from pm3py.core.protocol import crc16_a

def test_crc16_a_empty():
    assert crc16_a(b"") == 0x6363  # init 0xC6C6 reflected = 0x6363

def test_crc16_a_known_vector():
    # Verified against C implementation: compute_crc(CRC_14443_A, ...)
    # "123456789" is the standard CRC check string
    data = b"123456789"
    assert crc16_a(data) == 0xBF05

def test_crc16_a_ping_preamble():
    # A CMD_PING preamble: magic=0x61334d50, length|ng=0x8020, cmd=0x0109
    preamble = bytes.fromhex("504d3361208001090102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f")
    crc = crc16_a(preamble)
    assert isinstance(crc, int)
    assert 0 <= crc <= 0xFFFF