package org.simantics.databoard.util;

import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.Set;

public class IdentityHashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, java.io.Serializable
{
static final long serialVersionUID = -5024744406713321676L;

private transient IdentityHashMap<E,Object> map;

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

/**
 * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
 * default initial capacity (16) and load factor (0.75).
 */
public IdentityHashSet() {
map = new IdentityHashMap<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
 */
public IdentityHashSet(Collection<? extends E> c) {
map = new IdentityHashMap<E,Object>(Math.max((int) (c.size()/.75f) + 1, 16));
addAll(c);
}


/**
 * 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
 */
public IdentityHashSet(int initialCapacity) {
map = new IdentityHashMap<E,Object>(initialCapacity);
}

/**
 * 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
 */
public Iterator<E> iterator() {
return map.keySet().iterator();
}

/**
 * Returns the number of elements in this set (its cardinality).
 *
 * @return the number of elements in this set (its cardinality)
 */
public 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
 */
public boolean 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==null&nbsp;?&nbsp;e==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
 */
public boolean contains(Object 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==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 <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
 */
public boolean add(E e) {
return map.put(e, PRESENT)==null;
}

/**
 * Removes the specified element from this set if it is present.
 * More formally, removes an element <tt>e</tt> such that
 * <tt>(o==null&nbsp;?&nbsp;e==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
 */
public boolean remove(Object o) {
return map.remove(o)==PRESENT;
}

/**
 * Removes all of the elements from this set.
 * The set will be empty after this call returns.
 */
public 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
 */
@SuppressWarnings("unchecked")
public Object clone() {
try {
	IdentityHashSet<E> newSet = (IdentityHashSet<E>) super.clone();
    newSet.map = (IdentityHashMap<E, Object>) map.clone();
    return newSet;
} catch (CloneNotSupportedException e) {
    throw new InternalError();
}
}

/**
 * Save the state of this <tt>HashSet</tt> instance to a stream (that is,
 * serialize it).
 *
 * @serialData The capacity of the backing <tt>HashMap</tt> instance
 *		   (int), and its load factor (float) are emitted, followed by
 *		   the size of the set (the number of elements it contains)
 *		   (int), followed by all of its elements (each an Object) in
 *             no particular order.
 */
private void writeObject(java.io.ObjectOutputStream s)
    throws java.io.IOException {
// Write out any hidden serialization magic
s.defaultWriteObject();

    // Write out size
    s.writeInt(map.size());

// Write out all elements in the proper order.
for (Iterator<E> i=map.keySet().iterator(); i.hasNext(); )
        s.writeObject(i.next());
}

/**
 * Reconstitute the <tt>HashSet</tt> instance from a stream (that is,
 * deserialize it).
 */
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
    throws java.io.IOException, ClassNotFoundException {
// Read in any hidden serialization magic
s.defaultReadObject();

// 	Read in size
	int size = s.readInt();

    // Read in HashMap capacity and load factor and create backing HashMap
    map = new IdentityHashMap<E,Object>(size);


// Read in all elements in the proper order.
for (int i=0; i<size; i++) {
        E e = (E) s.readObject();
        map.put(e, PRESENT);
    }
}
}