/*
 * Web Worker for image optimization (P1). Offloads the expensive bitmap decode,
 * resize, and JPEG/PNG compression to a background thread so the UI remains
 * responsive while processing large photos.
 *
 * Uses OffscreenCanvas which is available in Chrome 69+, Firefox 105+, and
 * Safari 16.4+. The main module (images.js) detects support at runtime and
 * falls back to the main thread for older browsers.
 */

function fitIntoBox(originalWidth, originalHeight, maxWidth, maxHeight) {
  const ratio = Math.min(maxWidth / originalWidth, maxHeight / originalHeight, 1);

  return {
    width: Math.round(originalWidth * ratio),
    height: Math.round(originalHeight * ratio)
  };
}

self.onmessage = async (event) => {
  const { id, file, imageRules } = event.data;

  try {
    const imageBitmap = await createImageBitmap(file);
    const maxWidth = imageRules?.maxWidthPx || imageBitmap.width;
    const maxHeight = imageRules?.maxHeightPx || imageBitmap.height;
    const { width, height } = fitIntoBox(imageBitmap.width, imageBitmap.height, maxWidth, maxHeight);

    const canvas = new OffscreenCanvas(width, height);
    const context = canvas.getContext('2d');
    context.drawImage(imageBitmap, 0, 0, width, height);
    imageBitmap.close();

    const targetMimeType = file.type === 'image/png' ? 'image/png' : 'image/jpeg';
    const quality = Math.min(Math.max((imageRules?.jpegQuality || 82) / 100, 0.2), 0.95);
    const blob = await canvas.convertToBlob({ type: targetMimeType, quality });

    if (!blob) {
      throw new Error(`Failed to optimize image: ${file.name}`);
    }

    if (imageRules?.maxFileSizeBytes && blob.size > imageRules.maxFileSizeBytes) {
      throw new Error(`Optimized image still exceeds limit: ${file.name}`);
    }

    self.postMessage({
      id,
      result: {
        blob,
        width,
        height,
        extension: targetMimeType === 'image/png' ? 'png' : 'jpg'
      }
    });
  } catch (error) {
    self.postMessage({ id, error: error.message });
  }
};