/*
 * $Id: DomParser.java,v 1.1.1.1 2003-02-01 02:10:23 cbj Exp $
 * Copyright (C) 1999-2001 David Brownell
 * 
 * This file is part of GNU JAXP, a library.
 *
 * GNU JAXP is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * GNU JAXP 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 General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 * As a special exception, if you link this library with other files to
 * produce an executable, this library does not by itself cause the
 * resulting executable to be covered by the GNU General Public License.
 * This exception does not however invalidate any other reasons why the
 * executable file might be covered by the GNU General Public License. 
 */

package gnu.xml.util;

import java.util.Enumeration;
import java.util.Locale;

import org.xml.sax.*;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.helpers.NamespaceSupport;
import org.xml.sax.ext.DeclHandler;
import org.xml.sax.ext.DefaultHandler2;
import org.xml.sax.ext.LexicalHandler;

import org.w3c.dom.*;


/**
 * This parser emits SAX2 parsing events as it traverses a DOM tree, using
 * any conformant implementation of DOM.  It exposes all SAX1 features,
 * and the following SAX2 features and properties (as
 * identified by standard URIs which are not fully provided here).  Note
 * that if a Level 1 DOM implementation is given, then this behaves as if
 * namespaces were disabled, and namespace prefixes were enabled.  </p>
 *
 * <table border="1" width='100%' cellpadding='3' cellspacing='0'>
 * <tr bgcolor='#ccccff'>
 *	<th><font size='+1'>Name</font></th>
 *	<th><font size='+1'>Notes</font></th></tr>
 *
 * <tr><td colspan=2><center><em>Features ... URL prefix is
 * <b>http://xml.org/sax/features/</b></em></center></td></tr>
 *
 * <tr><td>(URL)/external-general-entities</td>
 *	<td>false (does no parsing)</td></tr>
 * <tr><td>(URL)/external-parameter-entities</td>
 *	<td>false (does no parsing)</td></tr>
 * <tr><td>(URL)/namespaces</td>
 *	<td>Value is fixed at <em>true</em></td></tr>
 * <tr><td>(URL)/namespace-prefixes</td>
 *	<td>Value is settable, defaulting to <em>false</em>
 *	(<code>xmlns</code> attributes hidden, and names aren't prefixed)
 *	</td></tr>
 * <tr><td>(URL)/string-interning</td>
 *	<td>Value is fixed at <em>false</em> (DOM provides no
 *	guarantees as to interning)</td></tr>
 * <tr><td>(URL)/validation</td>
 *	<td>false (does no parsing)</td></tr>
 * <tr><td>(URL)/lexical-handler/parameter-entities</td>
 *	<td>false (DOM doesn't do parameter entities)</td></tr>
 *
 * <tr><td colspan=2><center><em>Properties ... URL prefix is
 * <b>http://xml.org/sax/properties/</b></em></center></td></tr>
 *
 *
 * <tr><td>(URL)/dom-node</td>
 *	<td>This property may be set before parsing to hold a DOM
 *	<em>Document</em> node; any arguments given to <em>parse</em>
 *	methods are ignored.  When retrieved
 *	during a parse, this value contains the "current" DOM node.
 *	</td></tr>
 * <tr><td>(URL)/declaration-handler</td>
 *	<td>A declaration handler may be provided.  Declaration of external
 *	general entities is exposed, but not parameter entities; none of the
 *	entity names reported here will begin with "%". </td></tr>
 * <tr><td>(URL)/lexical-handler</td>
 *	<td>A lexical handler may be provided.  While the start and end of
 *	any external subset are reported, expansion of other parameter
 *	entities (e.g. inside attribute list declarations) is not exposed.
 *	Expansion of general entities within attributes is also not exposed
 *	(see below).</td></tr>
 * </table>
 *
 * <P> The consequences of modifying a DOM document tree as it is being walked
 * by this "parser" are unspecified; don't do it! </P>
 *
 * @author David Brownell
 * @version $Date: 2003-02-01 02:10:23 $
 */
final public class DomParser implements XMLReader
{
    // Stuff used internally to route events correctly
    private DefaultHandler2	defaultHandler = new DefaultHandler2 ();

