import atexit
import logging
import time
from enum import Enum
from multiprocessing import Process
from multiprocessing import Queue
from struct import error
from struct import unpack
from typing import Dict
from typing import List
from typing import Optional
from typing import Sequence
from typing import Tuple

from serial import Serial

from backend.monsun_backend.util import log_function_call

from . import commands
from .commands import Command
from .commands import CommandId
from .commands import Request
from .commands import Response
from .container import get_initialize_container

_logger = logging.getLogger(__file__)

_command_queue: Dict[str, Queue] = dict()
"""role name: command queue"""


class State(Enum):
    heart_beat = 0x0
    executing_command = 0x1
    executing_command_waiting_for_response = 0x2
    receiving_command = 0x10


def worker_process(
    role: str,
    queue: Queue,
):
    logging.basicConfig(
        level=logging.DEBUG,
        format="[%(asctime)s] [%(name)-20s] [%(levelname)-8s] --- %(message)s",
    )
    root_logger = logging.getLogger(role)
    root_logger.setLevel(logging.DEBUG)
    logger = root_logger.getChild("worker_process")
    logger.setLevel(logging.INFO)

    container = get_initialize_container()
    container.config.from_dict(
        {
            "role": role,
        },
    )
    heartbeat_interval = container.config.heartbeat_interval()
    serial_reconnection_wait_timeout = (
        container.config.serial_reconnection_wait_timeout()
    )
    connected = False

    logger.info("entering command loop...")
    while True:
        try:
            with container.serial() as serial:
                logger.info("connected with serial device")
                connected = True
                enter_fsm(
                    root_logger=root_logger,
                    serial=serial,
                    command_queue=queue,
                    heartbeat_interval=heartbeat_interval,
                )
        except OSError:
            if connected:
                logger.warning("connection to serial device lost")
            connected = False
            time.sleep(serial_reconnection_wait_timeout)
            logger.warning("reconnecting...")


def enter_fsm(
    root_logger: logging.Logger,
    serial: Serial,
    command_queue: Queue,
    heartbeat_interval: float,
):
    logger = root_logger.getChild("FSM")

    state = State.executing_command
    current_command: Optional[Command] = None
    responses_received: List[Response] = list()
    time_at_beginning_waiting_for_response: float = 0.0
    last_heart_beat_time: float = 0.0
    serial_receiver = SerialReceiver(
        root_logger=root_logger,
    )

    while True:
        if state == State.heart_beat:
            if time.time() - heartbeat_interval > last_heart_beat_time:
                command_queue.put(
                    commands.HeartbeatRequest(
                        root_logger=root_logger,
                    ),
                )
                last_heart_beat_time = time.time()

            state = State.executing_command
            continue

        elif state == State.executing_command:
            current_command = dequeue_command(queue=command_queue)
            if current_command is None:
                state = State.receiving_command
                continue

            current_command.execute(serial=serial)

            if isinstance(current_command, Request):
                time_at_beginning_waiting_for_response = time.time()
                state = State.executing_command_waiting_for_response
                continue

        elif state == State.executing_command_waiting_for_response:
            if not isinstance(current_command, Request):
                raise RuntimeError(
                    "entered state 'executing_command_waiting_for_response' but "
                    "current command does not expect a response.",
                )
            else:
                request: Request = current_command
            commands_, responses = serial_receiver.receive(
                serial=serial,
            )
            responses_received.extend(responses)
            for command in commands_:
                command_queue.put(command)

            while responses_received:
                received_response: Response = responses_received.pop(0)
                if request.response_identifier == received_response.identifier:
                    request.process_response(
                        response=received_response,
                    )
                    state = State.executing_command
                    break
                else:
                    logger.warning(
                        f"received response with ID {received_response.identifier} "
                        "but expected response with ID "
                        f"{request.response_identifier}",
                    )
            else:
                if (
                    time.time() - request.timeout
                    > time_at_beginning_waiting_for_response
                ):
                    logger.error(
                        "Timeout while waiting for response with ID "
                        f"{request.response_identifier}",
                    )
                    current_command = None
                    state = State.executing_command
                    continue

        elif state == State.receiving_command:
            commands_, responses = serial_receiver.receive(
                serial=serial,
            )
            responses_received.extend(responses)
            for command in commands_:
                command_queue.put(command)

            state = State.heart_beat
            continue

        else:
            raise RuntimeError(f"Invalid state: {state}")


def dequeue_command(
    queue: Queue,
) -> Optional[Command]:
    while not queue.empty():
        return queue.get()

    return None


def enqueue_command(
    role: str,
    command: Command,
):
    """Add a command to the command queue

