/* Alloy Analyzer 4 -- Copyright (c) 2006-2009, Felix Chang
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files
 * (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF
 * OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package edu.mit.csail.sdg.alloy4;

import java.util.AbstractSet;
import java.util.Collections;
import java.util.Set;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.Iterator;
import java.io.Serializable;

/** Immutable; implements a set based on hashCode() and equals(); null value is allowed.
 *
 * @param <K> - the type of element
 */

public final class ConstSet<K> extends AbstractSet<K> implements Serializable {

   /** This ensures this class can be serialized reliably. */
   private static final long serialVersionUID = 0;

   /** The underlying Collections.unmodifiableSet set. */
   private final Set<K> set;

   /** This caches a readonly empty Set. */
   private static final ConstSet<Object> emptyset = new ConstSet<Object>(new HashSet<Object>(0));

   /** Constructs an unmodifiable map with the given set as the backing store. */
   private ConstSet(Set<? extends K> set) {
      this.set = Collections.unmodifiableSet(set);
   }

   /** Returns an unmodifiable empty set. */
   @SuppressWarnings("unchecked")
   public static<K> ConstSet<K> make() {
      return (ConstSet<K>) emptyset;
   }

   /** Returns an unmodifiable set with the same elements and traversal order as the given set.
    * (If set==null, we'll return an unmodifiable empty set)
    */
   public static<K> ConstSet<K> make(Iterable<K> collection) {
      if (collection instanceof ConstSet) return (ConstSet<K>)collection;
      LinkedHashSet<K> ans = null;
      if (collection != null) for(K element: collection) {
         if (ans == null) ans = new LinkedHashSet<K>();
         ans.add(element);
      }
      if (ans==null) return make(); else return new ConstSet<K>(ans);
   }

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

   /** Returns a read-only iterator over this set. */
   @Override public Iterator<K> iterator() { return set.iterator(); }

   /** Returns true if the given object is in this set. */
   @Override public boolean contains(Object element) { return set.contains(element); }  // overridden for performance
}