/*
 * 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.commons.collections4;

import org.apache.commons.collections4.bag.CollectionBag;
import org.apache.commons.collections4.bag.HashBag;
import org.apache.commons.collections4.bag.PredicatedBag;
import org.apache.commons.collections4.bag.PredicatedSortedBag;
import org.apache.commons.collections4.bag.SynchronizedBag;
import org.apache.commons.collections4.bag.SynchronizedSortedBag;
import org.apache.commons.collections4.bag.TransformedBag;
import org.apache.commons.collections4.bag.TransformedSortedBag;
import org.apache.commons.collections4.bag.TreeBag;
import org.apache.commons.collections4.bag.UnmodifiableBag;
import org.apache.commons.collections4.bag.UnmodifiableSortedBag;

Provides utility methods and decorators for Bag and SortedBag instances. 
Since:
2.1/**
 * Provides utility methods and decorators for {@link Bag} and {@link SortedBag} instances.
 *
 * @since 2.1
 */
public class BagUtils {

    
An empty unmodifiable bag.
/**
     * An empty unmodifiable bag.
     */
    @SuppressWarnings("rawtypes") // OK, empty bag is compatible with any type
    public static final Bag EMPTY_BAG = UnmodifiableBag.unmodifiableBag(new HashBag<>());

    
An empty unmodifiable sorted bag.
/**
     * An empty unmodifiable sorted bag.
     */
    @SuppressWarnings("rawtypes") // OK, empty bag is compatible with any type
    public static final Bag EMPTY_SORTED_BAG =
            UnmodifiableSortedBag.unmodifiableSortedBag(new TreeBag<>());

    
Instantiation of BagUtils is not intended or required.
/**
     * Instantiation of BagUtils is not intended or required.
     */
    private BagUtils() {}

    //-----------------------------------------------------------------------
    
Returns a synchronized (thread-safe) bag backed by the given bag. In
order to guarantee serial access, it is critical that all access to the
backing bag is accomplished through the returned bag.

It is imperative that the user manually synchronize on the returned bag
when iterating over it:

Bag bag = BagUtils.synchronizedBag(new HashBag());
...
synchronized(bag) {
    Iterator i = bag.iterator(); // Must be in synchronized block
    while (i.hasNext())
        foo(i.next());
    }
}

Failure to follow this advice may result in non-deterministic behavior.
Params:
bag – the bag to synchronize, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the Bag is null
Returns:
a synchronized bag backed by that bag/**
     * Returns a synchronized (thread-safe) bag backed by the given bag. In
     * order to guarantee serial access, it is critical that all access to the
     * backing bag is accomplished through the returned bag.
     * <p>
     * It is imperative that the user manually synchronize on the returned bag
     * when iterating over it:
     * </p>
     *
     * <pre>
     * Bag bag = BagUtils.synchronizedBag(new HashBag());
     * ...
     * synchronized(bag) {
     *     Iterator i = bag.iterator(); // Must be in synchronized block
     *     while (i.hasNext())
     *         foo(i.next());
     *     }
     * }
     * </pre>
     *
     * Failure to follow this advice may result in non-deterministic behavior.
     *
     * @param <E> the element type
     * @param bag the bag to synchronize, must not be null
     * @return a synchronized bag backed by that bag
     * @throws NullPointerException if the Bag is null
     */
    public static <E> Bag<E> synchronizedBag(final Bag<E> bag) {
        return SynchronizedBag.synchronizedBag(bag);
    }

    
Returns an unmodifiable view of the given bag. Any modification attempts to the returned bag will raise an UnsupportedOperationException. 
Params:
bag – the bag whose unmodifiable view is to be returned, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the Bag is null
Returns:
an unmodifiable view of that bag/**
     * Returns an unmodifiable view of the given bag. Any modification attempts
     * to the returned bag will raise an {@link UnsupportedOperationException}.
     *
     * @param <E> the element type
     * @param bag the bag whose unmodifiable view is to be returned, must not be null
     * @return an unmodifiable view of that bag
     * @throws NullPointerException if the Bag is null
     */
    public static <E> Bag<E> unmodifiableBag(final Bag<? extends E> bag) {
        return UnmodifiableBag.unmodifiableBag(bag);
    }

    
Returns a predicated (validating) bag backed by the given bag.

Only objects that pass the test in the given predicate can be added to
the bag. Trying to add an invalid object results in an
IllegalArgumentException. It is important not to use the original bag
after invoking this method, as it is a backdoor for adding invalid
objects.

