/* xerces-based parser written by Terri Liebowitz Schwartz of SDSC (see CIPRES
license).

Executable takes three arguments:
	path-to-instance-document path-to-xml-schema namespace

*/
package validator;

import java.io.File;
import java.io.FileReader;
import java.util.Properties;

import org.apache.xerces.parsers.DOMParser;
import org.xml.sax.InputSource;

/*
 Note that first implementation of againstXSD is commented out and the
 real implementation has a third optional argument, a namespace.

 If the xml document references a schema, and it refers to a schema file
 that exists, that schema will be used.  It doesn't matter whether
 you specify a namespace or valid xsd file when invoking this, all that will
 be ignored if the document contains a reference to a schema file that exits.

 If the document references a schema file that doesn't exist, or doesn't reference
 a schema, then you can specify the schema and namespace (if any) here.

 */
public class XmlValidator
{
	/**
	 * @param xmlFilepath filepath to the xml file to be validated
	 * @param xsdFilepath filepath to the xsd file that the gui xml file
	 *            specified by xmlFilepath should be validated against
	 * @return error message generated by SAX parser or <b>null</b> if no
	 *         errors are detected
	 */
	public static String againstXSD(final String xmlFilepath, final String xsdFilepath, final String namespace) {
		try {
			// make sure both paths specify a valid file
			File config_fp = new File(xmlFilepath);
			if (!config_fp.exists())
				return "Unable to open file " + xmlFilepath;
			config_fp = new File(xsdFilepath);
			if (!config_fp.exists())
				return "Unable to open file " + xsdFilepath;
			final DOMParser parser = new DOMParser();
			parser.setFeature("http://xml.org/sax/features/validation", true);
			parser.setFeature("http://apache.org/xml/features/validation/schema", true);
			if (namespace == null || namespace.trim().equals(""))
				parser.setProperty("http://apache.org/xml/properties/schema/external-noNamespaceSchemaLocation", xsdFilepath);
			else
				parser.setProperty("http://apache.org/xml/properties/schema/external-schemaLocation", namespace.trim() + " " + xsdFilepath);
			parser.parse(new InputSource(new FileReader(xmlFilepath)));
			return null;
		}
		catch (final Exception e) {
			e.printStackTrace();
			return e.getMessage();
		}
	}

	public static void main(final String args[]) {
		final Properties p = System.getProperties();
		final String xml = p.getProperty("xml");
		final String xsd = p.getProperty("xsd");
		final String ns = p.getProperty("ns");
		if (xml == null || xsd == null) {
			System.out.println("Two system properties are required, xml=xml_file and xsd=xsd_file");
			System.out.println("ns=namespace is optional.");
			System.exit(1);
		}
		final String retval = againstXSD(xml, xsd, ns);
		if (retval == null) {
			System.exit(0);
		}
		System.out.println("Validation error: " + retval);
		System.exit(1);
	}
}