opaldecode.py

#!/usr/bin/env python3

import binascii
import enum
import typing


class Mode(enum.IntEnum):
    RAIL = 0
    FERRY = 1
    BUS = 2


class Usage(enum.IntEnum):
    UNUSED = 0
    NEW_JOURNEY = 1
    TRANSFER_SAME_MODE = 2
    TRANSFER_INTERMODE = 3
    NEW_JOURNEY_MCQ = 4
    TRANSFER_SAME_MODE_MCQ = 5
    TRANSFER_INTERMODE_MCQ = 6
    DISTANCE_BASED_FARE = 7
    FLAT_FARE = 8
    AUTO_COMPLETE_JOURNEY = 9
    END_NO_START = 10
    TAP_REVERSAL = 11
    UNSUCCESSFUL = 12


class FreeReadData(typing.NamedTuple):
    serial: str
    serial_check: int
    blocked: bool
    seq_num: int
    balance: int
    last_date: int
    last_time: int
    last_mode: Mode
    last_usage: Usage
    auto_topup_enabled: bool
    journey_count: int
    crc16: int


def twos_complement(input_value: int, num_bits: int) -> int:
    """Calculate a two's complement integer from the given input value's bits."""
    mask = 1 << (num_bits - 1)
    return (input_value & ~mask) - (input_value & mask)


def split_bits(data: int, num_bits: int) -> typing.Tuple[int, int]:
    return data & ((1 << num_bits) - 1), data >> num_bits


def parse_data(b: bytes) -> FreeReadData:
    assert len(b) == 16
    data = int.from_bytes(b, "little")

    serial = "%09d" % (data & 0xFFFFFFFF)
    data >>= 32
    serial_check = data & 0xF
    data >>= 4
    blocked = bool(data & 1)
    data >>= 1
    seq_num = data & 0xFFFF
    data >>= 16
    balance_unsigned, data = split_bits(data, 21)
    last_date, data = split_bits(data, 15)
    last_time, data = split_bits(data, 11)
    last_mode = Mode(data & 0b111)
    data >>= 3
    last_usage = Usage(data & 0xF)
    data >>= 4
    auto_topup_enabled = bool(data & 1)
    data >>= 1
    journey_count = data & 0xF
    data >>= 4
    crc16 = data

    balance = twos_complement(balance_unsigned, 21)

    return FreeReadData(
        serial,
        serial_check,
        blocked,
        seq_num,
        balance,
        last_date,
        last_time,
        last_mode,
        last_usage,
        auto_topup_enabled,
        journey_count,
        crc16,
    )


if __name__ == "__main__":
    b = bytes.fromhex(input())
    data = parse_data(b)
    print(data)
    # print(binascii.crc_hqx(b[:-2], 0))