Params:
bag – the bag to predicate, must not be null
predicate – the predicate for the bag, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the Bag or Predicate is null
Returns:
a predicated bag backed by the given bag/**
     * Returns a predicated (validating) bag backed by the given bag.
     * <p>
     * Only objects that pass the test in the given predicate can be added to
     * the bag. Trying to add an invalid object results in an
     * IllegalArgumentException. It is important not to use the original bag
     * after invoking this method, as it is a backdoor for adding invalid
     * objects.
     * </p>
     *
     * @param <E> the element type
     * @param bag the bag to predicate, must not be null
     * @param predicate the predicate for the bag, must not be null
     * @return a predicated bag backed by the given bag
     * @throws NullPointerException if the Bag or Predicate is null
     */
    public static <E> Bag<E> predicatedBag(final Bag<E> bag, final Predicate<? super E> predicate) {
        return PredicatedBag.predicatedBag(bag, predicate);
    }

    
Returns a transformed bag backed by the given bag.

Each object is passed through the transformer as it is added to the Bag.
It is important not to use the original bag after invoking this method,
as it is a backdoor for adding untransformed objects.

 Existing entries in the specified bag will not be transformed. If you want that behaviour, see TransformedBag.transformedBag(Bag<Object>, Transformer<? super Object,? extends Object>). 
Params:
bag – the bag to predicate, must not be null
transformer – the transformer for the bag, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the Bag or Transformer is null
Returns:
a transformed bag backed by the given bag/**
     * Returns a transformed bag backed by the given bag.
     * <p>
     * Each object is passed through the transformer as it is added to the Bag.
     * It is important not to use the original bag after invoking this method,
     * as it is a backdoor for adding untransformed objects.
     * </p>
     * <p>
     * Existing entries in the specified bag will not be transformed.
     * If you want that behaviour, see {@link TransformedBag#transformedBag(Bag, Transformer)}.
     * </p>
     *
     * @param <E> the element type
     * @param bag the bag to predicate, must not be null
     * @param transformer the transformer for the bag, must not be null
     * @return a transformed bag backed by the given bag
     * @throws NullPointerException if the Bag or Transformer is null
     */
    public static <E> Bag<E> transformingBag(final Bag<E> bag, final Transformer<? super E, ? extends E> transformer) {
        return TransformedBag.transformingBag(bag, transformer);
    }

    
Returns a bag that complies to the Collection contract, backed by the given bag.
Params:
bag – the bag to decorate, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if bag is null
Returns:
a Bag that complies to the Collection contract
Since:
4.0/**
     * Returns a bag that complies to the Collection contract, backed by the given bag.
     *
     * @param <E> the element type
     * @param bag the bag to decorate, must not be null
     * @return a Bag that complies to the Collection contract
     * @throws NullPointerException if bag is null
     * @since 4.0
     */
    public static <E> Bag<E> collectionBag(final Bag<E> bag) {
        return CollectionBag.collectionBag(bag);
    }

    //-----------------------------------------------------------------------
    
Returns a synchronized (thread-safe) sorted bag backed by the given
sorted bag. In order to guarantee serial access, it is critical that all
access to the backing bag is accomplished through the returned bag.

It is imperative that the user manually synchronize on the returned bag
when iterating over it:

SortedBag bag = BagUtils.synchronizedSortedBag(new TreeBag());
...
synchronized(bag) {
    Iterator i = bag.iterator(); // Must be in synchronized block
    while (i.hasNext())
        foo(i.next());
    }
}

Failure to follow this advice may result in non-deterministic behavior.
Params:
bag – the bag to synchronize, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the SortedBag is null
Returns:
a synchronized bag backed by that bag/**
     * Returns a synchronized (thread-safe) sorted bag backed by the given
     * sorted bag. In order to guarantee serial access, it is critical that all
     * access to the backing bag is accomplished through the returned bag.
     * <p>
     * It is imperative that the user manually synchronize on the returned bag
     * when iterating over it:
     * </p>
     *
     * <pre>
     * SortedBag bag = BagUtils.synchronizedSortedBag(new TreeBag());
     * ...
     * synchronized(bag) {
     *     Iterator i = bag.iterator(); // Must be in synchronized block
     *     while (i.hasNext())
     *         foo(i.next());
     *     }
     * }
     * </pre>
     *
     * Failure to follow this advice may result in non-deterministic behavior.
     *
     * @param <E> the element type
     * @param bag the bag to synchronize, must not be null
     * @return a synchronized bag backed by that bag
     * @throws NullPointerException if the SortedBag is null
     */
    public static <E> SortedBag<E> synchronizedSortedBag(final SortedBag<E> bag) {
        return SynchronizedSortedBag.synchronizedSortedBag(bag);
    }

