/*
 * 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.io.File;
import java.net.URL;

import org.apache.commons.lang3.StringUtils;

/**
 * <p>
 * A specialized implementation of {@code FileLocationStrategy} which searches for files in the user's home directory or
 * another special configurable directory.
 * </p>
 * <p>
 * This strategy implementation ignores the URL stored in the passed in {@link FileLocator}. It constructs a file path
 * from the configured home directory (which is the user's home directory per default, but can be changed to another
 * path), optionally the base path, and the file name. If the resulting path points to an existing file, its URL is
 * returned.
 * </p>
 * <p>
 * When constructing an instance it can be configured whether the base path should be taken into account. If this option
 * is set, the base path is appended to the home directory if it is not <b>null</b>. This is useful for instance to
 * select a specific sub directory of the user's home directory. If this option is set to <b>false</b>, the base path is
 * always ignored, and only the file name is evaluated.
 * </p>
 */
public class HomeDirectoryLocationStrategy implements FileLocationStrategy {
    /** Constant for the system property with the user's home directory. */
    private static final String PROP_HOME = "user.home";

    /** The home directory to be searched for the requested file. */
    private final String homeDirectory;

    /** The flag whether the base path is to be taken into account. */
    private final boolean evaluateBasePath;

    /**
     * Creates a new instance of {@code HomeDirectoryLocationStrategy} and initializes it with the specified settings.
     *
     * @param homeDir the path to the home directory (can be <b>null</b>)
     * @param withBasePath a flag whether the base path should be evaluated
     */
    public HomeDirectoryLocationStrategy(final String homeDir, final boolean withBasePath) {
        homeDirectory = fetchHomeDirectory(homeDir);
        evaluateBasePath = withBasePath;
    }

    /**
     * Creates a new instance of {@code HomeDirectoryLocationStrategy} and initializes the base path flag. The home
     * directory is set to the user's home directory.
     *
     * @param withBasePath a flag whether the base path should be evaluated
     */
    public HomeDirectoryLocationStrategy(final boolean withBasePath) {
        this(null, withBasePath);
    }

    /**
     * Creates a new instance of {@code HomeDirectoryLocationStrategy} with default settings. The home directory is set to
     * the user's home directory. The base path flag is set to <b>false</b> (which means that the base path is ignored).
     */
    public HomeDirectoryLocationStrategy() {
        this(false);
    }

    /**
     * Gets the home directory. In this directory the strategy searches for files.
     *
     * @return the home directory used by this object
     */
    public String getHomeDirectory() {
        return homeDirectory;
    }

    /**
     * Returns a flag whether the base path is to be taken into account when searching for a file.
     *
     * @return the flag whether the base path is evaluated
     */
    public boolean isEvaluateBasePath() {
        return evaluateBasePath;
    }

    /**
     * {@inheritDoc} This implementation searches in the home directory for a file described by the passed in
     * {@code FileLocator}. If the locator defines a base path and the {@code evaluateBasePath} property is <b>true</b>, a
     * sub directory of the home directory is searched.
     */
    @Override
    public URL locate(final FileSystem fileSystem, final FileLocator locator) {
        if (StringUtils.isNotEmpty(locator.getFileName())) {
            final String basePath = fetchBasePath(locator);
            final File file = FileLocatorUtils.constructFile(basePath, locator.getFileName());
            if (file.isFile()) {
                return FileLocatorUtils.convertFileToURL(file);
            }
        }

        return null;
    }

    /**
     * Determines the base path to be used for the current locate() operation.
     *
     * @param locator the {@code FileLocator}
     * @return the base path to be used
     */
    private String fetchBasePath(final FileLocator locator) {
        if (isEvaluateBasePath() && StringUtils.isNotEmpty(locator.getBasePath())) {
            return FileLocatorUtils.appendPath(getHomeDirectory(), locator.getBasePath());
        }
        return getHomeDirectory();
    }

    /**
     * Obtains the home directory to be used by a new instance. If a directory name is provided, it is used. Otherwise, the
     * user's home directory is looked up.
     *
     * @param homeDir the passed in home directory
     * @return the directory to be used
     */
    private static String fetchHomeDirectory(final String homeDir) {
        return homeDir != null ? homeDir : System.getProperty(PROP_HOME);
    }
}
