import asyncio
import copy
import enum
import ipaddress
import itertools
import logging
import random
import re
import secrets
import socket
import threading
from collections.abc import Callable
from typing import Optional, Union, cast

import ifaddr

from . import mdns, stun, turn
from .candidate import Candidate, candidate_foundation, candidate_priority
from .utils import random_string

logger = logging.getLogger(__name__)

ICE_COMPLETED = 1
ICE_FAILED = 2

CONSENT_FAILURES = 6
CONSENT_INTERVAL = 5

connection_id = itertools.count()
protocol_id = itertools.count()

_mdns = threading.local()


class TransportPolicy(enum.Enum):
    ALL = 0
    """
    All ICE candidates will be considered.
    """

    RELAY = 1
    """
    Only ICE candidates whose IP addresses are being relayed,
    such as those being passed through a STUN or TURN server,
    will be considered.
    """


async def get_or_create_mdns_protocol(subscriber: object) -> mdns.MDnsProtocol:
    if not hasattr(_mdns, "lock"):
        _mdns.lock = asyncio.Lock()
        _mdns.protocol = None
        _mdns.subscribers = set()
    async with _mdns.lock:
        if _mdns.protocol is None:
            _mdns.protocol = await mdns.create_mdns_protocol()
        _mdns.subscribers.add(subscriber)
    return _mdns.protocol


async def unref_mdns_protocol(subscriber: object) -> None:
    if hasattr(_mdns, "lock"):
        async with _mdns.lock:
            _mdns.subscribers.discard(subscriber)
            if _mdns.protocol and not _mdns.subscribers:
                await _mdns.protocol.close()
                _mdns.protocol = None


def candidate_pair_priority(
    local: Candidate, remote: Candidate, ice_controlling: bool
) -> int:
    """
    See RFC 5245 - 5.7.2. Computing Pair Priority and Ordering Pairs
    """
    G = ice_controlling and local.priority or remote.priority
    D = ice_controlling and remote.priority or local.priority
    return (1 << 32) * min(G, D) + 2 * max(G, D) + (G > D and 1 or 0)


def get_host_addresses(use_ipv4: bool, use_ipv6: bool) -> list[str]:
    """
    Get local IP addresses.
    """
    addresses = []
    for adapter in ifaddr.get_adapters():
        for ip in adapter.ips:
            if isinstance(ip.ip, str) and use_ipv4 and ip.ip != "127.0.0.1":
                addresses.append(ip.ip)
            elif use_ipv6 and ip.ip[0] != "::1" and ip.ip[2] == 0:
                addresses.append(ip.ip[0])
    return addresses


async def relayed_candidate(
    component: int,
    protocol_factory: Callable[[], "StunProtocol"],
    turn_server: tuple[str, int],
    turn_username: Optional[str],
    turn_password: Optional[str],
    turn_ssl: bool,
    turn_transport: str,
) -> tuple[Candidate, "StunProtocol"]:
    """
    Connect to a TURN server to obtain a relayed candidate.
    """
    # Connect to TURN server.
    _, protocol = await turn.create_turn_endpoint(
        protocol_factory,
        server_addr=turn_server,
        username=turn_username,
        password=turn_password,
        ssl=turn_ssl,
        transport=turn_transport,
    )

    # Build relayed candidate.
    candidate_address = protocol.transport.get_extra_info("sockname")
    related_address = protocol.transport.get_extra_info("related_address")
    protocol.local_candidate = Candidate(
        foundation=candidate_foundation("relay", "udp", candidate_address[0]),
        component=component,
        transport="udp",
        priority=candidate_priority(component, "relay"),
        host=candidate_address[0],
        port=candidate_address[1],
        type="relay",
        related_address=related_address[0],
        related_port=related_address[1],
    )
    return protocol.local_candidate, protocol


async def server_reflexive_candidate(
    protocol: "StunProtocol", stun_server: tuple[str, int]
) -> tuple[Candidate, None]:
    """
    Query STUN server to obtain a server-reflexive candidate.
    """
    # lookup address
    loop = asyncio.get_event_loop()
    stun_server = (
        await loop.run_in_executor(None, socket.gethostbyname, stun_server[0]),
        stun_server[1],
    )

