Move DfsPackDescription comparators to common location

There are several ways of comparing DfsPackDescriptions for different
purposes, such as object lookup search order and reftable ordering. Some
of these are later compounded into comparators on other objects, so they
appear in the code as Comparator<DfsReftable>, for example.

Put all the DfsPackDescription comparators in static methods on
DfsPackDescription itself. Stop implementing Comparable, to avoid giving
the impression that there is always one true and correct way of sorting
packs.

Change-Id: Ia5ca65249c13373f7ef5b8a5d1ad50a26577706c

1 files changed, 273 insertions, 0 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsPackDescriptionTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsPackDescriptionTest.java
new file mode 100644
index 0000000000..6029e9cae8
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/dfs/DfsPackDescriptionTest.java
@@ -0,0 +1,273 @@
+/*
+ * Copyright (C) 2018, Google LLC.
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - 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.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. 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.eclipse.jgit.internal.storage.dfs;
+
+import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.COMPACT;
+import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.GC;
+import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.GC_REST;
+import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.INSERT;
+import static org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource.RECEIVE;
+import static org.eclipse.jgit.internal.storage.pack.PackExt.INDEX;
+import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
+import static org.junit.Assert.assertEquals;
+
+import java.util.Comparator;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.eclipse.jgit.internal.storage.dfs.DfsObjDatabase.PackSource;
+import org.junit.Before;
+import org.junit.Test;
+
+public final class DfsPackDescriptionTest {
+	private AtomicInteger counter;
+
+	@Before
+	public void setUp() {
+		counter = new AtomicInteger();
+	}
+
+	@Test
+	public void objectLookupComparatorEqual() throws Exception {
+		DfsPackDescription a = create(RECEIVE);
+		a.setFileSize(PACK, 1);
+		a.setFileSize(INDEX, 1);
+		a.setLastModified(1);
+		a.setObjectCount(1);
+		a.setMaxUpdateIndex(1);
+
+		DfsPackDescription b = create(INSERT);
+		b.setFileSize(PACK, 1);
+		b.setFileSize(INDEX, 2);
+		b.setLastModified(1);
+		b.setObjectCount(1);
+		b.setMaxUpdateIndex(2);
+
+		assertComparesEqual(DfsPackDescription.objectLookupComparator(), a, b);
+	}
+
+	@Test
+	public void objectLookupComparatorPackSource() throws Exception {
+		DfsPackDescription a = create(COMPACT);
+		a.setFileSize(PACK, 2);
+		a.setLastModified(1);
+		a.setObjectCount(2);
+
+		DfsPackDescription b = create(GC);
+		b.setFileSize(PACK, 1);
+		b.setLastModified(2);
+		b.setObjectCount(1);
+
+		assertComparesLessThan(DfsPackDescription.objectLookupComparator(), a, b);
+	}
+
+	@Test
+	public void objectLookupComparatorGcFileSize() throws Exception {
+		// a is older and smaller.
+		DfsPackDescription a = create(GC_REST);
+		a.setFileSize(PACK, 100);
+		a.setLastModified(1);
+		a.setObjectCount(2);
+
+		// b is newer and larger.
+		DfsPackDescription b = create(GC_REST);
+		b.setFileSize(PACK, 200);
+		b.setLastModified(2);
+		b.setObjectCount(1);
+
+		// Since they have the same GC type, tiebreaker is size, and a comes first.
+		assertComparesLessThan(DfsPackDescription.objectLookupComparator(), a, b);
+	}
+
+	@Test
+	public void objectLookupComparatorNonGcLastModified()
+			throws Exception {
+		// a is older and smaller.
+		DfsPackDescription a = create(INSERT);
+		a.setFileSize(PACK, 100);
+		a.setLastModified(1);
+		a.setObjectCount(2);
+
+		// b is newer and larger.
+		DfsPackDescription b = create(INSERT);
