from __future__ import (absolute_import, print_function, division)

from .. import version
import threading
from ..exceptions import InvalidCredentials, HttpException, ProtocolException
from .layer import Layer
from libmproxy import utils
from libmproxy.controller import Channel
from libmproxy.protocol2.layer import Kill
from libmproxy.protocol import KILL, Error

from libmproxy.protocol.http import HTTPFlow
from libmproxy.protocol.http_wrappers import HTTPResponse, HTTPRequest
from libmproxy.proxy import Log
from libmproxy.proxy.connection import ServerConnection
from netlib import tcp
from netlib.http import status_codes, http1, http2, HttpErrorConnClosed, HttpError
from netlib.http.semantics import CONTENT_MISSING
from netlib import odict
from netlib.tcp import NetLibError, Address
from netlib.http.http1 import HTTP1Protocol
from netlib.http.http2 import HTTP2Protocol


# TODO: The HTTP2 layer is missing multiplexing, which requires a major rewrite.


class _HttpLayer(Layer):
    supports_streaming = False

    def read_request(self):
        raise NotImplementedError()

    def send_request(self, request):
        raise NotImplementedError()

    def read_response(self, request_method):
        raise NotImplementedError()

    def send_response(self, response):
        raise NotImplementedError()


class _StreamingHttpLayer(_HttpLayer):
    supports_streaming = True

    def read_response_headers(self):
        raise NotImplementedError

    def read_response_body(self, headers, request_method, response_code, max_chunk_size=None):
        raise NotImplementedError()
        yield "this is a generator"

    def send_response_headers(self, response):
        raise NotImplementedError

    def send_response_body(self, response, chunks):
        raise NotImplementedError()


class Http1Layer(_StreamingHttpLayer):
    def __init__(self, ctx, mode):
        super(Http1Layer, self).__init__(ctx)
        self.mode = mode
        self.client_protocol = HTTP1Protocol(self.client_conn)
        self.server_protocol = HTTP1Protocol(self.server_conn)

    def read_request(self):
        return HTTPRequest.from_protocol(
            self.client_protocol,
            body_size_limit=self.config.body_size_limit
        )

    def send_request(self, request):
        self.server_conn.send(self.server_protocol.assemble(request))

    def read_response(self, request_method):
        return HTTPResponse.from_protocol(
            self.server_protocol,
            request_method=request_method,
            body_size_limit=self.config.body_size_limit,
            include_body=True
        )

    def send_response(self, response):
        self.client_conn.send(self.client_protocol.assemble(response))

    def read_response_headers(self):
        return HTTPResponse.from_protocol(
            self.server_protocol,
            request_method=None,  # does not matter if we don't read the body.
            body_size_limit=self.config.body_size_limit,
            include_body=False
        )

    def read_response_body(self, headers, request_method, response_code, max_chunk_size=None):
        return self.server_protocol.read_http_body_chunked(
            headers,
            self.config.body_size_limit,
            request_method,
            response_code,
            False,
            max_chunk_size
        )

    def send_response_headers(self, response):
        h = self.client_protocol._assemble_response_first_line(response)
        self.client_conn.wfile.write(h + "\r\n")
        h = self.client_protocol._assemble_response_headers(
            response,
            preserve_transfer_encoding=True
        )
        self.client_conn.send(h + "\r\n")

    def send_response_body(self, response, chunks):
        if self.client_protocol.has_chunked_encoding(response.headers):
            chunks = (
                "%d\r\n%s\r\n" % (len(chunk), chunk)
                for chunk in chunks
            )
        for chunk in chunks:
            self.client_conn.send(chunk)

    def connect(self):
        self.ctx.connect()
        self.server_protocol = HTTP1Protocol(self.server_conn)

    def reconnect(self):
        self.ctx.reconnect()
        self.server_protocol = HTTP1Protocol(self.server_conn)

    def set_server(self, *args, **kwargs):
        self.ctx.set_server(*args, **kwargs)
        self.server_protocol = HTTP1Protocol(self.server_conn)

    def __call__(self):
        layer = HttpLayer(self, self.mode)
        layer()


