/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.collection.HashSet;

import hunt.collection.AbstractSet;
import hunt.collection.Collection;
import hunt.collection.HashMap;
import hunt.collection.LinkedHashMap;
import hunt.collection.Set;

import hunt.Object;

import std.algorithm;
import std.range;

/**
 * This class implements the <tt>Set</tt> interface, backed by a hash table
 * (actually a <tt>HashMap</tt> instance).  It makes no guarantees as to the
 * iteration order of the set; in particular, it does not guarantee that the
 * order will remain constant over time.  This class permits the <tt>null</tt>
 * element.
 *
 * <p>This class offers constant time performance for the basic operations
 * (<tt>add</tt>, <tt>remove</tt>, <tt>contains</tt> and <tt>size</tt>),
 * assuming the hash function disperses the elements properly among the
 * buckets.  Iterating over this set requires time proportional to the sum of
 * the <tt>HashSet</tt> instance's size (the number of elements) plus the
 * "capacity" of the backing <tt>HashMap</tt> instance (the number of
 * buckets).  Thus, it's very important not to set the initial capacity too
 * high (or the load factor too low) if iteration performance is important.
 *
 * <p><strong>Note that this implementation is not synchronized.</strong>
 * If multiple threads access a hash 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#synchronizedSet Collections.synchronizedSet}
 * method.  This is best done at creation time, to prevent accidental
 * unsynchronized access to the set:<pre>
 *   Set s = Collections.synchronizedSet(new HashSet(...));</pre>
 *
 * <p>The iterators returned by this class's <tt>iterator</tt> 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 <tt>remove</tt>
 * method, the Iterator throws 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 <tt>ConcurrentModificationException</tt> 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
 * @author  Neal Gafter
 * @see     Collection
 * @see     Set
 * @see     TreeSet
 * @see     HashMap
 */
class HashSet(E) : AbstractSet!E, Set!E {

    protected HashMap!(E, Object) map;

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

    shared static this() {
        PRESENT = new Object();
    }

    /**
     * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
     * default initial capacity (16) and load factor (0.75).
     */
    this() {
        map = new HashMap!(E, Object)();
    }

    /**
     * Constructs a new set containing the elements in the specified
     * collection.  The <tt>HashMap</tt> is created with default load factor
     * (0.75) and an initial capacity sufficient to contain the elements in
     * the specified collection.
     *
     * @param c the collection whose elements are to be placed into this set
     * @throws NullPointerException if the specified collection is null
     */
    this(Collection!E c) {
        map = new HashMap!(E, Object)(std.algorithm.max(cast(int)(c.size() / .75f) + 1, 16));
        addAll(c);
    }

    this(E[] c) {
        map = new HashMap!(E, Object)(std.algorithm.max(cast(int)(c.length / .75f) + 1, 16));
        addAll(c);
    }

    /**
     * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
     * the specified initial capacity and the specified load factor.
     *
     * @param      initialCapacity   the initial capacity of the hash map
     * @param      loadFactor        the load factor of the hash map
     * @throws     IllegalArgumentException if the initial capacity is less
     *             than zero, or if the load factor is nonpositive
     */
    this(int initialCapacity, float loadFactor) {
        map = new HashMap!(E, Object)(initialCapacity, loadFactor);
    }

    /**
     * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
     * the specified initial capacity and default load factor (0.75).
     *
     * @param      initialCapacity   the initial capacity of the hash table
     * @throws     IllegalArgumentException if the initial capacity is less
     *             than zero
     */
    this(int initialCapacity) {
        map = new HashMap!(E, Object)(initialCapacity);
    }

