/*

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.

  *

  * Copyright 1997-2009 Sun Microsystems, Inc. All rights reserved.

  *

  * The contents of this file are subject to the terms of either the GNU

  * General Public License Version 2 only ("GPL") or the Common

  * Development and Distribution License("CDDL") (collectively, the

  * "License"). You may not use this file except in compliance with the

  * License. You can obtain a copy of the License at

  * http://www.netbeans.org/cddl-gplv2.html

  * or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the

  * specific language governing permissions and limitations under the

  * License.  When distributing the software, include this License Header

  * Notice in each file and include the License file at

  * nbbuild/licenses/CDDL-GPL-2-CP.  Sun designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Sun in the GPL Version 2 section of the License file that

  * accompanied this code. If applicable, add the following below the

  * License Header, with the fields enclosed by brackets [] replaced by

  * your own identifying information:

  * "Portions Copyrighted [year] [name of copyright owner]"

  *

  * Contributor(s):

  *

  * The Original Software is NetBeans. The Initial Developer of the Original

  * Software is Sun Microsystems, Inc. Portions Copyright 1997-2006 Sun

  * Microsystems, Inc. All Rights Reserved.

  *

  * If you wish your version of this file to be governed by only the CDDL

  * or only the GPL Version 2, indicate your decision by adding

  * "[Contributor] elects to include this software in this distribution

  * under the [CDDL or GPL Version 2] license." If you do not indicate a

  * single choice of license, a recipient has the option to distribute

  * your version of this file under either the CDDL, the GPL Version 2 or

  * to extend the choice of license to its licensees as provided above.

  * However, if you add GPL Version 2 code and therefore, elected the GPL

  * Version 2 license, then the option applies only if the new code is

  * made subject to such option by the copyright holder.

  */

 package org.openide.util;

 import java.util.ArrayList;

 import java.util.Arrays;

 import java.util.Collection;

 import java.util.Collections;

 import java.util.Enumeration;

 import java.util.HashSet;

 import java.util.Iterator;

 import java.util.NoSuchElementException;

 import java.util.Set;

 /**

  * Factory methods for various types of {@link Enumeration}.

  * Allows composition of existing enumerations, filtering their contents, and/or modifying them.

  * All of this is designed to be done lazily, i.e. elements created on demand.

  * @since 4.37

  * @author Jaroslav Tulach

  * @see NbCollections#checkedEnumerationByFilter

  * @see NbCollections#iterable(Enumeration)

  */

 public final class Enumerations extends Object {

     /** No instances */

     private Enumerations() {

     }

     /**

      * An empty enumeration.

      * Always returns <code>false</code> from

      * <code>empty().hasMoreElements()</code> and throws <code>NoSuchElementException</code>

      * from <code>empty().nextElement()</code>.

      * @return the enumeration

      */

     public static final <T> Enumeration<T> empty() {

         Collection<T> emptyL = Collections.emptyList();

         return Collections.enumeration(emptyL);

     }

     /**

      * Creates an enumeration with one element.

      * @param obj the element to be present in the enumeration.

      * @return enumeration

      */

     public static <T> Enumeration<T> singleton(T obj) {

         return Collections.enumeration(Collections.singleton(obj));

     }

     /**

      * Concatenates the content of two enumerations into one.

      * Until the

      * end of <code>en1</code> is reached its elements are being served.

      * As soon as the <code>en1</code> has no more elements, the content

      * of <code>en2</code> is being returned.

      *

      * @param en1 first enumeration

      * @param en2 second enumeration

      * @return enumeration

      */

     public static <T> Enumeration<T> concat(Enumeration<? extends T> en1, Enumeration<? extends T> en2) {

         ArrayList<Enumeration<? extends T>> two = new ArrayList<Enumeration<? extends T>>();

         two.add(en1);

         two.add(en2);

         return new SeqEn<T>(Collections.enumeration(two));

     }

     /**

      * Concatenates the content of many enumerations.

      * The input value

      * is enumeration of Enumeration elements and the result is composed

      * all their content. Each of the provided enumeration is fully read

      * and their content returned before the next enumeration is asked for

      * their elements.

