MultiPackIndex: add findPosition method

We will need this method to implement the #findIdxPosition in a
DfsPackFile with multipack index.

Change-Id: If333de4e5109f58074f566c1c6ef4419d4b42b41

Author: ifradeo

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/midx/MultiPackIndexTest.java

@@ -213,7 +213,6 @@ public void jgit_resolve() throws IOException {
 		MultiPackIndex midx = MultiPackIndexLoader
 				.read(new ByteArrayInputStream(out.toByteArray()));
 
-
 		Set<ObjectId> results = new HashSet<>();
 		midx.resolve(results, abbrev, 100);
 
@@ -257,7 +256,6 @@ public void jgit_resolve_matchLimit() throws IOException {
 		MultiPackIndex midx = MultiPackIndexLoader
 				.read(new ByteArrayInputStream(out.toByteArray()));
 
-
 		Set<ObjectId> results = new HashSet<>();
 		midx.resolve(results, abbrev, 2);
 
@@ -273,8 +271,7 @@ public void jgit_resolve_noMatches() throws IOException {
 		AbbreviatedObjectId abbrev = AbbreviatedObjectId
 				.fromString("4400000000");
 
-		PackIndex idxOne = indexWith(
-				"0000000000000000000000000000000000000001",
+		PackIndex idxOne = indexWith("0000000000000000000000000000000000000001",
 				"3000000000000000000000000000000000000005",
 				"32fe829a1b000000000000000000000000000001",
 				"32fe829a1c000000000000000000000000000001",
@@ -315,13 +312,67 @@ public void jgit_resolve_empty() throws IOException {
 		MultiPackIndex midx = MultiPackIndexLoader
 				.read(new ByteArrayInputStream(out.toByteArray()));
 
-
 		Set<ObjectId> results = new HashSet<>();
 		midx.resolve(results, abbrev, 200);
 
 		assertEquals(0, results.size());
 	}
 
+	@Test
+	public void jgit_findPosition() throws IOException {
+		PackIndex idxOne = FakeIndexFactory.indexOf(List.of(
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000001", 500),
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000005", 12),
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000010", 1500)));
+		PackIndex idxTwo = FakeIndexFactory.indexOf(List.of(
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000002", 501),
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000003", 13),
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000015", 1501)));
+		PackIndex idxThree = FakeIndexFactory.indexOf(List.of(
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000004", 502),
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000007", 14),
+				new FakeIndexFactory.IndexObject(
+						"0000000000000000000000000000000000000012", 1502)));
+
+		Map<String, PackIndex> packs = Map.of("p1", idxOne, "p2", idxTwo, "p3",
+				idxThree);
+		MultiPackIndexWriter writer = new MultiPackIndexWriter();
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		writer.write(NullProgressMonitor.INSTANCE, out, packs);
+
+		MultiPackIndex midx = MultiPackIndexLoader
+				.read(new ByteArrayInputStream(out.toByteArray()));
+		assertEquals(3, midx.getPackNames().length);
+		assertEquals(0, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000001")));
+		assertEquals(1, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000002")));
+		assertEquals(2, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000003")));
+		assertEquals(3, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000004")));
+		assertEquals(4, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000005")));
+		assertEquals(5, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000007")));
+		assertEquals(6, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000010")));
+		assertEquals(7, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000012")));
+		assertEquals(8, midx.findPosition(ObjectId
+				.fromString("0000000000000000000000000000000000000015")));
+
+		assertNull(midx.find(ObjectId.zeroId()));
+	}
+
 	private static PackIndex indexWith(String... oids) {
 		List<FakeIndexFactory.IndexObject> idxObjs = new ArrayList<>(
 				oids.length);

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/midx/MultiPackIndex.java

@@ -51,6 +51,20 @@ public interface MultiPackIndex {
 	 */
 	PackOffset find(AnyObjectId objectId);
 
+	/**
+	 * Position of the object in this midx, when all covered objects are ordered
+	 * by SHA1.
+	 * <p>
+	 * As the midx removes duplicates, this position is NOT equivalent to
+	 * "position in pack + total count of objects in previous packs in the
+	 * stack".
+	 *
+	 * @param objectId
+	 *            an object id
+	 * @return position of the object in this multipack index
+	 */
+	int findPosition(AnyObjectId objectId);
+
 	/**
 	 * Find objects matching the prefix abbreviation.
 	 *

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/midx/MultiPackIndexV1.java

@@ -60,6 +60,11 @@ public boolean hasObject(AnyObjectId oid) {
 		return idx.findMultiPackIndexPosition(oid) != -1;
 	}
 
+	@Override
+	public int findPosition(AnyObjectId oid) {
+		return idx.findMultiPackIndexPosition(oid);
+	}
+
 	@Override
 	@Nullable
 	public PackOffset find(AnyObjectId objectId) {