class Packet:
    """Represents an 8-byte I2C packet."""
    LENGTH = 8

    def __init__(self, data=None):
        if data is None:
            data = [0] * self.LENGTH
        if len(data) != self.LENGTH:
            raise ValueError(f"Packet must be {self.LENGTH} bytes")
        self.bytes = data

    @classmethod
    def from_bytes(cls, byte_list):
        """Create Packet from list of bytes."""
        return cls(byte_list[:cls.LENGTH])

    def __getitem__(self, idx):
        return self.bytes[idx]

    def __setitem__(self, idx, value):
        self.bytes[idx] = value

    def __repr__(self):
        fields = [f"Byte {i}: 0x{b:02X}" for i, b in enumerate(self.bytes)]
        return "\n".join(fields)

    def as_list(self):
        return self.bytes

    def is_valid(self):
        """Verify checksum (XOR of bytes 0-6 equals byte 7)."""
        cs = 0
        for b in self.bytes[:-1]:
            cs ^= b
        return cs == self.bytes[-1]

def create_motor_state_packet(fl=None, fr=None, bl=None, br=None):
    """
    Create an 8-byte packet to set motor states for I2C transfer.
    Packet format:
    [0x01, 0x00, FL, FR, BL, BR, 0x00, checksum]
    - 0x01: Command for Motor State Packet
    - 0x00: Target/channel (set as needed)
    - FL, FR, BL, BR: Motor states (0x00 = off, 0x01 = forward, 0x02 = backward)
    - checksum: XOR of bytes 0-6
    """
    def getByteForState(state):
        if state:
            return 0x01
        elif not state:
            return 0x02
        else: 
            return 0x00

    packet = [0x01, 0x00, getByteForState(fl), getByteForState(fr), getByteForState(bl), getByteForState(br), 0x00]
    checksum = 0
    for b in packet:
        checksum ^= b
    packet.append(checksum)
    return Packet.from_bytes(bytes(packet))

def create_tail_wagging_packet(wagging=False):
    """
    Create an 8-byte packet to set wagging for I2C transfer.
    Packet format:
    [0x02, 0x00, Wagging, 0x00, 0x00, 0x00, 0x00, checksum]
    - 0x02: Command for Wagging Packet
    - 0x00: Target/channel (set as needed)
    - Wagging: 0x00 = false, 0x01 = true
    - checksum: XOR of bytes 0-6
    """
    packet = [0x02, 0x00, 0x01 if wagging else 0x00, 0x00, 0x00, 0x00, 0x00]
    checksum = 0
    for b in packet:
        checksum ^= b
    packet.append(checksum)
    return Packet.from_bytes(bytes(packet))

def create_set_led_mode(mode=0):
    """
    Create an 8-byte packet to set led mode for I2C transfer.
    Packet format:
    [0x02, 0x00, Mode, 0x00, 0x00, 0x00, 0x00, checksum]
    - 0x02: Command for led mode
    - 0x00: Target/channel (set as needed)
    - Wagging: 0x00 = standard, 0x01 = rot, 0x02 = rainbow
    - checksum: XOR of bytes 0-6
    """
    packet = [0x02, 0x00, mode & 0xFF, 0x00, 0x00, 0x00, 0x00]
    checksum = 0
    for b in packet:
        checksum ^= b
    packet.append(checksum)
    return Packet.from_bytes(bytes(packet))