/**
 * Licensed to Apereo under one or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information regarding copyright ownership. Apereo
 * licenses this file to you 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 the
 * following location:
 *
 * <p>http://www.apache.org/licenses/LICENSE-2.0
 *
 * <p>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.apereo.portal.portlet.registry;

import com.google.common.base.Function;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.apereo.portal.portlet.om.IPortletEntityDescriptor;
import org.apereo.portal.portlet.om.IPortletEntityId;
import org.apereo.portal.utils.threading.NoopLock;

/**
 * Utility for caching portlet entities and entity data in memory. Ensures a consistent view for
 * accessing the data by different sets of keys
 *
 * @param <T>
 */
class PortletEntityCache<T extends IPortletEntityDescriptor> implements Serializable {
    private static final long serialVersionUID = 1L;

    private final Lock writeLock;
    private final Lock readLock;

    private final Map<SubscribeKey, T> entitiesBySubscribeKey = new HashMap<SubscribeKey, T>();
    private final Map<IPortletEntityId, T> entitiesById = new HashMap<IPortletEntityId, T>();

    public PortletEntityCache() {
        this(true);
    }

    /**
     * @param threadSafe If set to false no locking is done around read or write operations and this
     *     class is NOT thread safe
     */
    public PortletEntityCache(boolean threadSafe) {
        if (threadSafe) {
            final ReadWriteLock cacheLock = new ReentrantReadWriteLock(true);
            writeLock = cacheLock.writeLock();
            readLock = cacheLock.readLock();
        } else {
            writeLock = NoopLock.INSTANCE;
            readLock = NoopLock.INSTANCE;
        }
    }

    public T storeIfAbsentEntity(
            IPortletEntityId portletEntityId, Function<IPortletEntityId, T> entityCreator) {
        //Check if the entity already exists (uses a read lock)
        T existingEntity = this.getEntity(portletEntityId);
        if (existingEntity != null) {
            return existingEntity;
        }

        writeLock.lock();
        try {
            //Check again inside the write lock
            existingEntity = this.entitiesById.get(portletEntityId);
            if (existingEntity != null) {
                return existingEntity;
            }

            final T entity = entityCreator.apply(portletEntityId);

            this.storeEntity(entity);

            return entity;
        } finally {
            writeLock.unlock();
        }
    }

    public T storeIfAbsentEntity(T entity) {
        final IPortletEntityId portletEntityId = entity.getPortletEntityId();

        //Check if the entity already exists (uses a read lock)
        T existingEntity = this.getEntity(portletEntityId);
        if (existingEntity != null) {
            return existingEntity;
        }

        writeLock.lock();
        try {
            //Check again inside the write lock
            existingEntity = this.entitiesById.get(portletEntityId);
            if (existingEntity != null) {
                return existingEntity;
            }

            this.storeEntity(entity);
        } finally {
            writeLock.unlock();
        }

        return entity;
    }

    public void storeEntity(T entity) {
        writeLock.lock();
        try {
            final SubscribeKey subscribeKey =
                    new SubscribeKey(entity.getUserId(), entity.getLayoutNodeId());
            this.entitiesBySubscribeKey.put(subscribeKey, entity);
            this.entitiesById.put(entity.getPortletEntityId(), entity);
        } finally {
            writeLock.unlock();
        }
    }

    public T getEntity(String layoutNodeId, int userId) {
        if (this.entitiesBySubscribeKey.isEmpty()) {
            return null;
        }

        readLock.lock();
        try {
            final SubscribeKey subscribeKey = new SubscribeKey(userId, layoutNodeId);
            return this.entitiesBySubscribeKey.get(subscribeKey);
        } finally {
            readLock.unlock();
        }
    }

    public T getEntity(IPortletEntityId portletEntityId) {
        if (this.entitiesById.isEmpty()) {
            return null;
        }

        readLock.lock();
        try {
            return this.entitiesById.get(portletEntityId);
        } finally {
            readLock.unlock();
        }
    }

    public void removeEntity(IPortletEntityId portletEntityId) {
        writeLock.lock();
        try {
            final T entity = this.entitiesById.remove(portletEntityId);
            if (entity != null) {
                final int userId = entity.getUserId();
                final String layoutNodeId = entity.getLayoutNodeId();
                final SubscribeKey subscribeKey = new SubscribeKey(userId, layoutNodeId);
                this.entitiesBySubscribeKey.remove(subscribeKey);
            }
        } finally {
            writeLock.unlock();
        }
    }
}