class Http2Layer(_HttpLayer):
    def __init__(self, ctx, mode):
        super(Http2Layer, self).__init__(ctx)
        self.mode = mode
        self.client_protocol = HTTP2Protocol(self.client_conn, is_server=True,
                                             unhandled_frame_cb=self.handle_unexpected_frame)
        self.server_protocol = HTTP2Protocol(self.server_conn, is_server=False,
                                             unhandled_frame_cb=self.handle_unexpected_frame)

    def read_request(self):
        request = HTTPRequest.from_protocol(
            self.client_protocol,
            body_size_limit=self.config.body_size_limit
        )
        self._stream_id = request.stream_id
        return request

    def send_request(self, message):
        # TODO: implement flow control and WINDOW_UPDATE frames
        self.server_conn.send(self.server_protocol.assemble(message))

    def read_response(self, request_method):
        return HTTPResponse.from_protocol(
            self.server_protocol,
            request_method=request_method,
            body_size_limit=self.config.body_size_limit,
            include_body=True,
            stream_id=self._stream_id
        )

    def send_response(self, message):
        # TODO: implement flow control and WINDOW_UPDATE frames
        self.client_conn.send(self.client_protocol.assemble(message))

    def connect(self):
        self.ctx.connect()
        self.server_protocol = HTTP2Protocol(self.server_conn, is_server=False,
                                             unhandled_frame_cb=self.handle_unexpected_frame)
        self.server_protocol.perform_connection_preface()

    def reconnect(self):
        self.ctx.reconnect()
        self.server_protocol = HTTP2Protocol(self.server_conn, is_server=False,
                                             unhandled_frame_cb=self.handle_unexpected_frame)
        self.server_protocol.perform_connection_preface()

    def set_server(self, *args, **kwargs):
        self.ctx.set_server(*args, **kwargs)
        self.server_protocol = HTTP2Protocol(self.server_conn, is_server=False,
                                             unhandled_frame_cb=self.handle_unexpected_frame)
        self.server_protocol.perform_connection_preface()

    def __call__(self):
        self.server_protocol.perform_connection_preface()
        layer = HttpLayer(self, self.mode)
        layer()

    def handle_unexpected_frame(self, frm):
        self.log("Unexpected HTTP2 Frame: %s" % frm.human_readable(), "info")


def make_error_response(status_code, message, headers=None):
    response = status_codes.RESPONSES.get(status_code, "Unknown")
    body = """
        <html>
            <head>
                <title>%d %s</title>
            </head>
            <body>%s</body>
        </html>
    """.strip() % (status_code, response, message)

    if not headers:
        headers = odict.ODictCaseless()
    headers["Server"] = [version.NAMEVERSION]
    headers["Connection"] = ["close"]
    headers["Content-Length"] = [len(body)]
    headers["Content-Type"] = ["text/html"]

    return HTTPResponse(
        (1, 1),  # FIXME: Should be a string.
        status_code,
        response,
        headers,
        body,
    )


def make_connect_request(address):
    address = Address.wrap(address)
    return HTTPRequest(
        "authority", "CONNECT", None, address.host, address.port, None, (1, 1),
        odict.ODictCaseless(), ""
    )


def make_connect_response(httpversion):
    headers = odict.ODictCaseless([
        ["Content-Length", "0"],
        ["Proxy-Agent", version.NAMEVERSION]
    ])
    return HTTPResponse(
        httpversion,
        200,
        "Connection established",
        headers,
        "",
    )


class ConnectServerConnection(object):
    """
    "Fake" ServerConnection to represent state after a CONNECT request to an upstream proxy.
    """

    def __init__(self, address, ctx):
        self.address = tcp.Address.wrap(address)
        self._ctx = ctx

