Conga Busher Image Effect Generator

/**
 * Conga Busher Image Effect Generator
 * This applies a vibrant, trailing "conga line" effect to the original image, 
 * with retreating, slightly brushed/blurred, and hue-rotated echoes to simulate 
 * rhythm and motion behind the main subject.
 */
function processImage(
    originalImg, 
    trailCopies = 6, 
    offsetX = 35, 
    offsetY = 15, 
    scaleStep = 0.85, 
    opacityStep = 0.75, 
    hueStep = 45
) {
    // Parse parameters to ensure type safety while allowing string inputs
    const copies = parseInt(trailCopies, 10) || 6;
    const dx = parseFloat(offsetX) || 35;
    const dy = parseFloat(offsetY) || 15;
    const scaleDecay = parseFloat(scaleStep) || 0.85;
    const opacityDecay = parseFloat(opacityStep) || 0.75;
    const dhue = parseFloat(hueStep) || 45;

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

    // Calculate canvas bounding box so all trails fit nicely 
    let minX = 0, minY = 0;
    let maxX = originalImg.width, maxY = originalImg.height;

    for (let i = 0; i < copies; i++) {
        const s = Math.pow(scaleDecay, i);
        const cx = i * dx;
        const cy = i * dy;
        const bw = originalImg.width * s;
        const bh = originalImg.height * s;
        
        if (cx < minX) minX = cx;
        if (cy < minY) minY = cy;
        if (cx + bw > maxX) maxX = cx + bw;
        if (cy + bh > maxY) maxY = cy + bh;
    }

    // Add extra padding to account for the "Busher" blur expansion
    const maxBlur = copies * 2;
    const padding = maxBlur + 10;
    
    canvas.width = (maxX - minX) + (padding * 2);
    canvas.height = (maxY - minY) + (padding * 2);

    // Draw the "Conga" trail from back to front (highest index down to 0)
    for (let i = copies - 1; i >= 0; i--) {
        const s = Math.pow(scaleDecay, i);
        const cx = (i * dx) - minX + padding;
        const cy = (i * dy) - minY + padding;
        const alpha = Math.pow(opacityDecay, i);

        ctx.save();
        ctx.globalAlpha = alpha;
        
        // Apply the "Busher" (brush/blur) and vibrant color-shifting to the trailing conga line
        if (i > 0) {
            ctx.filter = `blur(${i * 1.5}px) hue-rotate(${i * dhue}deg) contrast(1.1) saturate(1.2)`;
        } else {
            // The main image in the front remains sharp and clear
            ctx.filter = 'none';
        }

        ctx.translate(cx, cy);
        ctx.scale(s, s);
        
        // Draw the current echo
        ctx.drawImage(originalImg, 0, 0);
        
        ctx.restore();
    }

    return canvas;
}