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 * Copyright (C) 2016-2020 MicroEJ Corp. - EDC compliance and optimizations.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
 *
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package java.util;

import ej.annotation.Nullable;

/**
 * A {@link NavigableSet} implementation based on a {@link TreeMap}. The elements are ordered using their
 * {@linkplain Comparable natural ordering}, or by a {@link Comparator} provided at set creation time, depending on
 * which constructor is used.
 *
 * <p>
 * This implementation provides guaranteed log(n) time cost for the basic operations ({@code add}, {@code remove} and
 * {@code contains}).
 *
 * <p>
 * Note that the ordering maintained by a set (whether or not an explicit comparator is provided) must be <i>consistent
 * with equals</i> if it is to correctly implement the {@code Set} interface. (See {@code Comparable} or
 * {@code Comparator} for a precise definition of <i>consistent with equals</i>.) This is so because the {@code Set}
 * interface is defined in terms of the {@code equals} operation, but a {@code TreeSet} instance performs all element
 * comparisons using its {@code compareTo} (or {@code compare}) method, so two elements that are deemed equal by this
 * method are, from the standpoint of the set, equal. The behavior of a set <i>is</i> well-defined even if its ordering
 * is inconsistent with equals; it just fails to obey the general contract of the {@code Set} interface.
 *
 * <p>
 * <strong>Note that this implementation is not synchronized.</strong> If multiple threads access a tree set
 * concurrently, and at least one of the threads modifies the set, it <i>must</i> be synchronized externally. This is
 * typically accomplished by synchronizing on some object that naturally encapsulates the set. If no such object exists,
 * the set should be "wrapped" using the {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
 * method. This is best done at creation time, to prevent accidental unsynchronized access to the set:
 *
 * <pre>
 *   SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));
 * </pre>
 *
 * <p>
 * The iterators returned by this class's {@code iterator} method are <i>fail-fast</i>: if the set is modified at any
 * time after the iterator is created, in any way except through the iterator's own {@code remove} method, the iterator
 * will throw a {@link ConcurrentModificationException}. Thus, in the face of concurrent modification, the iterator
 * fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the
 * future.
 *
 * <p>
 * Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make
 * any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw
 * {@code ConcurrentModificationException} on a best-effort basis. Therefore, it would be wrong to write a program that
 * depended on this exception for its correctness: <i>the fail-fast behavior of iterators should be used only to detect
 * bugs.</i>
 *
 * <p>
 * This class is a member of the <a href="{@docRoot}/../technotes/guides/collections/index.html"> Java Collections
 * Framework</a>.
 *
 * @param <E>
 *            the type of elements maintained by this set
 *
 * @author Josh Bloch
 * @see Collection
 * @see Set
 * @see HashSet
 * @see Comparable
 * @see Comparator
 * @see TreeMap
 * @since 1.2
 */

public class TreeSet<E> extends AbstractSet<E> implements NavigableSet<E>, Cloneable, java.io.Serializable {
	/**
	 * The backing map.
	 */
	private transient NavigableMap<E, Object> m;

	// Dummy value to associate with an Object in the backing Map
	private static final Object PRESENT = new Object();

	/**
	 * Constructs a set backed by the specified navigable map.
	 */
	TreeSet(NavigableMap<E, Object> m) {
		this.m = m;
	}

	/**
	 * Constructs a new, empty tree set, sorted according to the natural ordering of its elements. All elements inserted
	 * into the set must implement the {@link Comparable} interface. Furthermore, all such elements must be <i>mutually
	 * comparable</i>: {@code e1.compareTo(e2)} must not throw a {@code ClassCastException} for any elements {@code e1}
	 * and {@code e2} in the set. If the user attempts to add an element to the set that violates this constraint (for
	 * example, the user attempts to add a string element to a set whose elements are integers), the {@code add} call
	 * will throw a {@code ClassCastException}.
	 */
	public TreeSet() {
		this(new TreeMap<E, Object>());
	}

	/**
	 * Constructs a new, empty tree set, sorted according to the specified comparator. All elements inserted into the
	 * set must be <i>mutually comparable</i> by the specified comparator: {@code comparator.compare(e1,
	 * e2)} must not throw a {@code ClassCastException} for any elements {@code e1} and {@code e2} in the set. If the
	 * user attempts to add an element to the set that violates this constraint, the {@code add} call will throw a
	 * {@code ClassCastException}.
	 *
	 * @param comparator
	 *            the comparator that will be used to order this set. If {@code null}, the {@linkplain Comparable
	 *            natural ordering} of the elements will be used.
	 */
	public TreeSet(@Nullable Comparator<? super E> comparator) {
		this(new TreeMap<>(comparator));
	}

