from collections import deque
from typing import Deque, Dict, List, Optional, Tuple

from twisted.internet import defer
from twisted.internet.base import ReactorBase
from twisted.internet.defer import Deferred
from twisted.internet.endpoints import HostnameEndpoint
from twisted.python.failure import Failure
from twisted.web.client import URI, BrowserLikePolicyForHTTPS, _StandardEndpointFactory
from twisted.web.error import SchemeNotSupported

from scrapy.core.downloader.contextfactory import AcceptableProtocolsContextFactory
from scrapy.core.http2.protocol import H2ClientFactory, H2ClientProtocol
from scrapy.http.request import Request
from scrapy.settings import Settings
from scrapy.spiders import Spider


class H2ConnectionPool:
    def __init__(self, reactor: ReactorBase, settings: Settings) -> None:
        self._reactor = reactor
        self.settings = settings

        # Store a dictionary which is used to get the respective
        # H2ClientProtocolInstance using the  key as Tuple(scheme, hostname, port)
        self._connections: Dict[Tuple, H2ClientProtocol] = {}

        # Save all requests that arrive before the connection is established
        self._pending_requests: Dict[Tuple, Deque[Deferred]] = {}

    def get_connection(
        self, key: Tuple, uri: URI, endpoint: HostnameEndpoint
    ) -> Deferred:
        if key in self._pending_requests:
            # Received a request while connecting to remote
            # Create a deferred which will fire with the H2ClientProtocol
            # instance
            d = Deferred()
            self._pending_requests[key].append(d)
            return d

        # Check if we already have a connection to the remote
        conn = self._connections.get(key, None)
        if conn:
            # Return this connection instance wrapped inside a deferred
            return defer.succeed(conn)

        # No connection is established for the given URI
        return self._new_connection(key, uri, endpoint)

    def _new_connection(
        self, key: Tuple, uri: URI, endpoint: HostnameEndpoint
    ) -> Deferred:
        self._pending_requests[key] = deque()

        conn_lost_deferred = Deferred()
        conn_lost_deferred.addCallback(self._remove_connection, key)

        factory = H2ClientFactory(uri, self.settings, conn_lost_deferred)
        conn_d = endpoint.connect(factory)
        conn_d.addCallback(self.put_connection, key)

        d = Deferred()
        self._pending_requests[key].append(d)
        return d

    def put_connection(self, conn: H2ClientProtocol, key: Tuple) -> H2ClientProtocol:
        self._connections[key] = conn

        # Now as we have established a proper HTTP/2 connection
        # we fire all the deferred's with the connection instance
        pending_requests = self._pending_requests.pop(key, None)
        while pending_requests:
            d = pending_requests.popleft()
            d.callback(conn)

        return conn

    def _remove_connection(self, errors: List[BaseException], key: Tuple) -> None:
        self._connections.pop(key)

        # Call the errback of all the pending requests for this connection
        pending_requests = self._pending_requests.pop(key, None)
        while pending_requests:
            d = pending_requests.popleft()
            d.errback(errors)

    def close_connections(self) -> None:
        """Close all the HTTP/2 connections and remove them from pool

        Returns:
            Deferred that fires when all connections have been closed
        """
        for conn in self._connections.values():
            conn.transport.abortConnection()


class H2Agent:
    def __init__(
        self,
        reactor: ReactorBase,
        pool: H2ConnectionPool,
        context_factory: BrowserLikePolicyForHTTPS = BrowserLikePolicyForHTTPS(),
        connect_timeout: Optional[float] = None,
        bind_address: Optional[bytes] = None,
    ) -> None:
        self._reactor = reactor
        self._pool = pool
        self._context_factory = AcceptableProtocolsContextFactory(
            context_factory, acceptable_protocols=[b"h2"]
        )
        self.endpoint_factory = _StandardEndpointFactory(
            self._reactor, self._context_factory, connect_timeout, bind_address
        )

    def get_endpoint(self, uri: URI):
        return self.endpoint_factory.endpointForURI(uri)

    def get_key(self, uri: URI) -> Tuple:
        """
        Arguments:
            uri - URI obtained directly from request URL
        """
        return uri.scheme, uri.host, uri.port

    def request(self, request: Request, spider: Spider) -> Deferred:
        uri = URI.fromBytes(bytes(request.url, encoding="utf-8"))
        try:
            endpoint = self.get_endpoint(uri)
        except SchemeNotSupported:
            return defer.fail(Failure())

        key = self.get_key(uri)
        d = self._pool.get_connection(key, uri, endpoint)
        d.addCallback(lambda conn: conn.request(request, spider))
        return d


class ScrapyProxyH2Agent(H2Agent):
    def __init__(
        self,
        reactor: ReactorBase,
        proxy_uri: URI,
        pool: H2ConnectionPool,
        context_factory: BrowserLikePolicyForHTTPS = BrowserLikePolicyForHTTPS(),
        connect_timeout: Optional[float] = None,
        bind_address: Optional[bytes] = None,
    ) -> None:
        super().__init__(
            reactor=reactor,
            pool=pool,
            context_factory=context_factory,
            connect_timeout=connect_timeout,
            bind_address=bind_address,
        )
        self._proxy_uri = proxy_uri

    def get_endpoint(self, uri: URI):
        return self.endpoint_factory.endpointForURI(self._proxy_uri)

    def get_key(self, uri: URI) -> Tuple:
        """We use the proxy uri instead of uri obtained from request url"""
        return "http-proxy", self._proxy_uri.host, self._proxy_uri.port