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/*
 * Copyright (c) CQSE GmbH
 *
 * 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.conqat.lib.commons.cache4j;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.conqat.lib.commons.cache4j.backend.ICacheBackend;
import org.conqat.lib.commons.error.NeverThrownRuntimeException;
import org.conqat.lib.commons.factory.IParameterizedFactory;

/**
 * Implementation of a cache that manages a separate backend for each thread, thus isolating threads
 * from each other. Note that accessing this cache from many temporary threads can lead to memory
 * leaks (as the cached data is still stored) for certain backends.
 * 
 * @param 
 *            the key type. This must have both {@link Object#equals(Object)} and
 *            {@link Object#hashCode()} correctly implemented.
 * @param 
 *            the value type. It is generally recommended to use an immutable type here, but this is
 *            not required.
 * @param 
 *            the type of exception thrown. If no exception will be throws, use
 *            {@link NeverThrownRuntimeException}.
 */
public class ThreadLocalCache implements ICache {

	/** The name of this cache (used for reporting). */
	private final String name;

	/** The factory used to obtain elements. */
	private final IParameterizedFactory factory;

	/** The backend used. */
	private final ICacheBackend backend;

	/** Stores all sub caches for reporting. */
	private final List> subCaches = Collections
			.synchronizedList(new ArrayList>());

	/** Manages the individual caches for each thread. */
	private final ThreadLocal> localCaches = new ThreadLocal>() {

		/** {@inheritDoc} */
		@Override
		protected BasicCache initialValue() {
			BasicCache cache = new BasicCache<>(name + ":" + Thread.currentThread().getId(), factory,
					backend.newInstance());
			subCaches.add(cache);
			return cache;
		}
	};

	/**
	 * Constructor.
	 * 
	 * @param factory
	 *            the factory has to either support multi-threaded access or to be synchronized!
	 */
	public ThreadLocalCache(String name, IParameterizedFactory factory, ICacheBackend backend) {
		this.name = name;
		this.factory = factory;
		this.backend = backend;
	}

	/** {@inheritDoc} */
	@Override
	public V obtain(K parameter) throws X {
		return localCaches.get().obtain(parameter);
	}

	/** {@inheritDoc} */
	@Override
	public void clear(boolean allThreads) {
		if (allThreads) {
			for (BasicCache cache : subCaches) {
				cache.clear(false);
			}
		} else {
			localCaches.get().clear(false);
		}
	}

	/** {@inheritDoc} */
	@Override
	public String getName() {
		return name;
	}

	/** {@inheritDoc} */
	@Override
	public int getHits() {
		int result = 0;
		for (BasicCache cache : subCaches) {
			result += cache.getHits();
		}
		return result;
	}

	/** {@inheritDoc} */
	@Override
	public int getMisses() {
		int result = 0;
		for (BasicCache cache : subCaches) {
			result += cache.getMisses();
		}
		return result;
	}

	/** {@inheritDoc} */
	@Override
	public long getMissCostMillis() {
		long result = 0;
		for (BasicCache cache : subCaches) {
			result += cache.getMissCostMillis();
		}
		return result;
	}
}