#
# Copyright 2017 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(Empty) 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, returnValue
from werkzeug.exceptions import ServiceUnavailable

from common.utils.asleep import asleep
from chameleon.protos import third_party
from chameleon.protos.schema_pb2 import SchemaServiceStub
from google.protobuf.empty_pb2 import Empty


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',
                 reconnect_callback=None):
        self.consul_endpoint = consul_endpoint
        self.endpoint = endpoint
        self.work_dir = work_dir
        self.reconnect_callback = reconnect_callback

        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.shutting_down = False
        self.connected = False

    def start(self):
        log.debug('starting')
        if not self.connected:
            reactor.callLater(0, self.connect)
        log.info('started')
        return self

    def stop(self):
        log.debug('stopping')
        if self.shutting_down:
            return
        self.shutting_down = True
        log.info('stopped')

    def set_reconnect_callback(self, reconnect_callback):
        self.reconnect_callback = reconnect_callback
        return self

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

        if self.shutting_down or self.connected:
            return

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

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

            swagger_from = self._retrieve_schema()
            self._compile_proto_files(swagger_from)
            self._clear_backoff()

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

            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

    @inlineCallbacks
    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())

        while True:
            log.debug('consul-lookup', host=host, port=port)
            consul = Consul(host=host, port=port)
            _, services = consul.catalog.service(service_name)
            log.debug('consul-response', services=services)
            if services:
                break
            log.warning('no-service', consul_host=host, consul_port=port,
                        service_name=service_name)
            yield asleep(1.0)

        # 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'])
        returnValue(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:
        schemas = stub.GetSchema(Empty())
        # 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 proto_file in schemas.protos:
            proto_fname = proto_file.file_name
            proto_content = proto_file.proto
            log.debug('saving-proto', fname=proto_fname, dir=self.work_dir,
                      length=len(proto_content))
            with open(os.path.join(self.work_dir, proto_fname), 'w') as f:
                f.write(proto_content)

            desc_content = decompress(proto_file.descriptor)
            desc_fname = proto_fname.replace('.proto', '.desc')
            log.debug('saving-descriptor', fname=desc_fname, dir=self.work_dir,
                      length=len(desc_content))
            with open(os.path.join(self.work_dir, desc_fname), 'wb') as f:
                f.write(desc_content)
        return schemas.swagger_from

    def _compile_proto_files(self, swagger_from):
        """
        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'
        ))

        chameleon_base_dir = os.path.abspath(os.path.join(
            os.path.dirname(__file__), '../..'
        ))

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

            need_swagger = fname == swagger_from
            log.debug('compiling', file=fname, need_swagger=need_swagger)
            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=. '
                '--plugin=protoc-gen-swagger=%s/swagger_gen.py '
                '%s'
                '%s' % (
                    self.work_dir,
                    ':'.join([os.environ['PATH'], self.plugin_dir]),
                    ':'.join([google_api_dir, chameleon_base_dir]),
                    google_api_dir,
                    self.plugin_dir,
                    self.plugin_dir,
                    '--swagger_out=. ' if need_swagger else '',
                    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)

    @inlineCallbacks
    def invoke(self, stub, method_name, request, metadata, retry=1):
        """
        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
        :param metadata: [(str, str), (str, str), ...]
        :return: The response protobuf message and returned trailing metadata
        """

        if not self.connected:
            raise ServiceUnavailable()

        try:
            method = getattr(stub(self.channel), method_name)
            response, rendezvous = method.with_call(request, metadata=metadata)
            returnValue((response, rendezvous.trailing_metadata()))

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

                if self.connected:
                    self.connected = False
                    yield self.connect()
                    if retry > 0:
                        response = yield self.invoke(stub, method_name,
                                                     request, metadata,
                                                     retry=retry - 1)
                        returnValue(response)

            elif code in (
                    grpc.StatusCode.NOT_FOUND,
                    grpc.StatusCode.INVALID_ARGUMENT,
                    grpc.StatusCode.ALREADY_EXISTS):

                pass  # don't log error, these occur naturally

            else:
                log.exception(e)

            raise e