+		b.setFileSize(PACK, 200);
+		b.setLastModified(2);
+		b.setObjectCount(1);
+
+		// Since they have the same type but not GC, tiebreaker is last modified,
+		// and b comes first.
+		assertComparesLessThan(DfsPackDescription.objectLookupComparator(), b, a);
+	}
+
+	@Test
+	public void objectLookupComparatorObjectCount() throws Exception {
+		DfsPackDescription a = create(INSERT);
+		a.setObjectCount(1);
+
+		DfsPackDescription b = create(INSERT);
+		b.setObjectCount(2);
+
+		assertComparesLessThan(DfsPackDescription.objectLookupComparator(), a, b);
+	}
+
+	@Test
+	public void reftableComparatorEqual() throws Exception {
+		DfsPackDescription a = create(INSERT);
+		a.setFileSize(PACK, 100);
+		a.setObjectCount(1);
+
+		DfsPackDescription b = create(INSERT);
+		b.setFileSize(PACK, 200);
+		a.setObjectCount(2);
+
+		assertComparesEqual(DfsPackDescription.reftableComparator(), a, b);
+	}
+
+	@Test
+	public void reftableComparatorPackSource() throws Exception {
+		DfsPackDescription a = create(INSERT);
+		a.setMaxUpdateIndex(1);
+		a.setLastModified(1);
+
+		DfsPackDescription b = create(GC);
+		b.setMaxUpdateIndex(2);
+		b.setLastModified(2);
+
+		assertComparesLessThan(DfsPackDescription.reftableComparator(), b, a);
+	}
+
+	@Test
+	public void reftableComparatorMaxUpdateIndex() throws Exception {
+		DfsPackDescription a = create(INSERT);
+		a.setMaxUpdateIndex(1);
+		a.setLastModified(2);
+
+		DfsPackDescription b = create(INSERT);
+		b.setMaxUpdateIndex(2);
+		b.setLastModified(1);
+
+		assertComparesLessThan(DfsPackDescription.reftableComparator(), a, b);
+	}
+
+	@Test
+	public void reftableComparatorLastModified() throws Exception {
+		DfsPackDescription a = create(INSERT);
+		a.setLastModified(1);
+
+		DfsPackDescription b = create(INSERT);
+		b.setLastModified(2);
+
+		assertComparesLessThan(DfsPackDescription.reftableComparator(), a, b);
+	}
+
+	@Test
+	public void reuseComparatorEqual() throws Exception {
+		DfsPackDescription a = create(RECEIVE);
+		a.setFileSize(PACK, 1);
+		a.setFileSize(INDEX, 1);
+		a.setLastModified(1);
+		a.setObjectCount(1);
+		a.setMaxUpdateIndex(1);
+
+		DfsPackDescription b = create(INSERT);
+		b.setFileSize(PACK, 2);
+		b.setFileSize(INDEX, 2);
+		b.setLastModified(2);
+		b.setObjectCount(2);
+		b.setMaxUpdateIndex(2);
+
+		assertComparesEqual(DfsPackDescription.reuseComparator(), a, b);
+	}
+
+	@Test
+	public void reuseComparatorGcPackSize() throws Exception {
+		DfsPackDescription a = create(GC_REST);
+		a.setFileSize(PACK, 1);
+		a.setFileSize(INDEX, 1);
+		a.setLastModified(2);
+		a.setObjectCount(1);
+		a.setMaxUpdateIndex(1);
+
+		DfsPackDescription b = create(GC_REST);
+		b.setFileSize(PACK, 2);
+		b.setFileSize(INDEX, 2);
+		b.setLastModified(1);
+		b.setObjectCount(2);
+		b.setMaxUpdateIndex(2);
+
+		assertComparesLessThan(DfsPackDescription.reuseComparator(), b, a);
+	}
+
+	private DfsPackDescription create(PackSource source) {
+		return new DfsPackDescription(
+				new DfsRepositoryDescription("repo"),
+				"pack_" + counter.incrementAndGet(),
+				source);
+	}
+
+	private static <T> void assertComparesEqual(
+			Comparator<T> comparator, T o1, T o2) {
+		assertEquals(
+				"first object must compare equal to itself",
+				0, comparator.compare(o1, o1));
+		assertEquals(
+				"second object must compare equal to itself",
+				0, comparator.compare(o2, o2));
+		assertEquals(
+				"first object must compare equal to second object",
+				0, comparator.compare(o1, o2));
+	}
+
+	private static <T> void assertComparesLessThan(
+			Comparator<T> comparator, T o1, T o2) {
+		assertEquals(
+				"first object must compare equal to itself",
+				0, comparator.compare(o1, o1));
+		assertEquals(
+				"second object must compare equal to itself",
+				0, comparator.compare(o2, o2));
+		assertEquals(
+				"first object must compare less than second object",
+				-1, comparator.compare(o1, o2));
+	}
+}