doneit-web/src/app/utils/imageCompressore.ts

import { err, ok, Result } from "neverthrow";

/**
 * Compresses an image represented as a Base64 string.
 *
 * This function resizes the image to fit within the specified maximum width and height while maintaining the aspect ratio.
 * The image is then compressed to a JPEG format with the given quality level.
 *
 * @param base64String - The Base64 string of the image to be compressed.
 * @param maxWidth - The maximum width of the compressed image. The aspect ratio is preserved.
 * @param maxHeight - The maximum height of the compressed image. The aspect ratio is preserved.
 * @param quality - The quality of the compressed image, ranging from 0 to 1, where 1 is the best quality.
 *
 * @returns A Promise that resolves to a `Result` containing either:
 * - `ok` with the compressed image as a Base64 string, or
 * - `err` with an error if the image fails to load or compress.
 *
 * @example
 * ```typescript
 * compressImageBase64('data:image/png;base64,...', 800, 600, 0.8)
 *   .then(result => {
 *     if (result.isOk()) {
 *       console.log('Compressed image:', result.value);
 *     } else {
 *       console.error('Error compressing image:', result.error);
 *     }
 *   });
 * ```
 */
export function compressImageBase64(base64String: string, maxWidth: number, maxHeight: number, quality: number): Promise<Result<string, any>> {
  return new Promise((resolve, reject) => {
    const image = new Image();
    image.src = base64String;

    image.onload = async () => {
      const canvas = document.createElement('canvas');
      let newWidth = image.width;
      let newHeight = image.height;

      if (newWidth > maxWidth) {
        newHeight *= maxWidth / newWidth;
        newWidth = maxWidth;
      }

      if (newHeight > maxHeight) {
        newWidth *= maxHeight / newHeight;
        newHeight = maxHeight;
      }

      canvas.width = newWidth;
      canvas.height = newHeight;

      const context = canvas.getContext('2d');
      context?.drawImage(image, 0, 0, newWidth, newHeight);

      const compressedBase64 = canvas.toDataURL('image/jpeg', quality);

      // Calculate the compression percentage
      const originalSize = base64String.length;
      const compressedSize = compressedBase64.length;
      const compressionPercentage = ((originalSize - compressedSize) / originalSize) * 100;

      console.log(`Compression achieved: ${compressionPercentage.toFixed(2)}%`);

      resolve(ok(compressedBase64));
    };

    image.onerror = (error) => {
      resolve(err(error));
    };
  });
}