    // per-parse SAX stuff
    private ContentHandler	contentHandler = defaultHandler;
    private DTDHandler		dtdHandler = defaultHandler;
    private DeclHandler		declHandler = defaultHandler;
    private LexicalHandler	lexicalHandler = defaultHandler;

    // shared context
    private ErrorHandler	errHandler = defaultHandler;
    private EntityResolver	resolver = defaultHandler;
    private Locale		locale = Locale.getDefault ();

    // parser state
    private Node		start;
    private Node		current;
    private boolean		isL2;
    private boolean		showNamespaces = true;
    private boolean		showXML1_0 = false;
    private NamespaceSupport	prefixStack = new NamespaceSupport ();
    private boolean		isDocument;


    /**
     * Constructs an unitialized <b>SAX2</b> parser.
     */
    public DomParser () {
    } 

    /**
     * Constructs an <b>SAX2</b> parser initialized to traverse the specified
     * DOM tree.  If the node is a document, the startDocument() and
     * endDocument() calls bracket the calls exposing children.
     */
    public DomParser (Node node) {
	setStart (node);
    } 


    // stuff that most components in an application should be sharing:
    // resolver and error locale.

    /**
     * <b>SAX2</b>: Returns the object used when resolving external
     * entities during parsing (both general and parameter entities).
     */
    public EntityResolver getEntityResolver ()
    {
	return resolver;
    }

    /**
     * <b>SAX1</b>: Provides an object which may be used when resolving external
     * entities during parsing (both general and parameter entities).
     */
    public void setEntityResolver (EntityResolver resolver)
    {
	if (resolver == null)
	    resolver = defaultHandler;
	this.resolver = resolver;
    }

    /**
     * <b>SAX1</b>: Identifies the locale which the parser should use for the
     * diagnostics it provides.
     *
     * @exception SAXException as defined in the specification for
     *	<em>org.xml.sax.Parser.setLocale()</em>
     */
    public void setLocale (Locale locale)
    throws SAXException
    {
	if (locale == null)
	    locale = Locale.getDefault ();
	this.locale = locale;
    }

    
    // different modules will tend to handle error handling the same,
    // but it may not be the same through the whole app

    /**
     * <b>SAX2</b>: Returns the object used to receive callbacks for XML
     * errors of all levels (fatal, nonfatal, warning).
     */
    public ErrorHandler getErrorHandler ()
    {
	return errHandler;
    }

    /**
     * <b>SAX1</b>: Provides an object which receives callbacks for XML errors
     * of all levels (fatal, nonfatal, warning).
     */
    public void setErrorHandler (ErrorHandler handler)
    {
	if (handler == null)
	    handler = defaultHandler;
	errHandler = handler;
    }


    // stuff different parts of a module will handle differently

    /**
     * <b>SAX2</b>: Returns the object used to report the logical
     * content of an XML document.
     */
    public ContentHandler getContentHandler ()
    {
	return contentHandler;
    }

    /**
     * <b>SAX2</b>: Assigns the object used to report the logical
     * content of an XML document.
     */
    public void setContentHandler (ContentHandler handler)
    {
	if (handler == null)
	    handler = defaultHandler;
	contentHandler = handler;
    }

    /**
     * <b>SAX2</b>: Returns the object used to process declarations related
     * to notations and unparsed entities.
     */
    public DTDHandler getDTDHandler ()
    {
	return dtdHandler;
    }

    /**
     * <b>SAX1</b>: Provides an object which may be used to intercept
     * declarations related to notations and unparsed entities.
     */
    public void setDTDHandler (DTDHandler handler)
    {
	if (handler == null)
	    handler = defaultHandler;
	dtdHandler = handler;
    }


