// ResolvingXMLFilter.java - An XMLFilter that performs catalog resolution

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (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.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.xml.resolver.tools;

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.Attributes;
import org.xml.sax.helpers.XMLFilterImpl;

import org.apache.xml.resolver.Catalog;
import org.apache.xml.resolver.CatalogManager;

import org.apache.xml.resolver.helpers.FileURL;

/**
 * A SAX XMLFilter that performs catalog-based entity resolution.
 *
 * <p>This class implements a SAX XMLFilter that performs entity resolution
 * using the CatalogResolver. The actual, underlying parser is obtained
 * from a SAXParserFactory.</p>
 * </p>
 *
 * @see CatalogResolver
 * @see org.xml.sax.XMLFilter
 *
 * @author Norman Walsh
 * <a href="mailto:Norman.Walsh@Sun.COM">Norman.Walsh@Sun.COM</a>
 *
 * @version 1.0
 */
public class ResolvingXMLFilter extends XMLFilterImpl {
  /**
   * Suppress explanatory message?
   *
   * @see #parse(InputSource)
   */
  public static boolean suppressExplanation = false;

  /** The manager for the underlying resolver. */
  private CatalogManager catalogManager = CatalogManager.getStaticManager();

  /** The underlying catalog resolver. */
  private CatalogResolver catalogResolver = null;

  /** A separate resolver for oasis-xml-pi catalogs. */
  private CatalogResolver piCatalogResolver = null;

  /** Are we in the prolog? Is an oasis-xml-catalog PI valid now? */
  private boolean allowXMLCatalogPI = false;

  /** Has an oasis-xml-catalog PI been seen? */
  private boolean oasisXMLCatalogPI = false;

  /** The base URI of the input document, if known. */
  private URL baseURL = null;

  /** Construct an empty XML Filter with no parent. */
  public ResolvingXMLFilter() {
    super();
    catalogResolver = new CatalogResolver(catalogManager);
  }

  /** Construct an XML filter with the specified parent. */
  public ResolvingXMLFilter(XMLReader parent) {
    super(parent);
    catalogResolver = new CatalogResolver(catalogManager);
  }

  /** Construct an XML filter with the specified parent. */
  public ResolvingXMLFilter(CatalogManager manager) {
    super();
    catalogManager = manager;
    catalogResolver = new CatalogResolver(catalogManager);
  }

  /** Construct an XML filter with the specified parent. */
  public ResolvingXMLFilter(XMLReader parent, CatalogManager manager) {
    super(parent);
    catalogManager = manager;
    catalogResolver = new CatalogResolver(catalogManager);
  }

  /**
   * Provide accessto the underlying Catalog.
   */
  public Catalog getCatalog() {
    return catalogResolver.getCatalog();
  }

  /**
   * SAX XMLReader API.
   *
   * <p>Note that the JAXP 1.1ea2 parser crashes with an InternalError if
   * it encounters a system identifier that appears to be a relative URI
   * that begins with a slash. For example, the declaration:</p>
   *
   * <pre>
   * &lt;!DOCTYPE book SYSTEM "/path/to/dtd/on/my/system/docbookx.dtd">
   * </pre>
   *
   * <p>would cause such an error. As a convenience, this method catches
   * that error and prints an explanation. (Unfortunately, it's not possible
   * to identify the particular system identifier that causes the problem.)
   * </p>
   *
   * <p>The underlying error is forwarded after printing the explanatory
   * message. The message is only every printed once and if
   * <code>suppressExplanation</code> is set to <code>false</code> before
   * parsing, it will never be printed.</p>
   */
  public void parse(InputSource input)
    throws IOException, SAXException {
    allowXMLCatalogPI = true;

    setupBaseURI(input.getSystemId());

    try {
      super.parse(input);
    } catch (InternalError ie) {
      explain(input.getSystemId());
      throw ie;
    }
  }

  /** SAX XMLReader API.
   *
   * @see #parse(InputSource)
   */
  public void parse(String systemId)
    throws IOException, SAXException {
    allowXMLCatalogPI = true;

    setupBaseURI(systemId);

    try {
      super.parse(systemId);
    } catch (InternalError ie) {
      explain(systemId);
      throw ie;
    }
  }

  /**
   * Implements the <code>resolveEntity</code> method
   * for the SAX interface, using an underlying CatalogResolver
   * to do the real work.
   */
  public InputSource resolveEntity (String publicId, String systemId) {
    allowXMLCatalogPI = false;
    String resolved = catalogResolver.getResolvedEntity(publicId, systemId);

    if (resolved == null && piCatalogResolver != null) {
      resolved = piCatalogResolver.getResolvedEntity(publicId, systemId);
    }

    if (resolved != null) {
      try {
	InputSource iSource = new InputSource(resolved);
	iSource.setPublicId(publicId);

