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//
// Copyright 2015, 2016 Charles W. Rapp
//
// 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 net.sf.eBus.client;

import java.util.HashMap;
import java.util.Map;
import net.sf.eBus.client.sysmessages.KeyMessage;
import net.sf.eBus.client.sysmessages.SystemMessageType;
import net.sf.eBus.messages.EMessageHeader;
import net.sf.eBus.messages.EMessageKey;

/**
 * This class is responsible for mapping message classes to a
 * unique identifier (uniqueness scoped to within this JVM). This
 * mapping is shared with remote eBus applications upon
 * successful connection, where upon the remote eBus connection
 * maps the class identifier with a message reader. This message
 * reader contains both the message class de-serializer and
 * method handle to the message destination.
 * 
 * Using a class identifier in message transmission minimizes the
 * {@code ByteBuffer} de-serialization time and forwarding the
 * message to its ultimate destination. Without this feature,
 * eBus would have to insert the fully-qualified class name into
 * each message which takes more time and space to serialize and
 * de-serialize.
 * 
 *
 * @author Charles W. Rapp
 */

/* package */ final class MessageKeyStore
{
//---------------------------------------------------------------
// Member data.
//

    //-----------------------------------------------------------
    // Locals.
    //

    /**
     * This message class store belongs to this eBus remote
     * application connection. Forward newly defined message
     * class identifiers on this connection.
     */
    private final ERemoteApp mConnection;

    /**
     * Maps message key to its unique integer identifier. This
     * identifier is used in encoded eBus message header rather
     * than the class name and subject allowing the header to be
     * a fixed size.
     */
    private final Map mIds;

    /**
     * Assign the next new message key this identifier. Starts at
     * zero.
     */
    private int mNextId;

//---------------------------------------------------------------
// Member methods.
//

    //-----------------------------------------------------------
    // Constructors.
    //

    /**
     * Creates the message class-to-identifier store for the
     * given eBus remote application connection.
     * @param connection remote connection.
     */
    /* package */ MessageKeyStore(final ERemoteApp connection)
    {
        mConnection = connection;
        mIds = new HashMap<>();
        mNextId = 0;
    } // end of MessageKeyStore(ERemoteApp)

    //
    // end of Constructors.
    //-----------------------------------------------------------

    //-----------------------------------------------------------
    // Get Methods.
    //

    /**
     * Returns the identifier associated with the given message
     * class. If the message class is not in the message store,
     * then it is assigned the next available identifier and that
     * pairing is stored.
     * @param key return this message key.
     * @return unique message class identifier.
     */
    /* package */ synchronized int findOrCreate(final EMessageKey key)
    {
        int retval;

        if (mIds.containsKey(key))
        {
            retval = mIds.get(key);
        }
        else
        {
            retval = mNextId;
            mNextId++;
            mIds.put(key, retval);

            // Forward this new message class, identifier pair on
            // the remote eBus connection.
            mConnection.send(
                new EMessageHeader(
                    (SystemMessageType.KEY_UPDATE).keyId(),
                    0,
                    0,
                    (KeyMessage.builder()).keyId(retval)
                                          .messageKey(key)
                                          .build()));
        }

        return (retval);
    } // end of findOrCreate(EMessageKey)

    //
    // end of Get Methods.
    //-----------------------------------------------------------
} // end of class MessageKeyStore