export type CompressionResult = {
  blob: Blob;
  originalSize: number;
  compressedSize: number;
  width: number;
  height: number;
};

const COMPRESSIBLE_TYPES = ['image/jpeg', 'image/png'];

/** Returns true if this file type can be compressed (JPEG or PNG, any size). */
export function isCompressible(file: File): boolean {
  return COMPRESSIBLE_TYPES.includes(file.type);
}

/**
 * Compress an image file via canvas.toBlob.
 * Returns null if the file type is not compressible (GIF, SVG, WebP, video, audio, etc.).
 */
export async function compressImage(file: File, quality = 0.82): Promise<CompressionResult | null> {
  if (!COMPRESSIBLE_TYPES.includes(file.type)) return null;

  const img = await loadImage(file);
  const canvas = document.createElement('canvas');
  canvas.width = img.naturalWidth;
  canvas.height = img.naturalHeight;
  const ctx = canvas.getContext('2d')!;
  ctx.drawImage(img, 0, 0);

  return new Promise((resolve) => {
    canvas.toBlob(
      (blob) => {
        if (!blob) {
          resolve(null);
          return;
        }
        resolve({
          blob,
          originalSize: file.size,
          compressedSize: blob.size,
          width: img.naturalWidth,
          height: img.naturalHeight,
        });
      },
      'image/jpeg',
      quality,
    );
  });
}

function loadImage(file: File): Promise<HTMLImageElement> {
  return new Promise((resolve, reject) => {
    const url = URL.createObjectURL(file);
    const img = new Image();
    img.onload = () => {
      URL.revokeObjectURL(url);
      resolve(img);
    };
    img.onerror = reject;
    img.src = url;
  });
}

export function formatFileSize(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
}