    # perform STUN query
    request = stun.Message(
        message_method=stun.Method.BINDING, message_class=stun.Class.REQUEST
    )
    response, _ = await protocol.request(request, stun_server)

    local_candidate = protocol.local_candidate
    return Candidate(
        foundation=candidate_foundation("srflx", "udp", local_candidate.host),
        component=local_candidate.component,
        transport=local_candidate.transport,
        priority=candidate_priority(local_candidate.component, "srflx"),
        host=response.attributes["XOR-MAPPED-ADDRESS"][0],
        port=response.attributes["XOR-MAPPED-ADDRESS"][1],
        type="srflx",
        related_address=local_candidate.host,
        related_port=local_candidate.port,
    ), None


def sort_candidate_pairs(pairs: list["CandidatePair"], ice_controlling: bool) -> None:
    """
    Sort a list of candidate pairs.
    """

    def pair_priority(pair: CandidatePair) -> int:
        return -candidate_pair_priority(
            pair.local_candidate, pair.remote_candidate, ice_controlling
        )

    pairs.sort(key=pair_priority)


def validate_password(value: str) -> None:
    """
    Check the password is well-formed.

    See RFC 5245 - 15.4. "ice-ufrag" and "ice-pwd" Attributes
    """
    if not re.match("^[a-zA-Z0-9+/]{22,256}$", value):
        raise ValueError("Password must satisfy 22*256ice-char")


def validate_remote_candidate(candidate: Candidate) -> Candidate:
    """
    Check the remote candidate is supported.
    """
    if candidate.type not in ["host", "relay", "srflx"]:
        raise ValueError('Unexpected candidate type "%s"' % candidate.type)
    ipaddress.ip_address(candidate.host)
    return candidate


def validate_username(value: str) -> None:
    """
    Check the username is well-formed.

    See RFC 5245 - 15.4. "ice-ufrag" and "ice-pwd" Attributes
    """
    if not re.match("^[a-zA-Z0-9+/]{4,256}$", value):
        raise ValueError("Username must satisfy 4*256ice-char")


class CandidatePair:
    def __init__(self, protocol: "StunProtocol", remote_candidate: Candidate) -> None:
        self.task: Optional[asyncio.Task] = None
        self.nominated = False
        self.protocol = protocol
        self.remote_candidate = remote_candidate
        self.remote_nominated = False
        self.state = CandidatePair.State.FROZEN

    def __repr__(self) -> str:
        return "CandidatePair(%s -> %s)" % (self.local_addr, self.remote_addr)

    @property
    def component(self) -> int:
        return self.local_candidate.component

    @property
    def local_addr(self) -> tuple[str, int]:
        return (self.local_candidate.host, self.local_candidate.port)

    @property
    def local_candidate(self) -> Candidate:
        return self.protocol.local_candidate

    @property
    def remote_addr(self) -> tuple[str, int]:
        return (self.remote_candidate.host, self.remote_candidate.port)

    class State(enum.Enum):
        FROZEN = 0
        WAITING = 1
        IN_PROGRESS = 2
        SUCCEEDED = 3
        FAILED = 4


class StunProtocol(asyncio.DatagramProtocol):
    def __init__(self, receiver: "Connection") -> None:
        self.__closed: asyncio.Future[bool] = asyncio.Future()
        self.id = next(protocol_id)
        self.local_candidate: Optional[Candidate] = None
        self.receiver = receiver
        self.transport: Optional[asyncio.DatagramTransport] = None
        self.transactions: dict[bytes, stun.Transaction] = {}

    def connection_lost(self, exc: Exception) -> None:
        self.__log_debug("connection_lost(%s)", exc)
        if not self.__closed.done():
            self.receiver.data_received(None, None)
            self.__closed.set_result(True)

    def connection_made(self, transport: asyncio.BaseTransport) -> None:
        self.__log_debug("connection_made(%s)", transport)
        self.transport = cast(asyncio.DatagramTransport, transport)

    def datagram_received(self, data: Union[bytes, str], addr: tuple) -> None:
        # force IPv6 four-tuple to a two-tuple
        addr = (addr[0], addr[1])
        data = cast(bytes, data)

        try:
            message = stun.parse_message(data)
            self.__log_debug("< %s %s", addr, message)
        except ValueError:
            self.receiver.data_received(data, self.local_candidate.component)
            return

        if (
            message.message_class == stun.Class.RESPONSE
            or message.message_class == stun.Class.ERROR
        ) and message.transaction_id in self.transactions:
            transaction = self.transactions[message.transaction_id]
            transaction.response_received(message, addr)
        elif message.message_class == stun.Class.REQUEST:
            self.receiver.request_received(message, addr, self, data)

    def error_received(self, exc: Exception) -> None:
        self.__log_debug("error_received(%s)", exc)

