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Fixtures to assist in testing via FitNesse
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package nl.hsac.fitnesse.fixture.util;

import fit.exception.FitFailureException;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;

import javax.xml.namespace.NamespaceContext;
import javax.xml.namespace.QName;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import java.io.StringReader;
import java.util.ArrayList;
import java.util.List;

/**
 * Helper to evaluate XPath expressions.
 */
public class XPathHelper {
    /**
     * Evaluates xPathExpr against xml, returning single match.
     * @param xml xml document to apply XPath to.
     * @param xPathExpr XPath expression to evaluate.
     * @return result of evaluation, null if xml is null.
     */
    public static String getXPath(NamespaceContext context, String xml, String xPathExpr) {
        return (String) evaluateXpath(context, xml, xPathExpr, null);
    }
    
    
    /**
     * Evaluates xPathExpr against xml, returning all matches.
     * @param xml xml document to apply XPath to.
     * @param xPathExpr XPath expression to evaluate.
     * @return text() of all nodes matching XPath, null if xml is null.
     */
    public static List getAllXPath(NamespaceContext context, String xml, String xPathExpr) {
        List result = null;
        
        NodeList nodes = (NodeList) evaluateXpath(context, xml, xPathExpr, XPathConstants.NODESET);
        if (nodes != null) {
            result = new ArrayList(nodes.getLength());
            for (int i = 0; i < nodes.getLength(); i++) {
                result.add(nodes.item(i).getNodeValue());
            }
        }

        return result;
    }
    
    private static Object evaluateXpath(NamespaceContext context, String xml, String xPathExpr, QName returnType) {
        Object result = null;
        if (xml != null) {
            if (!xml.startsWith("<")) {
                throw new FitFailureException("Cannot perform XPATH on non-xml: " + xml);
            }
            XPathFactory xPathfactory = XPathFactory.newInstance();
            XPath xpath = xPathfactory.newXPath();
            if (context != null) {
                xpath.setNamespaceContext(context);
            }
            try {
                XPathExpression expr = xpath.compile(xPathExpr);
                InputSource source = new InputSource(new StringReader(xml));
                
                if (returnType != null) {
                	result = expr.evaluate(source, returnType);
                } else {
                	result = expr.evaluate(source);
                }
                
            } catch (XPathExpressionException e) {
                String msg = getMessage(e);
                throw new FitFailureException("Unable to evaluate xpath: " + xPathExpr + "\n" + msg);
            }
        }
        return result;
    }

    private static String getMessage(XPathExpressionException e) {
        String msg;
        Throwable t = e;
        do {
            msg = t.getMessage();
            t = t.getCause();
        } while (msg == null && t != null);
        return msg;
    }
}