    /**
     * <b>SAX1</b>:  Parses the previously provided DOM document (the
     * input parameter is ignored).  When this returns, that same
     * document may be parsed again without needing a "reset".
     *
     * @param uri ignored (pass an empty string)
     * @exception SAXException as defined in the specification for
     *	<em>org.xml.sax.Parser.parse()</em>
     */
    public void parse (String uri) throws SAXException
    {
	parse ();
    }

    /**
     * <b>SAX1</b>:  Parses the previously provided DOM document (the
     * input parameter is ignored).  When this returns, that same
     * document may be parsed again without needing a "reset".
     *
     * @param input ignored
     * @exception SAXException as defined in the specification for
     *	<em>org.xml.sax.Parser.parse()</em>
     */
    public void parse (InputSource input) throws SAXException
    {
	parse ();
    }

    private void parse () throws SAXException
    {
	try {
	    walk ();
	} finally {
	    if (isDocument)
		contentHandler.endDocument ();
	    current = null;
	    prefixStack.reset ();
	}
    }

    private boolean getIsL2 (Node node)
    {
	DOMImplementation	impl;
	Document		doc;

	if (node instanceof Document)
	    doc = (Document) node;
	else
	    doc = node.getOwnerDocument ();
	if (doc == null)
	    throw new RuntimeException ("? unowned node - L2 DTD ?");
	impl = doc.getImplementation ();
	return impl.hasFeature ("XML", "2.0");
    }


    private static final String FEATURES = "http://xml.org/sax/features/";
    private static final String HANDLERS = "http://xml.org/sax/properties/";

    /**
     * <b>SAX2</b>: Tells whether this parser supports the specified feature.
     */
    public boolean getFeature (String name)
    throws SAXNotRecognizedException, SAXNotSupportedException
    {
	// basically, none are relevant -- they relate more to
	// parsing than to walking a "parse tree".

		// FIXME: DOM feature to expose interning?

	if ((FEATURES + "validation").equals (name)
		|| (FEATURES + "external-general-entities")
		    .equals (name)
		|| (FEATURES + "external-parameter-entities")
		    .equals (name)
		|| (FEATURES + "string-interning").equals (name)
		)
	    return false;
    
	if ((FEATURES + "namespaces").equals (name))
	    return showNamespaces;
	if ((FEATURES + "namespace-prefixes").equals (name))
	    return showXML1_0;

	throw new SAXNotRecognizedException (name);
    }

    /**
     * <b>SAX2</b>:  Returns the specified property.  At this time only
     * the declaration and lexical handlers, and current the "DOM" node,
     * are supported.
     */
    public Object getProperty (String name)
    throws SAXNotRecognizedException, SAXNotSupportedException
    {
	if ((HANDLERS + "declaration-handler").equals (name))
	    return declHandler == defaultHandler ? null : declHandler;
	if ((HANDLERS + "lexical-handler").equals (name))
	    return lexicalHandler == defaultHandler ? null : lexicalHandler;

	if ((HANDLERS + "dom-node").equals (name))
	    return current;

	// unknown properties
	throw new SAXNotRecognizedException (name);
    }

    /**
     * <b>SAX2</b>:  Sets the state of features supported in this parser.
     * Only the namespace support features are mutable.
     */
    public void setFeature (String name, boolean state)
    throws SAXNotRecognizedException, SAXNotSupportedException
    {
	if (current != null)
	    throw new IllegalStateException ("feature change midparse");

	boolean value = getFeature (name);

	if (value == state)
	    return;

	if ((FEATURES + "namespaces").equals (name)) {
	    if (!showXML1_0 && state == false)
		throw new SAXNotSupportedException ("Illegal namespace "
			+ "processing configuration");
	    showNamespaces = state;
	    return;
	}
	if ((FEATURES + "namespace-prefixes").equals (name)) {
	    if (!showNamespaces && state == false)
		throw new SAXNotSupportedException ("Illegal namespace "
			+ "processing configuration");
	    showXML1_0 = state;
	    return;
	}

