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/*
 * Licensed to The Apereo Foundation under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 *
 * The Apereo Foundation licenses this file to you under the Educational
 * Community 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://opensource.org/licenses/ecl2.txt
 *
 * 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.opencastproject.util;

import static com.entwinemedia.fn.Stream.$;
import static org.opencastproject.util.EqualsUtil.eq;
import static org.opencastproject.util.data.Option.option;

import org.opencastproject.util.data.Function0;

import com.entwinemedia.fn.Fn;
import com.entwinemedia.fn.Fn2;
import com.entwinemedia.fn.Stream;
import com.entwinemedia.fn.data.Opt;
import com.entwinemedia.fn.fns.Booleans;

import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

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

public final class XmlNamespaceContext implements NamespaceContext {
  // the number of default bindings
  private static final int DEFAULT_BINDINGS = 2;

  // prefix -> namespace URI
  private final Map prefixToUri = new HashMap();

  /**
   * Create a new namespace context with bindings from prefix to URI and bind the
   * default namespaces as described in the documentation of {@link javax.xml.namespace.NamespaceContext}.
   */
  public XmlNamespaceContext(Map prefixToUri) {
    this.prefixToUri.putAll(prefixToUri);
    this.prefixToUri.put(XMLConstants.XML_NS_PREFIX, XMLConstants.XML_NS_URI);
    this.prefixToUri.put(XMLConstants.XMLNS_ATTRIBUTE, XMLConstants.XMLNS_ATTRIBUTE_NS_URI);
  }

  public static XmlNamespaceContext mk(Map prefixToUri) {
    return new XmlNamespaceContext(prefixToUri);
  }

  public static XmlNamespaceContext mk(XmlNamespaceBinding... bindings) {
    return mk($(bindings));
  }

  public static XmlNamespaceContext mk(String prefix, String namespaceUri) {
    return new XmlNamespaceContext(Collections.singletonMap(prefix, namespaceUri));
  }

  public static XmlNamespaceContext mk(List bindings) {
    return mk($(bindings));
  }

  public static XmlNamespaceContext mk(Stream bindings) {
    return new XmlNamespaceContext(
            bindings.foldl(
                    new HashMap(),
                    new Fn2, XmlNamespaceBinding, HashMap>() {
                      @Override
                      public HashMap apply(
                              HashMap prefixToUri, XmlNamespaceBinding binding) {
                        prefixToUri.put(binding.getPrefix(), binding.getNamespaceURI());
                        return prefixToUri;
                      }
                    }));
  }

  @Override
  public String getNamespaceURI(String prefix) {
    return Opt.nul(prefixToUri.get(prefix)).getOr(XMLConstants.NULL_NS_URI);
  }

  @Override
  public String getPrefix(String uri) {
    return $(prefixToUri.entrySet()).find(Booleans.eq(RequireUtil.notNull(uri, "uri")).o(value)).map(key).orNull();
  }

  @Override
  public Iterator getPrefixes(String uri) {
    return $(prefixToUri.entrySet()).filter(Booleans.eq(uri).o(value)).map(key).iterator();
  }

  public List getBindings() {
    return $(prefixToUri.entrySet()).map(toBinding).toList();
  }

  /** Create a new context with the given bindings added. Existing bindings will not be overwritten. */
  public XmlNamespaceContext add(XmlNamespaceBinding... bindings) {
    return add($(bindings));
  }

  /** Create a new context with the given bindings added. Existing bindings will not be overwritten. */
  public XmlNamespaceContext add(XmlNamespaceContext bindings) {
    if (bindings.prefixToUri.size() == DEFAULT_BINDINGS) {
      // bindings contains only the default bindings
      return this;
    } else {
      return add($(bindings.getBindings()));
    }
  }

  private XmlNamespaceContext add(Stream bindings) {
    return mk(bindings.append(getBindings()));
  }

  private static final Fn, String> key = new Fn, String>() {
    @Override public String apply(Entry e) {
      return e.getKey();
    }
  };

  private static final Fn, String> value = new Fn, String>() {
    @Override public String apply(Entry e) {
      return e.getValue();
    }
  };

  private static final Fn, XmlNamespaceBinding> toBinding = new Fn, XmlNamespaceBinding>() {
    @Override public XmlNamespaceBinding apply(Entry e) {
      return new XmlNamespaceBinding(e.getKey(), e.getValue());
    }
  };

  public NamespaceContext merge(final NamespaceContext precedence) {
    return merge(this, precedence);
  }

  /** Merge b into a so that b takes precedence over a. */
  public static NamespaceContext merge(final NamespaceContext a, final NamespaceContext b) {
    return new NamespaceContext() {
      @Override public String getNamespaceURI(String prefix) {
        final String uri = b.getNamespaceURI(prefix);
        if (eq(XMLConstants.DEFAULT_NS_PREFIX, prefix) && eq(XMLConstants.NULL_NS_URI, uri)) {
          return a.getNamespaceURI(prefix);
        } else {
          return uri;
        }
      }

      @Override public String getPrefix(final String uri) {
        return option(b.getPrefix(uri)).getOrElse(new Function0() {
          @Override public String apply() {
            return a.getPrefix(uri);
          }
        });
      }

      @Override public Iterator getPrefixes(String uri) {
        final Iterator prefixes = b.getPrefixes(uri);
        if (prefixes.hasNext()) {
          return prefixes;
        } else {
          return a.getPrefixes(uri);
        }
      }
    };
  }
}