"""
This module implements an OS and hardware independent
virtual CAN interface for testing purposes.

Any VirtualBus instances connecting to the same channel
and reside in the same process will receive the same messages.
"""

import logging
import queue
import time
from copy import deepcopy
from random import randint
from threading import RLock
from typing import TYPE_CHECKING, Any, Dict, List, Optional, Tuple

from can import CanOperationError
from can.bus import BusABC, CanProtocol
from can.message import Message
from can.typechecking import AutoDetectedConfig

logger = logging.getLogger(__name__)


# Channels are lists of queues, one for each connection
if TYPE_CHECKING:
    # https://mypy.readthedocs.io/en/stable/runtime_troubles.html#using-classes-that-are-generic-in-stubs-but-not-at-runtime
    channels: Dict[Optional[Any], List[queue.Queue[Message]]] = {}
else:
    channels = {}
channels_lock = RLock()


class VirtualBus(BusABC):
    """
    A virtual CAN bus using an internal message queue. It can be used for
    example for testing.

    In this interface, a channel is an arbitrary object used as
    an identifier for connected buses.

    Implements :meth:`can.BusABC._detect_available_configs`; see
    :meth:`_detect_available_configs` for how it
    behaves here.

    .. note::
        The timeout when sending a message applies to each receiver
        individually. This means that sending can block up to 5 seconds
        if a message is sent to 5 receivers with the timeout set to 1.0.

    .. warning::
        This interface guarantees reliable delivery and message ordering, but
        does *not* implement rate limiting or ID arbitration/prioritization
        under high loads. Please refer to the section
        :ref:`virtual_interfaces_doc` for more information on this and a
        comparison to alternatives.
    """

    def __init__(
        self,
        channel: Any = None,
        receive_own_messages: bool = False,
        rx_queue_size: int = 0,
        preserve_timestamps: bool = False,
        protocol: CanProtocol = CanProtocol.CAN_20,
        **kwargs: Any,
    ) -> None:
        """
        The constructed instance has access to the bus identified by the
        channel parameter. It is able to see all messages transmitted on the
        bus by virtual instances constructed with the same channel identifier.

        :param channel: The channel identifier. This parameter can be an
            arbitrary value. The bus instance will be able to see messages
            from other virtual bus instances that were created with the same
            value.
        :param receive_own_messages: If set to True, sent messages will be
            reflected back on the input queue.
        :param rx_queue_size: The size of the reception queue. The reception
            queue stores messages until they are read. If the queue reaches
            its capacity, it will start dropping the oldest messages to make
            room for new ones. If set to 0, the queue has an infinite capacity.
            Be aware that this can cause memory leaks if messages are read
            with a lower frequency than they arrive on the bus.
        :param preserve_timestamps: If set to True, messages transmitted via
            :func:`~can.BusABC.send` will keep the timestamp set in the
            :class:`~can.Message` instance. Otherwise, the timestamp value
            will be replaced with the current system time.
        :param protocol: The protocol implemented by this bus instance. The
            value does not affect the operation of the bus instance and can
            be set to an arbitrary value for testing purposes.
        :param kwargs: Additional keyword arguments passed to the parent
            constructor.
        """
        super().__init__(
            channel=channel,
            receive_own_messages=receive_own_messages,
            **kwargs,
        )

        # the channel identifier may be an arbitrary object
        self.channel_id = channel
        self._can_protocol = protocol
        self.channel_info = f"Virtual bus channel {self.channel_id}"
        self.receive_own_messages = receive_own_messages
        self.preserve_timestamps = preserve_timestamps
        self._open = True

        with channels_lock:
            # Create a new channel if one does not exist
            if self.channel_id not in channels:
                channels[self.channel_id] = []
            self.channel = channels[self.channel_id]

            self.queue: queue.Queue[Message] = queue.Queue(rx_queue_size)
            self.channel.append(self.queue)

    def _check_if_open(self) -> None:
        """Raises :exc:`~can.exceptions.CanOperationError` if the bus is not open.

        Has to be called in every method that accesses the bus.
        """
        if not self._open:
            raise CanOperationError("Cannot operate on a closed bus")

    def _recv_internal(
        self, timeout: Optional[float]
    ) -> Tuple[Optional[Message], bool]:
        self._check_if_open()
        try:
            msg = self.queue.get(block=True, timeout=timeout)
        except queue.Empty:
            return None, False
        else:
            return msg, False

    def send(self, msg: Message, timeout: Optional[float] = None) -> None:
        self._check_if_open()

        timestamp = msg.timestamp if self.preserve_timestamps else time.time()
        # Add message to all listening on this channel
        all_sent = True
        for bus_queue in self.channel:
            if bus_queue is self.queue and not self.receive_own_messages:
                continue
            msg_copy = deepcopy(msg)
            msg_copy.timestamp = timestamp
            msg_copy.channel = self.channel_id
            msg_copy.is_rx = bus_queue is not self.queue
            try:
                bus_queue.put(msg_copy, block=True, timeout=timeout)
            except queue.Full:
                all_sent = False

        if not all_sent:
            raise CanOperationError("Could not send message to one or more recipients")

    def shutdown(self) -> None:
        super().shutdown()
        if self._open:
            self._open = False

            with channels_lock:
                self.channel.remove(self.queue)

                # remove if empty
                if not self.channel:
                    del channels[self.channel_id]

    @staticmethod
    def _detect_available_configs() -> List[AutoDetectedConfig]:
        """
        Returns all currently used channels as well as
        one other currently unused channel.

        .. note::

            This method will run into problems if thousands of
            autodetected buses are used at once.

        """
        with channels_lock:
            available_channels = list(channels.keys())

        # find a currently unused channel
        def get_extra():
            return f"channel-{randint(0, 9999)}"

        extra = get_extra()
        while extra in available_channels:
            extra = get_extra()

        available_channels += [extra]

        return [
            {"interface": "virtual", "channel": channel}
            for channel in available_channels
        ]