    # custom

    async def close(self) -> None:
        self.transport.close()
        await self.__closed

    async def request(
        self,
        request: stun.Message,
        addr: tuple[str, int],
        integrity_key: Optional[bytes] = None,
        retransmissions: Optional[int] = None,
    ) -> tuple[stun.Message, tuple[str, int]]:
        """
        Execute a STUN transaction and return the response.
        """
        assert request.transaction_id not in self.transactions

        if integrity_key is not None:
            request.add_message_integrity(integrity_key)

        transaction = stun.Transaction(
            request, addr, self, retransmissions=retransmissions
        )
        self.transactions[request.transaction_id] = transaction
        try:
            return await transaction.run()
        finally:
            del self.transactions[request.transaction_id]

    async def send_data(self, data: bytes, addr: tuple[str, int]) -> None:
        self.transport.sendto(data, addr)

    def send_stun(self, message: stun.Message, addr: tuple[str, int]) -> None:
        """
        Send a STUN message.
        """
        self.__log_debug("> %s %s", addr, message)
        self.transport.sendto(bytes(message), addr)

    def __log_debug(self, msg: str, *args: object) -> None:
        logger.debug("%s %s " + msg, self.receiver, self, *args)

    def __repr__(self) -> str:
        return "protocol(%s)" % self.id


class ConnectionEvent:
    pass


class ConnectionClosed(ConnectionEvent):
    pass


class Connection:
    """
    An ICE connection for a single media stream.

    :param ice_controlling: Whether the local peer has the controlling role.
    :param components: The number of components.
    :param stun_server: The address of the STUN server or `None`.
    :param turn_server: The address of the TURN server or `None`.
    :param turn_username: The username for the TURN server.
    :param turn_password: The password for the TURN server.
    :param turn_ssl: Whether to use TLS for the TURN server.
    :param turn_transport: The transport for TURN server, `"udp"` or `"tcp"`.
    :param use_ipv4: Whether to use IPv4 candidates.
    :param use_ipv6: Whether to use IPv6 candidates.
    :param transport_policy: Transport policy.
    :param local_username: An optional local username, otherwise a random one
                           will be generated.
    :param local_password: An optional local password, otherwise a random one
                           will be generated.
    """

    def __init__(
        self,
        ice_controlling: bool,
        components: int = 1,
        stun_server: Optional[tuple[str, int]] = None,
        turn_server: Optional[tuple[str, int]] = None,
        turn_username: Optional[str] = None,
        turn_password: Optional[str] = None,
        turn_ssl: bool = False,
        turn_transport: str = "udp",
        use_ipv4: bool = True,
        use_ipv6: bool = True,
        transport_policy: TransportPolicy = TransportPolicy.ALL,
        local_username: Optional[str] = None,
        local_password: Optional[str] = None,
    ) -> None:
        self.ice_controlling = ice_controlling

        if local_username is None:
            local_username = random_string(4)
        else:
            validate_username(local_username)

        if local_password is None:
            local_password = random_string(22)
        else:
            validate_password(local_password)

        #: Whether the remote party is an ICE Lite implementation.
        self.remote_is_lite = False
        #: Remote username, which you need to set.
        self.remote_username: Optional[str] = None
        #: Remote password, which you need to set.
        self.remote_password: Optional[str] = None

        self.stun_server = stun_server
        self.turn_server = turn_server
        self.turn_username = turn_username
        self.turn_password = turn_password
        self.turn_ssl = turn_ssl
        self.turn_transport = turn_transport

        # private
        self._closed = False
        self._components = set(range(1, components + 1))
        self._check_list: list[CandidatePair] = []
        self._check_list_done = False
        self._check_list_state: asyncio.Queue = asyncio.Queue()
        self._early_checks: list[
            tuple[stun.Message, tuple[str, int], StunProtocol]
        ] = []
        self._early_checks_done = False
        self._event_waiter: Optional[asyncio.Future[ConnectionEvent]] = None
        self._id = next(connection_id)
        self._local_candidates: list[Candidate] = []
        self._local_candidates_end = False
        self._local_candidates_start = False
        self._local_password = local_password
        self._local_username = local_username
        self._nominated: dict[int, CandidatePair] = {}
        self._nominating: set[int] = set()
        self._protocols: list[StunProtocol] = []
        self._remote_candidates: list[Candidate] = []
        self._remote_candidates_end = False
        self._query_consent_task: Optional[asyncio.Task] = None
        self._queue: asyncio.Queue[tuple[Optional[bytes], Optional[int]]] = (
            asyncio.Queue()
        )
        self._tie_breaker = secrets.randbits(64)
        self._use_ipv4 = use_ipv4
        self._use_ipv6 = use_ipv6

        if (
            stun_server is None
            and turn_server is None
            and transport_policy == TransportPolicy.RELAY
        ):
            raise ValueError(
                "Relay transport policy requires a STUN and/or TURN server."
            )

        self._transport_policy = transport_policy

    @property
    def local_candidates(self) -> list[Candidate]:
        """
        Local candidates, automatically set by :meth:`gather_candidates`.
        """
        return self._local_candidates[:]

