/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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
 *
 *      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.apache.commons.discovery.resource.names;

import org.apache.commons.discovery.ResourceNameDiscover;
import org.apache.commons.discovery.ResourceNameIterator;

/**
 * Helper class for methods implementing the ResourceNameDiscover interface.
 */
public abstract class ResourceNameDiscoverImpl implements ResourceNameDiscover {

    /**
     * Locate names of resources that are bound to {@code resourceName}.
     *
     * @param resourceName The resource name to locate
     * @return A new {@link ResourceNameIterator}
     */
    public abstract ResourceNameIterator findResourceNames(String resourceName);

    /**
     * Locate names of resources that are bound to {@code inputNames}.
     *
     * @param inputNames The resource names to locate
     * @return A new {@link ResourceNameIterator}
     */
    public ResourceNameIterator findResourceNames(final ResourceNameIterator inputNames) {
        return new ResourceNameIterator() {

            private ResourceNameIterator resourceNames = null;

            private String resourceName = null;

            public boolean hasNext() {
                if (resourceName == null) {
                    resourceName = getNextResourceName();
                }
                return resourceName != null;
            }

            public String nextResourceName() {
                String name = resourceName;
                resourceName = null;
                return name;
            }

            private String getNextResourceName() {
                while (inputNames.hasNext() && (resourceNames == null  ||  !resourceNames.hasNext())) {
                    resourceNames =
                        findResourceNames(inputNames.nextResourceName());
                }

                return (resourceNames != null  &&  resourceNames.hasNext())
                       ? resourceNames.nextResourceName()
                       : null;
            }
        };
    }

}
