fix: close ObjectReader, DiffFormatter and RevWalk in getDiffStats

Author: Fikri-20

plugin-modernizer-core/src/main/java/io/jenkins/tools/pluginmodernizer/core/github/DiffStatsCalculator.java

@@ -1237,8 +1237,86 @@ private void deleteLegacyPrs(Plugin plugin) {
      * @return DiffStats (no. of additions, deletions and changed files)
      */
     public DiffStats getDiffStats(Plugin plugin, boolean dryRun) {
-        try {
-            return new DiffStatsCalculator().calculate(plugin, dryRun);
+        Path gitDirPath = Settings.DEFAULT_CACHE_PATH
+                .resolve(plugin.getName())
+                .resolve("sources")
+                .resolve(".git")
+                .normalize();
+        File gitDir = gitDirPath.toFile();
+
+        try (Repository repository = new FileRepositoryBuilder()
+                        .setGitDir(gitDir)
+                        .readEnvironment()
+                        .findGitDir()
+                        .build();
+                Git git = new Git(repository);
+                ObjectReader reader = repository.newObjectReader();
+                DiffFormatter formatter = new DiffFormatter(new ByteArrayOutputStream())) {
+
+            formatter.setRepository(repository);
+            formatter.setDiffComparator(RawTextComparator.DEFAULT);
+            formatter.setDetectRenames(true);
+
+            int additions = 0;
+            int deletions = 0;
+            int changedFiles = 0;
+            if (dryRun) {
+                // UNSTAGED: Working Directory vs Index
+                DirCacheIterator indexTree = new DirCacheIterator(repository.readDirCache());
+                FileTreeIterator workingTree = new FileTreeIterator(repository);
+
+                List<DiffEntry> unstagedDiffs = git.diff()
+                        .setOldTree(indexTree)
+                        .setNewTree(workingTree)
+                        .setShowNameAndStatusOnly(false)
+                        .call();
+
+                for (DiffEntry diff : unstagedDiffs) {
+                    try {
+                        EditList edits = formatter.toFileHeader(diff).toEditList();
+                        for (Edit edit : edits) {
+                            additions += edit.getEndB() - edit.getBeginB();
+                            deletions += edit.getEndA() - edit.getBeginA();
+                        }
+                        changedFiles++;
+                    } catch (MissingObjectException e) {
+                        LOG.warn("Skipping diff for {}: {}", diff.getNewPath(), e.getMessage());
+                    }
+                }
+                return new DiffStats(additions, deletions, changedFiles);
+            }
+            // COMMITTED: HEAD vs default branch or previous commit
+            ObjectId head = repository.resolve("HEAD");
+            String defaultBranchName = plugin.getRemoteRepository(this).getDefaultBranch();
+            ObjectId defaultBranch = repository.resolve("refs/heads/" + defaultBranchName);
+
+            if (defaultBranch == null) {
+                throw new IOException("Could not resolve default branch.");
+            }
+
+            CanonicalTreeParser oldTree = new CanonicalTreeParser();
+            CanonicalTreeParser newTree = new CanonicalTreeParser();
+            try (RevWalk revWalk = new RevWalk(repository)) {
+                oldTree.reset(reader, revWalk.parseTree(defaultBranch));
+                newTree.reset(reader, revWalk.parseTree(head));
+            }
+
+            List<DiffEntry> committedDiffs = git.diff()
+                    .setOldTree(oldTree)
+                    .setNewTree(newTree)
+                    .setShowNameAndStatusOnly(false)
+                    .call();
+
+            for (DiffEntry diff : committedDiffs) {
+                EditList edits = formatter.toFileHeader(diff).toEditList();
+                for (Edit edit : edits) {
+                    additions += edit.getEndB() - edit.getBeginB();
+                    deletions += edit.getEndA() - edit.getBeginA();
+                }
+                changedFiles++;
+            }
+            return new DiffStats(additions, deletions, changedFiles);
+
         } catch (IOException | GitAPIException e) {
             plugin.addError("Failed to get diff stats", e);
             plugin.raiseLastError();