/*
 * Copyright 2018-present Open Networking Foundation
 *
 * 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.
 */
package protocols.gnmi.ctl.java.org.onosproject.gnmi.ctl;

import gnmi.Gnmi.CapabilityRequest;
import gnmi.Gnmi.CapabilityResponse;
import gnmi.Gnmi.GetRequest;
import gnmi.Gnmi.GetResponse;
import gnmi.Gnmi.Path;
import gnmi.Gnmi.PathElem;
import gnmi.Gnmi.SetRequest;
import gnmi.Gnmi.SetResponse;
import gnmi.Gnmi.SubscribeRequest;
import gnmi.Gnmi.SubscribeResponse;
import gnmi.gNMIGrpc;
import io.grpc.ManagedChannel;
import io.grpc.Status;
import io.grpc.StatusRuntimeException;
import io.grpc.stub.ClientCallStreamObserver;
import io.grpc.stub.StreamObserver;
import org.onosproject.gnmi.api.GnmiClient;
import org.onosproject.gnmi.api.GnmiClientKey;
import org.onosproject.gnmi.api.GnmiEvent;
import org.onosproject.gnmi.api.GnmiUpdate;
import org.onosproject.grpc.ctl.AbstractGrpcClient;
import org.slf4j.Logger;

import java.net.ConnectException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicBoolean;

import static java.lang.String.format;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * Implementation of gNMI client.
 */
public class GnmiClientImpl extends AbstractGrpcClient implements GnmiClient {
    private static final PathElem DUMMY_PATH_ELEM = PathElem.newBuilder().setName("onos-gnmi-test").build();
    private static final Path DUMMY_PATH = Path.newBuilder().addElem(DUMMY_PATH_ELEM).build();
    private static final GetRequest DUMMY_REQUEST = GetRequest.newBuilder().addPath(DUMMY_PATH).build();
    private final Logger log = getLogger(getClass());
    private final gNMIGrpc.gNMIBlockingStub blockingStub;
    private StreamChannelManager streamChannelManager;
    private GnmiControllerImpl controller;

    GnmiClientImpl(GnmiClientKey clientKey, ManagedChannel managedChannel, GnmiControllerImpl controller) {
        super(clientKey);
        this.blockingStub = gNMIGrpc.newBlockingStub(managedChannel);
        this.streamChannelManager = new StreamChannelManager(managedChannel);
        this.controller = controller;
    }

    @Override
    public CompletableFuture<CapabilityResponse> capability() {
        return supplyInContext(this::doCapability, "capability");
    }

    @Override
    public CompletableFuture<GetResponse> get(GetRequest request) {
        return supplyInContext(() -> doGet(request), "get");
    }

    @Override
    public CompletableFuture<SetResponse> set(SetRequest request) {
        return supplyInContext(() -> doSet(request), "set");
    }

    @Override
    public boolean subscribe(SubscribeRequest request) {
        return streamChannelManager.send(request);
    }

    @Override
    public void terminateSubscriptionChannel() {
        streamChannelManager.complete();
    }

    @Override
    public CompletableFuture<Boolean> isServiceAvailable() {
        return supplyInContext(this::doServiceAvailable, "isServiceAvailable");
    }

    @Override
    protected Void doShutdown() {
        streamChannelManager.complete();
        return super.doShutdown();
    }

    private CapabilityResponse doCapability() {
        CapabilityRequest request = CapabilityRequest.newBuilder().build();
        try {
            return blockingStub.capabilities(request);
        } catch (StatusRuntimeException e) {
            log.warn("Unable to get capability from {}: {}", deviceId, e.getMessage());
            return null;
        }
    }

    private GetResponse doGet(GetRequest request) {
        try {
            return blockingStub.get(request);
        } catch (StatusRuntimeException e) {
            log.warn("Unable to get data from {}: {}", deviceId, e.getMessage());
            return null;
        }
    }

    private SetResponse doSet(SetRequest request) {
        try {
            return blockingStub.set(request);
        } catch (StatusRuntimeException e) {
            log.warn("Unable to set data to {}: {}", deviceId, e.getMessage());
            return null;
        }
    }

    private boolean doServiceAvailable() {
        try {
            return blockingStub.get(DUMMY_REQUEST) != null;
        } catch (StatusRuntimeException e) {
            // This gRPC call should throw INVALID_ARGUMENT status exception
            // since "/onos-gnmi-test" path does not exists in any config model
            // For other status code such as UNIMPLEMENT, means the gNMI
            // service is not available on the device.
            return e.getStatus().getCode().equals(Status.Code.INVALID_ARGUMENT);
        }
    }


