/**
 * Copyright 2005-2013 The Kuali Foundation
 *
 * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
 *
 * 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.kuali.rice.krad.util;

import java.lang.management.ManagementFactory;
import java.lang.management.MemoryMXBean;
import java.lang.management.MemoryNotificationInfo;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryType;
import java.util.ArrayList;
import java.util.Collection;

import javax.management.Notification;
import javax.management.NotificationEmitter;
import javax.management.NotificationListener;

import org.apache.log4j.Logger;

public class MemoryMonitor {
    private final Collection<Listener> listeners = new ArrayList<Listener>();
    private static final Logger LOG = Logger.getLogger(MemoryMonitor.class);
    private String springContextId;

    public interface Listener {
        public void memoryUsageLow(String springContextId, long usedMemory, long maxMemory);
    }

    public MemoryMonitor() {
        LOG.info("initializing");
        this.springContextId = "Unknown";
        MemoryMXBean mbean = ManagementFactory.getMemoryMXBean();
        NotificationEmitter emitter = (NotificationEmitter) mbean;
        emitter.addNotificationListener(new NotificationListener() {
            public void handleNotification(Notification n, Object hb) {
                if (n.getType().equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {
                    long maxMemory = tenuredGenPool.getUsage().getMax();
                    long usedMemory = tenuredGenPool.getUsage().getUsed();
                    for (Listener listener : listeners) {
                        listener.memoryUsageLow(springContextId, usedMemory, maxMemory);
                    }
                }
            }
        }, null, null);
    }

    public MemoryMonitor(String springContextId) {
        this();
        this.springContextId = springContextId;
    }

    public boolean addListener(Listener listener) {
        return listeners.add(listener);
    }

    public boolean removeListener(Listener listener) {
        return listeners.remove(listener);
    }

    private static final MemoryPoolMXBean tenuredGenPool = findTenuredGenPool();

    public static void setPercentageUsageThreshold(double percentage) {
        if (percentage <= 0.0 || percentage > 1.0) {
            throw new IllegalArgumentException("percentage not in range");
        }
        long maxMemory = tenuredGenPool.getUsage().getMax();
        long warningThreshold = (long) (maxMemory * percentage);
        tenuredGenPool.setUsageThreshold(warningThreshold);
    }

    private static MemoryPoolMXBean findTenuredGenPool() {
        for (MemoryPoolMXBean pool : ManagementFactory.getMemoryPoolMXBeans()) {
            if (pool.getType() == MemoryType.HEAP && pool.isUsageThresholdSupported()) {
                return pool;
            }
        }
        throw new AssertionError("could not find tenured space");
    }
}
