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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

}