    @property
    def local_password(self) -> str:
        """
        Local password, set at construction time.
        """
        return self._local_password

    @property
    def local_username(self) -> str:
        """
        Local username, set at construction time.
        """
        return self._local_username

    @property
    def remote_candidates(self) -> list[Candidate]:
        """
        Remote candidates, which you need to populate using
        :meth:`add_remote_candidate`.
        """
        return self._remote_candidates[:]

    async def add_remote_candidate(self, remote_candidate: Optional[Candidate]) -> None:
        """
        Add a remote candidate or signal end-of-candidates.

        To signal end-of-candidates, pass `None`.

        :param remote_candidate: A :class:`Candidate` instance or `None`.
        """
        if self._remote_candidates_end:
            raise ValueError("Cannot add remote candidate after end-of-candidates.")

        # end-of-candidates
        if remote_candidate is None:
            self._prune_components()
            self._remote_candidates_end = True
            return

        # resolve mDNS candidate
        if mdns.is_mdns_hostname(remote_candidate.host):
            mdns_protocol = await get_or_create_mdns_protocol(self)
            remote_addr = await mdns_protocol.resolve(remote_candidate.host)
            if remote_addr is None:
                self.__log_info(
                    f'Remote candidate "{remote_candidate.host}" could not be resolved'
                )
                return
            self.__log_info(
                f'Remote candidate "{remote_candidate.host}" resolved to {remote_addr}'
            )

            copy_candidate = copy.copy(remote_candidate)
            copy_candidate.host = remote_addr
            await self.add_remote_candidate(copy_candidate)
            return

        # validate the remote candidate
        try:
            validate_remote_candidate(remote_candidate)
        except ValueError as e:
            self.__log_info(
                f'Remote candidate "{remote_candidate.host}" is not valid: {e}'
            )
            return
        self._remote_candidates.append(remote_candidate)

        # pair the remote candidate
        for protocol in self._protocols:
            if protocol.local_candidate.can_pair_with(
                remote_candidate
            ) and not self._find_pair(protocol, remote_candidate):
                pair = CandidatePair(protocol, remote_candidate)
                self._check_list.append(pair)
        self.sort_check_list()

    async def gather_candidates(self) -> None:
        """
        Gather local candidates.

        You **must** call this coroutine before calling :meth:`connect`.
        """
        if not self._local_candidates_start:
            self._local_candidates_start = True
            addresses = get_host_addresses(
                use_ipv4=self._use_ipv4, use_ipv6=self._use_ipv6
            )
            coros = [
                self.get_component_candidates(component=component, addresses=addresses)
                for component in self._components
            ]
            for candidates in await asyncio.gather(*coros):
                self._local_candidates += candidates
            self._local_candidates_end = True

    def get_default_candidate(self, component: int) -> Optional[Candidate]:
        """
        Get the default local candidate for the specified component.

        :param component: The component whose default candidate is requested.
        """
        for candidate in sorted(self._local_candidates, key=lambda x: x.priority):
            if candidate.component == component:
                return candidate
        return None

    async def connect(self) -> None:
        """
        Perform ICE handshake.

        This coroutine returns if a candidate pair was successfuly nominated
        and raises an exception otherwise.
        """
        if not self._local_candidates_end:
            raise ConnectionError("Local candidates gathering was not performed")

        if self.remote_username is None or self.remote_password is None:
            raise ConnectionError("Remote username or password is missing")

        # 5.7.1. Forming Candidate Pairs
        for remote_candidate in self._remote_candidates:
            for protocol in self._protocols:
                if protocol.local_candidate.can_pair_with(
                    remote_candidate
                ) and not self._find_pair(protocol, remote_candidate):
                    pair = CandidatePair(protocol, remote_candidate)
                    self._check_list.append(pair)
        self.sort_check_list()

        self._unfreeze_initial()

        # handle early checks
        for early_check in self._early_checks:
            self.check_incoming(*early_check)
        self._early_checks = []
        self._early_checks_done = True

        # perform checks
        while True:
            if not self.check_periodic():
                break
            await asyncio.sleep(0.02)

        # wait for completion
        if self._check_list:
            res = await self._check_list_state.get()
        else:
            res = ICE_FAILED

        # cancel remaining checks
        for check in self._check_list:
            if check.task:
                check.task.cancel()

        if res != ICE_COMPLETED:
            raise ConnectionError("ICE negotiation failed")