	throw new SAXNotSupportedException (name);
    }

    /**
     * <b>SAX2</b>:  Assigns the specified property.  At this time only
     * declaration and lexical handlers, and the initial DOM document, are
     * supported.  These must not be changed to values of the wrong type.
     * Like SAX1 handlers, these handlers may be changed at any time.
     * Like SAX1 input source or document URI, the initial DOM document
     * may not be changed during a parse.
     */
    public void setProperty (String name, Object state)
    throws SAXNotRecognizedException, SAXNotSupportedException
    {
	if ((HANDLERS + "declaration-handler").equals (name)) {
	    if (!(state instanceof DeclHandler || state == null))
		throw new SAXNotSupportedException (name);
	    declHandler = (DeclHandler) state;
	    return;
	}

	if ((HANDLERS + "lexical-handler").equals (name)) {
	    if (!(state instanceof LexicalHandler || state == null))
		throw new SAXNotSupportedException (name);
	    lexicalHandler = (LexicalHandler) state;
	    return;
	}

	if ((HANDLERS + "dom-node").equals (name)) {
	    if (state == null || state instanceof Node) {
		if (current != null)
		    throw new SAXNotSupportedException (
			"property is readonly during parse:  " + name);
		setStart ((Node) state);
		return;
	    }
	    throw new SAXNotSupportedException ("not a DOM Node");
	}

	// unknown properties
	throw new SAXNotRecognizedException (name);
    }

    private void setStart (Node property)
    {
	start = property;
	if (start != null) {
	    isL2 = getIsL2 (start);
	    isDocument = (start instanceof Document);
	}
    }

    //
    // Non-recursive walk, using DOM state when backtracking is needed
    //
    private void walk ()
    throws SAXException
    {
	int			type;
	NamedNodeMap		nodes;
	int			length;
	AttributesImpl		attrs = new AttributesImpl ();
	char			chars [];
	String			ns, local;

	synchronized (this) {
	    if (current != null)
		throw new IllegalStateException ("already walking tree");

	    // JVM guarantees assignments are atomic; so no other
	    // thread could get this far till this walk's done.
	    current = start;
	}
    
	for (;;) {
	    type = current.getNodeType ();

	    //
	    // First, visit the current node, including any "start" calls
	    //
	    switch (type) {

	      case Node.DOCUMENT_NODE:
	        contentHandler.startDocument ();
		break;

	      case Node.ELEMENT_NODE:
		nodes = current.getAttributes ();
		length = nodes.getLength ();
		prefixStack.pushContext ();
		for (int i = 0; i < length; i++) {
		    Attr	attr = (Attr) nodes.item (i);
		    String	name = attr.getNodeName ();

		    if (showNamespaces && name.startsWith ("xmlns")) {
			String	prefix;
			String	uri;
			
			// NOTE: DOM L2 (CR2+ and REC) violate the
			// Namespaces REC, treat "xmlns" like a strange
			// attribute instead of a magic token
			if ("xmlns".equals (name))
			    prefix = "";
			else
			    prefix = name.substring (6);
			uri = attr.getNodeValue ();

			prefixStack.declarePrefix (prefix, uri);
			contentHandler.startPrefixMapping (prefix, uri);
			
			if (!showXML1_0)
			    continue;
		    }

		    //
		    // NOTE:  DOM doesn't record the attribute type info
		    // which SAX exposes; so this always reports CDATA.
		    //
		    // NOTE:  SAX doesn't expose the isSpecified info which
		    // DOM exposes; that's discarded here.  Similarly with
		    // the information DOM hides inside itself about what
		    // the default values for an attribute are.
		    //
		    if (showNamespaces) {
			if (isL2) {
			    if ((ns = attr.getNamespaceURI ()) == null)
				ns = "";
			    // Note:  SAX2 and DOM handle "local" names
			    // differently
			    if ((local = attr.getLocalName ()) == null)
				local = name;
			} else {
// XXX
			    throw new RuntimeException (
				"NYI, ns lookup when parsing L1 DOM");
			}
		    } else
			ns = local = "";
		    attrs.addAttribute (ns, local, name,
			"CDATA", attr.getNodeValue ());
		}
		if (showNamespaces) {
		    if (isL2) {
			if ((ns = current.getNamespaceURI ()) == null)
			    ns = "";
			// Note:  SAX2 and DOM handle "local" names differently
			if ((local = current.getLocalName ()) == null)
			    local = current.getNodeName ();
		    } else {
// XXX
			throw new RuntimeException (
			    "NYI, ns lookup when parsing L1 DOM");
		    }
		} else
		    ns = local = "";
		contentHandler.startElement  (ns, local,
		    current.getNodeName (), attrs);
		if (length != 0)
		    attrs.clear ();
		break;