      *

      * @param enumOfEnums Enumeration of Enumeration elements

      * @return enumeration

      */

     public static <T> Enumeration<T> concat(Enumeration<? extends Enumeration<? extends T>> enumOfEnums) {

         return new SeqEn<T>(enumOfEnums);

     }

     /**

      * Filters the input enumeration to new one that should contain

      * each of the provided elements just once.

      * The elements are compared

      * using their default <code>equals</code> and <code>hashCode</code> methods.

      *

      * @param en enumeration to filter

      * @return enumeration without duplicated items

      */

     public static <T> Enumeration<T> removeDuplicates(Enumeration<T> en) {

         class RDupls implements Processor<T,T> {

             private Set<T> set = new HashSet<T>();

             public T process(T o, Collection<T> nothing) {

                 return set.add(o) ? o : null;

             }

         }

         return filter(en, new RDupls());

     }

     /**

      * Returns an enumeration that iterates over provided array.

      * @param arr the array of object

      * @return enumeration of those objects

      */

     public static <T> Enumeration<T> array(T... arr) {

         return Collections.enumeration(Arrays.asList(arr));

     }

     /**

      * Removes all <code>null</code>s from the input enumeration.

      * @param en enumeration that can contain nulls

      * @return new enumeration without null values

      */

     public static <T> Enumeration<T> removeNulls(Enumeration<T> en) {

         return filter(en, new RNulls<T>());

     }

     /**

      * For each element of the input enumeration <code>en</code> asks the

      * {@link Processor} to provide a replacement.

      * The <code>toAdd</code> argument of the processor is always null.

      * <p>

      * Example to convert any objects into strings:

      * <pre>

      * Processor convertToString = new Processor() {

      *     public Object process(Object obj, Collection alwaysNull) {

      *         return obj.toString(); // converts to string

      *     }

      * };

      * Enumeration strings = Enumerations.convert(elems, convertToString);

      * </pre>

      *

      * @param en enumeration of any objects

      * @param processor a callback processor for the elements (its toAdd arguments is always null)

      * @return new enumeration where all elements has been processed

      */

     public static <T,R> Enumeration<R> convert(Enumeration<? extends T> en, Processor<T,R> processor) {

         return new AltEn<T,R>(en, processor);

     }

     /**

      * Filters some elements out from the input enumeration.

      * Just make the

      * {@link Processor} return <code>null</code>. Please notice the <code>toAdd</code>

      * argument of the processor is always <code>null</code>.

      * <p>

      * Example to remove all objects that are not strings:

      * <pre>

      * Processor onlyString = new Processor() {

      *     public Object process(Object obj, Collection alwaysNull) {

      *         if (obj instanceof String) {

      *             return obj;

      *         } else {

      *             return null;

      *         }

      *     }

      * };

      * Enumeration strings = Enumerations.filter(elems, onlyString);

      * </pre>

      *

      * @param en enumeration of any objects

      * @param filter a callback processor for the elements (its toAdd arguments is always null)

      * @return new enumeration which does not include non-processed (returned null from processor) elements

      * @see NbCollections#checkedEnumerationByFilter

      */

     public static <T,R> Enumeration<R> filter(Enumeration<? extends T> en, Processor<T,R> filter) {

         Parameters.notNull("en", en);

         Parameters.notNull("filter", filter);

         return new FilEn<T,R>(en, filter);

     }

     /**

      * Support for breadth-first enumerating.

      * Before any element is returned

      * for the resulting enumeration it is processed in the {@link Processor} and

      * the processor is allowed to modify it and also add additional elements

      * at the (current) end of the <q>queue</q> by calling <code>toAdd.add</code>

      * or <code>toAdd.addAll</code>. No other methods can be called on the

      * provided <code>toAdd</code> collection.

      * <p>

      * Example of doing breadth-first walk through a tree:

      * <pre>

      * Processor queueSubnodes = new Processor() {

      *     public Object process(Object obj, Collection toAdd) {

      *         Node n = (Node)obj;

      *         toAdd.addAll (n.getChildrenList());

      *         return n;

      *     }

      * };

      * Enumeration strings = Enumerations.queue(elems, queueSubnodes);

      * </pre>

      *

      * @param en initial content of the resulting enumeration

      * @param filter the processor that is called for each element and can

      *        add and addAll elements to its toAdd Collection argument and

      *        also change the value to be returned

      * @return enumeration with the initial and queued content (it can contain

      *       <code>null</code> if the filter returned <code>null</code> from its

      *       {@link Processor#process} method.

