/**
 * 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.proxy;

import java.util.LinkedList;
import java.util.Queue;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.filterchain.IoFilter.NextFilter;
import org.apache.mina.core.future.DefaultWriteFuture;
import org.apache.mina.core.future.WriteFuture;
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.proxy.filter.ProxyFilter;
import org.apache.mina.proxy.filter.ProxyHandshakeIoBuffer;
import org.apache.mina.proxy.session.ProxyIoSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * AbstractProxyLogicHandler.java - Helper class to handle proxy handshaking logic. Derived classes 
 * implement proxy type specific logic.
 * <p>
 * Based upon SSLHandler from mina-filter-ssl.
 * 
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 * @since MINA 2.0.0-M3
 */
public abstract class AbstractProxyLogicHandler implements ProxyLogicHandler {

    private static final Logger LOGGER = LoggerFactory
            .getLogger(AbstractProxyLogicHandler.class);

    /**
     * Object that contains all the proxy authentication session informations.
     */
    private ProxyIoSession proxyIoSession;

    /**
     * Queue of write events which occurred before the proxy handshake had completed.
     */
    private Queue<Event> writeRequestQueue = null;

    /**
     * Has the handshake been completed.
     */
    private boolean handshakeComplete = false;

    /**
     * Creates a new {@link AbstractProxyLogicHandler}.
     * 
     * @param proxyIoSession {@link ProxyIoSession} in use.
     */
    public AbstractProxyLogicHandler(ProxyIoSession proxyIoSession) {
        this.proxyIoSession = proxyIoSession;
    }

    /**
     * Returns the proxy filter {@link ProxyFilter}.
     */
    protected ProxyFilter getProxyFilter() {
        return proxyIoSession.getProxyFilter();
    }

    /**
     * Returns the session.
     */
    protected IoSession getSession() {
        return proxyIoSession.getSession();
    }

    /**
     * Returns the {@link ProxyIoSession} object.
     */
    public ProxyIoSession getProxyIoSession() {
        return proxyIoSession;
    }

    /**
     * Writes data to the proxy server.
     * 
     * @param nextFilter the next filter
     * @param data Data buffer to be written.
     */
    protected WriteFuture writeData(final NextFilter nextFilter,
            final IoBuffer data) {
        // write net data
        ProxyHandshakeIoBuffer writeBuffer = new ProxyHandshakeIoBuffer(data);

        LOGGER.debug("   session write: {}", writeBuffer);

        WriteFuture writeFuture = new DefaultWriteFuture(getSession());
        getProxyFilter().writeData(nextFilter, getSession(),
                new DefaultWriteRequest(writeBuffer, writeFuture), true);

        return writeFuture;
    }

    /**
     * Returns <code>true</code> if handshaking is complete and
     * data can be sent through the proxy.
     */
    public boolean isHandshakeComplete() {
        synchronized (this) {
            return handshakeComplete;
        }
    }

    /**
     * Signals that the handshake has finished.
     */
    protected final void setHandshakeComplete() {
        synchronized (this) {
            handshakeComplete = true;
        }

        ProxyIoSession proxyIoSession = getProxyIoSession();
        proxyIoSession.getConnector()
                .fireConnected(proxyIoSession.getSession())
                .awaitUninterruptibly();

        LOGGER.debug("  handshake completed");

        // Connected OK
        try {
            proxyIoSession.getEventQueue().flushPendingSessionEvents();
            flushPendingWriteRequests();
        } catch (Exception ex) {
            LOGGER.error("Unable to flush pending write requests", ex);
        }
    }

    /**
     * Send any write requests which were queued whilst waiting for handshaking to complete.
     */
    protected synchronized void flushPendingWriteRequests() throws Exception {
        LOGGER.debug(" flushPendingWriteRequests()");

        if (writeRequestQueue == null) {
            return;
        }

        Event scheduledWrite;
        while ((scheduledWrite = writeRequestQueue.poll()) != null) {
            LOGGER.debug(" Flushing buffered write request: {}",
                    scheduledWrite.data);

            getProxyFilter().filterWrite(scheduledWrite.nextFilter,
                    getSession(), (WriteRequest) scheduledWrite.data);
        }

        // Free queue
        writeRequestQueue = null;
    }

    /**
     * Enqueue a message to be written once handshaking is complete.
     */
    public synchronized void enqueueWriteRequest(final NextFilter nextFilter,
            final WriteRequest writeRequest) {
        if (writeRequestQueue == null) {
            writeRequestQueue = new LinkedList<>();
        }

        writeRequestQueue.offer(new Event(nextFilter, writeRequest));
    }

    /**
     * Closes the session.
     * 
     * @param message the error message
     * @param t the exception which caused the session closing
     */
    protected void closeSession(final String message, final Throwable t) {
        if (t != null) {
            LOGGER.error(message, t);
            proxyIoSession.setAuthenticationFailed(true);
        } else {
            LOGGER.error(message);
        }

        getSession().close(true);
    }

    /**
     * Closes the session.
     * 
     * @param message the error message
     */
    protected void closeSession(final String message) {
        closeSession(message, null);
    }

    /**
     * Event wrapper class for enqueued events.
     */
    private static final class Event {
        private final NextFilter nextFilter;

        private final Object data;

        Event(final NextFilter nextFilter, final Object data) {
            this.nextFilter = nextFilter;
            this.data = data;
        }

        public Object getData() {
            return data;
        }

        public NextFilter getNextFilter() {
            return nextFilter;
        }
    }
}