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Library implementing Paxos and Heartbeat components required for High Availability Neo4j
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/*
 * Copyright (c) 2002-2016 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see .
 */
package org.neo4j.cluster.com.message;

import java.io.Serializable;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;

/**
 * Message for state machines which can be sent out to instances in the cluster as well.
 * 
 * These are typically produced and consumed by a {@link org.neo4j.cluster.statemachine.StateMachine}.
 */
public class Message
        implements Serializable
{
    private static final long serialVersionUID = 7043669983188264476L;

    public static  Message to( MESSAGETYPE messageType, URI to )
    {
        return to( messageType, to, null );
    }

    public static  Message to( MESSAGETYPE messageType, URI to,
                                                                             Object payload )
    {
        return new Message( messageType, payload ).setHeader( TO, to.toString() );
    }

    public static  Message respond( MESSAGETYPE messageType,
                                                                                  Message message, Object payload )
    {
        return message.hasHeader( Message.FROM ) ?
                new Message( messageType, payload ).setHeader( TO, message.getHeader( Message.FROM ) ) :
                internal( messageType, payload );
    }

    public static  Message internal( MESSAGETYPE message )
    {
        return internal( message, null );
    }

    public static  Message internal( MESSAGETYPE message, Object payload )
    {
        return new Message( message, payload );
    }

    public static  Message timeout( MESSAGETYPE message,
                                                                                  Message causedBy )
    {
        return timeout( message, causedBy, null );
    }

    public static  Message timeout( MESSAGETYPE message,
                                                                                  Message causedBy, Object payload )
    {
        Message timeout = causedBy.copyHeadersTo( new Message<>( message, payload ),
                Message.CONVERSATION_ID, Message.CREATED_BY );
        int timeoutCount = 0;
        if ( causedBy.hasHeader( TIMEOUT_COUNT ) )
        {
            timeoutCount = Integer.parseInt( causedBy.getHeader( TIMEOUT_COUNT ) ) + 1;
        }
        timeout.setHeader( TIMEOUT_COUNT, "" + timeoutCount );
        return timeout;
    }

    // Standard headers
    public static final String CONVERSATION_ID = "conversation-id";
    public static final String CREATED_BY = "created-by";
    public static final String TIMEOUT_COUNT = "timeout-count";
    public static final String FROM = "from";
    public static final String TO = "to";
    public static final String INSTANCE_ID = "instance-id";

    private MESSAGETYPE messageType;
    private Object payload;
    private Map headers = new HashMap();

    protected Message( MESSAGETYPE messageType, Object payload )
    {
        this.messageType = messageType;
        this.payload = payload;
    }

    public MESSAGETYPE getMessageType()
    {
        return messageType;
    }

    public  T getPayload()
    {
        return (T) payload;
    }

    public Message setHeader( String name, String value )
    {
        if ( value == null )
        {
            throw new IllegalArgumentException( String.format( "Header %s may not be set to null", name ) );
        }

        headers.put( name, value );
        return this;
    }

    public boolean hasHeader( String name )
    {
        return headers.containsKey( name );
    }

    public boolean isInternal()
    {
        return !headers.containsKey( Message.TO );
    }

    public String getHeader( String name )
            throws IllegalArgumentException
    {
        String value = headers.get( name );
        if ( value == null )
        {
            throw new IllegalArgumentException( "No such header:" + name );
        }
        return value;
    }

    public  Message copyHeadersTo( Message message,
                                                                                 String... names )
    {
        if ( names.length == 0 )
        {
            for ( Map.Entry header : headers.entrySet() )
            {
                if ( !message.hasHeader( header.getKey() ) )
                {
                    message.setHeader( header.getKey(), header.getValue() );
                }
            }
        }
        else
        {
            for ( String name : names )
            {
                String value = headers.get( name );
                if ( value != null && !message.hasHeader( name ) )
                {
                    message.setHeader( name, value );
                }
            }
        }
        return message;
    }

    @Override
    public boolean equals( Object o )
    {
        if ( this == o )
        {
            return true;
        }
        if ( o == null || getClass() != o.getClass() )
        {
            return false;
        }

        Message message = (Message) o;

        if ( headers != null ? !headers.equals( message.headers ) : message.headers != null )
        {
            return false;
        }
        if ( messageType != null ? !messageType.equals( message.messageType ) : message.messageType != null )
        {
            return false;
        }
        if ( payload != null ? !payload.equals( message.payload ) : message.payload != null )
        {
            return false;
        }

        return true;
    }

    @Override
    public int hashCode()
    {
        int result = messageType != null ? messageType.hashCode() : 0;
        result = 31 * result + (payload != null ? payload.hashCode() : 0);
        result = 31 * result + (headers != null ? headers.hashCode() : 0);
        return result;
    }

    @Override
    public String toString()
    {
        return messageType.name() + headers + (payload != null && payload instanceof String ? ": " + payload : "");
    }
}