const GIF_WORKER_URL = "https://cdn.jsdelivr.net/npm/gif.js@0.2.0/dist/gif.worker.js";

function loadImage(src) {
  return new Promise((resolve, reject) => {
    const img = new Image();
    img.onload = () => resolve(img);
    img.onerror = () => reject(new Error("Failed to load generated frame."));
    img.src = src;
  });
}

export async function createGifFromFrames(frameUrls, { fps = 4 } = {}) {
  if (!Array.isArray(frameUrls) || !frameUrls.length) {
    throw new Error("No frames available for GIF encoding.");
  }

  if (typeof window.GIF !== "function") {
    throw new Error("GIF encoder is not loaded.");
  }

  const images = await Promise.all(frameUrls.map(loadImage));
  const first = images[0];
  const delay = Math.max(20, Math.round(1000 / Math.max(1, Number(fps) || 4)));

  return new Promise((resolve, reject) => {
    const gif = new window.GIF({
      workers: 2,
      quality: 10,
      repeat: 0,
      width: first.naturalWidth || first.width,
      height: first.naturalHeight || first.height,
      workerScript: GIF_WORKER_URL,
    });

    for (const img of images) {
      gif.addFrame(img, { delay });
    }

    gif.on("finished", (blob) => resolve(blob));
    gif.on("abort", () => reject(new Error("GIF rendering aborted.")));

    try {
      gif.render();
    } catch (err) {
      reject(err);
    }
  });
}