/* Resolver.java -- 
   Copyright (C) 1999,2000,2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath 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, or (at your option)
any later version.

GNU Classpath 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 GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package gnu.xml.util;

import java.io.File;
import java.io.IOException;
import java.util.Dictionary;

import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * Utility implementation of a SAX resolver, which can be used to improve
 * network utilization of SAX based XML components.  It does this by
 * supporting local caches of external entities.
 * SAX parsers <em>should</em> use such local caches when possible.
 *
 * @see XCat
 */
public class Resolver implements EntityResolver, Cloneable
{
    /**
     * Updates a dictionary used to map PUBLIC identifiers to file names,
     * so that it uses the mappings in a specified directory.
     *
     * @param mappings Array of string pairs, where the first member
     *	of each pair is a PUBLIC identifier and the second is the
     *	name of a file, relative to the specified directory.
     * @param directory File holding the specified files.
     */
    public static void addDirectoryMapping (
	Dictionary	table,
	String		mappings [][],
	File		directory
    ) throws IOException
    {
	for (int i = 0; i < mappings.length; i++) {
	    File	file = new File (directory, mappings [i][1]);
	    String	temp;

	    if (!file.exists ())	// ?? log a warning ??
		continue;

	    temp = fileToURL (file);
	    table.put (mappings [i][0], temp);
	}
    }

	// FIXME: these *URL routines don't quite belong here, except
	// that they're all in the same spirit of making it easy to
	// use local filesystem URIs with XML parsers.

    /**
     * Provides the URL for a named file, without relying on the JDK 1.2
     * {@link java.io.File#toURL File.toURL}() utility method.
     *
     * @param filename the file name to convert.  Relative file names
     *	are resolved the way the JVM resolves them (current to the
     *	process-global current working directory).
     *
     * @exception IOException if the file does not exist
     */
    public static String fileNameToURL (String filename)
    throws IOException
    {
	return fileToURL (new File (filename));
    }

    /**
     * Provides the URL for a file, without relying on the JDK 1.2
     * {@link java.io.File#toURL File.toURL}() utility method.
     *
     * @param f the file to convert.  Relative file names
     *	are resolved the way the JVM resolves them (current to the
     *	process-global current working directory).
     *
     * @exception IOException if the file does not exist
     */
    public static String fileToURL (File f)
    throws IOException
    {
	String	temp;

	// NOTE:  the javax.xml.parsers.DocumentBuilder and
	// javax.xml.transform.stream.StreamSource versions
	// of this don't have this test.  Some JVM versions
	// don't report this error sanely through URL code. 
	if (!f.exists ())
	    throw new IOException ("no such file: " + f.getName ());

	    // FIXME: getAbsolutePath() seems buggy; I'm seeing components
	    // like "/foo/../" which are clearly not "absolute"
	    // and should have been resolved with the filesystem.

	    // Substituting "/" would be wrong, "foo" may have been
	    // symlinked ... the URL code will make that change
	    // later, so that things can get _really_ broken!

	temp = f.getAbsolutePath ();

	if (File.separatorChar != '/')
	    temp = temp.replace (File.separatorChar, '/');
	if (!temp.startsWith ("/"))
	    temp = "/" + temp;
	if (!temp.endsWith ("/") && f.isDirectory ())
	    temp = temp + "/";
	return "file:" + temp;
    }


    /**
     * Returns a URL string.  Note that if a malformed URL is provided, or
     * the parameter names a nonexistent file, the resulting URL may be
     * malformed.
     *
     * @param fileOrURL If this is the name of a file which exists,
     *	then its URL is returned.  Otherwise the argument is returned.
     */
    public static String getURL (String fileOrURL)
    {
	try {
	    return fileNameToURL (fileOrURL);
	} catch (Exception e) {
	    return fileOrURL;
	}
    }


    // note:  cloneable, this is just copied; unguarded against mods
    private Dictionary		pubidMapping;

    /**
     * Constructs a resolver which understands how to map PUBLIC identifiers
     * to other URIs, typically for local copies of standard DTD components.
     * 
     * @param dictionary maps PUBLIC identifiers to URIs.  This is not
     *	copied; subsequent modifications will be reported through the
     *	resolution operations.
     */
    public Resolver (Dictionary dict)
	{ pubidMapping = dict; }

    
    // FIXME: want notion of a "system default" resolver, presumably
    // loaded with all sorts of useful stuff.  At the same time need
    // a notion of resolver chaining (failure --> next) so that subsystems
    // can set up things that won't interfere with other ones.

    /**
     * This parses most MIME content type strings that have <em>charset=...</em>
     * encoding declarations to and returns the specified encoding.  This
     * conforms to RFC 3023, and is useful when constructing InputSource
     * objects from URLConnection objects or other objects using MIME
     * content typing.
     *
     * @param contentType the MIME content type that will be parsed; must
     *	not be null.
     * @return the appropriate encoding, or null if the content type is
     *	not text and there's no <code>charset=...</code> attribute
     */
    static public String getEncoding (String contentType)
    {
	// currently a dumb parsing algorithm that works "mostly" and handles
	//	..anything...charset=ABC
	//	..anything...charset=ABC;otherAttr=DEF
	//	..anything...charset=ABC (comment);otherAttr=DEF
	//	..anything...charset= "ABC" (comment);otherAttr=DEF

	int	temp;
	String	encoding;
	String	defValue = null;

	if (contentType.startsWith ("text/"))
	    defValue = contentType.startsWith ("text/html")
		    ? "ISO-8859-1" : "US-ASCII";

	// Assumes 'charset' is only an attribute name, not part
	// of a value, comment, or other attribute name
	// ALSO assumes no escaped values like "\;" or "\)"
	if ((temp = contentType.indexOf ("charset")) != -1) {
	    // strip out everything up to '=' ...
	    temp = contentType.indexOf ('=', temp);
	    if (temp == -1)
		return defValue;
	    encoding = contentType.substring (temp + 1);
	    // ... and any subsequent attributes
	    if ((temp = encoding.indexOf (';')) != -1)
		encoding = encoding.substring (0, temp);
	    // ... and any comments after value
	    if ((temp = encoding.indexOf ('(')) != -1)
		encoding = encoding.substring (0, temp);
	    // ... then whitespace, and any (double) quotes
	    encoding = encoding.trim ();
	    if (encoding.charAt (0) == '"')
		encoding = encoding.substring (1, encoding.length () - 1);
	} else
	    encoding = defValue;
	return encoding;
    }


    /**
     * Uses a local dictionary of public identifiers to resolve URIs,
     * normally with the goal of minimizing network traffic or latencies.
     */
    public InputSource resolveEntity (String publicId, String systemId)
    throws IOException, SAXException
    {
	InputSource	retval = null;
	String		uri;

	if (publicId != null
		&& ((uri = (String) pubidMapping.get (publicId)) != null)) {
	    retval = new InputSource (uri);
	    retval.setPublicId (publicId);
	}

	// Could do URN resolution here

	// URL resolution always done by parser

	// FIXME: chain to "next" resolver

	return retval;
    }
}