        # start consent freshness tests
        self._query_consent_task = asyncio.create_task(self.query_consent())

    async def close(self) -> None:
        """
        Close the connection.
        """
        # stop consent freshness tests
        if self._query_consent_task and not self._query_consent_task.done():
            self._query_consent_task.cancel()
            try:
                await self._query_consent_task
            except asyncio.CancelledError:
                pass

        # stop check list
        if self._check_list and not self._check_list_done:
            self._check_list_state.put_nowait(ICE_FAILED)

        # unreference mDNS
        await unref_mdns_protocol(self)

        self._nominated.clear()
        for protocol in self._protocols:
            await protocol.close()
        self._protocols.clear()
        self._local_candidates.clear()

        # emit event
        if not self._closed:
            self._emit_event(ConnectionClosed())
            self._closed = True

    async def get_event(self) -> Optional[ConnectionEvent]:
        """
        Return the next `ConnectionEvent` or `None` if the connection is
        already closed.

        This method may only be called once at a time.
        """
        assert self._event_waiter is None, "already awaiting event"
        if self._closed:
            return None
        loop = asyncio.get_event_loop()
        self._event_waiter = loop.create_future()
        return await asyncio.shield(self._event_waiter)

    async def recv(self) -> bytes:
        """
        Receive the next datagram.

        The return value is a `bytes` object representing the data received.

        If the connection is not established, a `ConnectionError` is raised.
        """
        data, component = await self.recvfrom()
        return data

    async def recvfrom(self) -> tuple[bytes, int]:
        """
        Receive the next datagram.

        The return value is a `(bytes, component)` tuple where `bytes` is a
        bytes object representing the data received and `component` is the
        component on which the data was received.

        If the connection is not established, a `ConnectionError` is raised.
        """
        if not len(self._nominated):
            raise ConnectionError("Cannot receive data, not connected")

        result = await self._queue.get()
        if result[0] is None:
            raise ConnectionError("Connection lost while receiving data")
        return result

    async def send(self, data: bytes) -> None:
        """
        Send a datagram on the first component.

        If the connection is not established, a `ConnectionError` is raised.

        :param data: The data to be sent.
        """
        await self.sendto(data, 1)

    async def sendto(self, data: bytes, component: int) -> None:
        """
        Send a datagram on the specified component.

        If the connection is not established, a `ConnectionError` is raised.

        :param data: The data to be sent.
        :param component: The component on which to send the data.
        """
        active_pair = self._nominated.get(component)
        if active_pair:
            await active_pair.protocol.send_data(data, active_pair.remote_addr)
        else:
            raise ConnectionError("Cannot send data, not connected")

    def set_selected_pair(
        self, component: int, local_foundation: str, remote_foundation: str
    ) -> None:
        """
        Force the selected candidate pair.

        If the remote party does not support ICE, you should using this
        instead of calling :meth:`connect`.
        """
        # find local candidate
        protocol = None
        for p in self._protocols:
            if (
                p.local_candidate.component == component
                and p.local_candidate.foundation == local_foundation
            ):
                protocol = p
                break

        # find remote candidate
        remote_candidate = None
        for c in self._remote_candidates:
            if c.component == component and c.foundation == remote_foundation:
                remote_candidate = c

        assert protocol and remote_candidate
        self._nominated[component] = CandidatePair(protocol, remote_candidate)

    # private

    def build_request(self, pair: CandidatePair, nominate: bool) -> stun.Message:
        tx_username = "%s:%s" % (self.remote_username, self.local_username)
        request = stun.Message(
            message_method=stun.Method.BINDING, message_class=stun.Class.REQUEST
        )
        request.attributes["USERNAME"] = tx_username
        request.attributes["PRIORITY"] = candidate_priority(pair.component, "prflx")
        if self.ice_controlling:
            request.attributes["ICE-CONTROLLING"] = self._tie_breaker
            if nominate:
                request.attributes["USE-CANDIDATE"] = None
        else:
            request.attributes["ICE-CONTROLLED"] = self._tie_breaker
        return request

    def check_complete(self, pair: CandidatePair) -> None:
        pair.task = None

        if pair.state == CandidatePair.State.SUCCEEDED:
            if pair.nominated:
                self._nominated[pair.component] = pair

                # 8.1.2.  Updating States
                #
                # The agent MUST remove all Waiting and Frozen pairs in the check
                # list and triggered check queue for the same component as the
                # nominated pairs for that media stream.
                for p in self._check_list:
                    if p.component == pair.component and p.state in [
                        CandidatePair.State.WAITING,
                        CandidatePair.State.FROZEN,
                    ]:
                        self.check_state(p, CandidatePair.State.FAILED)

