import socket
from abc import abstractmethod
from io import IOBase
from ipaddress import IPv4Address, IPv6Address
from socket import AddressFamily
from types import TracebackType
from typing import (
    Any, AsyncContextManager, Callable, Collection, Dict, List, Mapping, Optional, Tuple, Type,
    TypeVar, Union)

from .._core._typedattr import TypedAttributeProvider, TypedAttributeSet, typed_attribute
from ._streams import ByteStream, Listener, T_Stream, UnreliableObjectStream
from ._tasks import TaskGroup

IPAddressType = Union[str, IPv4Address, IPv6Address]
IPSockAddrType = Tuple[str, int]
SockAddrType = Union[IPSockAddrType, str]
UDPPacketType = Tuple[bytes, IPSockAddrType]
T_Retval = TypeVar('T_Retval')


class _NullAsyncContextManager:
    async def __aenter__(self) -> None:
        pass

    async def __aexit__(self, exc_type: Optional[Type[BaseException]],
                        exc_val: Optional[BaseException],
                        exc_tb: Optional[TracebackType]) -> Optional[bool]:
        return None


class SocketAttribute(TypedAttributeSet):
    #: the address family of the underlying socket
    family: AddressFamily = typed_attribute()
    #: the local socket address of the underlying socket
    local_address: SockAddrType = typed_attribute()
    #: for IP addresses, the local port the underlying socket is bound to
    local_port: int = typed_attribute()
    #: the underlying stdlib socket object
    raw_socket: socket.socket = typed_attribute()
    #: the remote address the underlying socket is connected to
    remote_address: SockAddrType = typed_attribute()
    #: for IP addresses, the remote port the underlying socket is connected to
    remote_port: int = typed_attribute()


class _SocketProvider(TypedAttributeProvider):
    @property
    def extra_attributes(self) -> Mapping[Any, Callable[[], Any]]:
        from .._core._sockets import convert_ipv6_sockaddr as convert

        attributes: Dict[Any, Callable[[], Any]] = {
            SocketAttribute.family: lambda: self._raw_socket.family,
            SocketAttribute.local_address: lambda: convert(self._raw_socket.getsockname()),
            SocketAttribute.raw_socket: lambda: self._raw_socket
        }
        try:
            peername: Optional[Tuple[str, int]] = convert(self._raw_socket.getpeername())
        except OSError:
            peername = None

        # Provide the remote address for connected sockets
        if peername is not None:
            attributes[SocketAttribute.remote_address] = lambda: peername

        # Provide local and remote ports for IP based sockets
        if self._raw_socket.family in (AddressFamily.AF_INET, AddressFamily.AF_INET6):
            attributes[SocketAttribute.local_port] = lambda: self._raw_socket.getsockname()[1]
            if peername is not None:
                remote_port = peername[1]
                attributes[SocketAttribute.remote_port] = lambda: remote_port

        return attributes

    @property
    @abstractmethod
    def _raw_socket(self) -> socket.socket:
        pass


class SocketStream(ByteStream, _SocketProvider):
    """
    Transports bytes over a socket.

    Supports all relevant extra attributes from :class:`~SocketAttribute`.
    """


class UNIXSocketStream(SocketStream):
    @abstractmethod
    async def send_fds(self, message: bytes, fds: Collection[Union[int, IOBase]]) -> None:
        """
        Send file descriptors along with a message to the peer.

        :param message: a non-empty bytestring
        :param fds: a collection of files (either numeric file descriptors or open file or socket
            objects)
        """

    @abstractmethod
    async def receive_fds(self, msglen: int, maxfds: int) -> Tuple[bytes, List[int]]:
        """
        Receive file descriptors along with a message from the peer.

        :param msglen: length of the message to expect from the peer
        :param maxfds: maximum number of file descriptors to expect from the peer
        :return: a tuple of (message, file descriptors)
        """


class SocketListener(Listener[SocketStream], _SocketProvider):
    """
    Listens to incoming socket connections.

    Supports all relevant extra attributes from :class:`~SocketAttribute`.
    """

    @abstractmethod
    async def accept(self) -> SocketStream:
        """Accept an incoming connection."""

    async def serve(self, handler: Callable[[T_Stream], Any],
                    task_group: Optional[TaskGroup] = None) -> None:
        from .. import create_task_group

        context_manager: AsyncContextManager
        if task_group is None:
            task_group = context_manager = create_task_group()
        else:
            # Can be replaced with AsyncExitStack once on py3.7+
            context_manager = _NullAsyncContextManager()

        async with context_manager:
            while True:
                stream = await self.accept()
                task_group.start_soon(handler, stream)


class UDPSocket(UnreliableObjectStream[UDPPacketType], _SocketProvider):
    """
    Represents an unconnected UDP socket.

    Supports all relevant extra attributes from :class:`~SocketAttribute`.
    """

    async def sendto(self, data: bytes, host: str, port: int) -> None:
        """Alias for :meth:`~.UnreliableObjectSendStream.send` ((data, (host, port)))."""
        return await self.send((data, (host, port)))


class ConnectedUDPSocket(UnreliableObjectStream[bytes], _SocketProvider):
    """
    Represents an connected UDP socket.

    Supports all relevant extra attributes from :class:`~SocketAttribute`.
    """