import struct, os, sys

def _png_size(data):
    # PNG IHDR chunk at offset 16: 4 bytes width, 4 bytes height
    return struct.unpack_from('>II', data, 16)

def png_to_ico(png_path, ico_path):
    with open(png_path, 'rb') as f:
        png_data = f.read()
    w, h = _png_size(png_data)
    png_data = png_data  # full PNG data as icon payload
    header = struct.pack('<HHH', 0, 1, 1)
    entry = struct.pack('<BBBBHHII',
        w if w < 256 else 0,
        h if h < 256 else 0,
        0, 0, 1, 32, len(png_data), 22)
    with open(ico_path, 'wb') as f:
        f.write(header + entry + png_data)

if __name__ == '__main__':
    png_to_ico(sys.argv[1], sys.argv[2])