    /**
     * A manager for the gNMI stream channel that opportunistically creates
     * new stream RCP stubs (e.g. when one fails because of errors) and posts
     * subscribe events via the gNMI controller.
     */
    private final class StreamChannelManager {

        private final ManagedChannel channel;
        private final AtomicBoolean open;
        private final StreamObserver<SubscribeResponse> responseObserver;
        private ClientCallStreamObserver<SubscribeRequest> requestObserver;

        private StreamChannelManager(ManagedChannel channel) {
            this.channel = channel;
            this.responseObserver = new InternalStreamResponseObserver(this);
            this.open = new AtomicBoolean(false);
        }

        private void initIfRequired() {
            if (requestObserver == null) {
                log.debug("Creating new stream channel for {}...", deviceId);
                requestObserver = (ClientCallStreamObserver<SubscribeRequest>)
                        gNMIGrpc.newStub(channel).subscribe(responseObserver);
                open.set(false);
            }
        }

        public boolean send(SubscribeRequest value) {
            synchronized (this) {
                initIfRequired();
                try {
                    requestObserver.onNext(value);
                    return true;
                } catch (Throwable ex) {
                    if (ex instanceof StatusRuntimeException) {
                        log.warn("Unable to send subscribe request to {}: {}",
                                deviceId, ex.getMessage());
                    } else {
                        log.warn("Exception while sending subscribe request to {}",
                                deviceId, ex);
                    }
                    complete();
                    return false;
                }
            }
        }

        public void complete() {
            synchronized (this) {
                if (requestObserver != null) {
                    requestObserver.onCompleted();
                    requestObserver.cancel("Terminated", null);
                    requestObserver = null;
                }
            }
        }
    }


    /**
     * Handles messages received from the device on the stream channel.
     */
    private final class InternalStreamResponseObserver
            implements StreamObserver<SubscribeResponse> {

        private final StreamChannelManager streamChannelManager;

        private InternalStreamResponseObserver(
                StreamChannelManager streamChannelManager) {
            this.streamChannelManager = streamChannelManager;
        }

        @Override
        public void onNext(SubscribeResponse message) {
            executorService.submit(() -> doNext(message));
        }

        private void doNext(SubscribeResponse message) {
            try {
                log.debug("Received message on stream channel from {}: {}",
                        deviceId, message.toString());
                GnmiUpdate update = new GnmiUpdate(deviceId, message.getUpdate(), message.getSyncResponse());
                GnmiEvent event = new GnmiEvent(GnmiEvent.Type.UPDATE, update);
                controller.postEvent(event);
            } catch (Throwable ex) {
                log.error("Exception while processing stream message from {}",
                        deviceId, ex);
            }
        }

        @Override
        public void onError(Throwable throwable) {
            if (throwable instanceof StatusRuntimeException) {
                StatusRuntimeException sre = (StatusRuntimeException) throwable;
                if (sre.getStatus().getCause() instanceof ConnectException) {
                    log.warn("Device {} is unreachable ({})",
                            deviceId, sre.getCause().getMessage());
                } else {
                    log.warn("Received error on stream channel for {}: {}",
                            deviceId, throwable.getMessage());
                }
            } else {
                log.warn(format("Received exception on stream channel for %s",
                        deviceId), throwable);
            }
            streamChannelManager.complete();
        }

        @Override
        public void onCompleted() {
            log.warn("Stream channel for {} has completed", deviceId);
            streamChannelManager.complete();
        }
    }
}