export function loadImage(src: string): Promise<HTMLImageElement> {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.onload = () => resolve(img);
    img.onerror = reject;
    img.src = src;
  });
}

export async function loadImages(
  ...srcs: string[]
): Promise<HTMLImageElement[]> {
  return Promise.all(srcs.map(loadImage));
}

export class ImageLoader {
  private images: Map<string, HTMLImageElement> = new Map();
  private loadPromise: Promise<void> | null = null;

  constructor(imageSources: Record<string, string>) {
    this.loadPromise = this.loadAll(imageSources);
  }

  private async loadAll(imageSources: Record<string, string>): Promise<void> {
    const entries = Object.entries(imageSources);
    const images = await loadImages(...entries.map(([_, src]) => src));

    entries.forEach(([key], index) => {
      this.images.set(key, images[index]);
    });
  }

  public async ready(): Promise<void> {
    await this.loadPromise;
  }

  public get isReady(): boolean {
    return this.loadPromise !== null && this.images.size > 0;
  }

  public get(key: string): HTMLImageElement | undefined {
    return this.images.get(key);
  }

  public require(key: string): HTMLImageElement {
    const image = this.images.get(key);
    if (!image) {
      throw new Error(`Image not found: ${key}`);
    }
    return image;
  }
}