/*
 * 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;

import org.apache.commons.discovery.Resource;
import org.apache.commons.discovery.ResourceDiscover;
import org.apache.commons.discovery.ResourceIterator;
import org.apache.commons.discovery.ResourceNameIterator;
import org.apache.commons.discovery.resource.names.ResourceNameDiscoverImpl;

/**
 * Helper class for methods implementing the ResourceDiscover interface.
 */
public abstract class ResourceDiscoverImpl extends ResourceNameDiscoverImpl implements ResourceDiscover {

    private ClassLoaders classLoaders;

    /**
     * Construct a new resource discoverer.
     */
    public ResourceDiscoverImpl() {
    }

    /**
     * Construct a new resource discoverer.
     *
     * @param classLoaders The class laoders holder
     */
    public ResourceDiscoverImpl(ClassLoaders classLoaders) {
        setClassLoaders(classLoaders);
    }

    /**
     * Specify set of class loaders to be used in searching.
     *
     * @param loaders The class laoders holder
     */
    public void setClassLoaders(ClassLoaders loaders) {
        classLoaders = loaders;
    }

    /**
     * Specify a new class loader to be used in searching.
     *
     * The order of loaders determines the order of the result.
     * It is recommended to add the most specific loaders first.
     *
     * @param loader The new class loader to be added
     */
    public void addClassLoader(ClassLoader loader) {
        getClassLoaders().put(loader);
    }

    /**
     * Returns the class loaders holder.
     *
     * @return The class loaders holder
     */
    protected ClassLoaders getClassLoaders() {
        if (classLoaders == null) {
            classLoaders = ClassLoaders.getLibLoaders(this.getClass(), null, true);
        }
        return classLoaders;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public ResourceNameIterator findResourceNames(String resourceName) {
        return findResources(resourceName);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public ResourceNameIterator findResourceNames(ResourceNameIterator resourceNames) {
        return findResources(resourceNames);
    }

    /**
     * Locate resources that are bound to {@code resourceName}.
     *
     * @param resourceName The resource name has to be located
     * @return The located resources iterator
     */
    public abstract ResourceIterator findResources(String resourceName);

    /**
     * Locate resources that are bound to <code>resourceNames</code>.
     *
     * @param inputNames The resources name iterator has to be located
     * @return The located resources iterator
     */
    public ResourceIterator findResources(final ResourceNameIterator inputNames) {
        return new ResourceIterator() {

            private ResourceIterator resources = null;

            private Resource resource = null;

            public boolean hasNext() {
                if (resource == null) {
                    resource = getNextResource();
                }
                return resource != null;
            }

            @Override
            public Resource nextResource() {
                Resource rsrc = resource;
                resource = null;
                return rsrc;
            }

            private Resource getNextResource() {
                while (inputNames.hasNext() &&
                       (resources == null  ||  !resources.hasNext())) {
                    resources = findResources(inputNames.nextResourceName());
                }

                return (resources != null  &&  resources.hasNext())
                       ? resources.nextResource()
                       : null;
            }
        };
    }

}