    /**
     * Constructs a new, empty linked hash set.  (This package private
     * constructor is only used by LinkedHashSet.) The backing
     * HashMap instance is a LinkedHashMap with the specified initial
     * capacity and the specified load factor.
     *
     * @param      initialCapacity   the initial capacity of the hash map
     * @param      loadFactor        the load factor of the hash map
     * @param      dummy             ignored (distinguishes this
     *             constructor from other int, float constructor.)
     * @throws     IllegalArgumentException if the initial capacity is less
     *             than zero, or if the load factor is nonpositive
     */
    this(int initialCapacity, float loadFactor, bool dummy) {
        map = new LinkedHashMap!(E, Object)(initialCapacity, loadFactor);
    }

    /**
     * Returns an iterator over the elements in this set.  The elements
     * are returned in no particular order.
     *
     * @return an Iterator over the elements in this set
     * @see ConcurrentModificationException
     */
    override InputRange!E iterator() {
        return map.byKey;
    }

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

    /**
     * Returns <tt>true</tt> if this set contains no elements.
     *
     * @return <tt>true</tt> if this set contains no elements
     */
    override bool isEmpty() {
        return map.isEmpty();
    }

    /**
     * Returns <tt>true</tt> if this set contains the specified element.
     * More formally, returns <tt>true</tt> if and only if this set
     * contains an element <tt>e</tt> such that
     * <tt>(o is null&nbsp;?&nbsp;e is null&nbsp;:&nbsp;o.equals(e))</tt>.
     *
     * @param o element whose presence in this set is to be tested
     * @return <tt>true</tt> if this set contains the specified element
     */
    override bool contains(E o) {
        return map.containsKey(o);
    }

    /**
     * Adds the specified element to this set if it is not already present.
     * More formally, adds the specified element <tt>e</tt> to this set if
     * this set contains no element <tt>e2</tt> such that
     * <tt>(e is null&nbsp;?&nbsp;e2 is null&nbsp;:&nbsp;e.equals(e2))</tt>.
     * If this set already contains the element, the call leaves the set
     * unchanged and returns <tt>false</tt>.
     *
     * @param e element to be added to this set
     * @return <tt>true</tt> if this set did not already contain the specified
     * element
     */
    override bool add(E e) {
        return map.put(e, PRESENT) is null;
    }

    /**
     * Removes the specified element from this set if it is present.
     * More formally, removes an element <tt>e</tt> such that
     * <tt>(o is null&nbsp;?&nbsp;e is null&nbsp;:&nbsp;o.equals(e))</tt>,
     * if this set contains such an element.  Returns <tt>true</tt> 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 <tt>true</tt> if the set contained the specified element
     */
    override bool remove(E o) {
        return map.remove(o) == PRESENT;
    }

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

    /**
     * Returns a shallow copy of this <tt>HashSet</tt> instance: the elements
     * themselves are not cloned.
     *
     * @return a shallow copy of this set
     */
    // 
    // Object clone() {
    //     try {
    //         HashSet<E> newSet = (HashSet<E>) super.clone();
    //         newSet.map = (HashMap<E, Object>) map.clone();
    //         return newSet;
    //     } catch (CloneNotSupportedException e) {
    //         throw new InternalError(e);
    //     }
    // }

    /**
     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
     * and <em>fail-fast</em> {@link Spliterator} over the elements in this
     * set.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
     * {@link Spliterator#DISTINCT}.  Overriding implementations should document
     * the reporting of additional characteristic values.
     *
     * @return a {@code Spliterator} over the elements in this set
     */
    // Spliterator<E> spliterator() {
    //     return new HashMap.KeySpliterator!(E, Object)(map, 0, -1, 0, 0);
    // }

    override int opApply(scope int delegate(ref E) dg) {
        int result = 0;
        foreach (E v; map.byKey) {
            result = dg(v);
            if (result != 0)
                return result;
        }
        return result;
    }

    override bool opEquals(IObject o) {
        return opEquals(cast(Object) o);
    }

    override bool opEquals(Object o) {
        return super.opEquals(o);
    }

    override size_t toHash() @trusted nothrow {
        return super.toHash();
    }

    override string toString() {
        return super.toString();
    }
}