/*
 This file is part of the software framework JStatCom, 
 a library for building applications for data based analysis.

 Copyright (C) 2000-2005  Markus Kraetzig

 This library is free software; you can redistribute it and/or modify
 it under the terms of the GNU Lesser General Public License as
 published by the Free Software Foundation; either version 2.1 of the
 License, or (at your option) any later version.

 This library 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
 Lesser General Public License for more details.

 You should have received a copy of the GNU Lesser General Public
 License along with this library; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 USA
 */

package com.jstatcom.engine;

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

import org.apache.log4j.Logger;

/**
 * This class contains an enumeration of constants that define different types
 * of information needed for a certain engine to run, for example the location
 * of the executable, the temporary directory, etc. This class needs to be
 * subclassed to define the necessary constants for a certain engine.
 * 

 * It implements the typesave enum pattern (Joshua Bloch, "Effective
 * Java", Item 21) . If you compare ConfigKeys, always
 * use the == operator.
 * 
 * @author Markus Kraetzig 
 */
public abstract class ConfigKeys {
    private static final Logger log = Logger.getLogger(ConfigKeys.class);

    /**
     * The name of this ConfigKey.
     */
    private final String name;

    /**
     * Creates a new config key.
     * 
     * @param name
     *            the identifier of the new key
     * @throws IllegalArgumentException
     *             if (name == null)
     */
    public ConfigKeys(String name) {

        if (name == null)
            throw new IllegalArgumentException("Argument was null");

        this.name = name;

    }

    /**
     * Gets the default value for this config key. If no reasonable defaul
     * exists for that setting, this method should return an empty string.
     * 
     * @return string with default setting or "" if no reasonable
     *         default exists
     */
    public abstract String defaultVal();

    /**
     * Override prevention method to enforce a.equals(b) if and
     * only if a==b.
     * 
     * @param o
     *            object to compare with
     * @return true if equal, false otherwise
     */
    public final boolean equals(Object o) {
        return super.equals(o);
    }

    /**
     * Gets a map of all public keys defined in class c. All key
     * objects are stored with its name as the respective key.
     * 
     * @return the config keys map
     * @throws IllegalArgumentException
     *             if (c.getSuperclass() != ConfigKeys.class) or
     *             if (c == null)
     */
    public static Map getAllKeys(Class c) {

        if (c == null)
            throw new IllegalArgumentException("Argument was null.");

        if (c.getSuperclass() != ConfigKeys.class)
            throw new IllegalArgumentException("Class argument: " + c
                    + " not inherited from ConfigKeys.");

        Field[] publicFields = c.getFields();
        Map keysMap = new HashMap();

        try {
            for (int i = 0; i < publicFields.length; i++) {
                Object obj = null;
                if (publicFields[i].getType().equals(c))
                    obj = publicFields[i].get(publicFields[i].getType());

                if (obj instanceof ConfigKeys) {
                    ConfigKeys key = (ConfigKeys) obj;
                    keysMap.put(key.name, (ConfigKeys) obj);
                }
            }
        } catch (SecurityException e) {
            log.error("Security error while reflective inspection", e);
        } catch (IllegalAccessException e) {
            log.error("Access error while reflective inspection", e);

        }

        return keysMap;
    }

    /**
     * Override prevention method invokes super method.
     * 
     * @return hash code
     */
    public final int hashCode() {
        return super.hashCode();
    }

    /**
     * Gets whether value is valid for this.
     * 
     * @param value
     *            a string value for this key
     * @return null if valid, an error string if not valid
     */
    public abstract String isValid(String value);

    /**
     * Gets the name of this.
     * 
     * @return the name of the key
     */
    public final String name() {
        return name;
    }

    /**
     * Gets a string representation.
     * 
     * @return a string representation of this
     */
    public final String toString() {
        return name;
    }
}