/**
 * 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 nokogiri.internals.c14n;

import java.io.Serializable;
import java.util.Comparator;


import org.w3c.dom.Attr;

/**
 * Compares two attributes based on the C14n specification.
 *
 * <UL>
 * <LI>Namespace nodes have a lesser document order position than attribute 
 *   nodes.
 * <LI> An element's namespace nodes are sorted lexicographically by
 *   local name (the default namespace node, if one exists, has no
 *   local name and is therefore lexicographically least).
 * <LI> An element's attribute nodes are sorted lexicographically with
 *   namespace URI as the primary key and local name as the secondary
 *   key (an empty namespace URI is lexicographically least).
 * </UL>
 *
 * @author Christian Geuer-Pollmann
 */
public class AttrCompare implements Comparator<Attr>, Serializable {

    private static final long serialVersionUID = -7113259629930576230L;
    private static final int ATTR0_BEFORE_ATTR1 = -1;
    private static final int ATTR1_BEFORE_ATTR0 = 1;
    private static final String XMLNS = Constants.NamespaceSpecNS;

    /**
     * Compares two attributes based on the C14n specification.
     *
     * <UL>
     * <LI>Namespace nodes have a lesser document order position than 
     *   attribute nodes.
     * <LI> An element's namespace nodes are sorted lexicographically by
     *   local name (the default namespace node, if one exists, has no
     *   local name and is therefore lexicographically least).
     * <LI> An element's attribute nodes are sorted lexicographically with
     *   namespace URI as the primary key and local name as the secondary
     *   key (an empty namespace URI is lexicographically least).
     * </UL>
     *
     * @param attr0
     * @param attr1
     * @return returns a negative integer, zero, or a positive integer as 
     *   obj0 is less than, equal to, or greater than obj1
     *
     */
    public int compare(Attr attr0, Attr attr1) {
        String namespaceURI0 = attr0.getNamespaceURI();      
        String namespaceURI1 = attr1.getNamespaceURI();
      
        boolean isNamespaceAttr0 = XMLNS.equals(namespaceURI0);
        boolean isNamespaceAttr1 = XMLNS.equals(namespaceURI1);

        if (isNamespaceAttr0) {
            if (isNamespaceAttr1) {
                // both are namespaces
                String localname0 = attr0.getLocalName();
                String localname1 = attr1.getLocalName();

                if ("xmlns".equals(localname0)) {
                    localname0 = "";
                }

                if ("xmlns".equals(localname1)) {
                    localname1 = "";
                }

                return localname0.compareTo(localname1);
            }
            // attr0 is a namespace, attr1 is not
            return ATTR0_BEFORE_ATTR1;
        } else if (isNamespaceAttr1) {
            // attr1 is a namespace, attr0 is not
            return ATTR1_BEFORE_ATTR0;
        } 

        // none is a namespace
        if (namespaceURI0 == null) {
            if (namespaceURI1 == null) {
                String name0 = attr0.getName();
                String name1 = attr1.getName();
                return name0.compareTo(name1);
            }
            return ATTR0_BEFORE_ATTR1;
        } else if (namespaceURI1 == null) {
            return ATTR1_BEFORE_ATTR0;
        } 

        int a = namespaceURI0.compareTo(namespaceURI1);
        if (a != 0) {
            return a;
        }
      
        return (attr0.getLocalName()).compareTo(attr1.getLocalName());
    }
}