// Copyright 2026 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

const MAX_DIMENSION_PX = 1024;

let compressImplementation = realCompress;

export function setCompressImplementationForTest(impl: typeof realCompress|null): void {
  compressImplementation = impl ?? realCompress;
}

/**
 * Decodes and scales an image file so that its largest dimension does not exceed 1024 pixels,
 * preserving the original aspect ratio. The image is then compressed to a JPEG format at 80% quality.
 *
 * This reduces the payload size for base64 encoding and prevents out-of-memory errors in the AIDA API.
 *
 * @param file The raw Image file to be resized and compressed.
 * @returns A promise resolving to the base64-encoded string and MIME type.
 */
export async function compress(file: File): Promise<{data: string, mimeType: string}> {
  return await compressImplementation(file);
}

async function realCompress(file: File): Promise<{data: string, mimeType: string}> {
  const bitmap = await createImageBitmap(file);
  try {
    let width = bitmap.width;
    let height = bitmap.height;

    if (width > MAX_DIMENSION_PX || height > MAX_DIMENSION_PX) {
      if (width > height) {
        height = Math.round((height * MAX_DIMENSION_PX) / width);
        width = MAX_DIMENSION_PX;
      } else {
        width = Math.round((width * MAX_DIMENSION_PX) / height);
        height = MAX_DIMENSION_PX;
      }
    }

    const canvas = new OffscreenCanvas(width, height);
    const ctx = canvas.getContext('2d');
    if (!ctx) {
      throw new Error('Failed to get 2d context');
    }

    ctx.drawImage(bitmap, 0, 0, width, height);

    const blob = await canvas.convertToBlob({
      type: 'image/jpeg',
      quality: 0.8,
    });

    const base64 = await new Promise<string>((resolve, reject) => {
      const reader = new FileReader();
      reader.onloadend = () => {
        const result = reader.result as string;
        const base64Data = result.split(',')[1];
        resolve(base64Data);
      };
      reader.onerror = () => reject(new Error('Failed to read compressed blob'));
      reader.readAsDataURL(blob);
    });

    return {
      data: base64,
      mimeType: 'image/jpeg',
    };
  } finally {
    // Explicitly close the ImageBitmap to prevent GPU/graphics memory leaks.
    bitmap.close();
  }
}