/*
Copyright (c) 2011+, HL7, Inc
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

 * Redistributions of source code must retain the above copyright notice, this 
   list of conditions and the following disclaimer.
 * Redistributions in binary form must reproduce the above copyright notice, 
   this list of conditions and the following disclaimer in the documentation 
   and/or other materials provided with the distribution.
 * Neither the name of HL7 nor the names of its contributors may be used to 
   endorse or promote products derived from this software without specific 
   prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND 
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
POSSIBILITY OF SUCH DAMAGE.

*/
package org.hl7.fhir.utilities.xml;

// see http://illegalargumentexception.blogspot.com.au/2009/05/java-using-xpath-with-namespaces-and.html

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;

/**
* An implementation of <a
* href="http://java.sun.com/javase/6/docs/api/javax/xml/namespace/NamespaceContext.html">
* NamespaceContext </a>. Instances are immutable.
* 
* @author McDowell
*/
public final class NamespaceContextMap implements NamespaceContext {

 private final Map<String, String> prefixMap;
 private final Map<String, Set<String>> nsMap;

 /**
  * Constructor that takes a map of XML prefix-namespaceURI values. A defensive
  * copy is made of the map. An IllegalArgumentException will be thrown if the
  * map attempts to remap the standard prefixes defined in the NamespaceContext
  * contract.
  * 
  * @param prefixMappings
  *          a map of prefix:namespaceURI values
  */
 public NamespaceContextMap(
     Map<String, String> prefixMappings) {
   prefixMap = createPrefixMap(prefixMappings);
   nsMap = createNamespaceMap(prefixMap);
 }

 /**
  * Convenience constructor.
  * 
  * @param mappingPairs
  *          pairs of prefix-namespaceURI values
  */
 public NamespaceContextMap(String... mappingPairs) {
   this(toMap(mappingPairs));
 }

 private static Map<String, String> toMap(
     String... mappingPairs) {
   Map<String, String> prefixMappings = new HashMap<String, String>(
       mappingPairs.length / 2);
   for (int i = 0; i < mappingPairs.length; i++) {
     prefixMappings
         .put(mappingPairs[i], mappingPairs[++i]);
   }
   return prefixMappings;
 }

 private Map<String, String> createPrefixMap(
     Map<String, String> prefixMappings) {
   Map<String, String> prefixMap = new HashMap<String, String>(
       prefixMappings);
   addConstant(prefixMap, XMLConstants.XML_NS_PREFIX,
       XMLConstants.XML_NS_URI);
   addConstant(prefixMap, XMLConstants.XMLNS_ATTRIBUTE,
       XMLConstants.XMLNS_ATTRIBUTE_NS_URI);
   return Collections.unmodifiableMap(prefixMap);
 }

 private void addConstant(Map<String, String> prefixMap,
     String prefix, String nsURI) {
   String previous = prefixMap.put(prefix, nsURI);
   if (previous != null && !previous.equals(nsURI)) {
     throw new IllegalArgumentException(prefix + " -> "
         + previous + "; see NamespaceContext contract");
   }
 }

 private Map<String, Set<String>> createNamespaceMap(
     Map<String, String> prefixMap) {
   Map<String, Set<String>> nsMap = new HashMap<String, Set<String>>();
   for (Map.Entry<String, String> entry : prefixMap
       .entrySet()) {
     String nsURI = entry.getValue();
     Set<String> prefixes = nsMap.get(nsURI);
     if (prefixes == null) {
       prefixes = new HashSet<String>();
       nsMap.put(nsURI, prefixes);
     }
     prefixes.add(entry.getKey());
   }
   for (Map.Entry<String, Set<String>> entry : nsMap
       .entrySet()) {
     Set<String> readOnly = Collections
         .unmodifiableSet(entry.getValue());
     entry.setValue(readOnly);
   }
   return nsMap;
 }

 @Override
 public String getNamespaceURI(String prefix) {
   checkNotNull(prefix);
   String nsURI = prefixMap.get(prefix);
   return nsURI == null ? XMLConstants.NULL_NS_URI : nsURI;
 }

 @Override
 public String getPrefix(String namespaceURI) {
   checkNotNull(namespaceURI);
   Set<String> set = nsMap.get(namespaceURI);
   return set == null ? null : set.iterator().next();
 }

 @Override
 public Iterator<String> getPrefixes(String namespaceURI) {
   checkNotNull(namespaceURI);
   Set<String> set = nsMap.get(namespaceURI);
   return set.iterator();
 }

 private void checkNotNull(String value) {
   if (value == null) {
     throw new IllegalArgumentException("null");
   }
 }

 /**
  * @return an unmodifiable map of the mappings in the form prefix-namespaceURI
  */
 public Map<String, String> getMap() {
   return prefixMap;
 }

}