/*
 *  Copyright 2001-2009 Stephen Colebourne
 *
 *  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.joda.time.tz;

import java.util.Collections;
import java.util.Set;

import org.joda.time.DateTimeZone;

/**
 * Simple time zone provider that supports only UTC.
 * <p>
 * UTCProvider is thread-safe and immutable.
 *
 * @author Brian S O'Neill
 * @since 1.0
 */
public final class UTCProvider implements Provider {

    /**
     * The available IDs.
     */
    private static final Set<String> AVAILABLE_IDS = Collections.singleton("UTC");

    /**
     * Constructor.
     */
    public UTCProvider() {
        super();
    }

    /**
     * Returns {@link DateTimeZone#UTC UTC} for <code>"UTC"</code>, null
     * otherwise.
     */
    public DateTimeZone getZone(String id) {
        if ("UTC".equalsIgnoreCase(id)) {
            return DateTimeZone.UTC;
        }
        return null;
    }

    /**
     * Returns a singleton collection containing only <code>"UTC"</code>.
     */    
    public Set<String> getAvailableIDs() {
        return AVAILABLE_IDS;
    }

}
