#!/usr/bin/env python3
"""Fail if any recorded frame contains a near-white opaque block.

This is the image-level regression guard for the P13/P14 lantern blow-out: a
premultiplied-alpha mistake painted ~75x75 pure white (255,255,255) squares
where the night lantern glow should fall off softly.

A "white block" is any window of at least MIN_SIDE x MIN_SIDE pixels where every
pixel is fully opaque (alpha >= 250) and every colour channel is >= 250.

Usage:
    python3 scripts/check-no-white-blocks.py <png-or-dir> [more...]

Exit code 0 when clean, 1 when a block is found, 2 on usage/read error.
"""

import os
import sys

import numpy as np
from PIL import Image

MIN_SIDE = 64
CHANNEL_MIN = 250
ALPHA_MIN = 250


def first_white_block(path, min_side=MIN_SIDE):
    image = Image.open(path)
    rgba = np.asarray(image.convert("RGBA"), dtype=np.uint8)
    if rgba.shape[0] < min_side or rgba.shape[1] < min_side:
        return None
    white_opaque = (
        (rgba[:, :, 0] >= CHANNEL_MIN)
        & (rgba[:, :, 1] >= CHANNEL_MIN)
        & (rgba[:, :, 2] >= CHANNEL_MIN)
        & (rgba[:, :, 3] >= ALPHA_MIN)
    ).astype(np.int64)
    # Summed-area table so any k x k window is one lookup.
    integral = np.zeros((white_opaque.shape[0] + 1, white_opaque.shape[1] + 1), dtype=np.int64)
    integral[1:, 1:] = white_opaque.cumsum(0).cumsum(1)
    rows, cols = white_opaque.shape
    for y in range(0, rows - min_side + 1):
        for x in range(0, cols - min_side + 1):
            total = (
                integral[y + min_side, x + min_side]
                - integral[y, x + min_side]
                - integral[y + min_side, x]
                + integral[y, x]
            )
            if total == min_side * min_side:
                return (x, y, min_side, min_side)
    return None


def iter_pngs(targets):
    for target in targets:
        if os.path.isdir(target):
            for root, _, files in os.walk(target):
                for name in sorted(files):
                    if name.lower().endswith(".png"):
                        yield os.path.join(root, name)
        else:
            yield target


def main(argv):
    if len(argv) < 2:
        sys.stderr.write(__doc__)
        return 2
    checked = 0
    failures = []
    for path in iter_pngs(argv[1:]):
        try:
            block = first_white_block(path)
        except Exception as error:  # noqa: BLE001 - report and continue
            sys.stderr.write(f"unreadable: {path}: {error}\n")
            return 2
        checked += 1
        if block is not None:
            x, y, side, _ = block
            failures.append(f"{path}: white block {side}x{side} at ({x},{y})")
    for line in failures:
        print(f"FAIL {line}")
    if failures:
        print(f"checked={checked} failures={len(failures)}")
        return 1
    print(f"checked={checked} failures=0 OK")
    return 0


if __name__ == "__main__":
    raise SystemExit(main(sys.argv))