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/**
    This file is part of the Zeidon Java Object Engine (Zeidon JOE).

    Zeidon JOE is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    Zeidon JOE is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with Zeidon JOE.  If not, see .

    Copyright 2009-2015 QuinSoft
 */

package com.quinsoft.zeidon;

/**
 * 
 * Cache maps are a way to store objects in Zeidon objects in a thread-safe way.  The
 * life of the CacheMap is tied to the implementing object.  For example, a value stored
 * in the CacheMap of a view will live until the View is garbage collected.
 * The key is a class object to help reduce the number of possible key collisions.
 * 
 * For example, application code could cache a value in a task like this:
 * 
 * Task task = ...
 * MyCache value = task.getCacheMap().get( MyCache.class );
 * if ( value == null ) {
 *     value = new MyCache( 1, 2, 3 );
 *     value = task.getCacheMap().putCacheMap( putCacheMap( MyCache.class, value );
 * }
 * 
 * If the constructor for the cached value takes no arguments then this can be
 * simplified to:
 * 
 * MyCache value = task.getCachMap().getOrCreate( MyCache.class );
 * 
 *
 */
public interface CacheMap
{
    /**
     * putTaskCache puts 'value' into the cache.  If the value already exists in the
     * cache for the specified key then 'value' is *not* added and the current value
     * from the cache map is returned.
     *
     * @param 
     * @param key
     * @param value
     * @return
     */
     T put( Class key, T value );

    /**
     * putTaskCache puts 'value' into the cache using value.getClass() as the key.
     * If the value already exists in the
     * cache for the specified key then 'value' is *not* added and the current value
     * from the cache map is returned.
     *
     * @param 
     * @param value
     * @return
     */
     T put( T value );

    /**
     * Retrieves a value from the cache map.
     *
     * @param key the map key.
     * @return the value stored in the cache map.
     */
     T get( Class key );

    /**
     * Retrieves a value from the cache map.  If the value is null (or doesn't exist)
     * then a value will be instantiated using the empty constructor of the class and
     * inserted in the CacheMap before returning.
     *
     * @param key
     * @return
     */
     T getOrCreate( Class key );
}