/*******************************************************************************
* Copyright (c) 2009-2011 Luaj.org. All rights reserved.
*
* 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.luaj.vm2;


/** Upvalue used with Closure formulation
 * <p>
 * @see LuaClosure
 * @see Prototype
 */
public final class UpValue {

	LuaValue[] array; // initially the stack, becomes a holder 
	int index;

	/**
	 *  Create an upvalue relative to a stack
	 * @param stack the stack
	 * @param index the index on the stack for the upvalue
	 */
	public UpValue( LuaValue[] stack, int index) {
		this.array = stack;
		this.index = index;
	}

	public String toString() {
		return index + "/" + array.length + " " + array[index];
	}
	
	/** 
	 * Convert this upvalue to a Java String
	 * @return the Java String for this upvalue.
	 * @see LuaValue#tojstring()
	 */
	public String tojstring() {
		return array[index].tojstring();
	}
	
	/**
	 * Get the value of the upvalue
	 * @return the {@link LuaValue} for this upvalue
	 */
	public final LuaValue getValue() {
		return array[index];
	}
	
	/**
	 * Set the value of the upvalue
	 * @param value the {@link LuaValue} to set it to
	 */
	public final void setValue( LuaValue value ) {
		array[index] = value;
	}
	
	/**
	 * Close this upvalue so it is no longer on the stack
	 */
	public final void close() {
		LuaValue[] old = array;
		array = new LuaValue[] { old[index] };
		old[index] = null;
		index = 0;
	}
}
