PackDirectory: Use PackFile to ensure we find preserved packs

Update scanPacksImpl and listPackDirectory (renamed to
getPackFilesByExtById) to use the new PackFile functionality to
validate file names and complete pack file sets (.pack, .idx, etc).

Most importantly, this allows a later change to rely on scanPacks() to
complete a packList that contains packs with the 'old-' prefix in their
extension.

This also eliminates duplication of logic for how to identify and
construct pack files.

Change-Id: I7175e5fefb187a29e0a7cf53c392aee922314f31
Signed-off-by: Nasser Grainawi <quic_nasserg@quicinc.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/PackDirectory.java

@@ -10,6 +10,8 @@
 
 package org.eclipse.jgit.internal.storage.file;
 
+import static org.eclipse.jgit.internal.storage.pack.PackExt.BITMAP_INDEX;
+import static org.eclipse.jgit.internal.storage.pack.PackExt.INDEX;
 import static org.eclipse.jgit.internal.storage.pack.PackExt.PACK;
 
 import java.io.File;
@@ -21,7 +23,6 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -398,43 +399,32 @@ class PackDirectory {
 	private PackList scanPacksImpl(PackList old) {
 		final Map<String, Pack> forReuse = reuseMap(old);
 		final FileSnapshot snapshot = FileSnapshot.save(directory);
-		final Set<String> names = listPackDirectory();
-		final List<Pack> list = new ArrayList<>(names.size() >> 2);
+		Map<String, Map<PackExt, PackFile>> packFilesByExtById = getPackFilesByExtById();
+		List<Pack> list = new ArrayList<>(packFilesByExtById.size());
 		boolean foundNew = false;
-		for (String indexName : names) {
-			// Must match "pack-[0-9a-f]{40}.idx" to be an index.
-			//
-			if (indexName.length() != 49 || !indexName.endsWith(".idx")) { //$NON-NLS-1$
-				continue;
-			}
-
-			final String base = indexName.substring(0, indexName.length() - 3);
-			int extensions = 0;
-			for (PackExt ext : PackExt.values()) {
-				if (names.contains(base + ext.getExtension())) {
-					extensions |= ext.getBit();
-				}
-			}
-
-			if ((extensions & PACK.getBit()) == 0) {
+		for (Map<PackExt, PackFile> packFilesByExt : packFilesByExtById
+				.values()) {
+			PackFile packFile = packFilesByExt.get(PACK);
+			if (packFile == null || !packFilesByExt.containsKey(INDEX)) {
 				// Sometimes C Git's HTTP fetch transport leaves a
 				// .idx file behind and does not download the .pack.
 				// We have to skip over such useless indexes.
-				//
+				// Also skip if we don't have any index for this id
 				continue;
 			}
 
-			final String packName = base + PACK.getExtension();
-			final File packFile = new File(directory, packName);
-			final Pack oldPack = forReuse.get(packName);
+			Pack oldPack = forReuse.get(packFile.getName());
 			if (oldPack != null
 					&& !oldPack.getFileSnapshot().isModified(packFile)) {
-				forReuse.remove(packName);
+				forReuse.remove(packFile.getName());
 				list.add(oldPack);
 				continue;
 			}
 
-			list.add(new Pack(packFile, extensions));
+			list.add(new Pack(packFile,
+					packFilesByExt.containsKey(BITMAP_INDEX)
+							? BITMAP_INDEX.getBit()
+							: 0));
 			foundNew = true;
 		}
 
@@ -487,18 +477,40 @@ class PackDirectory {
 		return forReuse;
 	}
 
-	private Set<String> listPackDirectory() {
+	/**
+	 * Scans the pack directory for
+	 * {@link org.eclipse.jgit.internal.storage.file.PackFile}s and returns them
+	 * organized by their extensions and their pack ids
+	 *
+	 * Skips files in the directory that we cannot create a
+	 * {@link org.eclipse.jgit.internal.storage.file.PackFile} for.
+	 *
+	 * @return a map of {@link org.eclipse.jgit.internal.storage.file.PackFile}s
+	 *         and {@link org.eclipse.jgit.internal.storage.pack.PackExt}s keyed
+	 *         by pack ids
+	 */
+	private Map<String, Map<PackExt, PackFile>> getPackFilesByExtById() {
 		final String[] nameList = directory.list();
 		if (nameList == null) {
-			return Collections.emptySet();
+			return Collections.emptyMap();
 		}
-		final Set<String> nameSet = new HashSet<>(nameList.length << 1);
+		Map<String, Map<PackExt, PackFile>> packFilesByExtById = new HashMap<>(
+				nameList.length / 2); // assume roughly 2 files per id
 		for (String name : nameList) {
-			if (name.startsWith("pack-")) { //$NON-NLS-1$
-				nameSet.add(name);
+			try {
+				PackFile pack = new PackFile(directory, name);
+				Map<PackExt, PackFile> packByExt = packFilesByExtById
+						.get(pack.getId());
+				if (packByExt == null) {
+					packByExt = new HashMap<>(PackExt.values().length);
+					packFilesByExtById.put(pack.getId(), packByExt);
+				}
+				packByExt.put(pack.getPackExt(), pack);
+			} catch (IllegalArgumentException e) {
+				continue;
 			}
 		}
-		return nameSet;
+		return packFilesByExtById;
 	}
 
 	static final class PackList {