    @property
    def via(self):
        return self._ctx.server_conn

    def __getattr__(self, item):
        return getattr(self.via, item)


class UpstreamConnectLayer(Layer):
    def __init__(self, ctx, connect_request):
        super(UpstreamConnectLayer, self).__init__(ctx)
        self.connect_request = connect_request
        self.server_conn = ConnectServerConnection(
            (connect_request.host, connect_request.port),
            self.ctx
        )

    def __call__(self):
        layer = self.ctx.next_layer(self)
        layer()

    def connect(self):
        if not self.server_conn:
            self.ctx.connect()
            self.send_request(self.connect_request)
        else:
            pass  # swallow the message

    def reconnect(self):
        self.ctx.reconnect()
        self.send_request(self.connect_request)
        resp = self.read_response("CONNECT")
        if resp.code != 200:
            raise ProtocolException("Reconnect: Upstream server refuses CONNECT request")

    def set_server(self, address, server_tls=None, sni=None, depth=1):
        if depth == 1:
            if self.ctx.server_conn:
                self.ctx.reconnect()
            address = Address.wrap(address)
            self.connect_request.host = address.host
            self.connect_request.port = address.port
            self.server_conn.address = address
        else:
            self.ctx.set_server(address, server_tls, sni, depth - 1)


class HttpLayer(Layer):
    def __init__(self, ctx, mode):
        super(HttpLayer, self).__init__(ctx)
        self.mode = mode
        self.__original_server_conn = None
        "Contains the original destination in transparent mode, which needs to be restored"
        "if an inline script modified the target server for a single http request"

    def __call__(self):
        if self.mode == "transparent":
            self.__original_server_conn = self.server_conn
        while True:
            try:
                flow = HTTPFlow(self.client_conn, self.server_conn, live=self)

                try:
                    request = self.read_request()
                except tcp.NetLibError:
                    # don't throw an error for disconnects that happen
                    # before/between requests.
                    return

                self.log("request", "debug", [repr(request)])

                # Handle Proxy Authentication
                self.authenticate(request)

                # Regular Proxy Mode: Handle CONNECT
                if self.mode == "regular" and request.form_in == "authority":
                    self.handle_regular_mode_connect(request)
                    return

                # Make sure that the incoming request matches our expectations
                self.validate_request(request)

                flow.request = request
                self.process_request_hook(flow)

                if not flow.response:
                    self.establish_server_connection(flow)
                    self.get_response_from_server(flow)

                self.send_response_to_client(flow)

                if self.check_close_connection(flow):
                    return

                # TODO: Implement HTTP Upgrade

                # Upstream Proxy Mode: Handle CONNECT
                if flow.request.form_in == "authority" and flow.response.code == 200:
                    self.handle_upstream_mode_connect(flow.request.copy())
                    return

            except (HttpErrorConnClosed, NetLibError, HttpError, ProtocolException) as e:
                try:
                    self.send_response(make_error_response(
                        getattr(e, "code", 502),
                        repr(e)
                    ))
                except NetLibError:
                    pass
                if isinstance(e, ProtocolException):
                    raise e
                else:
                    raise ProtocolException("Error in HTTP connection: %s" % repr(e), e)
            finally:
                flow.live = False

    def handle_regular_mode_connect(self, request):
        self.set_server((request.host, request.port))
        self.send_response(make_connect_response(request.httpversion))
        layer = self.ctx.next_layer(self)
        layer()

    def handle_upstream_mode_connect(self, connect_request):
        layer = UpstreamConnectLayer(self, connect_request)
        layer()

    def check_close_connection(self, flow):
        """
            Checks if the connection should be closed depending on the HTTP
            semantics. Returns True, if so.
        """

        # TODO: add logic for HTTP/2

        close_connection = (
            http1.HTTP1Protocol.connection_close(
                flow.request.httpversion,
                flow.request.headers
            ) or http1.HTTP1Protocol.connection_close(
                flow.response.httpversion,
                flow.response.headers
            ) or http1.HTTP1Protocol.expected_http_body_size(
                flow.response.headers,
                False,
                flow.request.method,
                flow.response.code) == -1
        )
        if flow.request.form_in == "authority" and flow.response.code == 200:
            # Workaround for
            # https://github.com/mitmproxy/mitmproxy/issues/313: Some
            # proxies (e.g. Charles) send a CONNECT response with HTTP/1.0
            # and no Content-Length header

