import cv2
import numpy as np
from scipy import signal
import matplotlib.pyplot as plt

def get_video_signal(path):
    cap = cv2.VideoCapture(path)
    motion_signal = []
    prev_gray = None
    
    while True:
        ret, frame = cap.read()
        if not ret:
            break
            
        # 1. Shrink the frame (makes it faster and removes noise)
        small_frame = cv2.resize(frame, (160, 90))
        gray = cv2.cvtColor(small_frame, cv2.COLOR_BGR2GRAY)
        
        if prev_gray is not None:
            # 2. Calculate the difference between this frame and the last
            # This detects the "movement" or "cuts"
            diff = cv2.absdiff(gray, prev_gray)
            motion_signal.append(np.sum(diff))
        else:
            motion_signal.append(0)
            
        prev_gray = gray
        
    cap.release()
    return np.array(motion_signal)

def find_offset(video_a, video_b):
    # print("Extracting signals (this may take a moment)...")
    sig_a = get_video_signal(video_a)
    # print("sig_a finished")
    sig_b = get_video_signal(video_b)
    # print("sig_b finished")

    # Normalize signals (subtract mean, divide by std dev) to improve correlation
    sig_a = (sig_a - np.mean(sig_a)) / (np.std(sig_a) + 1e-5)
    sig_b = (sig_b - np.mean(sig_b)) / (np.std(sig_b) + 1e-5)

    # Perform Cross-Correlation
    correlation = signal.correlate(sig_a, sig_b, mode='full')
    lags = signal.correlation_lags(len(sig_a), len(sig_b), mode='full')
    # plt.plot(lags)
    
    # The peak of the correlation is our offset in frames
    best_lag = lags[np.argmax(correlation)]
    
    return best_lag

# Usage
# for i in range(1, 12):
#     # print(f"{i:02}")
#     video_a = f"/home/honney/projects/mkv/AnoHana The Flower We Saw That Day (2011-2011) [imdbid-tt1913273]/Season 01/AnoHana The Flower We Saw That Day S01E0{i:02}.mkv"
#     video_b = f"/home/honney/projects/mkv/Anohana - The Flower We Saw That Day - S01 (BD 1080p HEVC Opus) [derpie]/[derpie] Anohana - The Flower We Saw That Day - S01E{i:02} (BD 1080p HEVC Opus) [Dual Audio].mkv"

#     offset_frames = find_offset(video_a, video_b)
#     print(f"{i}: Video B is offset by {offset_frames} frames relative to Video A.")

# print(f"{i:02}")
video_a = f"/home/honney/projects/mkv/output.mkv"
video_b = f"/home/honney/projects/mkv/Anohana - The Flower We Saw That Day - S01 (BD 1080p HEVC Opus) [derpie]/[derpie] Anohana - The Flower We Saw That Day - S01E01 (BD 1080p HEVC Opus) [Dual Audio].mkv"

offset_frames = find_offset(video_a, video_b)
print(f"Video B is offset by {offset_frames} frames relative to Video A.")