"""
Performance metrics for comparing original and mosaic images
"""
import numpy as np
from PIL import Image
from skimage.metrics import structural_similarity as ssim
import cv2


def resize_to_match(original, mosaic):
    """Resize mosaic to match original image dimensions"""
    return mosaic.resize(original.size, Image.BICUBIC)


def calculate_mse(original, mosaic):
    """
    Calculate Mean Squared Error between two images
    Lower values indicate better similarity (0 = perfect match)
    """
    mosaic_resized = resize_to_match(original, mosaic)

    orig_array = np.array(original, dtype=np.float32)
    mosaic_array = np.array(mosaic_resized, dtype=np.float32)

    mse = np.mean((orig_array - mosaic_array) ** 2)
    return float(mse)


def calculate_ssim(original, mosaic):
    """
    Calculate Structural Similarity Index
    Range: [-1, 1], higher values indicate better similarity (1 = perfect match)
    """
    mosaic_resized = resize_to_match(original, mosaic)

    # Convert to grayscale for SSIM calculation
    orig_gray = np.array(original.convert('L'))
    mosaic_gray = np.array(mosaic_resized.convert('L'))

    ssim_value = ssim(orig_gray, mosaic_gray)
    return float(ssim_value)


def calculate_histogram_correlation(original, mosaic):
    """
    Calculate histogram correlation for each RGB channel
    Range: [-1, 1], higher values indicate better similarity
    """
    mosaic_resized = resize_to_match(original, mosaic)

    orig_array = np.array(original)
    mosaic_array = np.array(mosaic_resized)

    correlations = []
    for channel in range(3):  # RGB channels
        hist_orig = cv2.calcHist([orig_array[:, :, channel]], [0], None, [256], [0, 256])
        hist_mosaic = cv2.calcHist([mosaic_array[:, :, channel]], [0], None, [256], [0, 256])

        # Normalize histograms
        hist_orig = hist_orig.flatten() / np.sum(hist_orig)
        hist_mosaic = hist_mosaic.flatten() / np.sum(hist_mosaic)

        # Calculate correlation
        correlation = np.corrcoef(hist_orig, hist_mosaic)[0, 1]
        correlations.append(correlation)

    return float(np.mean(correlations))


def calculate_edge_similarity(original, mosaic):
    """
    Calculate edge similarity using Canny edge detection
    Range: [0, 1], higher values indicate better similarity
    """
    mosaic_resized = resize_to_match(original, mosaic)

    # Convert to grayscale
    orig_gray = np.array(original.convert('L'))
    mosaic_gray = np.array(mosaic_resized.convert('L'))

    # Apply Canny edge detection
    orig_edges = cv2.Canny(orig_gray, 50, 150)
    mosaic_edges = cv2.Canny(mosaic_gray, 50, 150)

    # Calculate intersection over union (IoU) of edges
    intersection = np.logical_and(orig_edges, mosaic_edges).sum()
    union = np.logical_or(orig_edges, mosaic_edges).sum()

    if union == 0:
        return 1.0  # No edges in either image

    edge_similarity = intersection / union
    return float(edge_similarity)


def calculate_all_metrics(original, mosaic):
    """
    Calculate all performance metrics and return as dictionary
    """
    metrics = {}

    try:
        metrics['MSE'] = calculate_mse(original, mosaic)
        metrics['SSIM'] = calculate_ssim(original, mosaic)
        metrics['Histogram_Correlation'] = calculate_histogram_correlation(original, mosaic)
        metrics['Edge_Similarity'] = calculate_edge_similarity(original, mosaic)

        # Calculate overall quality score
        metrics['Overall_Quality'] = (
            metrics['SSIM'] * 0.4 +
            metrics['Histogram_Correlation'] * 0.3 +
            metrics['Edge_Similarity'] * 0.3
        )

    except Exception as e:
        print(f"Error calculating metrics: {e}")
        # Return default values if calculation fails
        metrics = {
            'MSE': float('nan'),
            'SSIM': float('nan'),
            'Histogram_Correlation': float('nan'),
            'Edge_Similarity': float('nan'),
            'Overall_Quality': float('nan')
        }

    return metrics


def format_metrics_report(metrics):
    """
    Format metrics into a readable report string
    """
    if not metrics:
        return "No metrics calculated"

    report = "Performance Metrics:\n\n"

    # Core metrics
    mse = metrics.get('MSE', float('nan'))
    ssim_val = metrics.get('SSIM', float('nan'))
    hist_corr = metrics.get('Histogram_Correlation', float('nan'))
    edge_sim = metrics.get('Edge_Similarity', float('nan'))

    if not np.isnan(mse):
        report += f"MSE: {mse:.2f} (lower is better)\n"
    if not np.isnan(ssim_val):
        report += f"SSIM: {ssim_val:.4f} (higher is better)\n"
    if not np.isnan(hist_corr):
        report += f"Histogram Correlation: {hist_corr:.4f} (higher is better)\n"
    if not np.isnan(edge_sim):
        report += f"Edge Similarity: {edge_sim:.4f} (higher is better)\n\n"

    # Overall quality
    overall = metrics.get('Overall_Quality', float('nan'))
    if not np.isnan(overall):
        report += f"Overall Quality Score: {overall:.4f}\n"

        if overall > 0.8:
            report += "Quality: Excellent"
        elif overall > 0.6:
            report += "Quality: Good"
        elif overall > 0.4:
            report += "Quality: Fair"
        elif overall > 0.2:
            report += "Quality: Poor"
        else:
            report += "Quality: Very Poor"

    return report