/*---------------------------------------------------------------------------*\
 $Id: 1786269f59d2cd9be5ab99ffaf0cc4e82fad9982 $
\*---------------------------------------------------------------------------*/

package org.clapper.util.text;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Map;

/**

/**
 * 
The MultipleMapVariableDereferencer class implements the
 * VariableDereferencer interface and resolves variable
 * references by looking them up in one or more supplied Map
 * objects.
 *
 * 
The keys and values in the supplied Map objects
 * must be String objects.
 *
 * 
If more than one contained map has a value for a specific key, the
 * first map's value will be used. ("First", in this case, means the first
 * map added to the MultipleMapVariableDereference object.)
 *
 * @see VariableDereferencer
 * @see VariableSubstituter
 * @see MapVariableDereferencer
 *
 * @version $Revision: 6735 $
 *
 * @author Copyright © 2004-2007 Brian M. Clapper
 */
public class MultipleMapVariableDereferencer implements VariableDereferencer
{
    /*----------------------------------------------------------------------*\
                               Private Constants
    \*----------------------------------------------------------------------*/

    /*----------------------------------------------------------------------*\
                             Private Instance Data
    \*----------------------------------------------------------------------*/

    private Collection> mapList =
        new ArrayList>();

    /*----------------------------------------------------------------------*\
                                   Constructor
    \*----------------------------------------------------------------------*/

    /**
     * Creates a new instance of MultipleMapVariableDereferencer
     * that has no associated Map objects. Map objects
     * can be added with the {@link #addMap} method.
     */
    public MultipleMapVariableDereferencer()
    {
    }

    /**
     * Creates a new instance of MultipleMapVariableDereferencer
     * that is initialized with a specified set of maps.
     *
     * @param maps  the maps to use
     */
    public MultipleMapVariableDereferencer(Map... maps)
    {
        for (Map map : maps)
            addMap(map);
    }

    /*----------------------------------------------------------------------*\
                                Public Methods
    \*----------------------------------------------------------------------*/

    /**
     * Add a map to the list of maps to use when dereferencing variable values.
     * The map is added to the end of the list.
     *
     * @param map  The map to add
     */
    public final void addMap(Map map)
    {
        mapList.add(map);
    }

    /**
     * Get the value associated with a given variable.
     *
     * @param varName  The name of the variable for which the value is
     *                 desired.
     * @param context  a context object, passed through from the caller
     *                 to the dereferencer, or null if there isn't one.
     *                 Ignored here.
     *
     * @return The variable's value. If the variable has no value, this
     *         method must return null.
     */
    public String getVariableValue (String varName, Object context)
    {
        String result = null;

        for (Map map : mapList)
        {
            result = map.get(varName);
            if (result != null)
                break;
        }

        return result;
    }
}