      */

     public static <T,R> Enumeration<R> queue(Enumeration<? extends T> en, Processor<T,R> filter) {

         QEn<T,R> q = new QEn<T,R>(filter);

         while (en.hasMoreElements()) {

             q.put(en.nextElement());

         }

         return q;

     }

     /**

      * Processor interface that can filter out objects from the enumeration,

      * change them or add aditional objects to the end of the current enumeration.

      */

     public static interface Processor<T,R> {

         /** @param original the object that is going to be returned from the enumeration right now

          * @return a replacement for this object

          * @param toAdd can be non-null if one can add new objects at the end of the enumeration

          */

         public R process(T original, Collection<T> toAdd);

     }

     /** Altering enumeration implementation */

     private static final class AltEn<T,R> extends Object implements Enumeration<R> {

         /** enumeration to filter */

         private Enumeration<? extends T> en;

         /** map to alter */

         private Processor<T,R> process;

         /**

         * @param en enumeration to filter

         */

         public AltEn(Enumeration<? extends T> en, Processor<T,R> process) {

             this.en = en;

             this.process = process;

         }

         /** @return true if there is more elements in the enumeration

         */

         public boolean hasMoreElements() {

             return en.hasMoreElements();

         }

         /** @return next object in the enumeration

         * @exception NoSuchElementException can be thrown if there is no next object

         *   in the enumeration

         */

         public R nextElement() {

             return process.process(en.nextElement(), null);

         }

     }

      // end of AltEn

     /** Sequence of enumerations */

     private static final class SeqEn<T> extends Object implements Enumeration<T> {

         /** enumeration of Enumerations */

         private Enumeration<? extends Enumeration<? extends T>> en;

         /** current enumeration */

         private Enumeration<? extends T> current;

         /** is {@link #current} up-to-date and has more elements?

         * The combination <CODE>current == null</CODE> and

         * <CODE>checked == true means there are no more elements

         * in this enumeration.

         */

         private boolean checked = false;

         /** Constructs new enumeration from already existing. The elements

         * of <CODE>en</CODE> should be also enumerations. The resulting

         * enumeration contains elements of such enumerations.

         *

         * @param en enumeration of Enumerations that should be sequenced

         */

         public SeqEn(Enumeration<? extends Enumeration <? extends T>> en) {

             this.en = en;

         }

         /** Ensures that current enumeration is set. If there aren't more

         * elements in the Enumerations, sets the field <CODE>current</CODE> to null.

         */

         private void ensureCurrent() {

             while ((current == null) || !current.hasMoreElements()) {

                 if (en.hasMoreElements()) {

                     current = en.nextElement();

                 } else {

                     // no next valid enumeration

                     current = null;

                     return;

                 }

             }

         }

         /** @return true if we have more elements */

         public boolean hasMoreElements() {

             if (!checked) {

                 ensureCurrent();

                 checked = true;

             }

             return current != null;

         }

         /** @return next element

         * @exception NoSuchElementException if there is no next element

         */

         public T nextElement() {

             if (!checked) {

                 ensureCurrent();

             }

             if (current != null) {

                 checked = false;

                 return current.nextElement();

             } else {

                 checked = true;

                 throw new java.util.NoSuchElementException();

             }

         }

     }

      // end of SeqEn

     /** QueueEnumeration

      */

     private static class QEn<T,R> extends Object implements Enumeration<R> {

         /** next object to be returned */

         private ListItem<T> next = null;

         /** last object in the queue */

         private ListItem<T> last = null;

         /** processor to use */

         private Processor<T,R> processor;

         public QEn(Processor<T,R> p) {

             this.processor = p;

         }

         /** Put adds new object to the end of queue.

         * @param o the object to add

         */

         public void put(T o) {

             if (last != null) {

                 ListItem<T> li = new ListItem<T>(o);

                 last.next = li;

                 last = li;

             } else {

                 next = last = new ListItem<T>(o);

             }

         }

         /** Adds array of objects into the queue.

