# -*- coding: utf-8 -*-
# Copyright 2014, 2015 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


from synapse.api.errors import (
    cs_exception, SynapseError, CodeMessageException, UnrecognizedRequestError
)
from synapse.util.logcontext import LoggingContext
import synapse.metrics

from syutil.jsonutil import (
    encode_canonical_json, encode_pretty_printed_json
)

from twisted.internet import defer, reactor
from twisted.web import server, resource
from twisted.web.server import NOT_DONE_YET
from twisted.web.util import redirectTo

import collections
import logging
import urllib

logger = logging.getLogger(__name__)

metrics = synapse.metrics.get_metrics_for(__name__)

incoming_requests_counter = metrics.register_counter(
    "requests",
    labels=["method", "servlet"],
)
outgoing_responses_counter = metrics.register_counter(
    "responses",
    labels=["method", "code"],
)

response_timer = metrics.register_distribution(
    "response_time",
    labels=["method", "servlet"]
)


class HttpServer(object):
    """ Interface for registering callbacks on a HTTP server
    """

    def register_path(self, method, path_pattern, callback):
        """ Register a callback that gets fired if we receive a http request
        with the given method for a path that matches the given regex.

        If the regex contains groups these gets passed to the calback via
        an unpacked tuple.

        Args:
            method (str): The method to listen to.
            path_pattern (str): The regex used to match requests.
            callback (function): The function to fire if we receive a matched
                request. The first argument will be the request object and
                subsequent arguments will be any matched groups from the regex.
                This should return a tuple of (code, response).
        """
        pass


class JsonResource(HttpServer, resource.Resource):
    """ This implements the HttpServer interface and provides JSON support for
    Resources.

    Register callbacks via register_path()
    """

    isLeaf = True

    _PathEntry = collections.namedtuple("_PathEntry", ["pattern", "callback"])

    def __init__(self, hs):
        resource.Resource.__init__(self)

        self.clock = hs.get_clock()
        self.path_regexs = {}
        self.version_string = hs.version_string
        self.hs = hs

    def register_path(self, method, path_pattern, callback):
        self.path_regexs.setdefault(method, []).append(
            self._PathEntry(path_pattern, callback)
        )

    def start_listening(self, port):
        """ Registers the http server with the twisted reactor.

        Args:
            port (int): The port to listen on.

        """
        reactor.listenTCP(
            port,
            server.Site(self),
            interface=self.hs.config.bind_host
        )

    def render(self, request):
        """ This gets called by twisted every time someone sends us a request.
        """
        self._async_render_with_logging_context(request)
        return server.NOT_DONE_YET

    _request_id = 0

    @defer.inlineCallbacks
    def _async_render_with_logging_context(self, request):
        request_id = "%s-%s" % (request.method, JsonResource._request_id)
        JsonResource._request_id += 1
        with LoggingContext(request_id) as request_context:
            request_context.request = request_id
            yield self._async_render(request)

    @defer.inlineCallbacks
    def _async_render(self, request):
        """ This gets called by twisted every time someone sends us a request.
            This checks if anyone has registered a callback for that method and
            path.
        """
        code = None
        start = self.clock.time_msec()
        try:
            # Just say yes to OPTIONS.
            if request.method == "OPTIONS":
                self._send_response(request, 200, {})
                return

            # Loop through all the registered callbacks to check if the method
            # and path regex match
            for path_entry in self.path_regexs.get(request.method, []):
                m = path_entry.pattern.match(request.path)
                if not m:
                    continue

                # We found a match! Trigger callback and then return the
                # returned response. We pass both the request and any
                # matched groups from the regex to the callback.