	      case Node.CDATA_SECTION_NODE:
		lexicalHandler.startCDATA ();
		chars = current.getNodeValue ().toCharArray ();
		contentHandler.characters (chars, 0, chars.length);
		lexicalHandler.endCDATA ();
		break;

	      case Node.COMMENT_NODE:
		chars = current.getNodeValue ().toCharArray ();
		lexicalHandler.comment (chars, 0, chars.length);
		break;

	      case Node.DOCUMENT_TYPE_NODE:
		{
		    DocumentType	doctype = (DocumentType) current;

		    //
		    // Only DOM L2 supports recreating even some DTDs in full.
		    //
		    if (isL2) {
			lexicalHandler.startDTD (doctype.getName (),
				doctype.getPublicId (),
				doctype.getSystemId ());
		    } else
			lexicalHandler.startDTD (doctype.getName (),
				null, null);
		    
		    //
		    // The only sure way to recreate is to provide both the
		    // internal and external subsets.  Otherwise, only part
		    // of the job can be done ... because from the DTD, DOM
		    // discards both the critical data, like the attribute and
		    // element declarations, as well as the PIs and comments
		    // that are used to hold their documentation.
		    //
		    // Even the entity and notation declarations that it can
		    // expose can't be recorded without proprietary extensions.
		    //
		    // We construct a comment to tell what we know about how
		    // (in)complete this particular really DTD is.
		    //
		    {
			String message;
			char buf [];

			//
			// Though DOM L2 lets the whole doctype be recreated,
			// SAX2 can't represent it (input or output).
			// So this will be the typical case.
			//
			if (isL2 && doctype.getInternalSubset () != null)
			    message =
		    " Full DTD known; can't be shown using SAX2. ";

			//
			// Otherwise, we'll concoct a partial DTD.  If there's
			// any more data here at all, it was provided using a
			// (proprietary) extension to DOM.
			//
			else
			    message =
	    " This DTD was was recreated using incomplete DOM L2 records. ";

			buf = message.toCharArray ();
			lexicalHandler.comment (buf, 0, buf.length);
		    }

		    // report notations first
		    nodes = doctype.getNotations ();
		    length = nodes.getLength ();
		    for (int i = 0; i < length; i++) {
			Notation notation = (Notation) nodes.item (i);
			    dtdHandler.notationDecl (
				notation.getNodeName (),
				notation.getPublicId (),
				notation.getSystemId ());
		    }

		    // then parsed and unparsed external general entities
		    nodes = doctype.getEntities ();
		    length = nodes.getLength ();
		    for (int i = 0; i < length; i++) {
			Entity	entity = (Entity) nodes.item (i);
			String	notation = entity.getNotationName ();

			if (notation != null)
			    dtdHandler.unparsedEntityDecl (
				entity.getNodeName (),
				entity.getPublicId (),
				entity.getSystemId (),
				notation);
			else if (entity.getSystemId () != null)
			    declHandler.externalEntityDecl (
				entity.getNodeName (),
				entity.getPublicId (),
				entity.getSystemId ());
			
			//
			// NOTE:  DOM doesn't clearly provide internal
			// entity support; but in case someone tries to
			// fudge such support, we defend ourselves above.
			//
			// NOTE:  DOM doesn't expose parameter entities
			// (thank you thank you thank you thank you)
			//
		    }

