import argparse

import cv2
import numpy as np


def main():
    parser = argparse.ArgumentParser(description="Overlay mask video on original video.")
    parser.add_argument("--video", required=True, help="Input video path (mp4).")
    parser.add_argument("--mask", required=True, help="Mask video path (mkv, single channel).")
    parser.add_argument("--output", required=True, help="Output mp4 path.")
    parser.add_argument("--alpha", type=float, default=0.3, help="Mask overlay strength.")
    args = parser.parse_args()

    cap = cv2.VideoCapture(args.video)
    mask_cap = cv2.VideoCapture(args.mask)
    if not cap.isOpened():
        raise RuntimeError(f"Failed to open video: {args.video}")
    if not mask_cap.isOpened():
        raise RuntimeError(f"Failed to open mask video: {args.mask}")

    fps = cap.get(cv2.CAP_PROP_FPS) or 25.0
    width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
    height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
    fourcc = cv2.VideoWriter_fourcc(*"mp4v")
    writer = cv2.VideoWriter(args.output, fourcc, fps, (width, height), isColor=True)

    frame_idx = 0
    try:
        while True:
            ret, frame = cap.read()
            ret_mask, mask = mask_cap.read()
            if not ret or not ret_mask:
                break

            if mask.ndim == 3:
                mask_gray = cv2.cvtColor(mask, cv2.COLOR_BGR2GRAY)
            else:
                mask_gray = mask

            if mask_gray.shape[0] != height or mask_gray.shape[1] != width:
                mask_gray = cv2.resize(mask_gray, (width, height), interpolation=cv2.INTER_NEAREST)

            color = np.zeros_like(frame)
            color[:, :, 1] = mask_gray
            overlay = cv2.addWeighted(frame, 1.0 - args.alpha, color, args.alpha, 0)
            writer.write(overlay)
            frame_idx += 1
    finally:
        cap.release()
        mask_cap.release()
        writer.release()

    print(f"Saved {frame_idx} frames to {args.output}")


if __name__ == "__main__":
    main()