import ssl
import sys
from types import TracebackType
from typing import Iterable, Iterator, Iterable, List, Optional, Type

from .._backends.sync import SyncBackend
from .._backends.base import SOCKET_OPTION, NetworkBackend
from .._exceptions import ConnectionNotAvailable, UnsupportedProtocol
from .._models import Origin, Request, Response
from .._synchronization import Event, ShieldCancellation, ThreadLock
from .connection import HTTPConnection
from .interfaces import ConnectionInterface, RequestInterface


class PoolRequest:
    def __init__(self, request: Request) -> None:
        self.request = request
        self.connection: Optional[ConnectionInterface] = None
        self._connection_acquired = Event()

    def assign_to_connection(
        self, connection: Optional[ConnectionInterface]
    ) -> None:
        self.connection = connection
        self._connection_acquired.set()

    def clear_connection(self) -> None:
        self.connection = None
        self._connection_acquired = Event()

    def wait_for_connection(
        self, timeout: Optional[float] = None
    ) -> ConnectionInterface:
        if self.connection is None:
            self._connection_acquired.wait(timeout=timeout)
        assert self.connection is not None
        return self.connection

    def is_queued(self) -> bool:
        return self.connection is None


class ConnectionPool(RequestInterface):
    """
    A connection pool for making HTTP requests.
    """

    def __init__(
        self,
        ssl_context: Optional[ssl.SSLContext] = None,
        max_connections: Optional[int] = 10,
        max_keepalive_connections: Optional[int] = None,
        keepalive_expiry: Optional[float] = None,
        http1: bool = True,
        http2: bool = False,
        retries: int = 0,
        local_address: Optional[str] = None,
        uds: Optional[str] = None,
        network_backend: Optional[NetworkBackend] = None,
        socket_options: Optional[Iterable[SOCKET_OPTION]] = None,
    ) -> None:
        """
        A connection pool for making HTTP requests.

        Parameters:
            ssl_context: An SSL context to use for verifying connections.
                If not specified, the default `httpcore.default_ssl_context()`
                will be used.
            max_connections: The maximum number of concurrent HTTP connections that
                the pool should allow. Any attempt to send a request on a pool that
                would exceed this amount will block until a connection is available.
            max_keepalive_connections: The maximum number of idle HTTP connections
                that will be maintained in the pool.
            keepalive_expiry: The duration in seconds that an idle HTTP connection
                may be maintained for before being expired from the pool.
            http1: A boolean indicating if HTTP/1.1 requests should be supported
                by the connection pool. Defaults to True.
            http2: A boolean indicating if HTTP/2 requests should be supported by
                the connection pool. Defaults to False.
            retries: The maximum number of retries when trying to establish a
                connection.
            local_address: Local address to connect from. Can also be used to connect
                using a particular address family. Using `local_address="0.0.0.0"`
                will connect using an `AF_INET` address (IPv4), while using
                `local_address="::"` will connect using an `AF_INET6` address (IPv6).
            uds: Path to a Unix Domain Socket to use instead of TCP sockets.
            network_backend: A backend instance to use for handling network I/O.
            socket_options: Socket options that have to be included
             in the TCP socket when the connection was established.
        """
        self._ssl_context = ssl_context

        self._max_connections = (
            sys.maxsize if max_connections is None else max_connections
        )
        self._max_keepalive_connections = (
            sys.maxsize
            if max_keepalive_connections is None
            else max_keepalive_connections
        )
        self._max_keepalive_connections = min(
            self._max_connections, self._max_keepalive_connections
        )

        self._keepalive_expiry = keepalive_expiry
        self._http1 = http1
        self._http2 = http2
        self._retries = retries
        self._local_address = local_address
        self._uds = uds

        self._network_backend = (
            SyncBackend() if network_backend is None else network_backend
        )
        self._socket_options = socket_options