         * @param arr array of objects to put into the queue

         */

         public void put(Collection<? extends T> arr) {

             for (T e : arr) {

                 put(e);

             }

         }

         /** Is there any next object?

         * @return true if there is next object, false otherwise

         */

         public boolean hasMoreElements() {

             return next != null;

         }

         /** @return next object in enumeration

         * @exception NoSuchElementException if there is no next object

         */

         public R nextElement() {

             if (next == null) {

                 throw new NoSuchElementException();

             }

             T res = next.object;

             if ((next = next.next) == null) {

                 last = null;

             }

             ;

             ToAdd<T,R> toAdd = new ToAdd<T,R>(this);

             R out = processor.process(res, toAdd);

             toAdd.finish();

             return out;

         }

         /** item in linked list of Objects */

         private static final class ListItem<T> {

             T object;

             ListItem<T> next;

             /** @param o the object for this item */

             ListItem(T o) {

                 object = o;

             }

         }

         /** Temporary collection that supports only add and addAll operations*/

         private static final class ToAdd<T,R> extends Object implements Collection<T> {

             private QEn<T,R> q;

             public ToAdd(QEn<T,R> q) {

                 this.q = q;

             }

             public void finish() {

                 this.q = null;

             }

             public boolean add(T o) {

                 q.put(o);

                 return true;

             }

             public boolean addAll(Collection<? extends T> c) {

                 q.put(c);

                 return true;

             }

             private String msg() {

                 return "Only add and addAll are implemented"; // NOI18N

             }

             public void clear() {

                 throw new UnsupportedOperationException(msg());

             }

             public boolean contains(Object o) {

                 throw new UnsupportedOperationException(msg());

             }

             public boolean containsAll(Collection c) {

                 throw new UnsupportedOperationException(msg());

             }

             public boolean isEmpty() {

                 throw new UnsupportedOperationException(msg());

             }

             public Iterator<T> iterator() {

                 throw new UnsupportedOperationException(msg());

             }

             public boolean remove(Object o) {

                 throw new UnsupportedOperationException(msg());

             }

             public boolean removeAll(Collection c) {

                 throw new UnsupportedOperationException(msg());

             }

             public boolean retainAll(Collection c) {

                 throw new UnsupportedOperationException(msg());

             }

             public int size() {

                 throw new UnsupportedOperationException(msg());

             }

             public Object[] toArray() {

                 throw new UnsupportedOperationException(msg());

             }

             public<X> X[] toArray(X[] a) {

                 throw new UnsupportedOperationException(msg());

             }

         }

          // end of ToAdd

     }

      // end of QEn

     /** Filtering enumeration */

     private static final class FilEn<T,R> extends Object implements Enumeration<R> {

         /** marker object stating there is no nexte element prepared */

         private static final Object EMPTY = new Object();

         /** enumeration to filter */

         private Enumeration<? extends T> en;

         /** element to be returned next time or {@link #EMPTY} if there is

         * no such element prepared */

         private R next = empty();

         /** the set to use as filter */

         private Processor<T,R> filter;

         /**

         * @param en enumeration to filter

         */

         public FilEn(Enumeration<? extends T> en, Processor<T,R> filter) {

             this.en = en;

             this.filter = filter;

         }

         /** @return true if there is more elements in the enumeration

         */

         public boolean hasMoreElements() {

             if (next != empty()) {

                 // there is a object already prepared

                 return true;

             }

             while (en.hasMoreElements()) {

                 // read next

                 next = filter.process(en.nextElement(), null);

                 if (next != null) {

                     // if the object is accepted

                     return true;

                 }

                 ;

             }

             next = empty();

             return false;

         }

         /** @return next object in the enumeration

         * @exception NoSuchElementException can be thrown if there is no next object

         *   in the enumeration

         */

         public R nextElement() {

             if ((next == EMPTY) && !hasMoreElements()) {

                 throw new NoSuchElementException();

             }

             R res = next;

             next = empty();

             return res;

         }

         @SuppressWarnings("unchecked")

         private R empty() {

             return (R)EMPTY;

         }

     }

      // end of FilEn

     /** Returns true from contains if object is not null */

     private static class RNulls<T> implements Processor<T,T> {

         public T process(T original, Collection<T> toAdd) {

             return original;

         }

     }

      // end of RNulls

 }