    :param role: The role name
    :param command: The command to enqueue
    """
    _command_queue[role].put(command)


class CommandInterpretationError(Exception):
    """Raised in case the command could not be interpreted"""


class CommandBytesReadInsufficient(CommandInterpretationError):
    """Raised in case the command could not be interpreted"""


class CommandInterpreter:
    header_size = 4

    def __init__(
        self,
        root_logger: logging.Logger,
    ) -> None:
        self._logger = root_logger.getChild(self.__class__.__name__)
        self._logger.setLevel(logging.INFO)
        self.command_id_int = 0
        self.data_length = 0
        self.payload = bytes()

    def interpret(
        self,
        bytes_read: bytes,
    ) -> bytes:
        """Interpret the first command in a byte stream.

        :param bytes_read: The bytes which are not yet parsed.
        :returns: The byte which are not yet parsed.
        :raises CommandInterpretationError: If the command could not be parsed.
        :raises CommandBytesReadInsufficient: Not enough bytes to fully parse the
            command.
        """
        self._logger.debug(f"bytes: {bytes_read.hex()}")
        try:
            self.command_id_int, self.data_length, _ = unpack(
                ">BHB",
                bytes_read[: self.header_size],
            )
        except error:
            self._logger.error("error while interpreting command header")
            raise CommandBytesReadInsufficient()

        try:
            self.payload = bytes(
                bytes_read[self.header_size : self.header_size + self.data_length],
            )
        except IndexError:
            self._logger.error(
                "There are less bytes than expected: "
                f"Expected={self.header_size + self.data_length -1}, "
                f"received={len(bytes_read)}",
            )
            self._logger.debug(f"bytes: {bytes_read.hex()}")
            raise CommandBytesReadInsufficient()

        try:
            stop_byte = bytes_read[self.header_size + self.data_length]
        except IndexError:
            self._logger.error("could not get stop byte")
            raise CommandBytesReadInsufficient()

        if stop_byte != 0xFF:
            self._logger.error("Invalid stop byte")
            raise CommandInterpretationError()

        try:
            return bytes_read[self.header_size + self.data_length + 1 :]
        except IndexError:
            return bytes()


class SerialReceiver:
    def __init__(
        self,
        root_logger: logging.Logger,
    ) -> None:
        self.root_logger = root_logger
        self._logger = root_logger.getChild(self.__class__.__name__)
        self._logger.setLevel(logging.INFO)

        self._bytes_unread = bytearray()

    def receive(
        self,
        serial: Serial,
    ) -> Tuple[Sequence[Command], Sequence[Response]]:
        commands_received: List[Command] = list()
        responses_received: List[Response] = list()

        self._bytes_unread.extend(serial.read(serial.in_waiting))

        while self._bytes_unread:

            try:
                command_interpreter = CommandInterpreter(
                    root_logger=self.root_logger,
                )
                self._bytes_unread = bytearray(
                    command_interpreter.interpret(
                        bytes_read=self._bytes_unread,
                    ),
                )
            # except CommandBytesReadInsufficient:
            #     return commands_received, responses_received
            except CommandInterpretationError:
                return commands_received, responses_received

            try:
                command_id = CommandId(command_interpreter.command_id_int)
            except ValueError:
                self._logger.error(
                    f"invalid command {command_interpreter.command_id_int} with "
                    f"payload {str(command_interpreter.payload)}",
                )

            if command_id == CommandId.command_log:
                command = commands.LogCommand(
                    root_logger=self.root_logger,
                    data=command_interpreter.payload,
                )
                commands_received.append(command)
            elif command_id == CommandId.command_heartbeat_response:
                responses_received.append(
                    commands.HeartbeatResponse(command_interpreter.payload),
                )
            elif command_id == CommandId.command_led_response:
                responses_received.append(
                    commands.LEDResponse(command_interpreter.payload),
                )
            elif command_id == CommandId.command_gp_response:
                responses_received.append(
                    commands.GPResponse(command_interpreter.payload),
                )
            else:
                raise RuntimeError

        return commands_received, responses_received


_process: Dict[str, Process] = dict()
"""role name: process"""


def _end_running_process():
    process: Process
    for process in _process.values():
        process.kill()


@log_function_call
def start_backgroup_process():
    global _process
    global _command_queue
    container = get_initialize_container()

    role_name: str
    for role_name in container.config.roles():
        _command_queue[role_name] = Queue()

        _process[role_name] = Process(
            target=worker_process,
            args=(
                role_name,
                _command_queue[role_name],
            ),
        )
        _process[role_name].start()

    atexit.register(_end_running_process)