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A framework for reading and editing Concourse configuration files
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/*
 * The MIT License (MIT)
 * 
 * Copyright (c) 2014 Jeff Nelson, Cinchapi Software Collective
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.cinchapi.concourse.config;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import org.apache.commons.configuration.ConfigurationException;

import com.google.common.base.Throwables;

/**
 * An abstract wrapper around a Concourse prefs file that provides the caller
 * with a seamless way to get variables in a configured or default state. This
 * class should be extended to handle specific variables that are defined in a
 * specific prefs file.
 * 
 * @author jnelson
 */
public abstract class AbstractPreferences {

    /**
     * The preferences file that contains the system variables to configure.
     */
    private final String file;

    /**
     * The parser of and handler to the underlying preferences file. The
     * subclass should use this object to access variables from the preferences
     * file.
     */
    private ConcourseConfiguration handler;

    /**
     * Construct a new instance.
     * 
     * @param file
     */
    protected AbstractPreferences(String file) {
        this.file = file;
        reload();
    }

    /**
     * Return the handler to the underlying preferences file. The subclass
     * should use the handler to read/write data.
     * 
     * @return the preferences file handler
     */
    protected final ConcourseConfiguration getHandler() {
        return handler;
    }

    /**
     * Set the value associated with {@code key} and persist it to the
     * underlying preferences file.
     * 
     * @param key
     * @param value
     */
    protected final void set(String key, Object value) {
        handler.setProperty(key, value);
        try {
            handler.save();
        }
        catch (ConfigurationException e) {
            throw Throwables.propagate(e);
        }
    }

    /**
     * Reload the data from the configuration file, in case anything has
     * changed.
     */
    protected final void reload() {
        // Create an empty file if necessary. This means that the subclass can
        // handle defaults in a seamless manner.
        Path path = Paths.get(file);
        if(!Files.exists(path)) {
            try {
                if(path.getParent() != null) {
                    Files.createDirectories(path.getParent());
                }
                Files.createFile(path);
            }
            catch (IOException e) {
                throw Throwables.propagate(e);
            }
        }
        handler = ConcourseConfiguration.loadConfig(file);
    }
}