import { rewriteBlobUrl } from '../api/blobRewrite';

const preloaded = new Set<string>();
const inFlight = new Map<string, Promise<void>>();

export function preloadImage(rawUrl: string): Promise<void> {
  const url = rewriteBlobUrl(rawUrl) ?? rawUrl;

  if (preloaded.has(url)) return Promise.resolve();

  const existing = inFlight.get(url);
  if (existing) return existing;

  const promise = new Promise<void>((resolve) => {
    const img = new Image();
    img.onload = () => finish();
    img.onerror = () => finish();
    img.src = url;

    function finish() {
      preloaded.add(url);
      inFlight.delete(url);
      resolve();
    }
  });

  inFlight.set(url, promise);
  return promise;
}

export function preloadImages(rawUrls: string[]): Promise<void[]> {
  return Promise.all(rawUrls.map((u) => preloadImage(u)));
}

export function isPreloaded(rawUrl: string): boolean {
  const url = rewriteBlobUrl(rawUrl) ?? rawUrl;
  return preloaded.has(url);
}

export function invalidatePreload(rawUrl: string): void {
  const url = rewriteBlobUrl(rawUrl) ?? rawUrl;
  preloaded.delete(url);
  inFlight.delete(url);
}