/**
 * Process image data to crop whitespace
 */
export async function cropImage(
  imageSrc: string, 
  options: {
    threshold?: number; // 0-255, higher means more colors are considered "white"
    padding?: number; // padding in pixels to keep around content
  } = {}
): Promise<string> {
  const { threshold = 252, padding = 20 } = options; // 252 covers pure white and very light compression artifacts

  return new Promise((resolve, reject) => {
    const img = new Image();
    // Enable CORS if needed, though usually data URLs don't need it
    img.crossOrigin = "anonymous"; 
    
    img.onload = () => {
      try {
        const canvas = document.createElement('canvas');
        canvas.width = img.width;
        canvas.height = img.height;
        const ctx = canvas.getContext('2d');
        
        if (!ctx) {
          resolve(imageSrc);
          return;
        }

        ctx.drawImage(img, 0, 0);
        const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
        const data = imageData.data;
        const { width, height } = canvas;

        // Check if pixel is "content" (darker than threshold)
        // Returns true if it is CONTENT
        const isContent = (r: number, g: number, b: number) => {
            return r < threshold || g < threshold || b < threshold;
        };

        let top = -1, bottom = -1, left = -1, right = -1;

        // Scan Top-down for top boundary
        for (let y = 0; y < height; y++) {
            for (let x = 0; x < width; x++) {
                const idx = (y * width + x) * 4;
                if (isContent(data[idx], data[idx+1], data[idx+2])) {
                    top = y;
                    break;
                }
            }
            if (top !== -1) break;
        }

        // If top is still -1, the image is empty (all white)
        if (top === -1) {
            resolve(imageSrc);
            return;
        }

        // Scan Bottom-up for bottom boundary
        for (let y = height - 1; y >= top; y--) {
            for (let x = 0; x < width; x++) {
                const idx = (y * width + x) * 4;
                if (isContent(data[idx], data[idx+1], data[idx+2])) {
                    bottom = y + 1;
                    break;
                }
            }
            if (bottom !== -1) break;
        }

        // Scan Left-right for left boundary
        // We only need to scan within the vertical bounds we found
        for (let x = 0; x < width; x++) {
            for (let y = top; y < bottom; y++) {
                const idx = (y * width + x) * 4;
                if (isContent(data[idx], data[idx+1], data[idx+2])) {
                    left = x;
                    break;
                }
            }
            if (left !== -1) break;
        }

        // Scan Right-left for right boundary
        for (let x = width - 1; x >= left; x--) {
            for (let y = top; y < bottom; y++) {
                const idx = (y * width + x) * 4;
                if (isContent(data[idx], data[idx+1], data[idx+2])) {
                    right = x + 1;
                    break;
                }
            }
            if (right !== -1) break;
        }

        // Calculate crop coordinates with padding
        const cropX = Math.max(0, left - padding);
        const cropY = Math.max(0, top - padding);
        
        // Calculate width/height ensuring we don't go out of bounds
        // right is exclusive index + 1, so width is right - left.
        // content width = right - left
        // target width = content width + 2 * padding
        // but limited by image bounds
        const contentWidth = right - left;
        const contentHeight = bottom - top;
        
        // Check if we found valid bounds
        if (contentWidth <= 0 || contentHeight <= 0) {
            resolve(imageSrc);
            return;
        }

        // Adjust padding to not exceed original image
        // Actually, we want the crop rect to include padding if it exists in source, 
        // or maybe just white pad if it doesn't?
        // The current logic `Math.max(0, left - padding)` keeps padding INSIDE the original image.
        // If the content is at the edge, we might want to ADD whitespace?
        // Usually cropping means reducing size. Let's stick to keeping what's in the image.
        
        const rectRight = Math.min(width, right + padding);
        const rectBottom = Math.min(height, bottom + padding);
        
        const finalWidth = rectRight - cropX;
        const finalHeight = rectBottom - cropY;

        const finalCanvas = document.createElement('canvas');
        finalCanvas.width = finalWidth;
        finalCanvas.height = finalHeight;
        const finalCtx = finalCanvas.getContext('2d');
        
        if (!finalCtx) {
             resolve(imageSrc);
             return;
        }

        // Fill with white in case of transparency (though we are copying from opaque usually)
        finalCtx.fillStyle = '#ffffff';
        finalCtx.fillRect(0, 0, finalWidth, finalHeight);

        finalCtx.drawImage(
            canvas, 
            cropX, cropY, finalWidth, finalHeight, // Source rect
            0, 0, finalWidth, finalHeight // Dest rect
        );

        resolve(finalCanvas.toDataURL('image/png'));

      } catch (e) {
        console.error("Image processing failed", e);
        resolve(imageSrc);
      }
    };
    img.onerror = (e) => {
        console.error("Image loading failed", e);
        resolve(imageSrc);
    };
    img.src = imageSrc;
  });
}