import cv2
import numpy as np
from skimage.metrics import structural_similarity
import matplotlib.pyplot as plt
import os

def compare_videos(video1_path, video2_path):
    # Open video files
    vidcap1 = cv2.VideoCapture(video1_path)
    vidcap2 = cv2.VideoCapture(video2_path)
    
    # Check if videos opened successfully
    if not vidcap1.isOpened() or not vidcap2.isOpened():
        raise ValueError("Error opening video files.")
    
    # Get video properties
    fps1 = vidcap1.get(cv2.CAP_PROP_FPS)
    fps2 = vidcap2.get(cv2.CAP_PROP_FPS)
    frame_count1 = int(vidcap1.get(cv2.CAP_PROP_FRAME_COUNT))
    frame_count2 = int(vidcap2.get(cv2.CAP_PROP_FRAME_COUNT))
    
    # Ensure videos have same duration (frame count)
    if frame_count1 != frame_count2 or abs(fps1 - fps2) > 0.1:
        vidcap1.release()
        vidcap2.release()
        raise ValueError("Videos must have the same duration and frame rate.")
    
    # Initialize lists for SSIM scores
    ssim_scores = []
    frame_number = 0
    
    # Video writer for difference video
    width = int(vidcap1.get(cv2.CAP_PROP_FRAME_WIDTH))
    height = int(vidcap1.get(cv2.CAP_PROP_FRAME_HEIGHT))
    out = cv2.VideoWriter(
        "utils/output/difference_video.mp4",
        cv2.VideoWriter_fourcc(*"mp4v"),
        fps1,
        (width, height),
        isColor=True
    )
    
    while True:
        success1, image1 = vidcap1.read()
        success2, image2 = vidcap2.read()
        
        if not success1 or not success2:
            break
        
        # Resize second video frame to match first video's resolution
        image2 = cv2.resize(image2, (width, height))
        
        # Convert to grayscale
        image1_gray = cv2.cvtColor(image1, cv2.COLOR_BGR2GRAY)
        image2_gray = cv2.cvtColor(image2, cv2.COLOR_BGR2GRAY)
        
        # Compute SSIM
        score, diff = structural_similarity(image1_gray, image2_gray, full=True)
        ssim_scores.append((1 - score) * 100)  # Convert to percentage difference
        
        # Convert difference to 8-bit unsigned for visualization
        diff = (diff * 255).astype("uint8")
        diff_color = cv2.cvtColor(diff, cv2.COLOR_GRAY2BGR)
        
        # Write to output video
        out.write(diff_color)
        
        frame_number += 1
    
    # Release resources
    vidcap1.release()
    vidcap2.release()
    out.release()
    
    # Plot differences
    plt.figure(figsize=(10, 6))
    plt.plot(range(frame_number), ssim_scores, 'ro-', markersize=2)
    plt.title("Frame-by-Frame Difference (SSIM)")
    plt.xlabel("Frame Number")
    plt.ylabel("Difference (%)")
    plt.grid(True)
    plot_path = "utils/output/difference_plot.png"
    plt.savefig(plot_path)
    plt.close()
    
    return plot_path, "utils/output/difference_video.mp4"