"""Convert the original GoldSrc additive explosion into a portable PNG atlas.

Read-only on the Half-Life installation. No native SPR importer needed at runtime.
"""
import argparse
import hashlib
import json
import struct
from pathlib import Path

from PIL import Image

ROOT = Path(__file__).resolve().parents[1]


def extract(source: Path, destination: Path) -> dict:
    raw = source.read_bytes()
    ident, version, orientation, fmt, radius, width, height, count, beam, sync = (
        struct.unpack_from('<4siiifiiifi', raw)
    )
    assert (ident, version, fmt) == (b'IDSP', 2, 1), 'Expected GoldSrc additive SPR v2'
    palette_count = struct.unpack_from('<H', raw, 40)[0]
    assert 1 <= palette_count <= 256 and count == 15 and (width, height) == (64, 64)
    palette = raw[42:42 + palette_count * 3]
    offset = 42 + len(palette)
    columns, rows, gutter = 5, 3, 2
    tile_w, tile_h = width + 2 * gutter, height + 2 * gutter
    atlas = Image.new('RGB', (columns * tile_w, rows * tile_h))
    origins = []
    for index in range(count):
        kind, x, y, w, h = struct.unpack_from('<5i', raw, offset)
        assert kind == 0 and (w, h) == (width, height), 'Unsupported frame/group'
        offset += 20
        pixels = raw[offset:offset + w * h]
        assert len(pixels) == w * h and max(pixels) < palette_count
        frame = Image.frombytes('P', (w, h), pixels)
        frame.putpalette(palette)
        # Preserve RGB: black contributes zero under additive blending, NOT alphatest.
        atlas.paste(frame.convert('RGB'),
                    ((index % columns) * tile_w + gutter, (index // columns) * tile_h + gutter))
        origins.append([x, y])
        offset += w * h
    assert offset == len(raw), 'Trailing or truncated sprite data'
    destination.mkdir(parents=True, exist_ok=True)
    output = destination / 'zerogxplode_atlas.png'
    atlas.save(output, optimize=True)
    manifest = {
        'source': 'Half-Life/valve/sprites/zerogxplode.spr',
        'source_sha256': hashlib.sha256(raw).hexdigest(),
        'destination': str(output.relative_to(ROOT)),
        'destination_sha256': hashlib.sha256(output.read_bytes()).hexdigest(),
        'format': 'IDSP v2 / SPR_ADDITIVE', 'frame_size': [width, height],
        'frame_count': count, 'columns': columns, 'rows': rows, 'gutter': gutter,
        'origins': origins, 'fps': 15,
        'fps_source': 'https://github.com/ValveSoftware/halflife/blob/master/dlls/ggrenade.cpp',
    }
    (destination / 'source_manifest.json').write_text(json.dumps(manifest, indent=2) + '\n')
    return manifest


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--source', type=Path, default=Path.home() /
                        '.steam/steam/steamapps/common/Half-Life/valve/sprites/zerogxplode.spr')
    args = parser.parse_args()
    print(json.dumps(extract(args.source, ROOT / 'assets/effects/explosion'), indent=2))