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/*
 * Copyright (c) 2001-2013 Oracle and/or its affiliates. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 *   - Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *
 *   - Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *
 *   - Neither the name of Oracle nor the names of its
 *     contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.sun.msv.reader;

import java.util.Set;
import java.util.Stack;
import java.util.Vector;

import org.xml.sax.Locator;

import com.sun.msv.grammar.AttributeExp;
import com.sun.msv.grammar.BinaryExp;
import com.sun.msv.grammar.ChoiceExp;
import com.sun.msv.grammar.ConcurExp;
import com.sun.msv.grammar.DataExp;
import com.sun.msv.grammar.ElementExp;
import com.sun.msv.grammar.Expression;
import com.sun.msv.grammar.ExpressionVisitorVoid;
import com.sun.msv.grammar.InterleaveExp;
import com.sun.msv.grammar.ListExp;
import com.sun.msv.grammar.MixedExp;
import com.sun.msv.grammar.OneOrMoreExp;
import com.sun.msv.grammar.OtherExp;
import com.sun.msv.grammar.ReferenceExp;
import com.sun.msv.grammar.SequenceExp;
import com.sun.msv.grammar.UnaryExp;
import com.sun.msv.grammar.ValueExp;

/**
 * makes sure that the expression does not run away.
 * 
 * "run-away" expressions are expressions like this.
 * 
 * <hedgeRule label="foo" />
 *   <hedgeRef label="foo" />
 * </hedgeRule>
 * 
 * Apparently, those expressions cannot be expressed in string regular expression.
 * Therefore run-away expressions are prohibited in both RELAX and TREX.
 * 
 * @author Kohsuke KAWAGUCHI
 */
public class RunAwayExpressionChecker implements ExpressionVisitorVoid
{
    /** this exception is thrown to abort check when a error is found. */
    protected static final RuntimeException eureka = new RuntimeException();
        
    /** set of ElementExps which are already confirmed as being not a run-away exp. */
    private final Set testedExps = new java.util.HashSet();
    
    /** Expressions which are used as the content model of current element. */
    private Set contentModel = new java.util.HashSet();
    
    /** 
     * visited Expressions.
     * this information is useful for the user to figure out where did they make a mistake.
     */
    private Stack refStack = new Stack();
    
    /**
     * Queue of unchecked element exps.
     */
    private Stack unprocessedElementExps = new Stack();
    
    private final GrammarReader reader;
    
    protected RunAwayExpressionChecker( GrammarReader reader ) { this.reader = reader; }

    private void check( Expression exp ) {
        try {
            exp.visit(this);
            
            while(!unprocessedElementExps.isEmpty()) {
                contentModel.clear();
                refStack.clear();
                ElementExp e = (ElementExp)unprocessedElementExps.pop();
                e.contentModel.visit(this);
            }
        } catch( RuntimeException e ) {
            if(e!=eureka)    throw e;
        }
    }
    
    public static void check( GrammarReader reader, Expression exp ) {
        new RunAwayExpressionChecker(reader).check(exp);
    }
    
    public void onAttribute( AttributeExp exp ) {
        enter(exp);
        exp.exp.visit(this);
        leave();
    }
    public void onConcur( ConcurExp exp )                { binaryVisit(exp);    }
    public void onInterleave( InterleaveExp exp )        { binaryVisit(exp);    }
    public void onSequence( SequenceExp exp )            { binaryVisit(exp); }
    public void onChoice( ChoiceExp exp )                { binaryVisit(exp); }
    public void onOneOrMore( OneOrMoreExp exp )            { unaryVisit(exp); }
    public void onMixed( MixedExp exp )                    { unaryVisit(exp); }
    public void onList( ListExp exp )                    { unaryVisit(exp); }
    public void onEpsilon()                                {}
    public void onNullSet()                                {}
    public void onAnyString()                            {}
    public void onData( DataExp exp )                    {}
    public void onValue( ValueExp exp )                    {}
    
    protected final void binaryVisit( BinaryExp exp ) {
        // do the tail recursion to avoid StackOverflowError as much as possible
        int cnt=0;
        
        while(true) {
            enter(exp);
            cnt++;
            exp.exp2.visit(this);
            if( exp.exp1 instanceof BinaryExp )
                exp = (BinaryExp)exp.exp1;
            else
                break;
        }
        
        exp.exp1.visit(this);
        
        for( ; cnt>0; cnt-- )
            leave();
    }
    protected final void unaryVisit( UnaryExp exp ) {
        enter(exp);
        exp.exp.visit(this);
        leave();
    }
    
    private void enter( Expression exp ) {
        if(contentModel.contains(exp)) {
            // this indicates that we have reached the same expression object
            // without visiting any ElementExp.
            // so this one is a run-away expression.
                
            // check stack to find actual sequence of reference.
            String s = "";
            int i = refStack.indexOf(exp);
            int sz = refStack.size();
            
            Vector locs = new Vector();
            
            for( ; i