/**
 * 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.utils.threading;

import java.util.concurrent.atomic.AtomicBoolean;
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;

/**
 * Provides a DoubleCheckedCreator impl that tracks the singleton instance internally
 *
 */
public abstract class SingletonDoubleCheckedCreator<T> extends DoubleCheckedCreator<T> {
    private final AtomicBoolean creating = new AtomicBoolean(false);
    private final AtomicBoolean created = new AtomicBoolean(false);
    private T instance;

    /**
     * Called only once as long as it returns successfully
     *
     * @see DoubleCheckedCreator#create(Object...)
     */
    protected abstract T createSingleton(Object... args);

    /* (non-Javadoc)
     * @see org.apereo.portal.utils.threading.DoubleCheckedCreator#create(java.lang.Object[])
     */
    @Override
    protected final T create(Object... args) {
        if (this.creating.get()) {
            throw new IllegalStateException(
                    "Singleton creator has been called again while creation is in progress, this is indicative of a creation loop in a single thread");
        }

        this.creating.set(true);
        try {
            final T instance = this.createSingleton(args);
            this.instance = instance;
            this.created.set(true);
            return instance;
        } finally {
            this.creating.set(false);
        }
    }

    /* (non-Javadoc)
     * @see org.apereo.portal.utils.threading.DoubleCheckedCreator#retrieve(java.lang.Object[])
     */
    @Override
    protected final T retrieve(Object... args) {
        return this.instance;
    }

    /** @return true if the singleton has been created as of this call */
    public final boolean isCreated() {
        return this.created.get();
    }

    /** @see java.lang.Object#toString() */
    @Override
    public String toString() {
        return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE)
                .append("instance", this.instance)
                .toString();
    }
}