            # Once there is at least one nominated pair in the valid list for
            # every component of at least one media stream and the state of the
            # check list is Running:
            if len(self._nominated) == len(self._components):
                if not self._check_list_done:
                    self.__log_info("ICE completed")
                    self._check_list_state.put_nowait(ICE_COMPLETED)
                    self._check_list_done = True
                return

            # 7.1.3.2.3.  Updating Pair States
            for p in self._check_list:
                if (
                    p.local_candidate.foundation == pair.local_candidate.foundation
                    and p.state == CandidatePair.State.FROZEN
                ):
                    self.check_state(p, CandidatePair.State.WAITING)

        for p in self._check_list:
            if p.state not in [
                CandidatePair.State.SUCCEEDED,
                CandidatePair.State.FAILED,
            ]:
                return

        if not self.ice_controlling:
            for p in self._check_list:
                if p.state == CandidatePair.State.SUCCEEDED:
                    return

        if not self._check_list_done:
            self.__log_info("ICE failed")
            self._check_list_state.put_nowait(ICE_FAILED)
            self._check_list_done = True

    def check_incoming(
        self, message: stun.Message, addr: tuple[str, int], protocol: StunProtocol
    ) -> None:
        """
        Handle a succesful incoming check.
        """
        component = protocol.local_candidate.component

        # find remote candidate
        remote_candidate = None
        for c in self._remote_candidates:
            if c.host == addr[0] and c.port == addr[1]:
                remote_candidate = c
                assert remote_candidate.component == component
                break
        if remote_candidate is None:
            # 7.2.1.3. Learning Peer Reflexive Candidates
            remote_candidate = Candidate(
                foundation=random_string(10),
                component=component,
                transport="udp",
                priority=message.attributes["PRIORITY"],
                host=addr[0],
                port=addr[1],
                type="prflx",
            )
            self._remote_candidates.append(remote_candidate)
            self.__log_info("Discovered peer reflexive candidate %s", remote_candidate)

        # find pair
        pair = self._find_pair(protocol, remote_candidate)
        if pair is None:
            pair = CandidatePair(protocol, remote_candidate)
            pair.state = CandidatePair.State.WAITING
            self._check_list.append(pair)
            self.sort_check_list()

        # triggered check
        if pair.state in [CandidatePair.State.WAITING, CandidatePair.State.FAILED]:
            self.check_start_task(pair)

        # 7.2.1.5. Updating the Nominated Flag
        if "USE-CANDIDATE" in message.attributes and not self.ice_controlling:
            pair.remote_nominated = True

            if pair.state == CandidatePair.State.SUCCEEDED:
                pair.nominated = True
                self.check_complete(pair)

    def check_periodic(self) -> bool:
        # find the highest-priority pair that is in the waiting state
        for pair in self._check_list:
            if pair.state == CandidatePair.State.WAITING:
                self.check_start_task(pair)
                return True

        # find the highest-priority pair that is in the frozen state
        for pair in self._check_list:
            if pair.state == CandidatePair.State.FROZEN:
                self.check_start_task(pair)
                return True

        # if we expect more candidates, keep going
        if not self._remote_candidates_end:
            return not self._check_list_done

        return False

    async def check_start(self, pair: CandidatePair) -> None:
        """
        Starts a check.
        """
        self.check_state(pair, CandidatePair.State.IN_PROGRESS)

        nominate = self.ice_controlling and not self.remote_is_lite
        request = self.build_request(pair, nominate=nominate)
        try:
            response, addr = await pair.protocol.request(
                request,
                pair.remote_addr,
                integrity_key=self.remote_password.encode("utf8"),
            )
        except stun.TransactionError as exc:
            # 7.1.3.1. Failure Cases
            if (
                exc.response
                and exc.response.attributes.get("ERROR-CODE", (None, None))[0] == 487
            ):
                if "ICE-CONTROLLING" in request.attributes:
                    self.switch_role(ice_controlling=False)
                elif "ICE-CONTROLLED" in request.attributes:
                    self.switch_role(ice_controlling=True)
                return await self.check_start(pair)
            else:
                self.check_state(pair, CandidatePair.State.FAILED)
                self.check_complete(pair)
                return

        # check remote address matches
        if addr != pair.remote_addr:
            self.__log_info("Check %s failed : source address mismatch", pair)
            self.check_state(pair, CandidatePair.State.FAILED)
            self.check_complete(pair)
            return

