/**
 * ============LICENSE_START====================================================
 * org.onap.aaf
 * ===========================================================================
 * Copyright (c) 2018 AT&T Intellectual Property. 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.
 * ============LICENSE_END====================================================
 *
 */

package org.onap.aaf.misc.env.util;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.onap.aaf.misc.env.APIException;
import org.onap.aaf.misc.env.Creatable;
import org.onap.aaf.misc.env.Env;
import org.onap.aaf.misc.env.LifeCycle;


/**
 * <h1>RefreshableThreadObject</h1>
 * This is a ThreadLocal like implementation, but it responds to 
 * the {@link LifeCycle} mechanism for configuration refreshes, and 
 * implements {@link Creatable} (for use in destroy, etc).<p>
 * 
 * In addition to the Thread instance semantics, it compares when the object
 * was created versus the last "refresh(env)" call when getting, for the
 * thread, and if necessary to replace the created object, destroying the 
 * previous.<p>
 * 
 * In most cases, it's better to use the new "Pool" mechanism, as it deals with 
 * gaining and returning resources on an as needed basis.  This, however, remains
 * in the cases where specific Objects need to be retained to specific Threads.<p>
 * 
 * There is no way to do this kind of specialized behavior in ThreadLocal.
 * 
 * @author Jonathan
 *
 * @param <T>
 */
public class RefreshableThreadObject<T extends Creatable<T>> {
    private Map<Thread,T> objs;
    private long refreshed;
    private Constructor<T> cnst;
    
    /**
     * The passed in class <b>must</b> implement the constructor
     * <pre>
     *   public MyClass(Env env) {
     *     ...
     *   }
     * </pre>
     * @param clss
     * @throws APIException
     */
    public RefreshableThreadObject(Class<T> clss) throws APIException {
        objs = new ConcurrentHashMap<>();
        try {
            cnst = clss.getConstructor(new Class[]{Env.class} );
        } catch (Exception e) {
            throw new APIException(e);
        }
    }
    
    /**
     * Get the "T" class from the current thread
     * 
     * @param env
     * @return T
     * @throws APIException
     */
    public T get(Env env) throws APIException {
        Thread t = Thread.currentThread();
        T obj = objs.get(t);
        if (obj==null || refreshed>obj.created()) {
            try {
                obj = cnst.newInstance(new Object[]{env});
            } catch (InvocationTargetException e) {
                throw new APIException(e.getTargetException());
            } catch (Exception e) {
                throw new APIException(e);
            }
            T destroyMe = objs.put(t,obj);
            if (destroyMe!=null) {
                destroyMe.destroy(env);
            }
        } 
        return obj;
    }
    
    /**
     * Mark the timestamp of refreshed.
     * 
     * @param env
     */
    public void refresh(Env env) {
        refreshed = System.currentTimeMillis();
    }
    
    /**
     * Remove the object from the Thread instances
     * @param env
     */
    public void remove(Env env) {
        T obj = objs.remove(Thread.currentThread());
        if (obj!=null)
            obj.destroy(env);
    }
}