            return False
        return close_connection

    def send_response_to_client(self, flow):
        if not (self.supports_streaming and flow.response.stream):
            # no streaming:
            # we already received the full response from the server and can
            # send it to the client straight away.
            self.send_response(flow.response)
        else:
            # streaming:
            # First send the headers and then transfer the response incrementally
            self.send_response_headers(flow.response)
            chunks = self.read_response_body(
                flow.response.headers,
                flow.request.method,
                flow.response.code,
                max_chunk_size=4096
            )
            if callable(flow.response.stream):
                chunks = flow.response.stream(chunks)
            self.send_response_body(flow.response, chunks)
            flow.response.timestamp_end = utils.timestamp()

    def get_response_from_server(self, flow):
        def get_response():
            self.send_request(flow.request)
            if self.supports_streaming:
                flow.response = self.read_response_headers()
            else:
                flow.response = self.read_response()

        try:
            get_response()
        except (tcp.NetLibError, HttpErrorConnClosed) as v:
            self.log(
                "server communication error: %s" % repr(v),
                level="debug"
            )
            # In any case, we try to reconnect at least once. This is
            # necessary because it might be possible that we already
            # initiated an upstream connection after clientconnect that
            # has already been expired, e.g consider the following event
            # log:
            # > clientconnect (transparent mode destination known)
            # > serverconnect (required for client tls handshake)
            # > read n% of large request
            # > server detects timeout, disconnects
            # > read (100-n)% of large request
            # > send large request upstream
            self.reconnect()
            get_response()

        # call the appropriate script hook - this is an opportunity for an
        # inline script to set flow.stream = True
        flow = self.channel.ask("responseheaders", flow)
        if flow is None or flow == KILL:
            raise Kill()

        if self.supports_streaming:
            if flow.response.stream:
                flow.response.content = CONTENT_MISSING
            else:
                flow.response.content = "".join(self.read_response_body(
                    flow.response.headers,
                    flow.request.method,
                    flow.response.code
                ))
            flow.response.timestamp_end = utils.timestamp()

        # no further manipulation of self.server_conn beyond this point
        # we can safely set it as the final attribute value here.
        flow.server_conn = self.server_conn

        self.log(
            "response",
            "debug",
            [repr(flow.response)]
        )
        response_reply = self.channel.ask("response", flow)
        if response_reply is None or response_reply == KILL:
            raise Kill()

    def process_request_hook(self, flow):
        # Determine .scheme, .host and .port attributes for inline scripts.
        # For absolute-form requests, they are directly given in the request.
        # For authority-form requests, we only need to determine the request scheme.
        # For relative-form requests, we need to determine host and port as
        # well.
        if self.mode == "regular":
            pass  # only absolute-form at this point, nothing to do here.
        elif self.mode == "upstream":
            if flow.request.form_in == "authority":
                flow.request.scheme = "http"  # pseudo value
        else:
            flow.request.host = self.__original_server_conn.address.host
            flow.request.port = self.__original_server_conn.address.port
            flow.request.scheme = "https" if self.__original_server_conn.tls_established else "http"

        request_reply = self.channel.ask("request", flow)
        if request_reply is None or request_reply == KILL:
            raise Kill()
        if isinstance(request_reply, HTTPResponse):
            flow.response = request_reply
            return

    def establish_server_connection(self, flow):
        address = tcp.Address((flow.request.host, flow.request.port))
        tls = (flow.request.scheme == "https")

        if self.mode == "regular" or self.mode == "transparent":
            # If there's an existing connection that doesn't match our expectations, kill it.
            if address != self.server_conn.address or tls != self.server_conn.ssl_established:
                self.set_server(address, tls, address.host)
            # Establish connection is neccessary.
            if not self.server_conn:
                self.connect()

            # SetServer is not guaranteed to work with TLS:
            # If there's not TlsLayer below which could catch the exception,
            # TLS will not be established.
            if tls and not self.server_conn.tls_established:
                raise ProtocolException(
                    "Cannot upgrade to SSL, no TLS layer on the protocol stack.")
        else:
            if not self.server_conn:
                self.connect()
            if tls:
                raise HttpException("Cannot change scheme in upstream proxy mode.")
            """
            # This is a very ugly (untested) workaround to solve a very ugly problem.
            if self.server_conn and self.server_conn.tls_established and not ssl:
                self.reconnect()
            elif ssl and not hasattr(self, "connected_to") or self.connected_to != address:
                if self.server_conn.tls_established:
                    self.reconnect()