    
Returns an unmodifiable view of the given sorted bag. Any modification attempts to the returned bag will raise an UnsupportedOperationException. 
Params:
bag – the bag whose unmodifiable view is to be returned, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the SortedBag is null
Returns:
an unmodifiable view of that bag/**
     * Returns an unmodifiable view of the given sorted bag. Any modification
     * attempts to the returned bag will raise an
     * {@link UnsupportedOperationException}.
     *
     * @param <E> the element type
     * @param bag the bag whose unmodifiable view is to be returned, must not be null
     * @return an unmodifiable view of that bag
     * @throws NullPointerException if the SortedBag is null
     */
    public static <E> SortedBag<E> unmodifiableSortedBag(final SortedBag<E> bag) {
        return UnmodifiableSortedBag.unmodifiableSortedBag(bag);
    }

    
Returns a predicated (validating) sorted bag backed by the given sorted
bag.

Only objects that pass the test in the given predicate can be added to
the bag. Trying to add an invalid object results in an
IllegalArgumentException. It is important not to use the original bag
after invoking this method, as it is a backdoor for adding invalid
objects.

Params:
bag – the sorted bag to predicate, must not be null
predicate – the predicate for the bag, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the SortedBag or Predicate is null
Returns:
a predicated bag backed by the given bag/**
     * Returns a predicated (validating) sorted bag backed by the given sorted
     * bag.
     * <p>
     * Only objects that pass the test in the given predicate can be added to
     * the bag. Trying to add an invalid object results in an
     * IllegalArgumentException. It is important not to use the original bag
     * after invoking this method, as it is a backdoor for adding invalid
     * objects.
     * </p>
     *
     * @param <E> the element type
     * @param bag the sorted bag to predicate, must not be null
     * @param predicate the predicate for the bag, must not be null
     * @return a predicated bag backed by the given bag
     * @throws NullPointerException if the SortedBag or Predicate is null
     */
    public static <E> SortedBag<E> predicatedSortedBag(final SortedBag<E> bag,
            final Predicate<? super E> predicate) {
        return PredicatedSortedBag.predicatedSortedBag(bag, predicate);
    }

    
Returns a transformed sorted bag backed by the given bag.

Each object is passed through the transformer as it is added to the Bag.
It is important not to use the original bag after invoking this method,
as it is a backdoor for adding untransformed objects.

 Existing entries in the specified bag will not be transformed. If you want that behaviour, see TransformedSortedBag.transformedSortedBag(SortedBag<Object>, Transformer<? super Object,? extends Object>). 
Params:
bag – the bag to predicate, must not be null
transformer – the transformer for the bag, must not be null
Type parameters:
<E> – the element type
Throws:
NullPointerException – if the Bag or Transformer is null
Returns:
a transformed bag backed by the given bag/**
     * Returns a transformed sorted bag backed by the given bag.
     * <p>
     * Each object is passed through the transformer as it is added to the Bag.
     * It is important not to use the original bag after invoking this method,
     * as it is a backdoor for adding untransformed objects.
     * </p>
     * <p>
     * Existing entries in the specified bag will not be transformed.
     * If you want that behaviour, see
     * {@link TransformedSortedBag#transformedSortedBag(SortedBag, Transformer)}.
     * </p>
     *
     * @param <E> the element type
     * @param bag the bag to predicate, must not be null
     * @param transformer the transformer for the bag, must not be null
     * @return a transformed bag backed by the given bag
     * @throws NullPointerException if the Bag or Transformer is null
     */
    public static <E> SortedBag<E> transformingSortedBag(final SortedBag<E> bag,
                                                         final Transformer<? super E, ? extends E> transformer) {
        return TransformedSortedBag.transformingSortedBag(bag, transformer);
    }

    
Get an empty Bag.
Type parameters:
<E> – the element type
Returns:
an empty Bag/**
     * Get an empty <code>Bag</code>.
     *
     * @param <E> the element type
     * @return an empty Bag
     */
    @SuppressWarnings("unchecked") // OK, empty bag is compatible with any type
    public static <E> Bag<E> emptyBag() {
        return EMPTY_BAG;
    }

    
Get an empty SortedBag.
Type parameters:
<E> – the element type
Returns:
an empty sorted Bag/**
     * Get an empty <code>SortedBag</code>.
     *
     * @param <E> the element type
     * @return an empty sorted Bag
     */
    @SuppressWarnings("unchecked") // OK, empty bag is compatible with any type
    public static <E> SortedBag<E> emptySortedBag() {
        return (SortedBag<E>) EMPTY_SORTED_BAG;
    }
}