/**
 * 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.firewall;

import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import org.apache.mina.core.filterchain.IoFilter;
import org.apache.mina.core.filterchain.IoFilterAdapter;
import org.apache.mina.core.session.IoSession;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A {@link IoFilter} which blocks connections from connecting
 * at a rate faster than the specified interval.
 *
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public class ConnectionThrottleFilter extends IoFilterAdapter {
    private static final long DEFAULT_TIME = 1000;

    private long allowedInterval;

    private final Map<String, Long> clients;

    private static final Logger LOGGER = LoggerFactory.getLogger(ConnectionThrottleFilter.class);
    /**
     * Default constructor.  Sets the wait time to 1 second
     */
    public ConnectionThrottleFilter() {
        this(DEFAULT_TIME);
    }

    /**
     * Constructor that takes in a specified wait time.
     *
     * @param allowedInterval
     *     The number of milliseconds a client is allowed to wait
     *     before making another successful connection
     *
     */
    public ConnectionThrottleFilter(long allowedInterval) {
        this.allowedInterval = allowedInterval;
        clients = Collections.synchronizedMap(new HashMap<>());
    }

    /**
     * Sets the interval between connections from a client.
     * This value is measured in milliseconds.
     *
     * @param allowedInterval
     *     The number of milliseconds a client is allowed to wait
     *     before making another successful connection
     */
    public void setAllowedInterval(long allowedInterval) {
        this.allowedInterval = allowedInterval;
    }

    /**
     * Method responsible for deciding if a connection is OK
     * to continue
     *
     * @param session
     *     The new session that will be verified
     * @return
     *     True if the session meets the criteria, otherwise false
     */
    protected boolean isConnectionOk(IoSession session) {
        SocketAddress remoteAddress = session.getRemoteAddress();
        if (remoteAddress instanceof InetSocketAddress) {
            InetSocketAddress addr = (InetSocketAddress) remoteAddress;
            long now = System.currentTimeMillis();

            if (clients.containsKey(addr.getAddress().getHostAddress())) {

                LOGGER.debug("This is not a new client");
                Long lastConnTime = clients.get(addr.getAddress()
                        .getHostAddress());

                clients.put(addr.getAddress().getHostAddress(), now);

                // if the interval between now and the last connection is
                // less than the allowed interval, return false
                if (now - lastConnTime < allowedInterval) {
                    LOGGER.warn("Session connection interval too short");
                    return false;
                }
                
                return true;
            }

            clients.put(addr.getAddress().getHostAddress(), now);
            return true;
        }

        return false;
    }

    @Override
    public void sessionCreated(NextFilter nextFilter, IoSession session)
            throws Exception {
        if (!isConnectionOk(session)) {
            LOGGER.warn("Connections coming in too fast; closing.");
            session.close(true);
        }
        nextFilter.sessionCreated(session);
    }
}
