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 * distributed with this work for additional information        *
 * regarding copyright ownership.  The ASF licenses this file   *
 * to you 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   *
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 *   http://www.apache.org/licenses/LICENSE-2.0                 *
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 * 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.                                           *
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package org.apache.james.imap.encode.base;

import java.io.IOException;

import org.apache.james.imap.api.ImapMessage;
import org.apache.james.imap.api.process.ImapSession;
import org.apache.james.imap.encode.ImapEncoder;
import org.apache.james.imap.encode.ImapResponseComposer;

/**
 * Abstract base class for chained {@link ImapEncoder} implementations.
 * Implementations of this will check if the {@link ImapMessage} should get
 * encoded by this Implementation or should get passed to the next
 * {@link ImapEncoder} in the chain
 */
public abstract class AbstractChainedImapEncoder implements ImapEncoder {

    private final ImapEncoder next;

    public AbstractChainedImapEncoder(ImapEncoder next) {
        super();
        this.next = next;
    }

    /**
     * Encode the {@link ImapMessage} if {@link #isAcceptable(ImapMessage)}
     * return true, if not pass it to the next encoder in the chain
     */
    @Override
    public void encode(ImapMessage message, ImapResponseComposer composer, ImapSession session) throws IOException {
        final boolean isAcceptable = isAcceptable(message);
        if (isAcceptable) {
            doEncode(message, composer, session);
        } else {
            chainEncode(message, composer, session);
        }
    }

    /**
     * Call next Encoder in the chain
     * 
     * @param message
     * @param composer
     * @param session
     * @throws IOException
     */
    protected void chainEncode(ImapMessage message, ImapResponseComposer composer, ImapSession session) throws IOException {
        next.encode(message, composer, session);
    }

    /**
     * Is the given message acceptable?
     * 
     * @param message
     *            <code>ImapMessage</code>, not null
     * @return true if the given message is encodable by this encoder
     */
    protected abstract boolean isAcceptable(ImapMessage message);

    /**
     * Processes an acceptable message. Only messages passing
     * {@link #isAcceptable(ImapMessage)} should be passed to this method.
     * 
     * @param acceptableMessage
     *            <code>ImapMessage</code>, not null
     * @param composer
     *            <code>ImapResponseComposer</code>, not null
     * @param session
     *            TODO
     */
    protected abstract void doEncode(ImapMessage acceptableMessage, ImapResponseComposer composer, ImapSession session) throws IOException;
}
