    constructor(
        onLoad?: () => void,
        onProgress?: (url: string, loaded: number, total: number) => void,
        onError?: (url: string) => void,
    );

    /**
     * Will be called when loading of an item starts.
     * @param url The url of the item that started loading.
     * @param loaded The number of items already loaded so far.
     * @param total The total amount of items to be loaded.
     */
    onStart?: ((url: string, loaded: number, total: number) => void) | undefined;

    /**
     * Will be called when all items finish loading.
     * The default is a function with empty body.
     */
    onLoad: () => void;

    /**
     * Will be called for each loaded item.
     * The default is a function with empty body.
     * @param url The url of the item just loaded.
     * @param loaded The number of items already loaded so far.
     * @param total The total amount of items to be loaded.
     */
    onProgress: (url: string, loaded: number, total: number) => void;

    /**
     * Will be called when item loading fails.
     * The default is a function with empty body.
     * @param url The url of the item that errored.
     */
    onError: (url: string) => void;

    /**
     * If provided, the callback will be passed each resource URL before a request is sent.
     * The callback may return the original URL, or a new URL to override loading behavior.
     * This behavior can be used to load assets from .ZIP files, drag-and-drop APIs, and Data URIs.
     * @param callback URL modifier callback. Called with url argument, and must return resolvedURL.
     */
    setURLModifier(callback?: (url: string) => string): this;

    /**
     * Given a URL, uses the URL modifier callback (if any) and returns a resolved URL.
     * If no URL modifier is set, returns the original URL.
     * @param url the url to load
     */
    resolveURL(url: string): string;

    itemStart(url: string): void;
    itemEnd(url: string): void;
    itemError(url: string): void;

    // handlers

    addHandler(regex: RegExp, loader: Loader): this;
    removeHandler(regex: RegExp): this;
    getHandler(file: string): Loader | null;
}