"""
wsproto/handshake
~~~~~~~~~~~~~~~~~~

An implementation of WebSocket handshakes.
"""
from collections import deque
from typing import (
    cast,
    Deque,
    Dict,
    Generator,
    Iterable,
    List,
    Optional,
    Sequence,
    Union,
)

import h11

from .connection import Connection, ConnectionState, ConnectionType
from .events import AcceptConnection, Event, RejectConnection, RejectData, Request
from .extensions import Extension
from .typing import Headers
from .utilities import (
    generate_accept_token,
    generate_nonce,
    LocalProtocolError,
    normed_header_dict,
    RemoteProtocolError,
    split_comma_header,
)

# RFC6455, Section 4.2.1/6 - Reading the Client's Opening Handshake
WEBSOCKET_VERSION = b"13"


class H11Handshake:
    """A Handshake implementation for HTTP/1.1 connections."""

    def __init__(self, connection_type: ConnectionType) -> None:
        self.client = connection_type is ConnectionType.CLIENT
        self._state = ConnectionState.CONNECTING

        if self.client:
            self._h11_connection = h11.Connection(h11.CLIENT)
        else:
            self._h11_connection = h11.Connection(h11.SERVER)

        self._connection: Optional[Connection] = None
        self._events: Deque[Event] = deque()
        self._initiating_request: Optional[Request] = None
        self._nonce: Optional[bytes] = None

    @property
    def state(self) -> ConnectionState:
        return self._state

    @property
    def connection(self) -> Optional[Connection]:
        """Return the established connection.

        This will either return the connection or raise a
        LocalProtocolError if the connection has not yet been
        established.

        :rtype: h11.Connection
        """
        return self._connection

    def initiate_upgrade_connection(self, headers: Headers, path: str) -> None:
        """Initiate an upgrade connection.

        This should be used if the request has already be received and
        parsed.

        :param list headers: HTTP headers represented as a list of 2-tuples.
        :param str path: A URL path.
        """
        if self.client:
            raise LocalProtocolError(
                "Cannot initiate an upgrade connection when acting as the client"
            )
        upgrade_request = h11.Request(method=b"GET", target=path, headers=headers)
        h11_client = h11.Connection(h11.CLIENT)
        self.receive_data(h11_client.send(upgrade_request))

    def send(self, event: Event) -> bytes:
        """Send an event to the remote.

        This will return the bytes to send based on the event or raise
        a LocalProtocolError if the event is not valid given the
        state.

        :returns: Data to send to the WebSocket peer.
        :rtype: bytes
        """
        data = b""
        if isinstance(event, Request):
            data += self._initiate_connection(event)
        elif isinstance(event, AcceptConnection):
            data += self._accept(event)
        elif isinstance(event, RejectConnection):
            data += self._reject(event)
        elif isinstance(event, RejectData):
            data += self._send_reject_data(event)
        else:
            raise LocalProtocolError(
                f"Event {event} cannot be sent during the handshake"
            )
        return data

    def receive_data(self, data: Optional[bytes]) -> None:
        """Receive data from the remote.

        A list of events that the remote peer triggered by sending
        this data can be retrieved with :meth:`events`.

        :param bytes data: Data received from the WebSocket peer.
        """
        self._h11_connection.receive_data(data)
        while True:
            try:
                event = self._h11_connection.next_event()
            except h11.RemoteProtocolError:
                raise RemoteProtocolError(
                    "Bad HTTP message", event_hint=RejectConnection()
                )
            if (
                isinstance(event, h11.ConnectionClosed)
                or event is h11.NEED_DATA
                or event is h11.PAUSED
            ):
                break

            if self.client:
                if isinstance(event, h11.InformationalResponse):
                    if event.status_code == 101:
                        self._events.append(self._establish_client_connection(event))
                    else:
                        self._events.append(
                            RejectConnection(
                                headers=event.headers,
                                status_code=event.status_code,
                                has_body=False,
                            )
                        )
                        self._state = ConnectionState.CLOSED
                elif isinstance(event, h11.Response):
                    self._state = ConnectionState.REJECTING
                    self._events.append(
                        RejectConnection(
                            headers=event.headers,
                            status_code=event.status_code,
                            has_body=True,
                        )
                    )
                elif isinstance(event, h11.Data):
                    self._events.append(
                        RejectData(data=event.data, body_finished=False)
                    )
                elif isinstance(event, h11.EndOfMessage):
                    self._events.append(RejectData(data=b"", body_finished=True))
                    self._state = ConnectionState.CLOSED
            else:
                if isinstance(event, h11.Request):
                    self._events.append(self._process_connection_request(event))

    def events(self) -> Generator[Event, None, None]:
        """Return a generator that provides any events that have been generated
        by protocol activity.

        :returns: a generator that yields H11 events.
