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/*
 ***** BEGIN LICENSE BLOCK *****
 * Version: CPL 1.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Common Public
 * License Version 1.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.eclipse.org/legal/cpl-v10.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * Copyright (C) 2001-2002 Jan Arne Petersen 
 * Copyright (C) 2001-2002 Benoit Cerrina 
 * Copyright (C) 2002-2004 Anders Bengtsson 
 * Copyright (C) 2004 Thomas E Enebo 
 * 
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the CPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the CPL, the GPL or the LGPL.
 ***** END LICENSE BLOCK *****/
package org.jruby.ast;

import java.util.List;

import org.jruby.Ruby;
import org.jruby.ast.types.INameNode;
import org.jruby.ast.visitor.NodeVisitor;
import org.jruby.lexer.yacc.ISourcePosition;
import org.jruby.runtime.Block;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.util.ByteList;

/**
 * The access to a Constant.
 */
public class ConstNode extends Node implements INameNode {
    private String name;
    private volatile transient IRubyObject cachedValue = null;
    private int generation = -1;
    
    public ConstNode(ISourcePosition position, String name) {
        super(position);
        this.name = name;
    }

    public NodeType getNodeType() {
        return NodeType.CONSTNODE;
    }
    
    /**
     * Accept for the visitor pattern.
     * @param iVisitor the visitor
     **/
    public Object accept(NodeVisitor iVisitor) {
        return iVisitor.visitConstNode(this);
    }

    /**
     * Gets the name.
     * @return Returns a String
     */
    public String getName() {
        return name;
    }
    
    public List childNodes() {
        return EMPTY_LIST;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    @Override
    public IRubyObject interpret(Ruby runtime, ThreadContext context, IRubyObject self, Block aBlock) {
        IRubyObject value = getValue(context);

        // We can callsite cache const_missing if we want
        return value != null ? value :
            context.getCurrentScope().getStaticScope().getModule().callMethod(context, "const_missing", runtime.fastNewSymbol(name));
    }

    @Override
    public ByteList definition(Ruby runtime, ThreadContext context, IRubyObject self, Block aBlock) {
        return context.getConstantDefined(name) ? CONSTANT_BYTELIST : null;
    }
    
    public IRubyObject getValue(ThreadContext context) {
        IRubyObject value = cachedValue; // Store to temp so it does null out on us mid-stream

        return isCached(context, value) ? value : reCache(context, name);
    }
    
    private boolean isCached(ThreadContext context, IRubyObject value) {
        return value != null && generation == context.getRuntime().getConstantGeneration();
    }
    
    public IRubyObject reCache(ThreadContext context, String name) {
        int newGeneration = context.getRuntime().getConstantGeneration();
        IRubyObject value = context.getConstant(name);
            
        cachedValue = value;
            
        if (value != null) generation = newGeneration;
        
        return value;
    }
}