#
# Copyright 2016 the original author or 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.
#

"""
gRPC client meant to connect to a gRPC server endpoint, and query the
end-point's schema by calling SchemaService.Schema(NullMessage) and all of its
semantics are derived from the recovered schema.
"""

import os
import sys
from random import randint
from zlib import decompress

import grpc
from consul import Consul
from grpc._channel import _Rendezvous
from structlog import get_logger
from twisted.internet import reactor
from twisted.internet.defer import inlineCallbacks
from werkzeug.exceptions import ServiceUnavailable

from chameleon.asleep import asleep
from chameleon.protos.schema_pb2 import NullMessage, SchemaServiceStub

log = get_logger()


class GrpcClient(object):
    """
    Connect to a gRPC server, fetch its schema, and process the downloaded
    schema files to drive the customization of the north-bound interface(s)
    of Chameleon.
    """
    RETRY_BACKOFF = [0.05, 0.1, 0.2, 0.5, 1, 2, 5]

    def __init__(self, consul_endpoint, work_dir, endpoint='localhost:50055'):
        self.consul_endpoint = consul_endpoint
        self.endpoint = endpoint
        self.work_dir = work_dir
        self.plugin_dir = os.path.abspath(os.path.join(
            os.path.dirname(__file__), '../protoc_plugins'))

        self.channel = None
        self.schema = None
        self.retries = 0
        self.on_reconnect = None
        self.shutting_down = False
        self.connected = False

    def run(self, on_reconnect=None):
        self.on_reconnect = on_reconnect
        if not self.connected:
            reactor.callLater(0, self.connect)
        return self

    def shutdown(self):
        if self.shutting_down:
            return
        self.shutting_down = True
        pass

    @inlineCallbacks
    def connect(self):
        """
        (Re-)Connect to end-point
        """

        if self.shutting_down or self.connected:
            return

        try:
            if self.endpoint.startswith('@'):
                _endpoint = self._get_endpoint_from_consul(self.endpoint[1:])
            else:
                _endpoint = self.endpoint

            log.info('connecting', endpoint=_endpoint)
            self.channel = grpc.insecure_channel(_endpoint)

            self._retrieve_schema()
            self._compile_proto_files()
            self._clear_backoff()

            self.connected = True
            if self.on_reconnect is not None:
                reactor.callLater(0, self.on_reconnect)

            return

        except _Rendezvous, e:
            if e.code() == grpc.StatusCode.UNAVAILABLE:
                log.info('grpc-endpoint-not-available')
            else:
                log.exception(e)
            yield self._backoff('not-available')

        except Exception, e:
            if not self.shutting_down:
                log.exception('cannot-connect', endpoint=_endpoint)
            yield self._backoff('unknown-error')

        reactor.callLater(0, self.connect)

    def _backoff(self, msg):
        wait_time = self.RETRY_BACKOFF[min(self.retries,
                                           len(self.RETRY_BACKOFF) - 1)]
        self.retries += 1
        log.error(msg, retry_in=wait_time)
        return asleep(wait_time)

    def _clear_backoff(self):
        if self.retries:
            log.info('reconnected', after_retries=self.retries)
            self.retries = 0

    def _get_endpoint_from_consul(self, service_name):
        """
        Look up an appropriate grpc endpoint (host, port) from
        consul, under the service name specified by service-name
        """
        host = self.consul_endpoint.split(':')[0].strip()
        port = int(self.consul_endpoint.split(':')[1].strip())

        consul = Consul(host=host, port=port)
        _, services = consul.catalog.service(service_name)

        if len(services) == 0:
            raise Exception('Cannot find service %s in consul' % service_name)

        # pick a random entry
        # TODO should we prefer local IP addresses? Probably.

        service = services[randint(0, len(services) - 1)]
        endpoint = '{}:{}'.format(service['ServiceAddress'],
                                  service['ServicePort'])
        return endpoint

    def _retrieve_schema(self):
        """
        Retrieve schema from gRPC end-point, and save all *.proto files in
        the work directory.
        """
        assert isinstance(self.channel, grpc.Channel)
        stub = SchemaServiceStub(self.channel)
        # try:
        schema = stub.GetSchema(NullMessage())
        # except _Rendezvous, e:
        #     if e.code == grpc.StatusCode.UNAVAILABLE:
        #
        #     else:
        #         raise e

        os.system('mkdir -p %s' % self.work_dir)
        os.system('rm -fr /tmp/%s/*' %
                  self.work_dir.replace('/tmp/', ''))  # safer

        for fname in schema.protos:
            content = schema.protos[fname]
            log.debug('saving-proto',
                      fname=fname, dir=self.work_dir, length=len(content))
            with open(os.path.join(self.work_dir, fname), 'w') as f:
                f.write(content)

        for fname in schema.descriptors:
            content = decompress(schema.descriptors[fname])
            log.debug('saving-descriptor',
                      fname=fname, dir=self.work_dir, length=len(content))
            with open(os.path.join(self.work_dir, fname), 'wb') as f:
                f.write(content)

    def _compile_proto_files(self):
        """
        For each *.proto file in the work directory, compile the proto
        file into the respective *_pb2.py file as well as generate the
        web server gateway python file *_gw.py.
        :return: None
        """
        google_api_dir = os.path.abspath(os.path.join(
            os.path.dirname(__file__),
            '../protos/third_party'
        ))

        for fname in [f for f in os.listdir(self.work_dir)
                      if f.endswith('.proto')]:

            log.debug('compiling', file=fname)
            cmd = (
                'cd %s && '
                'env PATH=%s PYTHONPATH=%s '
                'python -m grpc.tools.protoc '
                '-I. '
                '-I%s '
                '--python_out=. '
                '--grpc_python_out=. '
                '--plugin=protoc-gen-gw=%s/gw_gen.py '
                '--gw_out=. '
                '%s' % (
                    self.work_dir,
                    ':'.join([os.environ['PATH'], self.plugin_dir]),
                    google_api_dir,
                    google_api_dir,
                    self.plugin_dir,
                    fname)
            )
            log.debug('executing', cmd=cmd, file=fname)
            os.system(cmd)
            log.info('compiled', file=fname)

        # test-load each _pb2 file to see all is right
        if self.work_dir not in sys.path:
            sys.path.insert(0, self.work_dir)

        for fname in [f for f in os.listdir(self.work_dir)
                      if f.endswith('_pb2.py')]:
            modname = fname[:-len('.py')]
            log.debug('test-import', modname=modname)
            _ = __import__(modname)

    def invoke(self, stub, method_name, request):
        """
        Invoke a gRPC call to the remote server and return the response.
        :param stub: Reference to the *_pb2 service stub
        :param method_name: The method name inside the service stub
        :param request: The request protobuf message
        :return: The response protobuf message
        """

        if not self.connected:
            raise ServiceUnavailable()

        try:
            response = getattr(stub(self.channel), method_name)(request)
            return response

        except grpc._channel._Rendezvous, e:
            if e.code() == grpc.StatusCode.UNAVAILABLE:
                e = ServiceUnavailable()
            else:
                log.exception(e)

            if self.connected :
                self.connected = False
                reactor.callLater(0, self.connect)

            raise e