Euro Driving Licence Photo Generator

function processImage(originalImg, outputMode = 'single', dpi = 300) {
    // Standard European Driving Licence photo dimensions: 35 mm x 45 mm
    const mmToInch = 25.4;
    
    // Validate and fallback parameters
    let parsedDpi = Number(dpi);
    if (isNaN(parsedDpi) || parsedDpi <= 0) parsedDpi = 300;
    
    let mode = (typeof outputMode === 'string') ? outputMode.trim().toLowerCase() : 'single';
    if (mode !== 'single' && mode !== 'print') mode = 'single';

    // Calculate exact pixel dimensions for 35x45mm at the specified DPI
    const photoWidthPx = Math.round((35 / mmToInch) * parsedDpi);
    const photoHeightPx = Math.round((45 / mmToInch) * parsedDpi);

    // 1. Create the single cropped Euro Licence Photo
    const photoCanvas = document.createElement('canvas');
    photoCanvas.width = photoWidthPx;
    photoCanvas.height = photoHeightPx;
    const ctx = photoCanvas.getContext('2d');
    
    // Fill white background in case of transparent images (like PNGs with no background)
    ctx.fillStyle = '#ffffff';
    ctx.fillRect(0, 0, photoWidthPx, photoHeightPx);

    // Smart Center Cropping Logic to match required aspect ratio
    const imgRatio = originalImg.width / originalImg.height;
    const targetRatio = photoWidthPx / photoHeightPx;
    
    let srcX = 0, srcY = 0;
    let srcW = originalImg.width, srcH = originalImg.height;
    
    if (imgRatio > targetRatio) {
        // Source image is wider than the target aspect ratio, crop the sides
        srcW = originalImg.height * targetRatio;
        srcX = (originalImg.width - srcW) / 2;
    } else {
        // Source image is taller than the target aspect ratio, crop top and bottom
        srcH = originalImg.width / targetRatio;
        // Shift focus by approx 15% towards the top, as faces in ID photos are usually upper-center
        srcY = (originalImg.height - srcH) * 0.15; 
    }
    
    // Draw and scale the cropped portion onto the photo canvas
    ctx.drawImage(originalImg, srcX, srcY, srcW, srcH, 0, 0, photoWidthPx, photoHeightPx);

    // Return the single standard photo if "single" mode is selected
    if (mode === 'single') {
        return photoCanvas;
    }

    // 2. Create a 4x6" Sheet with cut-guides for printing (if mode === 'print')
    const sheetCanvas = document.createElement('canvas');
    const sheetWidthPx = Math.round(4 * parsedDpi);   // 4 inches wide
    const sheetHeightPx = Math.round(6 * parsedDpi);  // 6 inches tall
    
    sheetCanvas.width = sheetWidthPx;
    sheetCanvas.height = sheetHeightPx;
    const pCtx = sheetCanvas.getContext('2d');

    // Fill standard white paper background
    pCtx.fillStyle = '#ffffff';
    pCtx.fillRect(0, 0, sheetWidthPx, sheetHeightPx);

    // Fit 6 photos perfectly onto a 4x6 inch paper (2 columns, 3 rows)
    const cols = 2;
    const rows = 3;
    
    const gridWidth = cols * photoWidthPx;
    const gridHeight = rows * photoHeightPx;
    
    // Space the photos evenly
    const gapX = (sheetWidthPx - gridWidth) / (cols + 1);
    const gapY = (sheetHeightPx - gridHeight) / (rows + 1);

    for (let r = 0; r < rows; r++) {
        for (let c = 0; c < cols; c++) {
            const x = Math.round(gapX + c * (photoWidthPx + gapX));
            const y = Math.round(gapY + r * (photoHeightPx + gapY));
            
            // Render the generated photo
            pCtx.drawImage(photoCanvas, x, y);
            
            // Draw subtle gray standard cut-lines
            pCtx.lineWidth = 1;
            pCtx.strokeStyle = '#cccccc';
            pCtx.strokeRect(x, y, photoWidthPx, photoHeightPx);
        }
    }
    
    return sheetCanvas;
}