/**
 * Copyright 2007-2016, Kaazing Corporation. All rights reserved.
 *
 * 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.apache.mina.filter.stream;

import java.io.IOException;
import java.util.Queue;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.filterchain.IoFilterAdapter;
import org.apache.mina.core.filterchain.IoFilterChain;
import org.apache.mina.core.session.AttributeKey;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.core.write.DefaultWriteRequest;
import org.apache.mina.core.write.WriteRequest;
import org.apache.mina.util.CircularQueue;

/**
 * TODO Add documentation
 * 
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public abstract class AbstractStreamWriteFilter<T> extends IoFilterAdapter {
    /**
     * The default buffer size this filter uses for writing.
     */
    public static final int DEFAULT_STREAM_BUFFER_SIZE = 4096;

    /**
     * The attribute name used when binding the streaming object to the session.
     */
    protected final AttributeKey CURRENT_STREAM = new AttributeKey(getClass(), "stream");

    protected final AttributeKey WRITE_REQUEST_QUEUE = new AttributeKey(getClass(), "queue");
    protected final AttributeKey CURRENT_WRITE_REQUEST = new AttributeKey(getClass(), "writeRequest");

    private int writeBufferSize = DEFAULT_STREAM_BUFFER_SIZE;


    @Override
    public void onPreAdd(IoFilterChain parent, String name,
            NextFilter nextFilter) throws Exception {
        Class<? extends IoFilterAdapter> clazz = getClass();
        if (parent.contains(clazz)) {
            throw new IllegalStateException(
                    "Only one " + clazz.getName() + " is permitted.");
        }
    }

    @Override
    public void filterWrite(NextFilter nextFilter, IoSession session,
                            WriteRequest writeRequest) throws Exception {
        // If we're already processing a stream we need to queue the WriteRequest.
        if (session.getAttribute(CURRENT_STREAM) != null) {
            Queue<WriteRequest> queue = getWriteRequestQueue(session);
            if (queue == null) {
                queue = new CircularQueue<>();
                session.setAttribute(WRITE_REQUEST_QUEUE, queue);
            }
            queue.add(writeRequest);
            return;
        }

        Object message = writeRequest.getMessage();

        if (getMessageClass().isInstance(message)) {

            T stream = getMessageClass().cast(message);

            IoBuffer buffer = getNextBuffer(stream);
            if (buffer == null) {
                // End of stream reached.
                writeRequest.getFuture().setWritten();
                nextFilter.messageSent(session, writeRequest);
            } else {
                session.setAttribute(CURRENT_STREAM, message);
                session.setAttribute(CURRENT_WRITE_REQUEST, writeRequest);

                nextFilter.filterWrite(session, new DefaultWriteRequest(
                        buffer));
            }

        } else {
            nextFilter.filterWrite(session, writeRequest);
        }
    }
    
    abstract protected Class<T> getMessageClass();

    @SuppressWarnings("unchecked")
    private Queue<WriteRequest> getWriteRequestQueue(IoSession session) {
        return (Queue<WriteRequest>) session.getAttribute(WRITE_REQUEST_QUEUE);
    }

    @SuppressWarnings("unchecked")
    private Queue<WriteRequest> removeWriteRequestQueue(IoSession session) {
        return (Queue<WriteRequest>) session.removeAttribute(WRITE_REQUEST_QUEUE);
    }
    
    @Override
    public void messageSent(NextFilter nextFilter, IoSession session,
                            WriteRequest writeRequest) throws Exception {
        T stream = getMessageClass().cast(session.getAttribute(CURRENT_STREAM));

        if (stream == null) {
            nextFilter.messageSent(session, writeRequest);
        } else {
            IoBuffer buffer = getNextBuffer(stream);

            if (buffer == null) {
                // End of stream reached.
                session.removeAttribute(CURRENT_STREAM);
                WriteRequest currentWriteRequest = (WriteRequest) session
                        .removeAttribute(CURRENT_WRITE_REQUEST);

                // Write queued WriteRequests.
                Queue<WriteRequest> queue = removeWriteRequestQueue(session);
                if (queue != null) {
                    WriteRequest wr = queue.poll();
                    while (wr != null) {
                        filterWrite(nextFilter, session, wr);
                        wr = queue.poll();
                    }
                }

                currentWriteRequest.getFuture().setWritten();
                nextFilter.messageSent(session, currentWriteRequest);
            } else {
                nextFilter.filterWrite(session, new DefaultWriteRequest(
                        buffer));
            }
        }
    }

    /**
     * Returns the size of the write buffer in bytes. Data will be read from the
     * stream in chunks of this size and then written to the next filter.
     *
     * @return the write buffer size.
     */
    public int getWriteBufferSize() {
        return writeBufferSize;
    }

    /**
     * Sets the size of the write buffer in bytes. Data will be read from the
     * stream in chunks of this size and then written to the next filter.
     *
     * @throws IllegalArgumentException if the specified size is &lt; 1.
     */
    public void setWriteBufferSize(int writeBufferSize) {
        if (writeBufferSize < 1) {
            throw new IllegalArgumentException(
                    "writeBufferSize must be at least 1");
        }
        this.writeBufferSize = writeBufferSize;
    }

    abstract protected IoBuffer getNextBuffer(T message) throws IOException;
}