        # The mutable state on a connection pool is the queue of incoming requests,
        # and the set of connections that are servicing those requests.
        self._connections: List[ConnectionInterface] = []
        self._requests: List[PoolRequest] = []

        # We only mutate the state of the connection pool within an 'optional_thread_lock'
        # context. This holds a threading lock unless we're running in async mode,
        # in which case it is a no-op.
        self._optional_thread_lock = ThreadLock()

    def create_connection(self, origin: Origin) -> ConnectionInterface:
        return HTTPConnection(
            origin=origin,
            ssl_context=self._ssl_context,
            keepalive_expiry=self._keepalive_expiry,
            http1=self._http1,
            http2=self._http2,
            retries=self._retries,
            local_address=self._local_address,
            uds=self._uds,
            network_backend=self._network_backend,
            socket_options=self._socket_options,
        )

    @property
    def connections(self) -> List[ConnectionInterface]:
        """
        Return a list of the connections currently in the pool.

        For example:

        ```python
        >>> pool.connections
        [
            <HTTPConnection ['https://example.com:443', HTTP/1.1, ACTIVE, Request Count: 6]>,
            <HTTPConnection ['https://example.com:443', HTTP/1.1, IDLE, Request Count: 9]> ,
            <HTTPConnection ['http://example.com:80', HTTP/1.1, IDLE, Request Count: 1]>,
        ]
        ```
        """
        return list(self._connections)

    def handle_request(self, request: Request) -> Response:
        """
        Send an HTTP request, and return an HTTP response.

        This is the core implementation that is called into by `.request()` or `.stream()`.
        """
        scheme = request.url.scheme.decode()
        if scheme == "":
            raise UnsupportedProtocol(
                "Request URL is missing an 'http://' or 'https://' protocol."
            )
        if scheme not in ("http", "https", "ws", "wss"):
            raise UnsupportedProtocol(
                f"Request URL has an unsupported protocol '{scheme}://'."
            )

        timeouts = request.extensions.get("timeout", {})
        timeout = timeouts.get("pool", None)

        with self._optional_thread_lock:
            # Add the incoming request to our request queue.
            pool_request = PoolRequest(request)
            self._requests.append(pool_request)

        try:
            while True:
                with self._optional_thread_lock:
                    # Assign incoming requests to available connections,
                    # closing or creating new connections as required.
                    closing = self._assign_requests_to_connections()
                self._close_connections(closing)

                # Wait until this request has an assigned connection.
                connection = pool_request.wait_for_connection(timeout=timeout)

                try:
                    # Send the request on the assigned connection.
                    response = connection.handle_request(
                        pool_request.request
                    )
                except ConnectionNotAvailable:
                    # In some cases a connection may initially be available to
                    # handle a request, but then become unavailable.
                    #
                    # In this case we clear the connection and try again.
                    pool_request.clear_connection()
                else:
                    break  # pragma: nocover

        except BaseException as exc:
            with self._optional_thread_lock:
                # For any exception or cancellation we remove the request from
                # the queue, and then re-assign requests to connections.
                self._requests.remove(pool_request)
                closing = self._assign_requests_to_connections()

            self._close_connections(closing)
            raise exc from None

        # Return the response. Note that in this case we still have to manage
        # the point at which the response is closed.
        assert isinstance(response.stream, Iterable)
        return Response(
            status=response.status,
            headers=response.headers,
            content=PoolByteStream(
                stream=response.stream, pool_request=pool_request, pool=self
            ),
            extensions=response.extensions,
        )

    def _assign_requests_to_connections(self) -> List[ConnectionInterface]:
        """
        Manage the state of the connection pool, assigning incoming
        requests to connections as available.

        Called whenever a new request is added or removed from the pool.

