/*
 *  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.tools.ant.util;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Dictionary;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Vector;

// CheckStyle:HideUtilityClassConstructorCheck OFF - bc

/**
 * A set of helper methods related to collection manipulation.
 *
 * @since Ant 1.5
 */
public class CollectionUtils {

    /**
     * Collections.emptyList() is Java5+.
     */
    @SuppressWarnings("rawtypes")
    @Deprecated
    public static final List EMPTY_LIST = Collections.EMPTY_LIST;

    /**
     * Please use Vector.equals() or List.equals().
     * @param v1 the first vector.
     * @param v2 the second vector.
     * @return true if the vectors are equal.
     * @since Ant 1.5
     * @deprecated since 1.6.x.
     */
    public static boolean equals(Vector<?> v1, Vector<?> v2) {
        if (v1 == v2) {
            return true;
        }

        if (v1 == null || v2 == null) {
            return false;
        }

        return v1.equals(v2);
    }

    /**
     * Dictionary does not have an equals.
     * Please use  Map.equals().
     *
     * <p>Follows the equals contract of Java 2's Map.</p>
     * @param d1 the first directory.
     * @param d2 the second directory.
     * @return true if the directories are equal.
     * @since Ant 1.5
     * @deprecated since 1.6.x.
     */
    public static boolean equals(Dictionary<?, ?> d1, Dictionary<?, ?> d2) {
        if (d1 == d2) {
            return true;
        }

        if (d1 == null || d2 == null) {
            return false;
        }

        if (d1.size() != d2.size()) {
            return false;
        }

        Enumeration<?> e1 = d1.keys();
        while (e1.hasMoreElements()) {
            Object key = e1.nextElement();
            Object value1 = d1.get(key);
            Object value2 = d2.get(key);
            if (value2 == null || !value1.equals(value2)) {
                return false;
            }
        }

        // don't need the opposite check as the Dictionaries have the
        // same size, so we've also covered all keys of d2 already.

        return true;
    }

    /**
     * Creates a comma separated list of all values held in the given
     * collection.
     *
     * @since Ant 1.8.0
     */
    public static String flattenToString(Collection<?> c) {
        final StringBuilder sb = new StringBuilder();
        for (Object o : c) {
            if (sb.length() != 0) {
                sb.append(",");
            }
            sb.append(o);
        }
        return sb.toString();
    }

    /**
     * Dictionary does not know the putAll method. Please use Map.putAll().
     * @param m1 the to directory.
     * @param m2 the from directory.
     * @since Ant 1.6
     * @deprecated since 1.6.x.
     */
    public static <K, V> void putAll(Dictionary<? super K, ? super V> m1, Dictionary<? extends K, ? extends V> m2) {
        for (Enumeration<? extends K> it = m2.keys(); it.hasMoreElements();) {
            K key = it.nextElement();
            m1.put(key, m2.get(key));
        }
    }

    /**
     * An empty enumeration.
     * @since Ant 1.6
     */
    public static final class EmptyEnumeration<E> implements Enumeration<E> {
        /** Constructor for the EmptyEnumeration */
        public EmptyEnumeration() {
        }

        /**
         * @return false always.
         */
        public boolean hasMoreElements() {
            return false;
        }

        /**
         * @return nothing.
         * @throws NoSuchElementException always.
         */
        public E nextElement() throws NoSuchElementException {
            throw new NoSuchElementException();
        }
    }

    /**
     * Append one enumeration to another.
     * Elements are evaluated lazily.
     * @param e1 the first enumeration.
     * @param e2 the subsequent enumeration.
     * @return an enumeration representing e1 followed by e2.
     * @since Ant 1.6.3
     */
    public static <E> Enumeration<E> append(Enumeration<E> e1, Enumeration<E> e2) {
        return new CompoundEnumeration<E>(e1, e2);
    }

    /**
     * Adapt the specified Iterator to the Enumeration interface.
     * @param iter the Iterator to adapt.
     * @return an Enumeration.
     */
    public static <E> Enumeration<E> asEnumeration(final Iterator<E> iter) {
        return new Enumeration<E>() {
            public boolean hasMoreElements() {
                return iter.hasNext();
            }
            public E nextElement() {
                return iter.next();
            }
        };
    }

    /**
     * Adapt the specified Enumeration to the Iterator interface.
     * @param e the Enumeration to adapt.
     * @return an Iterator.
     */
    public static <E> Iterator<E> asIterator(final Enumeration<E> e) {
        return new Iterator<E>() {
            public boolean hasNext() {
                return e.hasMoreElements();
            }
            public E next() {
                return e.nextElement();
            }
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    /**
     * Returns a collection containing all elements of the iterator.
     *
     * @since Ant 1.8.0
     */
    public static <T> Collection<T> asCollection(final Iterator<? extends T> iter) {
        List<T> l = new ArrayList<T>();
        while (iter.hasNext()) {
            l.add(iter.next());
        }
        return l;
    }

    private static final class CompoundEnumeration<E> implements Enumeration<E> {

        private final Enumeration<E> e1, e2;

        public CompoundEnumeration(Enumeration<E> e1, Enumeration<E> e2) {
            this.e1 = e1;
            this.e2 = e2;
        }

        public boolean hasMoreElements() {
            return e1.hasMoreElements() || e2.hasMoreElements();
        }

        public E nextElement() throws NoSuchElementException {
            if (e1.hasMoreElements()) {
                return e1.nextElement();
            } else {
                return e2.nextElement();
            }
        }

    }

    /**
     * Counts how often the given Object occurs in the given
     * collection using equals() for comparison.
     *
     * @since Ant 1.8.0
     */
    public static int frequency(Collection<?> c, Object o) {
        // same as Collections.frequency introduced with JDK 1.5
        int freq = 0;
        if (c != null) {
            for (Iterator<?> i = c.iterator(); i.hasNext(); ) {
                Object test = i.next();
                if (o == null ? test == null : o.equals(test)) {
                    freq++;
                }
            }
        }
        return freq;
    }

}
