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/***

 * ASM: a very small and fast Java bytecode manipulation framework

 * Copyright (c) 2000-2005 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 org.objectweb.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;

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

    SmallSet(Object e1, 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(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;

    }

}