        Any closing connections are returned, allowing the I/O for closing
        those connections to be handled seperately.
        """
        closing_connections = []

        # First we handle cleaning up any connections that are closed,
        # have expired their keep-alive, or surplus idle connections.
        for connection in list(self._connections):
            if connection.is_closed():
                # log: "removing closed connection"
                self._connections.remove(connection)
            elif connection.has_expired():
                # log: "closing expired connection"
                self._connections.remove(connection)
                closing_connections.append(connection)
            elif (
                connection.is_idle()
                and len([connection.is_idle() for connection in self._connections])
                > self._max_keepalive_connections
            ):
                # log: "closing idle connection"
                self._connections.remove(connection)
                closing_connections.append(connection)

        # Assign queued requests to connections.
        queued_requests = [request for request in self._requests if request.is_queued()]
        for pool_request in queued_requests:
            origin = pool_request.request.url.origin
            available_connections = [
                connection
                for connection in self._connections
                if connection.can_handle_request(origin) and connection.is_available()
            ]
            idle_connections = [
                connection for connection in self._connections if connection.is_idle()
            ]

            # There are three cases for how we may be able to handle the request:
            #
            # 1. There is an existing connection that can handle the request.
            # 2. We can create a new connection to handle the request.
            # 3. We can close an idle connection and then create a new connection
            #    to handle the request.
            if available_connections:
                # log: "reusing existing connection"
                connection = available_connections[0]
                pool_request.assign_to_connection(connection)
            elif len(self._connections) < self._max_connections:
                # log: "creating new connection"
                connection = self.create_connection(origin)
                self._connections.append(connection)
                pool_request.assign_to_connection(connection)
            elif idle_connections:
                # log: "closing idle connection"
                connection = idle_connections[0]
                self._connections.remove(connection)
                closing_connections.append(connection)
                # log: "creating new connection"
                connection = self.create_connection(origin)
                self._connections.append(connection)
                pool_request.assign_to_connection(connection)

        return closing_connections

    def _close_connections(self, closing: List[ConnectionInterface]) -> None:
        # Close connections which have been removed from the pool.
        with ShieldCancellation():
            for connection in closing:
                connection.close()

    def close(self) -> None:
        # Explicitly close the connection pool.
        # Clears all existing requests and connections.
        with self._optional_thread_lock:
            closing_connections = list(self._connections)
            self._connections = []
        self._close_connections(closing_connections)

    def __enter__(self) -> "ConnectionPool":
        return self

    def __exit__(
        self,
        exc_type: Optional[Type[BaseException]] = None,
        exc_value: Optional[BaseException] = None,
        traceback: Optional[TracebackType] = None,
    ) -> None:
        self.close()

    def __repr__(self) -> str:
        class_name = self.__class__.__name__
        with self._optional_thread_lock:
            request_is_queued = [request.is_queued() for request in self._requests]
            connection_is_idle = [
                connection.is_idle() for connection in self._connections
            ]

            num_active_requests = request_is_queued.count(False)
            num_queued_requests = request_is_queued.count(True)
            num_active_connections = connection_is_idle.count(False)
            num_idle_connections = connection_is_idle.count(True)

        requests_info = (
            f"Requests: {num_active_requests} active, {num_queued_requests} queued"
        )
        connection_info = (
            f"Connections: {num_active_connections} active, {num_idle_connections} idle"
        )

        return f"<{class_name} [{requests_info} | {connection_info}]>"


class PoolByteStream:
    def __init__(
        self,
        stream: Iterable[bytes],
        pool_request: PoolRequest,
        pool: ConnectionPool,
    ) -> None:
        self._stream = stream
        self._pool_request = pool_request
        self._pool = pool
        self._closed = False

    def __iter__(self) -> Iterator[bytes]:
        try:
            for part in self._stream:
                yield part
        except BaseException as exc:
            self.close()
            raise exc from None

    def close(self) -> None:
        if not self._closed:
            self._closed = True
            with ShieldCancellation():
                if hasattr(self._stream, "close"):
                    self._stream.close()

            with self._pool._optional_thread_lock:
                self._pool._requests.remove(self._pool_request)
                closing = self._pool._assign_requests_to_connections()

            self._pool._close_connections(closing)
