Photo Minimalist Mood Filter

function processImage(originalImg, saturation = 30, contrast = 120, brightness = 100, moodColor = "none", moodIntensity = 0.15) {
    // Ensure numeric parameters are within reasonable bounds.
    // CSS filters are generally forgiving, but this adds robustness.
    saturation = Math.max(0, saturation); // Percentage, typically 0-200+
    contrast = Math.max(0, contrast);   // Percentage, typically 0-200+
    brightness = Math.max(0, brightness); // Percentage, typically 0-200+
    moodIntensity = Math.max(0, Math.min(1, moodIntensity)); // Opacity, 0-1

    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');

    // Determine image dimensions. originalImg assumed to be a loaded HTMLImageElement.
    const imgWidth = originalImg.naturalWidth || originalImg.width;
    const imgHeight = originalImg.naturalHeight || originalImg.height;

    // Handle cases where image might not be loaded or has no dimensions
    if (imgWidth === 0 || imgHeight === 0) {
        console.error("Image has not loaded or has zero dimensions.");
        // Return a minimal canvas to avoid further errors downstream
        canvas.width = 1;
        canvas.height = 1;
        ctx.fillStyle = 'red'; // Indicate error
        ctx.fillRect(0,0,1,1);
        return canvas;
    }

    canvas.width = imgWidth;
    canvas.height = imgHeight;

    // 1. Apply base image adjustments (saturation, contrast, brightness)
    // These CSS-like filters apply to subsequent drawing operations on the context.
    let filterString = '';
    filterString += `saturate(${saturation}%) `;
    filterString += `contrast(${contrast}%) `;
    filterString += `brightness(${brightness}%)`;
    ctx.filter = filterString;

    // Draw the original image onto the canvas. It will be drawn with the filters applied.
    ctx.drawImage(originalImg, 0, 0, canvas.width, canvas.height);

    // 2. Apply mood color tint if specified
    // Check if moodColor is a valid string, not "none", not empty, and intensity is positive.
    if (moodColor && typeof moodColor === 'string' && moodColor.toLowerCase() !== "none" && moodColor.trim() !== "" && moodIntensity > 0) {
        // Reset the ctx.filter. We don't want the mood color rectangle itself
        // to be affected by the saturation/contrast/brightness filters.
        // The mood color should be pure and then blended onto the already-filtered image.
        ctx.filter = 'none';

        // Set the global composite operation for blending the mood color.
        // 'color': Preserves the luma of the destination (filtered image) and
        // adopts the hue and saturation of the source (mood color).
        // This is very effective for tinting.
        ctx.globalCompositeOperation = 'color';

        // Set the opacity for the mood color layer. This controls the strength of the tint.
        ctx.globalAlpha = moodIntensity;

        // Set the fill style to the specified mood color.
        ctx.fillStyle = moodColor;

        // Draw the mood color rectangle over the entire canvas.
        ctx.fillRect(0, 0, canvas.width, canvas.height);

        // Reset globalAlpha and globalCompositeOperation to their default values.
        // This is good practice if the context were to be used for further drawing,
        // though not strictly necessary here as we are about to return the canvas.
        ctx.globalAlpha = 1.0;
        ctx.globalCompositeOperation = 'source-over';
    }
    
    // Optionally, reset the filter on the context if it were to be used further.
    // ctx.filter = 'none'; // Not strictly needed as we return the canvas.

    return canvas;
}