	/**
	 * Constructs a new tree set containing the elements in the specified collection, sorted according to the <i>natural
	 * ordering</i> of its elements. All elements inserted into the set must implement the {@link Comparable} interface.
	 * Furthermore, all such elements must be <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
	 * {@code ClassCastException} for any elements {@code e1} and {@code e2} in the set.
	 *
	 * @param c
	 *            collection whose elements will comprise the new set
	 * @throws ClassCastException
	 *             if the elements in {@code c} are not {@link Comparable}, or are not mutually comparable
	 * @throws NullPointerException
	 *             if the specified collection is null
	 */
	public TreeSet(Collection<? extends E> c) {
		this();
		addAll(c);
	}

	/**
	 * Constructs a new tree set containing the same elements and using the same ordering as the specified sorted set.
	 *
	 * @param s
	 *            sorted set whose elements will comprise the new set
	 * @throws NullPointerException
	 *             if the specified sorted set is null
	 */
	public TreeSet(SortedSet<E> s) {
		this(s.comparator());
		addAll(s);
	}

	/**
	 * Returns an iterator over the elements in this set in ascending order.
	 *
	 * @return an iterator over the elements in this set in ascending order
	 */
	@Override
	public Iterator<E> iterator() {
		return this.m.navigableKeySet().iterator();
	}

	/**
	 * Returns an iterator over the elements in this set in descending order.
	 *
	 * @return an iterator over the elements in this set in descending order
	 * @since 1.6
	 */
	@Override
	public Iterator<E> descendingIterator() {
		return this.m.descendingKeySet().iterator();
	}

	/**
	 * @since 1.6
	 */
	@Override
	public NavigableSet<E> descendingSet() {
		return new TreeSet<>(this.m.descendingMap());
	}

	/**
	 * Returns the number of elements in this set (its cardinality).
	 *
	 * @return the number of elements in this set (its cardinality)
	 */
	@Override
	public int size() {
		return this.m.size();
	}

	/**
	 * Returns {@code true} if this set contains no elements.
	 *
	 * @return {@code true} if this set contains no elements
	 */
	@Override
	public boolean isEmpty() {
		return this.m.isEmpty();
	}

	/**
	 * Returns {@code true} if this set contains the specified element. More formally, returns {@code true} if and only
	 * if this set contains an element {@code e} such that
	 * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
	 *
	 * @param o
	 *            object to be checked for containment in this set
	 * @return {@code true} if this set contains the specified element
	 * @throws ClassCastException
	 *             if the specified object cannot be compared with the elements currently in the set
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 */
	@Override
	public boolean contains(Object o) {
		return this.m.containsKey(o);
	}

	/**
	 * Adds the specified element to this set if it is not already present. More formally, adds the specified element
	 * {@code e} to this set if the set contains no element {@code e2} such that
	 * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>. If this set already contains the element, the
	 * call leaves the set unchanged and returns {@code false}.
	 *
	 * @param e
	 *            element to be added to this set
	 * @return {@code true} if this set did not already contain the specified element
	 * @throws ClassCastException
	 *             if the specified object cannot be compared with the elements currently in this set
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 */
	@Override
	public boolean add(E e) {
		return this.m.put(e, PRESENT) == null;
	}

	/**
	 * Removes the specified element from this set if it is present. More formally, removes an element {@code e} such
	 * that <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>, if this set contains such an element.
	 * Returns {@code true} if this set contained the element (or equivalently, if this set changed as a result of the
	 * call). (This set will not contain the element once the call returns.)
	 *
	 * @param o
	 *            object to be removed from this set, if present
	 * @return {@code true} if this set contained the specified element
	 * @throws ClassCastException
	 *             if the specified object cannot be compared with the elements currently in this set
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 */
	@Override
	public boolean remove(Object o) {
		return this.m.remove(o) == PRESENT;
	}

	/**
	 * Removes all of the elements from this set. The set will be empty after this call returns.
	 */
	@Override
	public void clear() {
		this.m.clear();
	}

