content: /*
   * 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 org.apache.calcite.util;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.Map;
  import java.util.Set;
  import javax.xml.XMLConstants;
  import javax.xml.namespace.NamespaceContext;
  
  /**
   * Simple {@link javax.xml.namespace.NamespaceContext} implementation. Follows the standard
   * NamespaceContext contract, and is loadable via a {@link java.util.Map}
   */
  public class SimpleNamespaceContext implements NamespaceContext {
  
    private final Map<String, String> prefixToNamespaceUri = new HashMap<>();
    private final Map<String, Set<String>> namespaceUriToPrefixes = new HashMap<>();
  
    @SuppressWarnings({"method.invocation.invalid", "methodref.receiver.bound.invalid"})
    public SimpleNamespaceContext(Map<String, String> bindings) {
      bindNamespaceUri(XMLConstants.XML_NS_PREFIX, XMLConstants.XML_NS_URI);
      bindNamespaceUri(XMLConstants.XMLNS_ATTRIBUTE, XMLConstants.XMLNS_ATTRIBUTE_NS_URI);
      bindNamespaceUri(XMLConstants.DEFAULT_NS_PREFIX, "");
      bindings.forEach(this::bindNamespaceUri);
    }
  
    @Override public String getNamespaceURI(String prefix) {
      if (this.prefixToNamespaceUri.containsKey(prefix)) {
        return this.prefixToNamespaceUri.get(prefix);
      }
      return "";
    }
  
    @Override public @Nullable String getPrefix(String namespaceUri) {
      Set<String> prefixes = getPrefixesSet(namespaceUri);
      return !prefixes.isEmpty() ? prefixes.iterator().next() : null;
    }
  
    @Override public Iterator<String> getPrefixes(String namespaceUri) {
      return getPrefixesSet(namespaceUri).iterator();
    }
  
    private Set<String> getPrefixesSet(String namespaceUri) {
      Set<String> prefixes = this.namespaceUriToPrefixes.get(namespaceUri);
      return prefixes != null ? Collections.unmodifiableSet(prefixes) : Collections.emptySet();
    }
  
    private void bindNamespaceUri(String prefix, String namespaceUri) {
      this.prefixToNamespaceUri.put(prefix, namespaceUri);
      Set<String> prefixes = this.namespaceUriToPrefixes
          .computeIfAbsent(namespaceUri, k -> new LinkedHashSet<>());
      prefixes.add(prefix);
    }
  }
  