HistoryManager.java

/*
 * This file is part of the aidGer project.
 *
 * Copyright (C) 2010-2013 The aidGer Team
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package de.aidger.utils.history;

import static de.aidger.utils.Translation._;
import de.aidger.model.Runtime;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.List;
import java.util.ArrayList;

/**
 * Manages changes to the database.
 *
 * @author aidGer Team
 */
final public class HistoryManager {

    /**
     * The list of all events.
     */
    private List<HistoryEvent> events = new ArrayList<HistoryEvent>();

    /**
     * The name of the history file.
     */
    private String historyFile;

    /**
     * The only instance of the HistoryManager class.
     */
    private static HistoryManager instance = null;

    /**
     * Initializes the HistoryManager class
     *
     * @throws HistoryException
     */
    private HistoryManager() throws HistoryException {
        historyFile = Runtime.getInstance().getConfigPath() + "/history";
        loadFromFile();
    }

    /**
     * Get the only instance of the HistoryManager class.
     *
     * @return The instance
     * @throws HistoryException
     */
    public static HistoryManager getInstance() throws HistoryException {
        if (instance == null) {
            instance = new HistoryManager();
        }

        return instance;
    }

    /**
     * Get a list of all history events
     *
     * @return List of events
     */
    public List<HistoryEvent> getEvents() {
        return events;
    }

    /**
     * Add an event to the history.
     *
     * @param evt
     *          The event to add
     *
     * @throws HistoryException
     */
    public void addEvent(HistoryEvent evt) throws HistoryException {
        events.add(evt);
        if (events.size() > Integer.parseInt(Runtime.getInstance().getOption(
                "history-length", "100"))) {
            events.remove(0);
        }

        try {
            File history = new File(historyFile);
            if (!history.exists()) {
                history.createNewFile();
            }

            FileOutputStream out = new FileOutputStream(history);
            ObjectOutputStream obj = new ObjectOutputStream(out);
            obj.writeObject(events);
            obj.close();
            out.close();
        } catch (FileNotFoundException ex) {
            throw new HistoryException(_("Couldn't find the history file."));
        } catch (IOException ex) {
            throw new HistoryException(_("Writing to the history file failed."));
        }
    }

    /**
     * Load the history from a file.
     *
     * @throws HistoryException
     */
    protected void loadFromFile() throws HistoryException {
        File history = new File(historyFile);
        if (!history.exists()) {
            events = new ArrayList<HistoryEvent>();
            try {
                history.createNewFile();
                FileOutputStream out = new FileOutputStream(history);
                ObjectOutputStream obj = new ObjectOutputStream(out);
                obj.writeObject(events);
                obj.close();
                out.close();
            } catch (IOException ex) {
                throw new HistoryException(_("Creating the history file failed."));
            }
            return;
        }

        try {
            FileInputStream input = new FileInputStream(history);
            ObjectInputStream obj = new ObjectInputStream(input);
            events = (ArrayList<HistoryEvent>) obj.readObject();
            obj.close();
            input.close();
        } catch (FileNotFoundException ex) {
            throw new HistoryException(_("Couldn't find the history file."));
        } catch (IOException ex) {
            throw new HistoryException(_("Reading the history from file failed."));
        } catch (ClassNotFoundException ex) {
            throw new HistoryException(_("Illegal modifications of the history file have been detected."));
        }
    }
}