/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed 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 com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Collection;
import java.util.List;
import java.util.ListIterator;
import java.util.RandomAccess;
import java.util.Set;
import java.util.SortedSet;

import com.google.common.annotations.GwtCompatible;

/**
 * Factories and utilities pertaining to the {@link Constraint} interface.
 *
 * @author Mike Bostock
 * @author Jared Levy
 */
@GwtCompatible
final class Constraints {
	private Constraints() {
	}

	/**
	 * Returns a constrained view of the specified collection, using the specified
	 * constraint. Any operations that add new elements to the collection will call
	 * the provided constraint. However, this method does not verify that existing
	 * elements satisfy the constraint.
	 *
	 * <p>
	 * The returned collection is not serializable.
	 *
	 * @param collection the collection to constrain
	 * @param constraint the constraint that validates added elements
	 * @return a constrained view of the collection
	 */
	public static <E> Collection<E> constrainedCollection(Collection<E> collection, Constraint<? super E> constraint) {
		return new ConstrainedCollection<E>(collection, constraint);
	}

	/** @see Constraints#constrainedCollection */
	static class ConstrainedCollection<E> extends ForwardingCollection<E> {
		private final Collection<E> delegate;
		private final Constraint<? super E> constraint;

		public ConstrainedCollection(Collection<E> delegate, Constraint<? super E> constraint) {
			this.delegate = checkNotNull(delegate);
			this.constraint = checkNotNull(constraint);
		}

		@Override
		protected Collection<E> delegate() {
			return delegate;
		}

		@Override
		public boolean add(E element) {
			constraint.checkElement(element);
			return delegate.add(element);
		}

		@Override
		public boolean addAll(Collection<? extends E> elements) {
			return delegate.addAll(checkElements(elements, constraint));
		}
	}

	/**
	 * Returns a constrained view of the specified set, using the specified
	 * constraint. Any operations that add new elements to the set will call the
	 * provided constraint. However, this method does not verify that existing
	 * elements satisfy the constraint.
	 *
	 * <p>
	 * The returned set is not serializable.
	 *
	 * @param set        the set to constrain
	 * @param constraint the constraint that validates added elements
	 * @return a constrained view of the set
	 */
	public static <E> Set<E> constrainedSet(Set<E> set, Constraint<? super E> constraint) {
		return new ConstrainedSet<E>(set, constraint);
	}

	/** @see Constraints#constrainedSet */
	static class ConstrainedSet<E> extends ForwardingSet<E> {
		private final Set<E> delegate;
		private final Constraint<? super E> constraint;

		public ConstrainedSet(Set<E> delegate, Constraint<? super E> constraint) {
			this.delegate = checkNotNull(delegate);
			this.constraint = checkNotNull(constraint);
		}

		@Override
		protected Set<E> delegate() {
			return delegate;
		}

		@Override
		public boolean add(E element) {
			constraint.checkElement(element);
			return delegate.add(element);
		}

		@Override
		public boolean addAll(Collection<? extends E> elements) {
			return delegate.addAll(checkElements(elements, constraint));
		}
	}

	/**
	 * Returns a constrained view of the specified sorted set, using the specified
	 * constraint. Any operations that add new elements to the sorted set will call
	 * the provided constraint. However, this method does not verify that existing
	 * elements satisfy the constraint.
	 *
	 * <p>
	 * The returned set is not serializable.
	 *
	 * @param sortedSet  the sorted set to constrain
	 * @param constraint the constraint that validates added elements
	 * @return a constrained view of the sorted set
	 */
	public static <E> SortedSet<E> constrainedSortedSet(SortedSet<E> sortedSet, Constraint<? super E> constraint) {
		return new ConstrainedSortedSet<E>(sortedSet, constraint);
	}

	/** @see Constraints#constrainedSortedSet */
	private static class ConstrainedSortedSet<E> extends ForwardingSortedSet<E> {
		final SortedSet<E> delegate;
		final Constraint<? super E> constraint;

		ConstrainedSortedSet(SortedSet<E> delegate, Constraint<? super E> constraint) {
			this.delegate = checkNotNull(delegate);
			this.constraint = checkNotNull(constraint);
		}

		@Override
		protected SortedSet<E> delegate() {
			return delegate;
		}

		@Override
		public SortedSet<E> headSet(E toElement) {
			return constrainedSortedSet(delegate.headSet(toElement), constraint);
		}

		@Override
		public SortedSet<E> subSet(E fromElement, E toElement) {
			return constrainedSortedSet(delegate.subSet(fromElement, toElement), constraint);
		}

		@Override
		public SortedSet<E> tailSet(E fromElement) {
			return constrainedSortedSet(delegate.tailSet(fromElement), constraint);
		}

		@Override
		public boolean add(E element) {
			constraint.checkElement(element);
			return delegate.add(element);
		}

