from crc import Calculator, Crc8
from typing import Optional, Tuple
from dataclasses import dataclass
from enum import IntEnum
from struct import pack, unpack


PKT_START_SEQUENCE = [0xDE, 0xAD]


class Settings(IntEnum):
    TriggerThreshold = 0
    TriggerPeriod = 1
    DecayValue = 2
    DecayPeriod = 3
    Gain = 4
    CenterFreq = 5
    SamplingEnabled = 6


@dataclass
class CommandPacket:
    is_write: bool
    setting: Settings
    value: int

    def serialize(self) -> bytearray:
        buf = bytearray()

        # TODO raise exception if setting is invalid here
        buf.extend(PKT_START_SEQUENCE)
        command = int(self.setting)
        if self.is_write:
            command |= 1 << 7
        buf.append(command)
        buf.extend(pack("<I", self.value))

        # Append CRC
        crc = Calculator(Crc8.MAXIM_DOW).checksum(buf)
        buf.append(crc)

        return buf



@dataclass
class ResponsePacket:
    # Deserialization
    is_error: bool
    setting: Settings
    value: int


class PacketParser:
    def __init__(self):
        self.crc = Calculator(Crc8.MAXIM_DOW)
        self.reset()


    def parse_byte(self, b: int) -> Optional[ResponsePacket]:
        byte_index = len(self.packet_data)

        if byte_index == 0:
            if b != PKT_START_SEQUENCE[0]:
                self.reset()
                return

        elif byte_index == 1:
            if b != PKT_START_SEQUENCE[1]:
                self.reset()
                return

        elif byte_index == 7:
            # Final CRC byte, check and generate data
            packet = None
            if self.crc.verify(self.packet_data, b):
                packet = self.build_response_packet()

            self.reset()
            return packet

        # Pull packet data in otherwise
        self.packet_data.append(b)


    def parse_bytearray(self, bytes: bytearray) -> Tuple[bytearray, Optional[ResponsePacket]]:
        """
        Parse a bytearray for a packet. Returns a bytearray of bytes that haven't been processed.
        """
        for offset, byte in enumerate(bytes):
            packet = self.parse_byte(byte)

            if packet is not None:
                # Return packet and consumed bytearray
                return (bytes[offset:], packet)

        # No packets found, entire buffer has been read
        return (bytearray(), None)


    def build_response_packet(self) -> ResponsePacket:
        """Builds a response packet out of the data we have received"""
        if len(self.packet_data) < 7:
            raise Exception("Invalid amount of packet data received!")

        is_error = self.packet_data[2] & 0x80 != 0
        setting = Settings(self.packet_data[2] & 0x7F)
        value = unpack("<I", self.packet_data[3:7])

        return ResponsePacket(is_error, setting, value)

    def reset(self):
        self.packet_data = bytearray()