	// Ideally this method would not attempt to open the
	// InputStream, but there is a bug (in Xerces, at least)
	// that causes the parser to mistakenly open the wrong
	// system identifier if the returned InputSource does
	// not have a byteStream.
	//
	// It could be argued that we still shouldn't do this here,
	// but since the purpose of calling the entityResolver is
	// almost certainly to open the input stream, it seems to
	// do little harm.
	//
	URL url = new URL(resolved);
	InputStream iStream = url.openStream();
	iSource.setByteStream(iStream);

	return iSource;
      } catch (Exception e) {
	catalogManager.debug.message(1,
				     "Failed to create InputSource ("
				     + e.toString()
				     + ")", resolved);
	return null;
      }
    } else {
      return null;
    }
  }

  /** SAX DTDHandler API.
   *
   * <p>Captured here only to detect the end of the prolog so that
   * we can ignore subsequent oasis-xml-catalog PIs. Otherwise
   * the events are just passed through.</p>
   */
  public void notationDecl (String name, String publicId, String systemId)
    throws SAXException {
    allowXMLCatalogPI = false;
    super.notationDecl(name,publicId,systemId);
  }

  /** SAX DTDHandler API.
   *
   * <p>Captured here only to detect the end of the prolog so that
   * we can ignore subsequent oasis-xml-catalog PIs. Otherwise
   * the events are just passed through.</p>
   */
  public void unparsedEntityDecl (String name,
				  String publicId,
				  String systemId,
				  String notationName) 
    throws SAXException {
    allowXMLCatalogPI = false;
    super.unparsedEntityDecl (name, publicId, systemId, notationName);
  }

  /** SAX ContentHandler API.
   *
   * <p>Captured here only to detect the end of the prolog so that
   * we can ignore subsequent oasis-xml-catalog PIs. Otherwise
   * the events are just passed through.</p>
   */
  public void startElement (String uri, String localName, String qName,
			    Attributes atts)
    throws SAXException {
    allowXMLCatalogPI = false;
    super.startElement(uri,localName,qName,atts);
  }

  /** SAX ContentHandler API.
   *
   * <p>Detect and use the oasis-xml-catalog PI if it occurs.</p>
   */
  public void processingInstruction(String target, String pidata)
    throws SAXException {
    if (target.equals("oasis-xml-catalog")) {
      URL catalog = null;
      String data = pidata;

      int pos = data.indexOf("catalog=");
      if (pos >= 0) {
	data = data.substring(pos+8);
	if (data.length() > 1) {
	  String quote = data.substring(0,1);
	  data = data.substring(1);
	  pos = data.indexOf(quote);
	  if (pos >= 0) {
	    data = data.substring(0, pos);
	    try {
	      if (baseURL != null) {
		catalog = new URL(baseURL, data);
	      } else {
		catalog = new URL(data);
	      }
	    } catch (MalformedURLException mue) {
	      // nevermind
	    }
	  }
	}
      }

      if (allowXMLCatalogPI) {
	if (catalogManager.getAllowOasisXMLCatalogPI()) {
	  catalogManager.debug.message(4,"oasis-xml-catalog PI", pidata);

	  if (catalog != null) {
	    try {
	      catalogManager.debug.message(4,"oasis-xml-catalog", catalog.toString());
	      oasisXMLCatalogPI = true;

	      if (piCatalogResolver == null) {
		piCatalogResolver = new CatalogResolver(true);
	      }

	      piCatalogResolver.getCatalog().parseCatalog(catalog.toString());
	    } catch (Exception e) {
	      catalogManager.debug.message(3, "Exception parsing oasis-xml-catalog: "
			    + catalog.toString());
	    }
	  } else {
	    catalogManager.debug.message(3, "PI oasis-xml-catalog unparseable: " + pidata);
	  }
	} else {
	  catalogManager.debug.message(4,"PI oasis-xml-catalog ignored: " + pidata);
	}
      } else {
	catalogManager.debug.message(3, "PI oasis-xml-catalog occurred in an invalid place: "
		      + pidata);
      }
    } else {
      super.processingInstruction(target, pidata);
    }
  }

  /** Save the base URI of the document being parsed. */
  private void setupBaseURI(String systemId) {
    URL cwd = null;

    try {
      cwd = FileURL.makeURL("basename");
    } catch (MalformedURLException mue) {
      cwd = null;
    }

    try {
      baseURL = new URL(systemId);
    } catch (MalformedURLException mue) {
      if (cwd != null) {
	try {
	  baseURL = new URL(cwd, systemId);
	} catch (MalformedURLException mue2) {
	  // give up
	  baseURL = null;
	}
      } else {
	// give up
	baseURL = null;
      }
    }
  }

  /** Provide one possible explanation for an InternalError. */
  private void explain(String systemId) {
    if (!suppressExplanation) {
      System.out.println("XMLReader probably encountered bad URI in " + systemId);
      System.out.println("For example, replace '/some/uri' with 'file:/some/uri'.");
    }
    suppressExplanation = true;
  }
}