                callback = path_entry.callback

                servlet_instance = getattr(callback, "__self__", None)
                if servlet_instance is not None:
                    servlet_classname = servlet_instance.__class__.__name__
                else:
                    servlet_classname = "%r" % callback
                incoming_requests_counter.inc(request.method, servlet_classname)

                args = [
                    urllib.unquote(u).decode("UTF-8") for u in m.groups()
                ]

                logger.info(
                    "Received request: %s %s",
                    request.method, request.path
                )

                code, response = yield callback(request, *args)

                self._send_response(request, code, response)
                response_timer.inc_by(
                    self.clock.time_msec() - start, request.method, servlet_classname
                )

                return

            # Huh. No one wanted to handle that? Fiiiiiine. Send 400.
            raise UnrecognizedRequestError()
        except CodeMessageException as e:
            if isinstance(e, SynapseError):
                logger.info("%s SynapseError: %s - %s", request, e.code, e.msg)
            else:
                logger.exception(e)

            code = e.code
            self._send_response(
                request,
                code,
                cs_exception(e),
                response_code_message=e.response_code_message
            )
        except Exception as e:
            logger.exception(e)
            self._send_response(
                request,
                500,
                {"error": "Internal server error"}
            )
        finally:
            code = str(code) if code else "-"

            end = self.clock.time_msec()
            logger.info(
                "Processed request: %dms %s %s %s",
                end-start, code, request.method, request.path
            )

    def _send_response(self, request, code, response_json_object,
                       response_code_message=None):
        # could alternatively use request.notifyFinish() and flip a flag when
        # the Deferred fires, but since the flag is RIGHT THERE it seems like
        # a waste.
        if request._disconnected:
            logger.warn(
                "Not sending response to request %s, already disconnected.",
                request)
            return

        outgoing_responses_counter.inc(request.method, str(code))

        # TODO: Only enable CORS for the requests that need it.
        respond_with_json(
            request, code, response_json_object,
            send_cors=True,
            response_code_message=response_code_message,
            pretty_print=self._request_user_agent_is_curl,
            version_string=self.version_string,
        )

    @staticmethod
    def _request_user_agent_is_curl(request):
        user_agents = request.requestHeaders.getRawHeaders(
            "User-Agent", default=[]
        )
        for user_agent in user_agents:
            if "curl" in user_agent:
                return True
        return False


class RootRedirect(resource.Resource):
    """Redirects the root '/' path to another path."""

    def __init__(self, path):
        resource.Resource.__init__(self)
        self.url = path

    def render_GET(self, request):
        return redirectTo(self.url, request)

    def getChild(self, name, request):
        if len(name) == 0:
            return self  # select ourselves as the child to render
        return resource.Resource.getChild(self, name, request)


def respond_with_json(request, code, json_object, send_cors=False,
                      response_code_message=None, pretty_print=False,
                      version_string=""):
    if not pretty_print:
        json_bytes = encode_pretty_printed_json(json_object)
    else:
        json_bytes = encode_canonical_json(json_object)

    return respond_with_json_bytes(
        request, code, json_bytes,
        send_cors=send_cors,
        response_code_message=response_code_message,
        version_string=version_string
    )


def respond_with_json_bytes(request, code, json_bytes, send_cors=False,
                            version_string="", response_code_message=None):
    """Sends encoded JSON in response to the given request.

    Args:
        request (twisted.web.http.Request): The http request to respond to.
        code (int): The HTTP response code.
        json_bytes (bytes): The json bytes to use as the response body.
        send_cors (bool): Whether to send Cross-Origin Resource Sharing headers
            http://www.w3.org/TR/cors/
    Returns:
        twisted.web.server.NOT_DONE_YET"""

    request.setResponseCode(code, message=response_code_message)
    request.setHeader(b"Content-Type", b"application/json")
    request.setHeader(b"Server", version_string)
    request.setHeader(b"Content-Length", b"%d" % (len(json_bytes),))

    if send_cors:
        request.setHeader("Access-Control-Allow-Origin", "*")
        request.setHeader("Access-Control-Allow-Methods",
                          "GET, POST, PUT, DELETE, OPTIONS")
        request.setHeader("Access-Control-Allow-Headers",
                          "Origin, X-Requested-With, Content-Type, Accept")

    request.write(json_bytes)
    request.finish()
    return NOT_DONE_YET