		    //
		    // NOTE:  DOM (levels 1 and 2) doesn't expose real
		    // typing information (element or attribute decls),
		    // as exposed by SAX2 declaration handlers.
		    //
		    lexicalHandler.endDTD ();
		}
		break;

	      case Node.ENTITY_REFERENCE_NODE:
		// this isn't done except (a) in content, and
		// (b) not within a start tag (att value)
		lexicalHandler.startEntity (current.getNodeName ());
		break;

	      case Node.PROCESSING_INSTRUCTION_NODE:
	        contentHandler.processingInstruction (
		    current.getNodeName (), current.getNodeValue ());
		break;

	      case Node.TEXT_NODE:
		chars = current.getNodeValue ().toCharArray ();
		contentHandler.characters (chars, 0, chars.length);
		break;

	      default:
		// e.g. fragments, entities, notations, attributes
		throw new SAXException ("Illegal DOM Node type in Document:  "
		    +  current.getNodeType ());
	    }

	    //
	    // Then, pick the next node to visit.  If the next node isn't
	    // a child, an "end" call may be needed before moving on.
	    // If there's no next node, we're done.
	    //
	    Node		next;

	    switch (type) {
	      case Node.DOCUMENT_NODE:
	      case Node.ELEMENT_NODE:
	      case Node.ENTITY_REFERENCE_NODE:
		//
		// For elements that can have children, visit those
		// children before any siblings (i.e. depth first)
		// and after visiting this node (i.e. preorder)
		//
		next = current.getFirstChild ();
		if (next != null) {
		    current = next;
		    break;
		}
		//
		// Else treat this like other childless nodes, but
		// handle this node's "end" immediately.
		//
		callEnd (current);

		// FALLTHROUGH

	      case Node.CDATA_SECTION_NODE:
	      case Node.COMMENT_NODE:
	      case Node.DOCUMENT_TYPE_NODE:
	      case Node.ENTITY_NODE:
	      case Node.PROCESSING_INSTRUCTION_NODE:
	      case Node.TEXT_NODE:
		//
		// Use next sibling, if there is one.
		// Else, climb up a level (calling "end")
		//	until we find an ancestral sibling
		//	or until we we climb off the top (FINISH)
		//
		for (;;) {
		    if ((next = current.getNextSibling ()) != null)
			break;
		    current = current.getParentNode ();
		    if (current == null || current == start)
			return;
		    callEnd (current);
		}
		current = next;
		break;

	      default:
		throw new SAXException (
		    "Illegal DOM Node type found:  " +  current.getNodeType ());
	    }
	}
    }

    private void callEnd (Node node) throws SAXException
    {
	switch (node.getNodeType ()) {
	  // only these three container types may ever be found
	  // directly inside a Document.
	  case Node.DOCUMENT_NODE:
	    // for SAX conformance, endDocument must always
	    // be called ... it's done in a "finally" clause)
	    return;

	  case Node.ELEMENT_NODE:
	    if (showNamespaces) {
		if (isL2)
		    contentHandler.endElement (
			node.getNamespaceURI (),
			node.getLocalName (),
			node.getNodeName ());
		else
// XXX
		    throw new RuntimeException (
			"NYI, ns lookup when parsing L1 DOM");
		for (Enumeration e = prefixStack.getDeclaredPrefixes ();
			e.hasMoreElements ();
			) {
		    contentHandler.endPrefixMapping ((String) e.nextElement ());
		}
	    } else
		contentHandler.endElement ("", "", node.getNodeName ());
	    prefixStack.popContext ();
	    return;

	  case Node.ENTITY_REFERENCE_NODE:
	    // see above -- in content, outside start tags.
	    lexicalHandler.endEntity (node.getNodeName ());
	    return;

	  // these can be given at the top level
	  case Node.DOCUMENT_FRAGMENT_NODE:
	  case Node.ATTRIBUTE_NODE:
	    return;

	  default:
	    throw new SAXException (
		"Illegal DOM container type found:  "
			+  current.getNodeType ());
	}
    }
}