from argparse import ArgumentParser
from pathlib import Path

import cv2 as cv


parser = ArgumentParser(description="Subtract a video background with OpenCV MOG2.")
parser.add_argument("input_video", help="Input video path.")
parser.add_argument("mask_video", help="Output video path for the foreground mask.")
parser.add_argument(
    "--preview",
    default="output/foreground-mask-preview.png",
    help="Output PNG path for the strongest mask frame.",
)
parser.add_argument("--history", type=int, default=80)
parser.add_argument("--var-threshold", type=float, default=25.0)
parser.add_argument("--warmup", type=int, default=12)
args = parser.parse_args()

capture = cv.VideoCapture(args.input_video)
if not capture.isOpened():
    raise SystemExit(f"Could not open video: {args.input_video}")

fps = capture.get(cv.CAP_PROP_FPS) or 25.0
width = int(capture.get(cv.CAP_PROP_FRAME_WIDTH))
height = int(capture.get(cv.CAP_PROP_FRAME_HEIGHT))
if width <= 0 or height <= 0:
    raise SystemExit("Could not read frame size from the input video.")