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Access to the Neo4j graph database through Java
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/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * 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 org.neo4j.driver.internal.handlers;

import static java.lang.String.format;

import java.util.Map;
import java.util.Objects;
import org.neo4j.driver.AccessMode;
import org.neo4j.driver.Value;
import org.neo4j.driver.exceptions.ClientException;
import org.neo4j.driver.exceptions.ServiceUnavailableException;
import org.neo4j.driver.exceptions.SessionExpiredException;
import org.neo4j.driver.exceptions.TransientException;
import org.neo4j.driver.internal.BoltServerAddress;
import org.neo4j.driver.internal.RoutingErrorHandler;
import org.neo4j.driver.internal.spi.ResponseHandler;
import org.neo4j.driver.internal.util.Futures;

public class RoutingResponseHandler implements ResponseHandler {
    private final ResponseHandler delegate;
    private final BoltServerAddress address;
    private final AccessMode accessMode;
    private final RoutingErrorHandler errorHandler;

    public RoutingResponseHandler(
            ResponseHandler delegate,
            BoltServerAddress address,
            AccessMode accessMode,
            RoutingErrorHandler errorHandler) {
        this.delegate = delegate;
        this.address = address;
        this.accessMode = accessMode;
        this.errorHandler = errorHandler;
    }

    @Override
    public void onSuccess(Map metadata) {
        delegate.onSuccess(metadata);
    }

    @Override
    public void onFailure(Throwable error) {
        Throwable newError = handledError(error);
        delegate.onFailure(newError);
    }

    @Override
    public void onRecord(Value[] fields) {
        delegate.onRecord(fields);
    }

    @Override
    public boolean canManageAutoRead() {
        return delegate.canManageAutoRead();
    }

    @Override
    public void disableAutoReadManagement() {
        delegate.disableAutoReadManagement();
    }

    private Throwable handledError(Throwable receivedError) {
        Throwable error = Futures.completionExceptionCause(receivedError);

        if (error instanceof ServiceUnavailableException) {
            return handledServiceUnavailableException(((ServiceUnavailableException) error));
        } else if (error instanceof ClientException) {
            return handledClientException(((ClientException) error));
        } else if (error instanceof TransientException) {
            return handledTransientException(((TransientException) error));
        } else {
            return error;
        }
    }

    private Throwable handledServiceUnavailableException(ServiceUnavailableException e) {
        errorHandler.onConnectionFailure(address);
        return new SessionExpiredException(format("Server at %s is no longer available", address), e);
    }

    private Throwable handledTransientException(TransientException e) {
        String errorCode = e.code();
        if (Objects.equals(errorCode, "Neo.TransientError.General.DatabaseUnavailable")) {
            errorHandler.onConnectionFailure(address);
        }
        return e;
    }

    private Throwable handledClientException(ClientException e) {
        if (isFailureToWrite(e)) {
            // The server is unaware of the session mode, so we have to implement this logic in the driver.
            // In the future, we might be able to move this logic to the server.
            switch (accessMode) {
                case READ:
                    return new ClientException("Write queries cannot be performed in READ access mode.");
                case WRITE:
                    errorHandler.onWriteFailure(address);
                    return new SessionExpiredException(format("Server at %s no longer accepts writes", address));
                default:
                    throw new IllegalArgumentException(accessMode + " not supported.");
            }
        }
        return e;
    }

    private static boolean isFailureToWrite(ClientException e) {
        String errorCode = e.code();
        return Objects.equals(errorCode, "Neo.ClientError.Cluster.NotALeader")
                || Objects.equals(errorCode, "Neo.ClientError.General.ForbiddenOnReadOnlyDatabase");
    }
}