/*
 * 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.configuration2.io;

import java.net.URL;

/**
 * <p>
 * An interface allowing applications to customize the process of locating a file.
 * </p>
 * <p>
 * {@link FileHandler} uses {@link FileLocator} objects for referencing files. These objects are not guaranteed to
 * identify a file in a unique way. For instance, if only a file name is defined, this could mean a relative file name
 * in the current directory, the name of a resource to be loaded from the class path, or something else. Before the file
 * described by a {@code FileLocator} can be actually accessed, an unambiguous URL pointing to this file has to be
 * obtained. This is the job of a {@code FileLocationStrategy}.
 * </p>
 * <p>
 * This interface defines a method for locating a file provided as a {@code FileLocator} object. If location is
 * successful, a URL is returned. A concrete implementation can perform arbitrary actions to search for the file in
 * question at various places. There will also be an implementation allowing the combination of multiple
 * {@code FileLocationStrategy} implementations; so a file can be searched using multiple strategies until one of them
 * is successful.
 * </p>
 *
 * @since 2.0
 */
public interface FileLocationStrategy {
    /**
     * Tries to locate the specified file. The method also expects the {@code FileSystem} to be used. Note that the
     * {@code FileLocator} object may also contain a {@code FileSystem}, but this is optional. The passed in
     * {@code FileSystem} should be used, and callers must not pass a <b>null</b> reference for this argument. A concrete
     * implementation has to evaluate the properties stored in the {@code FileLocator} object and try to match them to an
     * existing file. If this can be done, a corresponding URL is returned. Otherwise, result is <b>null</b>.
     * Implementations should not throw an exception (unless parameters are <b>null</b>) as there might be alternative
     * strategies which can find the file in question.
     *
     * @param fileSystem the {@code FileSystem} to be used for this operation
     * @param locator the object describing the file to be located
     * @return a URL pointing to the referenced file if location was successful; <b>null</b> if the file could not be
     *         resolved
     */
    URL locate(FileSystem fileSystem, FileLocator locator);
}
