/** Ren'Py uses the mask movie's red channel as opacity, not its alpha channel. */
export function applyMovieMask(picture: Uint8ClampedArray, mask: Uint8ClampedArray) {
  if (picture.length !== mask.length) throw new Error("Размеры кадров маски не совпадают");
  for (let i = 3; i < picture.length; i += 4) picture[i] = Math.round(picture[i] * mask[i - 3] / 255);
}

export function movieDisplayable(source: string, mask: string | null, loop = true): HTMLElement {
  const video = document.createElement("video");
  video.src = source;
  video.autoplay = true;
  video.loop = loop;
  video.muted = true;
  video.playsInline = true;
  if (!mask) return video;
  const alpha = document.createElement("video");
  alpha.src = mask;
  alpha.loop = loop;
  alpha.muted = true;
  alpha.playsInline = true;
  const canvas = document.createElement("canvas");
  canvas.className = "pg-masked-movie";
  const maskCanvas = document.createElement("canvas");
  const ctx = canvas.getContext("2d", { willReadFrequently: true });
  const maskCtx = maskCanvas.getContext("2d", { willReadFrequently: true });
  if (!ctx || !maskCtx) throw new Error("Не удалось создать поверхность для видео с маской");
  let last = -1;
  let failed = false;
  const draw = () => {
    if (failed) return;
    if (!canvas.isConnected) { video.pause(); alpha.pause(); return; }
    if (video.readyState >= 2 && alpha.readyState >= 2 && video.videoWidth && video.currentTime !== last) {
      if (Math.abs(alpha.currentTime - video.currentTime) > 0.06) alpha.currentTime = video.currentTime;
      const w = video.videoWidth, h = video.videoHeight;
      if (canvas.width !== w || canvas.height !== h) {
        canvas.width = maskCanvas.width = w;
        canvas.height = maskCanvas.height = h;
      }
      ctx.clearRect(0, 0, w, h);
      ctx.drawImage(video, 0, 0, w, h);
      maskCtx.drawImage(alpha, 0, 0, w, h);
      const pixels = ctx.getImageData(0, 0, w, h);
      applyMovieMask(pixels.data, maskCtx.getImageData(0, 0, w, h).data);
      ctx.putImageData(pixels, 0, 0);
      last = video.currentTime;
    }
    if (video.ended && !loop) { video.pause(); alpha.pause(); return; }
    requestAnimationFrame(draw);
  };
  video.onerror = alpha.onerror = () => { failed = true; canvas.dataset.error = "Не удалось загрузить видео или его маску"; video.pause(); alpha.pause(); };
  void video.play().catch(() => {});
  void alpha.play().catch(() => {});
  requestAnimationFrame(draw);
  return canvas;
}