		@Override
		public boolean addAll(Collection<? extends E> elements) {
			return delegate.addAll(checkElements(elements, constraint));
		}
	}

	/**
	 * Returns a constrained view of the specified list, using the specified
	 * constraint. Any operations that add new elements to the list will call the
	 * provided constraint. However, this method does not verify that existing
	 * elements satisfy the constraint.
	 *
	 * <p>
	 * If {@code list} implements {@link RandomAccess}, so will the returned list.
	 * The returned list is not serializable.
	 *
	 * @param list       the list to constrain
	 * @param constraint the constraint that validates added elements
	 * @return a constrained view of the list
	 */
	public static <E> List<E> constrainedList(List<E> list, Constraint<? super E> constraint) {
		return (list instanceof RandomAccess) ? new ConstrainedRandomAccessList<E>(list, constraint)
				: new ConstrainedList<E>(list, constraint);
	}

	/** @see Constraints#constrainedList */
	@GwtCompatible
	private static class ConstrainedList<E> extends ForwardingList<E> {
		final List<E> delegate;
		final Constraint<? super E> constraint;

		ConstrainedList(List<E> delegate, Constraint<? super E> constraint) {
			this.delegate = checkNotNull(delegate);
			this.constraint = checkNotNull(constraint);
		}

		@Override
		protected List<E> delegate() {
			return delegate;
		}

		@Override
		public boolean add(E element) {
			constraint.checkElement(element);
			return delegate.add(element);
		}

		@Override
		public void add(int index, E element) {
			constraint.checkElement(element);
			delegate.add(index, element);
		}

		@Override
		public boolean addAll(Collection<? extends E> elements) {
			return delegate.addAll(checkElements(elements, constraint));
		}

		@Override
		public boolean addAll(int index, Collection<? extends E> elements) {
			return delegate.addAll(index, checkElements(elements, constraint));
		}

		@Override
		public ListIterator<E> listIterator() {
			return constrainedListIterator(delegate.listIterator(), constraint);
		}

		@Override
		public ListIterator<E> listIterator(int index) {
			return constrainedListIterator(delegate.listIterator(index), constraint);
		}

		@Override
		public E set(int index, E element) {
			constraint.checkElement(element);
			return delegate.set(index, element);
		}

		@Override
		public List<E> subList(int fromIndex, int toIndex) {
			return constrainedList(delegate.subList(fromIndex, toIndex), constraint);
		}
	}

	/** @see Constraints#constrainedList */
	static class ConstrainedRandomAccessList<E> extends ConstrainedList<E> implements RandomAccess {
		ConstrainedRandomAccessList(List<E> delegate, Constraint<? super E> constraint) {
			super(delegate, constraint);
		}
	}

	/**
	 * Returns a constrained view of the specified list iterator, using the
	 * specified constraint. Any operations that would add new elements to the
	 * underlying list will be verified by the constraint.
	 *
	 * @param listIterator the iterator for which to return a constrained view
	 * @param constraint   the constraint for elements in the list
	 * @return a constrained view of the specified iterator
	 */
	private static <E> ListIterator<E> constrainedListIterator(ListIterator<E> listIterator,
			Constraint<? super E> constraint) {
		return new ConstrainedListIterator<E>(listIterator, constraint);
	}

	/** @see Constraints#constrainedListIterator */
	static class ConstrainedListIterator<E> extends ForwardingListIterator<E> {
		private final ListIterator<E> delegate;
		private final Constraint<? super E> constraint;

		public ConstrainedListIterator(ListIterator<E> delegate, Constraint<? super E> constraint) {
			this.delegate = delegate;
			this.constraint = constraint;
		}

		@Override
		protected ListIterator<E> delegate() {
			return delegate;
		}

		@Override
		public void add(E element) {
			constraint.checkElement(element);
			delegate.add(element);
		}

		@Override
		public void set(E element) {
			constraint.checkElement(element);
			delegate.set(element);
		}
	}

	static <E> Collection<E> constrainedTypePreservingCollection(Collection<E> collection, Constraint<E> constraint) {
		if (collection instanceof SortedSet) {
			return constrainedSortedSet((SortedSet<E>) collection, constraint);
		} else if (collection instanceof Set) {
			return constrainedSet((Set<E>) collection, constraint);
		} else if (collection instanceof List) {
			return constrainedList((List<E>) collection, constraint);
		} else {
			return constrainedCollection(collection, constraint);
		}
	}

	/*
	 * TODO(kevinb): For better performance, avoid making a copy of the elements by
	 * having addAll() call add() repeatedly instead.
	 */

	private static <E> Collection<E> checkElements(Collection<E> elements, Constraint<? super E> constraint) {
		Collection<E> copy = Lists.newArrayList(elements);
		for (E element : copy) {
			constraint.checkElement(element);
		}
		return copy;
	}
}