	/**
	 * Adds all of the elements in the specified collection to this set.
	 *
	 * @param c
	 *            collection containing elements to be added to this set
	 * @return {@code true} if this set changed as a result of the call
	 * @throws ClassCastException
	 *             if the elements provided cannot be compared with the elements currently in the set
	 * @throws NullPointerException
	 *             if the specified collection is null or if any element is null and this set uses natural ordering, or
	 *             its comparator does not permit null elements
	 */
	@Override
	public boolean addAll(Collection<? extends E> c) {
		// Use linear-time version if applicable
		if (this.m.size() == 0 && c.size() > 0 && c instanceof SortedSet && this.m instanceof TreeMap) {
			SortedSet<? extends E> set = (SortedSet<? extends E>) c;
			TreeMap<E, Object> map = (TreeMap<E, Object>) this.m;
			Comparator<?> cc = set.comparator();
			Comparator<? super E> mc = map.comparator();
			if (cc == mc || (cc != null && cc.equals(mc))) {
				map.addAllForTreeSet(set, PRESENT);
				return true;
			}
		}
		return super.addAll(c);
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if {@code fromElement} or {@code toElement} is null and this set uses natural ordering, or its
	 *             comparator does not permit null elements
	 * @throws IllegalArgumentException
	 *             {@inheritDoc}
	 * @since 1.6
	 */
	@Override
	public NavigableSet<E> subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
		return new TreeSet<>(this.m.subMap(fromElement, fromInclusive, toElement, toInclusive));
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if {@code toElement} is null and this set uses natural ordering, or its comparator does not permit
	 *             null elements
	 * @throws IllegalArgumentException
	 *             {@inheritDoc}
	 * @since 1.6
	 */
	@Override
	public NavigableSet<E> headSet(E toElement, boolean inclusive) {
		return new TreeSet<>(this.m.headMap(toElement, inclusive));
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if {@code fromElement} is null and this set uses natural ordering, or its comparator does not permit
	 *             null elements
	 * @throws IllegalArgumentException
	 *             {@inheritDoc}
	 * @since 1.6
	 */
	@Override
	public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
		return new TreeSet<>(this.m.tailMap(fromElement, inclusive));
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if {@code fromElement} or {@code toElement} is null and this set uses natural ordering, or its
	 *             comparator does not permit null elements
	 * @throws IllegalArgumentException
	 *             {@inheritDoc}
	 */
	@Override
	public SortedSet<E> subSet(E fromElement, E toElement) {
		return subSet(fromElement, true, toElement, false);
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if {@code toElement} is null and this set uses natural ordering, or its comparator does not permit
	 *             null elements
	 * @throws IllegalArgumentException
	 *             {@inheritDoc}
	 */
	@Override
	public SortedSet<E> headSet(E toElement) {
		return headSet(toElement, false);
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if {@code fromElement} is null and this set uses natural ordering, or its comparator does not permit
	 *             null elements
	 * @throws IllegalArgumentException
	 *             {@inheritDoc}
	 */
	@Override
	public SortedSet<E> tailSet(E fromElement) {
		return tailSet(fromElement, true);
	}

	@Override
	@Nullable
	public Comparator<? super E> comparator() {
		return this.m.comparator();
	}

	/**
	 * @throws NoSuchElementException
	 *             {@inheritDoc}
	 */
	@Override
	public E first() {
		return this.m.firstKey();
	}

	/**
	 * @throws NoSuchElementException
	 *             {@inheritDoc}
	 */
	@Override
	public E last() {
		return this.m.lastKey();
	}

	// NavigableSet API methods

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 * @since 1.6
	 */
	@Override
	@Nullable
	public E lower(E e) {
		return this.m.lowerKey(e);
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 * @since 1.6
	 */
	@Override
	@Nullable
	public E floor(E e) {
		return this.m.floorKey(e);
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 * @since 1.6
	 */
	@Override
	@Nullable
	public E ceiling(E e) {
		return this.m.ceilingKey(e);
	}

	/**
	 * @throws ClassCastException
	 *             {@inheritDoc}
	 * @throws NullPointerException
	 *             if the specified element is null and this set uses natural ordering, or its comparator does not
	 *             permit null elements
	 * @since 1.6
	 */
	@Override
	@Nullable
	public E higher(E e) {
		return this.m.higherKey(e);
	}

	/**
	 * @since 1.6
	 */
	@Override
	@Nullable
	public E pollFirst() {
		Map.Entry<E, ?> e = this.m.pollFirstEntry();
		return (e == null) ? null : e.getKey();
	}

	/**
	 * @since 1.6
	 */
	@Override
	@Nullable
	public E pollLast() {
		Map.Entry<E, ?> e = this.m.pollLastEntry();
		return (e == null) ? null : e.getKey();
	}

	/**
	 * Returns a shallow copy of this {@code TreeSet} instance. (The elements themselves are not cloned.)
	 *
	 * @return a shallow copy of this set
	 */
	@Override
	@SuppressWarnings("unchecked")
	public Object clone() {
		TreeSet<E> clone;
		try {
			clone = (TreeSet<E>) super.clone();
		} catch (CloneNotSupportedException e) {
			InternalError error = new InternalError();
			error.initCause(e);
			throw error;
		}

		clone.m = new TreeMap<>(this.m);
		return clone;
	}

	private static final long serialVersionUID = -2479143000061671589L;
}