                self.send_request(make_connect_request(address))
                tls_layer = TlsLayer(self, False, True)
                tls_layer._establish_tls_with_server()
            """

    def validate_request(self, request):
        if request.form_in == "absolute" and request.scheme != "http":
            self.send_response(
                make_error_response(400, "Invalid request scheme: %s" % request.scheme))
            raise HttpException("Invalid request scheme: %s" % request.scheme)

        expected_request_forms = {
            "regular": ("absolute",),  # an authority request would already be handled.
            "upstream": ("authority", "absolute"),
            "transparent": ("relative",)
        }

        allowed_request_forms = expected_request_forms[self.mode]
        if request.form_in not in allowed_request_forms:
            err_message = "Invalid HTTP request form (expected: %s, got: %s)" % (
                " or ".join(allowed_request_forms), request.form_in
            )
            self.send_response(make_error_response(400, err_message))
            raise HttpException(err_message)

        if self.mode == "regular":
            request.form_out = "relative"

    def authenticate(self, request):
        if self.config.authenticator:
            if self.config.authenticator.authenticate(request.headers):
                self.config.authenticator.clean(request.headers)
            else:
                self.send_response(make_error_response(
                    407,
                    "Proxy Authentication Required",
                    odict.ODictCaseless(
                        [
                            [k, v] for k, v in
                            self.config.authenticator.auth_challenge_headers().items()
                            ])
                ))
                raise InvalidCredentials("Proxy Authentication Required")


class RequestReplayThread(threading.Thread):
    name = "RequestReplayThread"

    def __init__(self, config, flow, masterq, should_exit):
        """
            masterqueue can be a queue or None, if no scripthooks should be
            processed.
        """
        self.config, self.flow = config, flow
        if masterq:
            self.channel = Channel(masterq, should_exit)
        else:
            self.channel = None
        super(RequestReplayThread, self).__init__()

    def run(self):
        r = self.flow.request
        form_out_backup = r.form_out
        try:
            self.flow.response = None

            # If we have a channel, run script hooks.
            if self.channel:
                request_reply = self.channel.ask("request", self.flow)
                if request_reply is None or request_reply == KILL:
                    raise Kill()
                elif isinstance(request_reply, HTTPResponse):
                    self.flow.response = request_reply

            if not self.flow.response:
                # In all modes, we directly connect to the server displayed
                if self.config.mode == "upstream":
                    server_address = self.config.upstream_server.address
                    server = ServerConnection(server_address)
                    server.connect()
                    protocol = HTTP1Protocol(server)
                    if r.scheme == "https":
                        connect_request = make_connect_request((r.host, r.port))
                        server.send(protocol.assemble(connect_request))
                        resp = protocol.read_response("CONNECT")
                        if resp.code != 200:
                            raise HttpError(502, "Upstream server refuses CONNECT request")
                        server.establish_ssl(
                            self.config.clientcerts,
                            sni=self.flow.server_conn.sni
                        )
                        r.form_out = "relative"
                    else:
                        r.form_out = "absolute"
                else:
                    server_address = (r.host, r.port)
                    server = ServerConnection(server_address)
                    server.connect()
                    protocol = HTTP1Protocol(server)
                    if r.scheme == "https":
                        server.establish_ssl(
                            self.config.clientcerts,
                            sni=self.flow.server_conn.sni
                        )
                    r.form_out = "relative"

                server.send(protocol.assemble(r))
                self.flow.server_conn = server
                self.flow.response = HTTPResponse.from_protocol(
                    protocol,
                    r.method,
                    body_size_limit=self.config.body_size_limit,
                )
            if self.channel:
                response_reply = self.channel.ask("response", self.flow)
                if response_reply is None or response_reply == KILL:
                    raise Kill()
        except (HttpError, tcp.NetLibError) as v:
            self.flow.error = Error(repr(v))
            if self.channel:
                self.channel.ask("error", self.flow)
        except Kill:
            # KillSignal should only be raised if there's a channel in the
            # first place.
            self.channel.tell("log", Log("Connection killed", "info"))
        finally:
            r.form_out = form_out_backup