"""Generate solid-colour placeholder PNG icons for the PWA manifest."""
import struct
import zlib
from pathlib import Path


def _chunk(chunk_type, data):
    c = chunk_type + data
    crc = struct.pack(">I", zlib.crc32(c) & 0xFFFFFFFF)
    return struct.pack(">I", len(data)) + c + crc


def solid_png(width, height, r, g, b):
    header = b"\x89PNG\r\n\x1a\n"
    ihdr = _chunk(b"IHDR", struct.pack(">IIBBBBB", width, height, 8, 2, 0, 0, 0))
    raw = bytearray()
    for _ in range(height):
        raw.append(0)
        raw.extend(bytes([r, g, b]) * width)
    idat = _chunk(b"IDAT", zlib.compress(bytes(raw)))
    iend = _chunk(b"IEND", b"")
    return header + ihdr + idat + iend


if __name__ == "__main__":
    dst = Path(__file__).parent
    for size in (192, 512):
        path = dst / f"icon-{size}.png"
        path.write_bytes(solid_png(size, size, 0x1A, 0x1A, 0x2E))
        print(f"Created {path.name} ({size}x{size})")