ConditionalExpression.java

/*
 *  eXist Open Source Native XML Database
 *  Copyright (C) 2001-06 Wolfgang M. Meier
 *  wolfgang@exist-db.org
 *  http://exist.sourceforge.net
 *  
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public License
 *  as published by the Free Software Foundation; either version 2
 *  of the License, or (at your option) any later version.
 *  
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Lesser General Public License for more details.
 *  
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *  
 *  $Id$
 */
package org.exist.xquery;

import org.exist.dom.persistent.DocumentSet;
import org.exist.xquery.util.ExpressionDumper;
import org.exist.xquery.value.Item;
import org.exist.xquery.value.Sequence;
import org.exist.xquery.value.Type;

/**
 * XQuery if ... then ... else expression.
 * 
 * @author wolf
 */
public class ConditionalExpression extends AbstractExpression implements RewritableExpression {

    private Expression testExpr;
    private Expression thenExpr;
    private Expression elseExpr;

    public ConditionalExpression(XQueryContext context, Expression testExpr,
            Expression thenExpr, Expression elseExpr) {
        super(context);
        this.testExpr = testExpr.simplify();
        this.thenExpr = thenExpr.simplify();
        this.elseExpr = elseExpr.simplify();
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.AbstractExpression#getDependencies()
     */
    public int getDependencies() {
        return Dependency.CONTEXT_SET | Dependency.CONTEXT_ITEM;
    }

    public Expression getTestExpr() {
        return testExpr;
    }

    public Expression getThenExpr() {
        return thenExpr;
    }

    public Expression getElseExpr() {
        return elseExpr;
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.AbstractExpression#getCardinality()
     */
    public int getCardinality() {
        return thenExpr.getCardinality() | elseExpr.getCardinality();
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.Expression#analyze(org.exist.xquery.Expression)
     */
    public void analyze(AnalyzeContextInfo contextInfo) throws XPathException {
        AnalyzeContextInfo myContextInfo = new AnalyzeContextInfo(contextInfo);
        myContextInfo.setFlags(myContextInfo.getFlags() & (~IN_PREDICATE));
        myContextInfo.setParent(this);
        testExpr.analyze(myContextInfo);
        // parent may have been modified by testExpr: set it again
        myContextInfo.setParent(this);
        thenExpr.analyze(myContextInfo);
        myContextInfo.setParent(this);
        elseExpr.analyze(myContextInfo);
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.Expression#eval(org.exist.dom.persistent.DocumentSet, 
     * org.exist.xquery.value.Sequence, org.exist.xquery.value.Item)
     */
    public Sequence eval(Sequence contextSequence, Item contextItem) throws XPathException {
        context.expressionStart(this);
        final Sequence testSeq = testExpr.eval(contextSequence, contextItem);
        try {
            if (testSeq.effectiveBooleanValue()) {
                return thenExpr.eval(contextSequence, contextItem);
            } else {
                return elseExpr.eval(contextSequence, contextItem);
            }
        } catch (final XPathException e) {
            if (e.getLine() == 0)
                {e.setLocation(line, column);}
            throw e;
        } finally {
            context.expressionEnd(this);
        }
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.Expression#preselect(org.exist.dom.persistent.DocumentSet)
     */
    public DocumentSet preselect(DocumentSet in_docs) throws XPathException {
        return in_docs;
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.Expression#dump(org.exist.xquery.util.ExpressionDumper)
     */
    public void dump(ExpressionDumper dumper) {
        dumper.display("if (");
        dumper.startIndent();
        testExpr.dump(dumper);
        dumper.endIndent();
        dumper.nl().display(") then");
        dumper.startIndent();
        thenExpr.dump(dumper);
        dumper.endIndent();
        dumper.nl().display("else");
        dumper.startIndent();
        elseExpr.dump(dumper);
        dumper.endIndent();
    }

    public String toString() {
        return "if ( " + testExpr.toString() + " ) then " + thenExpr.toString() + " else " + elseExpr.toString();
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.Expression#returnsType()
     */
    public int returnsType() {
        return Type.getCommonSuperType(thenExpr.returnsType(), elseExpr.returnsType());
    }

    /* (non-Javadoc)
     * @see org.exist.xquery.AbstractExpression#resetState()
     */
    public void resetState(boolean postOptimization) {
        super.resetState(postOptimization);
        testExpr.resetState(postOptimization);
        thenExpr.resetState(postOptimization);
        elseExpr.resetState(postOptimization);
    }

    public void accept(ExpressionVisitor visitor) {
        visitor.visitConditional(this);
    }

    /* RewritableExpression API */
    @Override
    public void replace(Expression oldExpr, Expression newExpr) {
        if (testExpr == oldExpr)
            {testExpr = newExpr;}
        else if (thenExpr == oldExpr)
            {thenExpr = newExpr;}
        else if (elseExpr == oldExpr)
            {elseExpr = newExpr;}
    }

    @Override
    public Expression getPrevious(Expression current) {
        return null;
    }

    @Override
    public Expression getFirst() {
        return null;
    }

    @Override
    public void remove(Expression oldExpr) throws XPathException {
        //Nothing to do
    }
    /* END RewritableExpression API */
}