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/*******************************************************************************
 * 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 nl.weeaboo.lua2.vm;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import nl.weeaboo.lua2.io.LuaSerializable;

/**
 * Upvalue used with Closure formulation
 * 
 *
 * @see LuaClosure
 * @see Prototype
 */
@LuaSerializable
public final class UpValue implements Externalizable {

    public static final UpValue[] NOUPVALUES = new UpValue[0];

    private LuaValue sealed; //Gets set when closed
    private LuaValue[] array = LuaConstants.NOVALS;
    private int index;

    /**
     * Do not use. Required for efficient serialization.
     */
    @Deprecated
    public UpValue() {
    }

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

    static UpValue newSealedInstance() {
        UpValue upValue = new UpValue();
        upValue.index = -1;
        upValue.sealed = LuaNil.NIL;
        return upValue;
    }

    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        if (sealed != null) {
            out.writeInt(-1);
            out.writeObject(sealed);
        } else {
            out.writeInt(index);
            out.writeObject(array);
        }
    }

    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        index = in.readInt();
        if (index < 0) {
            sealed = (LuaValue)in.readObject();
        } else {
            array = (LuaValue[])in.readObject();
        }
    }

    /**
     * Convert this upvalue to a Java String
     *
     * @return the Java String for this upvalue.
     * @see LuaValue#tojstring()
     */
    public String tojstring() {
        return getValue().tojstring();
    }

    /**
     * Get the value of the upvalue
     *
     * @return the {@link LuaValue} for this upvalue
     */
    public final LuaValue getValue() {
        return (index < 0 ? sealed : array[index]);
    }

    /**
     * Set the value of the upvalue
     *
     * @param value the {@link LuaValue} to set it to
     */
    public final void setValue(LuaValue value) {
        if (index < 0) {
            sealed = value;
        } else {
            array[index] = value;
        }
    }

    /**
     * Close this upvalue so it is no longer on the stack
     */
    public final void close() {
        if (sealed == null) {
            sealed = array[index];
            array = LuaConstants.NOVALS;
            index = -1;
        }
    }

}