"""Generate kanjin.ico from a solid-colour PNG embedded in an ICO container."""
import struct
import zlib
from pathlib import Path


def _png_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_bytes(width, height, r, g, b):
    header = b"\x89PNG\r\n\x1a\n"
    ihdr = _png_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 = _png_chunk(b"IDAT", zlib.compress(bytes(raw)))
    iend = _png_chunk(b"IEND", b"")
    return header + ihdr + idat + iend


def make_ico(png_data):
    header = struct.pack("<HHH", 0, 1, 1)
    entry = struct.pack("<BBBBHHII", 0, 0, 0, 0, 1, 32, len(png_data), 22)
    return header + entry + png_data


if __name__ == "__main__":
    dst = Path(__file__).parent / "kanjin.ico"
    png = solid_png_bytes(256, 256, 0x1A, 0x1A, 0x2E)
    dst.write_bytes(make_ico(png))
    print(f"Created {dst.name}")