/*
 *    GLIEntityResolver.java
 *    Copyright (C) 2008 New Zealand Digital Library, http://www.nzdl.org
 *
 *    This program 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.
 *
 *    This program 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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

package org.greenstone.gatherer.util;

import org.greenstone.gatherer.Configuration;
import org.greenstone.gatherer.DebugStream;
import org.greenstone.gatherer.Gatherer;

import org.xml.sax.InputSource;
import org.xml.sax.EntityResolver;
import java.io.File;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;


/**
 * Uses a list of default search paths, or the file's own path if provided, to resolve entities referenced 
 * in the file. The search paths, including the file's own, have to be within GS.
 * By default, the GS3HOME/WEB-INF and toplevel GLI user directory are added to the list of search paths,
 * since this EntityResolver is used for web.xml to resolve its inclusion of servlets.xml, which can be
 * located in GS3HOME/WEB-INF for a local GLI or is extracted into the gli user directory for client-GLI.
 * If everything fails, it will try to resolve entities using the classloader, not otherwise used by GLI,
 * but this part has been copied over from GS3's GLIEntityResolver.java.
 * If ever needed, maybe to make things faster, can maintain a static list of default search paths.
 */
public class GLIEntityResolver implements EntityResolver {

    protected ArrayList<File> list_of_local_search_paths = new ArrayList<File>();
    ClassLoader class_loader = null;


    public GLIEntityResolver() {
	// Add the basic search paths:

	// add the GS3 web/WEB-INF folder as search location for servlets.xml, which web.xml 
	// includes and which is the reason for adding a GLIEntityResolver class into GLI

	if(Gatherer.GS3) {
	    //list_of_local_search_paths.add(new File(Configuration.gsdl3_path));
	    list_of_local_search_paths.add(new File(Configuration.gsdl3_path, "WEB-INF"));
	}

	// Add gli user dir for remote GS, since that is where the
	// web.xml and server.xml downloaded from the remote server will be unpacked to
	if(Gatherer.isGsdlRemote) {
	    list_of_local_search_paths.add(new File(Configuration.gli_user_directory_path));
	}
    }

    public GLIEntityResolver(File file) {
	this(); // adds default search paths

	// add file's own path as first in search list
	addSafeSearchPath(file, true);	
    }

    /* Methods with the ClassLoader parameter are unused at present */
    public GLIEntityResolver(ClassLoader loader) {
	this.class_loader = loader;
    }

    public GLIEntityResolver(File f, ClassLoader loader) {
	this(f);
	this.class_loader = loader;
    }

    public void setClassLoader(ClassLoader loader) {
	this.class_loader = loader;
    }
    
    public void addSafeSearchPath(File file, boolean prepend) {
	
	// add the file's directory to list of search paths,
	// if it is within the greenstone installation and not already in the list
	if((!Gatherer.GS3 && file.getAbsolutePath().startsWith(Configuration.gsdl_path))
	   || (Gatherer.GS3 && file.getAbsolutePath().startsWith(Configuration.gsdl3_src_path))) {

	    File path = file.getParentFile();
	    if(!list_of_local_search_paths.contains(path)) {
		if(prepend) {
		    list_of_local_search_paths.add(0, path);
		} else {
		    list_of_local_search_paths.add(path);
		}
	    }
	} else {
	    DebugStream.println("### Location of file " + file + " not within GS. Not adding to list of search paths.");
	}
    }

    /**
     * resolveEntity() is not called for every file:
     * http://www.postseek.com/meta/37735b65e6a459a6aa631f048cc5a0b6
     * 
     *  "I think the parser will call [resolveEntity() on an EntityResolver that has been set], if 
     *  [the parser] is unable to find the DTD that your XML file refers to. So if you try to parse 
     *  an XML file that doesn't refer to a DTD, it won't be called. And if you try to parse an XML 
     *  file where the parser can find the DTD, it won't be called either."
     * 
    */
    public InputSource resolveEntity (String public_id, String system_id) {
	
	DebugStream.println("### resolveEntity() called for " + system_id);

	String temp_id = system_id;
	if (temp_id.startsWith("file://")) {
	    File f = new File(system_id);
	    if (f.exists()) {		

		// check if inside GS2 or GS3 installation
		if(f.getAbsolutePath().startsWith(Configuration.gsdl_path) 
		   || f.getAbsolutePath().startsWith(Configuration.gsdl3_src_path)) {
		    
		    DebugStream.println("### file denoted by systemID is inside GS: " + f.getAbsolutePath());

		    return new InputSource(system_id); // problem solved
		} else {
		    DebugStream.println("\t### file denoted by systemID exists, but not located inside GS: " 
				       + f.getAbsolutePath());
		}
	    } else {
		
	        temp_id = f.getName();
		
		//check in list of search paths
		Iterator<File> i = list_of_local_search_paths.iterator();
		while(i.hasNext()) {
		    File searchPath = i.next();
		    DebugStream.println("### searching for entity '" + temp_id + "' in: "
				       + searchPath.getAbsolutePath());

		    File searchFile = new File(searchPath, temp_id);
		    
		    if(searchFile.exists()) {
				DebugStream.println("\t Found " + searchFile.getAbsolutePath());				
			
				String newpath = searchFile.getAbsolutePath();		
				if(Utility.isWindows()) {			
					newpath = "file:///" + newpath.replace("\\", "/");
				} else { // linux version, file protocol starts with file:// and slashes are already URL-style
					newpath = "file://" + newpath;
				}
				return new InputSource(newpath);
				
		    }
		}

		// else, external entity/file denoted by systemid is not in list of search paths, try classloader
		
	    }
	} else {

	    DebugStream.println("### Entity is not a file: " + system_id);

	    if (temp_id.indexOf("/")!= -1) {
		temp_id = temp_id.substring(temp_id.lastIndexOf("/")+1);
	    }
	}

	DebugStream.println("### Using classloader to attempt to resolve entity: " + temp_id);

	// try using a class loader. If none provided, use current class loader
	if (this.class_loader==null) { 
	    this.class_loader = this.getClass().getClassLoader();
	}
	URL url = class_loader.getResource(temp_id);
	if (url == null) {
	    return null;
	}

	return new InputSource("file://"+url.getFile());
    }
}