        # success
        if nominate or pair.remote_nominated:
            # nominated by agressive nomination or the remote party
            pair.nominated = True
        elif self.ice_controlling and pair.component not in self._nominating:
            # perform regular nomination
            self.__log_info("Check %s nominating pair", pair)
            self._nominating.add(pair.component)
            request = self.build_request(pair, nominate=True)
            try:
                await pair.protocol.request(
                    request,
                    pair.remote_addr,
                    integrity_key=self.remote_password.encode("utf8"),
                )
            except stun.TransactionError:
                self.__log_info("Check %s failed : could not nominate pair", pair)
                self.check_state(pair, CandidatePair.State.FAILED)
                self.check_complete(pair)
                return
            pair.nominated = True
        self.check_state(pair, CandidatePair.State.SUCCEEDED)
        self.check_complete(pair)

    def check_start_task(self, pair: CandidatePair) -> None:
        """
        Starts a check in a task, unless already started.
        """
        if pair.task is None:
            pair.task = asyncio.create_task(self.check_start(pair))

    def check_state(self, pair: CandidatePair, state: CandidatePair.State) -> None:
        """
        Updates the state of a check.
        """
        self.__log_info("Check %s %s -> %s", pair, pair.state, state)
        pair.state = state

    def _emit_event(self, event: ConnectionEvent) -> None:
        if self._event_waiter is not None:
            waiter = self._event_waiter
            self._event_waiter = None
            waiter.set_result(event)

    def _find_pair(
        self, protocol: StunProtocol, remote_candidate: Candidate
    ) -> Optional[CandidatePair]:
        """
        Find a candidate pair in the check list.
        """
        for pair in self._check_list:
            if pair.protocol == protocol and pair.remote_candidate == remote_candidate:
                return pair
        return None

    async def get_component_candidates(
        self, component: int, addresses: list[str], timeout: int = 5
    ) -> list[Candidate]:
        candidates = []
        loop = asyncio.get_event_loop()

        # gather host candidates
        host_protocols = []
        for address in addresses:
            # create transport
            try:
                transport, protocol = await loop.create_datagram_endpoint(
                    lambda: StunProtocol(self), local_addr=(address, 0)
                )
                sock = transport.get_extra_info("socket")
                if sock is not None:
                    sock.setsockopt(
                        socket.SOL_SOCKET, socket.SO_RCVBUF, turn.UDP_SOCKET_BUFFER_SIZE
                    )
            except OSError as exc:
                self.__log_info("Could not bind to %s - %s", address, exc)
                continue
            host_protocols.append(protocol)

            # add host candidate
            candidate_address = protocol.transport.get_extra_info("sockname")
            protocol.local_candidate = Candidate(
                foundation=candidate_foundation("host", "udp", candidate_address[0]),
                component=component,
                transport="udp",
                priority=candidate_priority(component, "host"),
                host=candidate_address[0],
                port=candidate_address[1],
                type="host",
            )
            if self._transport_policy == TransportPolicy.ALL:
                candidates.append(protocol.local_candidate)
        self._protocols += host_protocols

        tasks: list[asyncio.Task[tuple[Candidate, Optional[StunProtocol]]]] = []

        # Query STUN server for server-reflexive candidates (IPv4 only).
        if self.stun_server:
            for protocol in host_protocols:
                if ipaddress.ip_address(protocol.local_candidate.host).version == 4:
                    tasks.append(
                        asyncio.create_task(
                            server_reflexive_candidate(protocol, self.stun_server)
                        )
                    )

        # Connect to TURN server.
        if self.turn_server:
            tasks.append(
                asyncio.create_task(
                    relayed_candidate(
                        component=component,
                        protocol_factory=lambda: StunProtocol(self),
                        turn_server=self.turn_server,
                        turn_username=self.turn_username,
                        turn_password=self.turn_password,
                        turn_ssl=self.turn_ssl,
                        turn_transport=self.turn_transport,
                    )
                )
            )

        # Run tasks in parallel and handle exceptions.
        if len(tasks):
            done, pending = await asyncio.wait(tasks, timeout=timeout)
            for task in done:
                if task.exception() is None:
                    candidate, protocol = task.result()
                    candidates.append(candidate)
                    if protocol is not None:
                        self._protocols.append(protocol)
            for task in pending:
                task.cancel()

        return candidates

    def _prune_components(self) -> None:
        """
        Remove components for which the remote party did not provide any candidates.

