#!/usr/bin/env python3
"""Reject empty and nearly black captures by decoding pixels and measuring coverage."""
from __future__ import annotations

import argparse
import math
from pathlib import Path
import subprocess
import sys


LIMIT = ["taskset", "-c", "0-11", "prlimit", "--as=6442450944", "--"]


def inspect(path: Path) -> tuple[bool, str]:
    probe = subprocess.run([*LIMIT, "timeout", "30s", "ffmpeg", "-nostdin",
        "-hide_banner", "-loglevel", "error", "-i", str(path), "-frames:v", "1",
        "-f", "rawvideo", "-pix_fmt", "rgb24", "pipe:1"],
        stdout=subprocess.PIPE, stderr=subprocess.PIPE, timeout=30, check=False)
    if probe.returncode != 0 or not probe.stdout or len(probe.stdout) % 3:
        return False, f"decode_failed exit={probe.returncode} bytes={len(probe.stdout)}"
    raw = probe.stdout
    count = len(raw) // 3
    total = 0
    square_total = 0
    covered = 0
    for index in range(0, len(raw), 3):
        luminance = (77 * raw[index] + 150 * raw[index + 1] + 29 * raw[index + 2]) >> 8
        total += luminance
        square_total += luminance * luminance
        covered += luminance > 12
    mean = total / count
    variance = max(0.0, square_total / count - mean * mean)
    deviation = math.sqrt(variance)
    coverage = covered / count
    passed = deviation >= 2.0 and coverage >= 0.001
    return passed, (f"pixels={count} mean_luma={mean:.3f} stddev_luma={deviation:.3f} "
                    f"coverage_luma_gt12={coverage:.5f} thresholds=(stddev>=2.0,coverage>=0.001)")


def main() -> int:
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("image", type=Path)
    args = parser.parse_args()
    if not args.image.is_file():
        print(f"[CaptureQuality] image={args.image} status=FAIL reason=missing")
        return 1
    passed, detail = inspect(args.image)
    print(f"[CaptureQuality] image={args.image} {detail} status={'PASS' if passed else 'FAIL'}")
    return 0 if passed else 1


if __name__ == "__main__":
    raise SystemExit(main())