--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/tmatesoft/hg/internal/RevisionSet.java	Tue Jun 25 20:48:37 2013 +0200
@@ -0,0 +1,144 @@
+/*
+ * Copyright (c) 2013 TMate Software Ltd
+ *  
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * For information on how to redistribute this software under
+ * the terms of a license other than GNU General Public License
+ * contact TMate Software at support@hg4j.com
+ */
+package org.tmatesoft.hg.internal;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.tmatesoft.hg.core.Nodeid;
+
+/**
+ * Unmodifiable collection of revisions with handy set operations
+ * 
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+public final class RevisionSet {
+	
+	private final Set<Nodeid> elements;
+	
+	public RevisionSet(Collection<Nodeid> revisions) {
+		this(revisions == null ? new HashSet<Nodeid>() : new HashSet<Nodeid>(revisions));
+	}
+	
+	private RevisionSet(HashSet<Nodeid> revisions) {
+		if (revisions.isEmpty()) {
+			elements = Collections.<Nodeid>emptySet();
+		} else {
+			elements = revisions;
+		}
+	}
+
+	public RevisionSet roots() {
+		throw Internals.notImplemented();
+	}
+	
+	public RevisionSet heads() {
+		throw Internals.notImplemented();
+	}
+
+	public RevisionSet intersect(RevisionSet other) {
+		if (isEmpty()) {
+			return this;
+		}
+		if (other.isEmpty()) {
+			return other;
+		}
+		HashSet<Nodeid> copy = new HashSet<Nodeid>(elements);
+		copy.retainAll(other.elements);
+		return copy.size() == elements.size() ? this : new RevisionSet(copy);
+	}
+	
+	public RevisionSet subtract(RevisionSet other) {
+		if (isEmpty() || other.isEmpty()) {
+			return this;
+		}
+		HashSet<Nodeid> copy = new HashSet<Nodeid>(elements);
+		copy.removeAll(other.elements);
+		return copy.size() == elements.size() ? this : new RevisionSet(copy);
+	}
+
+	public RevisionSet union(RevisionSet other) {
+		if (isEmpty()) {
+			return other;
+		}
+		if (other.isEmpty()) {
+			return this;
+		}
+		HashSet<Nodeid> copy = new HashSet<Nodeid>(elements);
+		copy.addAll(other.elements);
+		return new RevisionSet(copy);
+	}
+
+	/**
+	 * A ^ B := (A\B).union(B\A)
+	 * A ^ B := A.union(B) \ A.intersect(B)
+	 */
+	public RevisionSet symmetricDifference(RevisionSet other) {
+		if (isEmpty()) {
+			return this;
+		}
+		if (other.isEmpty()) {
+			return other;
+		}
+		HashSet<Nodeid> copyA = new HashSet<Nodeid>(elements);
+		HashSet<Nodeid> copyB = new HashSet<Nodeid>(other.elements);
+		copyA.removeAll(other.elements);
+		copyB.removeAll(elements);
+		copyA.addAll(copyB);
+		return new RevisionSet(copyA);
+	}
+
+	public boolean isEmpty() {
+		return elements.isEmpty();
+	}
+
+	@Override
+	public String toString() {
+		StringBuilder sb = new StringBuilder();
+		sb.append('<');
+		if (!isEmpty()) {
+			sb.append(elements.size());
+			sb.append(':');
+		}
+		for (Nodeid n : elements) {
+			sb.append(n.shortNotation());
+			sb.append(',');
+		}
+		if (sb.length() > 1) {
+			sb.setCharAt(sb.length() - 1, '>');
+		} else {
+			sb.append('>');
+		}
+		return sb.toString();
+	}
+	
+	@Override
+	public boolean equals(Object obj) {
+		if (false == obj instanceof RevisionSet) {
+			return false;
+		}
+		return elements.equals(((RevisionSet) obj).elements);
+	}
+	
+	@Override
+	public int hashCode() {
+		return elements.hashCode();
+	}
+}