        """
        while self._events:
            yield self._events.popleft()

    ############ Server mode methods

    def _process_connection_request(  # noqa: MC0001
        self, event: h11.Request
    ) -> Request:
        if event.method != b"GET":
            raise RemoteProtocolError(
                "Request method must be GET", event_hint=RejectConnection()
            )
        connection_tokens = None
        extensions: List[str] = []
        host = None
        key = None
        subprotocols: List[str] = []
        upgrade = b""
        version = None
        headers: Headers = []
        for name, value in event.headers:
            name = name.lower()
            if name == b"connection":
                connection_tokens = split_comma_header(value)
            elif name == b"host":
                host = value.decode("ascii")
                continue  # Skip appending to headers
            elif name == b"sec-websocket-extensions":
                extensions = split_comma_header(value)
                continue  # Skip appending to headers
            elif name == b"sec-websocket-key":
                key = value
            elif name == b"sec-websocket-protocol":
                subprotocols = split_comma_header(value)
                continue  # Skip appending to headers
            elif name == b"sec-websocket-version":
                version = value
            elif name == b"upgrade":
                upgrade = value
            headers.append((name, value))
        if connection_tokens is None or not any(
            token.lower() == "upgrade" for token in connection_tokens
        ):
            raise RemoteProtocolError(
                "Missing header, 'Connection: Upgrade'", event_hint=RejectConnection()
            )
        if version != WEBSOCKET_VERSION:
            raise RemoteProtocolError(
                "Missing header, 'Sec-WebSocket-Version'",
                event_hint=RejectConnection(
                    headers=[(b"Sec-WebSocket-Version", WEBSOCKET_VERSION)],
                    status_code=426 if version else 400,
                ),
            )
        if key is None:
            raise RemoteProtocolError(
                "Missing header, 'Sec-WebSocket-Key'", event_hint=RejectConnection()
            )
        if upgrade.lower() != b"websocket":
            raise RemoteProtocolError(
                "Missing header, 'Upgrade: WebSocket'", event_hint=RejectConnection()
            )
        if host is None:
            raise RemoteProtocolError(
                "Missing header, 'Host'", event_hint=RejectConnection()
            )

        self._initiating_request = Request(
            extensions=extensions,
            extra_headers=headers,
            host=host,
            subprotocols=subprotocols,
            target=event.target.decode("ascii"),
        )
        return self._initiating_request

    def _accept(self, event: AcceptConnection) -> bytes:
        # _accept is always called after _process_connection_request.
        assert self._initiating_request is not None
        request_headers = normed_header_dict(self._initiating_request.extra_headers)

        nonce = request_headers[b"sec-websocket-key"]
        accept_token = generate_accept_token(nonce)

        headers = [
            (b"Upgrade", b"WebSocket"),
            (b"Connection", b"Upgrade"),
            (b"Sec-WebSocket-Accept", accept_token),
        ]

        if event.subprotocol is not None:
            if event.subprotocol not in self._initiating_request.subprotocols:
                raise LocalProtocolError(f"unexpected subprotocol {event.subprotocol}")
            headers.append(
                (b"Sec-WebSocket-Protocol", event.subprotocol.encode("ascii"))
            )

        if event.extensions:
            accepts = server_extensions_handshake(
                cast(Sequence[str], self._initiating_request.extensions),
                event.extensions,
            )
            if accepts:
                headers.append((b"Sec-WebSocket-Extensions", accepts))

        response = h11.InformationalResponse(
            status_code=101, headers=headers + event.extra_headers
        )
        self._connection = Connection(
            ConnectionType.CLIENT if self.client else ConnectionType.SERVER,
            event.extensions,
        )
        self._state = ConnectionState.OPEN
        return self._h11_connection.send(response)

    def _reject(self, event: RejectConnection) -> bytes:
        if self.state != ConnectionState.CONNECTING:
            raise LocalProtocolError(
                "Connection cannot be rejected in state %s" % self.state
            )

        headers = event.headers
        if not event.has_body:
            headers.append((b"content-length", b"0"))
        response = h11.Response(status_code=event.status_code, headers=headers)
        data = self._h11_connection.send(response)
        self._state = ConnectionState.REJECTING
        if not event.has_body:
            data += self._h11_connection.send(h11.EndOfMessage())
            self._state = ConnectionState.CLOSED
        return data

    def _send_reject_data(self, event: RejectData) -> bytes:
        if self.state != ConnectionState.REJECTING:
            raise LocalProtocolError(
                f"Cannot send rejection data in state {self.state}"
            )

        data = self._h11_connection.send(h11.Data(data=event.data))
        if event.body_finished:
            data += self._h11_connection.send(h11.EndOfMessage())
            self._state = ConnectionState.CLOSED
        return data

    ############ Client mode methods

    def _initiate_connection(self, request: Request) -> bytes:
        self._initiating_request = request
        self._nonce = generate_nonce()

        headers = [
            (b"Host", request.host.encode("ascii")),
            (b"Upgrade", b"WebSocket"),
            (b"Connection", b"Upgrade"),
            (b"Sec-WebSocket-Key", self._nonce),
            (b"Sec-WebSocket-Version", WEBSOCKET_VERSION),
        ]

        if request.subprotocols:
            headers.append(
                (
                    b"Sec-WebSocket-Protocol",
                    (", ".join(request.subprotocols)).encode("ascii"),
                )
            )

        if request.extensions:
            offers: Dict[str, Union[str, bool]] = {}
            for e in request.extensions:
                assert isinstance(e, Extension)
                offers[e.name] = e.offer()
            extensions = []
            for name, params in offers.items():
                bname = name.encode("ascii")
                if isinstance(params, bool):
                    if params:
                        extensions.append(bname)
                else:
                    extensions.append(b"%s; %s" % (bname, params.encode("ascii")))
            if extensions:
                headers.append((b"Sec-WebSocket-Extensions", b", ".join(extensions)))

        upgrade = h11.Request(
            method=b"GET",
            target=request.target.encode("ascii"),
            headers=headers + request.extra_headers,
        )
        return self._h11_connection.send(upgrade)

