export type CV = typeof import('@techstark/opencv-js');

// Everything returns { cv }: the cv module is a thenable, so resolving with it directly never settles.
let loading: Promise<{ cv: CV }> | null = null;

export function loadOpenCV(): Promise<{ cv: CV }> {
  loading ??= (async () => {
    const { cv } = typeof document === 'undefined' ? await importModule() : await loadScript();
    if (!cv.Mat) {
      await new Promise<void>((resolve) => {
        (cv as unknown as { onRuntimeInitialized: () => void }).onRuntimeInitialized = () => resolve();
      });
    }
    return { cv };
  })();
  return loading;
}

/** Node (tests). The variable specifier keeps the bundler from emitting a second OpenCV chunk. */
async function importModule(): Promise<{ cv: CV }> {
  const specifier = '@techstark/opencv-js';
  const mod = (await import(/* @vite-ignore */ specifier)) as { default: CV };
  return { cv: mod.default };
}

// A script tag, not import(): bundler CJS interop copies `then` and the import never settles.
async function loadScript(): Promise<{ cv: CV }> {
  const { default: url } = await import('@techstark/opencv-js/dist/opencv.js?url');
  await new Promise<void>((resolve, reject) => {
    const script = document.createElement('script');
    script.src = url;
    script.onload = () => resolve();
    script.onerror = () => reject(new Error('Failed to load OpenCV'));
    document.head.append(script);
  });
  return { cv: (window as unknown as { cv: CV }).cv };
}