        This can only be determined after end-of-candidates.
        """
        seen_components = set(map(lambda x: x.component, self._remote_candidates))
        missing_components = self._components - seen_components
        if missing_components:
            self.__log_info(
                "Components %s have no candidate pairs" % missing_components
            )
            self._components = seen_components

    async def query_consent(self) -> None:
        """
        Periodically check consent (RFC 7675).
        """
        failures = 0
        while True:
            # randomize between 0.8 and 1.2 times CONSENT_INTERVAL
            await asyncio.sleep(CONSENT_INTERVAL * (0.8 + 0.4 * random.random()))

            for pair in self._nominated.values():
                request = self.build_request(pair, nominate=False)
                try:
                    await pair.protocol.request(
                        request,
                        pair.remote_addr,
                        integrity_key=self.remote_password.encode("utf8"),
                        retransmissions=0,
                    )
                    failures = 0
                except stun.TransactionError:
                    failures += 1
                if failures >= CONSENT_FAILURES:
                    self.__log_info("Consent to send expired")
                    self._query_consent_task = None
                    return await self.close()

    def data_received(self, data: Optional[bytes], component: Optional[int]) -> None:
        self._queue.put_nowait((data, component))

    def request_received(
        self,
        message: stun.Message,
        addr: tuple[str, int],
        protocol: StunProtocol,
        raw_data: bytes,
    ) -> None:
        if message.message_method != stun.Method.BINDING:
            self.respond_error(message, addr, protocol, (400, "Bad Request"))
            return

        # authenticate request
        try:
            stun.parse_message(
                raw_data, integrity_key=self.local_password.encode("utf8")
            )
            if self.remote_username is not None:
                rx_username = "%s:%s" % (self.local_username, self.remote_username)
                if message.attributes.get("USERNAME") != rx_username:
                    raise ValueError("Wrong username")
        except ValueError:
            self.respond_error(message, addr, protocol, (400, "Bad Request"))
            return

        # 7.2.1.1. Detecting and Repairing Role Conflicts
        if self.ice_controlling and "ICE-CONTROLLING" in message.attributes:
            self.__log_info("Role conflict, expected to be controlling")
            if self._tie_breaker >= message.attributes["ICE-CONTROLLING"]:
                self.respond_error(message, addr, protocol, (487, "Role Conflict"))
                return
            self.switch_role(ice_controlling=False)
        elif not self.ice_controlling and "ICE-CONTROLLED" in message.attributes:
            self.__log_info("Role conflict, expected to be controlled")
            if self._tie_breaker < message.attributes["ICE-CONTROLLED"]:
                self.respond_error(message, addr, protocol, (487, "Role Conflict"))
                return
            self.switch_role(ice_controlling=True)

        # send binding response
        response = stun.Message(
            message_method=stun.Method.BINDING,
            message_class=stun.Class.RESPONSE,
            transaction_id=message.transaction_id,
        )
        response.attributes["XOR-MAPPED-ADDRESS"] = addr
        response.add_message_integrity(self.local_password.encode("utf8"))
        protocol.send_stun(response, addr)

        if not self._check_list and not self._early_checks_done:
            self._early_checks.append((message, addr, protocol))
        else:
            self.check_incoming(message, addr, protocol)

    def respond_error(
        self,
        request: stun.Message,
        addr: tuple[str, int],
        protocol: StunProtocol,
        error_code: tuple[int, str],
    ) -> None:
        response = stun.Message(
            message_method=request.message_method,
            message_class=stun.Class.ERROR,
            transaction_id=request.transaction_id,
        )
        response.attributes["ERROR-CODE"] = error_code
        response.add_message_integrity(self.local_password.encode("utf8"))
        protocol.send_stun(response, addr)

    def sort_check_list(self) -> None:
        sort_candidate_pairs(self._check_list, self.ice_controlling)

    def switch_role(self, ice_controlling: bool) -> None:
        self.__log_info(
            "Switching to %s role", ice_controlling and "controlling" or "controlled"
        )
        self.ice_controlling = ice_controlling
        self.sort_check_list()

    def _unfreeze_initial(self) -> None:
        # unfreeze first pair for the first component
        first_pair = None
        for pair in self._check_list:
            if pair.component == min(self._components):
                first_pair = pair
                break
        if first_pair is None:
            return
        if first_pair.state == CandidatePair.State.FROZEN:
            self.check_state(first_pair, CandidatePair.State.WAITING)

        # unfreeze pairs with same component but different foundations
        seen_foundations = set(first_pair.local_candidate.foundation)
        for pair in self._check_list:
            if (
                pair.component == first_pair.component
                and pair.local_candidate.foundation not in seen_foundations
                and pair.state == CandidatePair.State.FROZEN
            ):
                self.check_state(pair, CandidatePair.State.WAITING)
                seen_foundations.add(pair.local_candidate.foundation)

    def __log_info(self, msg: str, *args: object) -> None:
        logger.info("%s " + msg, self, *args)

    def __repr__(self) -> str:
        return "Connection(%s)" % self._id
