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Network support for the Zay-ES entity component system library.
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/*
 * $Id$
 * 
 * Copyright (c) 2015, Simsilica, LLC
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions 
 * are met:
 * 
 * 1. Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in 
 *    the documentation and/or other materials provided with the 
 *    distribution.
 * 
 * 3. Neither the name of the copyright holder nor the names of its 
 *    contributors may be used to endorse or promote products derived 
 *    from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.simsilica.es.server;

import com.simsilica.es.EntityComponent;
import com.simsilica.es.EntityId;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;


/**
 *  Keeps track of a 'frame' of 'version' for any active
 *  entity ID + component type combination.  Basically this is
 *  implementing a mark-and-sweep style usage tracking that the
 *  HostedEntityData will use to keep track of what's relevant
 *  for the client when sending updates.
 *
 *  @author    Paul Speed
 */
public class ComponentUsageTracker {
    
    private final Map, Map> map = new HashMap<>();
    
    public ComponentUsageTracker() {
    }
 
    protected Map getFrameMap( Class type, boolean create ) {
        Map result = map.get(type);
        if( result == null && create ) {
            result = new HashMap<>();
            map.put(type, result);
        }
        return result; 
    }
 
    /**
     *  Sets the current frame counter for the specified EntityId and component
     *  type combination. 
     */
    public Long set( EntityId id, Class type, Long frame ) {
        return getFrameMap(type, true).put(id, frame);
    }

    /**
     *  Sets the current frame counter for all of the specified EntityIds and component
     *  type combination. 
     */
    public void set( Collection ids, Class type, Long frame ) {
        Map frames = getFrameMap(type, true);
        for( EntityId id : ids ) {
            frames.put(id, frame);
        }
    }
 
    /**
     *  Returns the last stored version for the ID and type, removing it if the last
     *  stored version is older than the current version.  If there is no stored version
     *  then null is returned. 
     */   
    public Long getAndExpire( EntityId id, Class type, Long current ) {
        Map frames = getFrameMap(type, false);
        if( frames == null ) {
            return null;
        }
        Long last = frames.get(id);
        if( last == null ) {
            return null;
        }
        if( last == current.longValue() ) {
            // We're fine... everything is up to date
            return current;
        }
        
        // Else we need to remove the entry
        frames.remove(id);
        
        // We will clear the type entry if it is empty only because 
        // it lets the potentially-expanded internal storage of the
        // hashmap get GC'ed.  Generally, though, I'd expect these maps
        // to be long-living and relatively stable in size.
        if( frames.isEmpty() ) {
            map.remove(type);
        }
 
        return last;       
    }
 
    /** 
     *  Returns the last stored version for the specified ID and type or null
     *  if there is no tracking for the specified ID and type combination.
     */    
    public Long get( EntityId id, Class type ) {
        Map frames = getFrameMap(type, false);
        if( frames == null ) {
            return null;
        }
        return frames.get(id);
    }     
}