/***
 * ASM: a very small and fast Java bytecode manipulation framework
 * Copyright (c) 2000-2007 INRIA, France Telecom
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the copyright holders nor the names of its
 *    contributors may be used to endorse or promote products derived from
 *    this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */
package alterrs.asm.tree.analysis;

import java.util.AbstractSet;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * A set of at most two elements.
 * 
 * @author Eric Bruneton
 */
class SmallSet extends AbstractSet implements Iterator {

	// if e1 is null, e2 must be null; otherwise e2 must be different from e1

	Object e1, e2;

	static final Set EMPTY_SET = new SmallSet(null, null);

	SmallSet(final Object e1, final Object e2) {
		this.e1 = e1;
		this.e2 = e2;
	}

	// -------------------------------------------------------------------------
	// Implementation of inherited abstract methods
	// -------------------------------------------------------------------------

	public Iterator iterator() {
		return new SmallSet(e1, e2);
	}

	public int size() {
		return e1 == null ? 0 : (e2 == null ? 1 : 2);
	}

	// -------------------------------------------------------------------------
	// Implementation of the Iterator interface
	// -------------------------------------------------------------------------

	public boolean hasNext() {
		return e1 != null;
	}

	public Object next() {
		Object e = e1;
		e1 = e2;
		e2 = null;
		return e;
	}

	public void remove() {
	}

	// -------------------------------------------------------------------------
	// Utility methods
	// -------------------------------------------------------------------------

	Set union(final SmallSet s) {
		if ((s.e1 == e1 && s.e2 == e2) || (s.e1 == e2 && s.e2 == e1)) {
			return this; // if the two sets are equal, return this
		}
		if (s.e1 == null) {
			return this; // if s is empty, return this
		}
		if (e1 == null) {
			return s; // if this is empty, return s
		}
		if (s.e2 == null) { // s contains exactly one element
			if (e2 == null) {
				return new SmallSet(e1, s.e1); // necessarily e1 != s.e1
			} else if (s.e1 == e1 || s.e1 == e2) { // s is included in this
				return this;
			}
		}
		if (e2 == null) { // this contains exactly one element
			// if (s.e2 == null) { // cannot happen
			// return new SmallSet(e1, s.e1); // necessarily e1 != s.e1
			// } else
			if (e1 == s.e1 || e1 == s.e2) { // this in included in s
				return s;
			}
		}
		// here we know that there are at least 3 distinct elements
		HashSet r = new HashSet(4);
		r.add(e1);
		if (e2 != null) {
			r.add(e2);
		}
		r.add(s.e1);
		if (s.e2 != null) {
			r.add(s.e2);
		}
		return r;
	}
}
