# Copyright 2019 The gRPC Authors
#
# 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.
"""Client of the Python example of customizing authentication mechanism."""

import argparse
import contextlib
import logging

import grpc
import _credentials

helloworld_pb2, helloworld_pb2_grpc = grpc.protos_and_services(
    "helloworld.proto")

_LOGGER = logging.getLogger(__name__)
_LOGGER.setLevel(logging.INFO)

_SERVER_ADDR_TEMPLATE = 'localhost:%d'
_SIGNATURE_HEADER_KEY = 'x-signature'


class AuthGateway(grpc.AuthMetadataPlugin):

    def __call__(self, context, callback):
        """Implements authentication by passing metadata to a callback.

        Implementations of this method must not block.

        Args:
          context: An AuthMetadataContext providing information on the RPC that
            the plugin is being called to authenticate.
          callback: An AuthMetadataPluginCallback to be invoked either
            synchronously or asynchronously.
        """
        # Example AuthMetadataContext object:
        # AuthMetadataContext(
        #     service_url=u'https://localhost:50051/helloworld.Greeter',
        #     method_name=u'SayHello')
        signature = context.method_name[::-1]
        callback(((_SIGNATURE_HEADER_KEY, signature),), None)


@contextlib.contextmanager
def create_client_channel(addr):
    # Call credential object will be invoked for every single RPC
    call_credentials = grpc.metadata_call_credentials(AuthGateway(),
                                                      name='auth gateway')
    # Channel credential will be valid for the entire channel
    channel_credential = grpc.ssl_channel_credentials(
        _credentials.ROOT_CERTIFICATE)
    # Combining channel credentials and call credentials together
    composite_credentials = grpc.composite_channel_credentials(
        channel_credential,
        call_credentials,
    )
    channel = grpc.secure_channel(addr, composite_credentials)
    yield channel


def send_rpc(channel):
    stub = helloworld_pb2_grpc.GreeterStub(channel)
    request = helloworld_pb2.HelloRequest(name='you')
    try:
        response = stub.SayHello(request)
    except grpc.RpcError as rpc_error:
        _LOGGER.error('Received error: %s', rpc_error)
        return rpc_error
    else:
        _LOGGER.info('Received message: %s', response)
        return response


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument('--port',
                        nargs='?',
                        type=int,
                        default=50051,
                        help='the address of server')
    args = parser.parse_args()

    with create_client_channel(_SERVER_ADDR_TEMPLATE % args.port) as channel:
        send_rpc(channel)


if __name__ == '__main__':
    logging.basicConfig(level=logging.INFO)
    main()