    def _establish_client_connection(
        self, event: h11.InformationalResponse
    ) -> AcceptConnection:  # noqa: MC0001
        # _establish_client_connection is always called after _initiate_connection.
        assert self._initiating_request is not None
        assert self._nonce is not None

        accept = None
        connection_tokens = None
        accepts: List[str] = []
        subprotocol = None
        upgrade = b""
        headers: Headers = []
        for name, value in event.headers:
            name = name.lower()
            if name == b"connection":
                connection_tokens = split_comma_header(value)
                continue  # Skip appending to headers
            elif name == b"sec-websocket-extensions":
                accepts = split_comma_header(value)
                continue  # Skip appending to headers
            elif name == b"sec-websocket-accept":
                accept = value
                continue  # Skip appending to headers
            elif name == b"sec-websocket-protocol":
                subprotocol = value
                continue  # Skip appending to headers
            elif name == b"upgrade":
                upgrade = value
                continue  # Skip appending to headers
            headers.append((name, value))

        if connection_tokens is None or not any(
            token.lower() == "upgrade" for token in connection_tokens
        ):
            raise RemoteProtocolError(
                "Missing header, 'Connection: Upgrade'", event_hint=RejectConnection()
            )
        if upgrade.lower() != b"websocket":
            raise RemoteProtocolError(
                "Missing header, 'Upgrade: WebSocket'", event_hint=RejectConnection()
            )
        accept_token = generate_accept_token(self._nonce)
        if accept != accept_token:
            raise RemoteProtocolError("Bad accept token", event_hint=RejectConnection())
        if subprotocol is not None:
            subprotocol = subprotocol.decode("ascii")
            if subprotocol not in self._initiating_request.subprotocols:
                raise RemoteProtocolError(
                    f"unrecognized subprotocol {subprotocol}",
                    event_hint=RejectConnection(),
                )
        extensions = client_extensions_handshake(
            accepts, cast(Sequence[Extension], self._initiating_request.extensions)
        )

        self._connection = Connection(
            ConnectionType.CLIENT if self.client else ConnectionType.SERVER,
            extensions,
            self._h11_connection.trailing_data[0],
        )
        self._state = ConnectionState.OPEN
        return AcceptConnection(
            extensions=extensions, extra_headers=headers, subprotocol=subprotocol
        )

    def __repr__(self) -> str:
        return "{}(client={}, state={})".format(
            self.__class__.__name__, self.client, self.state
        )


def server_extensions_handshake(
    requested: Iterable[str], supported: List[Extension]
) -> Optional[bytes]:
    """Agree on the extensions to use returning an appropriate header value.

    This returns None if there are no agreed extensions
    """
    accepts: Dict[str, Union[bool, bytes]] = {}
    for offer in requested:
        name = offer.split(";", 1)[0].strip()
        for extension in supported:
            if extension.name == name:
                accept = extension.accept(offer)
                if isinstance(accept, bool):
                    if accept:
                        accepts[extension.name] = True
                elif accept is not None:
                    accepts[extension.name] = accept.encode("ascii")

    if accepts:
        extensions: List[bytes] = []
        for name, params in accepts.items():
            name_bytes = name.encode("ascii")
            if isinstance(params, bool):
                assert params
                extensions.append(name_bytes)
            else:
                if params == b"":
                    extensions.append(b"%s" % (name_bytes))
                else:
                    extensions.append(b"%s; %s" % (name_bytes, params))
        return b", ".join(extensions)

    return None


def client_extensions_handshake(
    accepted: Iterable[str], supported: Sequence[Extension]
) -> List[Extension]:
    # This raises RemoteProtocolError is the accepted extension is not
    # supported.
    extensions = []
    for accept in accepted:
        name = accept.split(";", 1)[0].strip()
        for extension in supported:
            if extension.name == name:
                extension.finalize(accept)
                extensions.append(extension)
                break
        else:
            raise RemoteProtocolError(
                f"unrecognized extension {name}", event_hint=RejectConnection()
            )
    return extensions