only clone if it is necessary

src/de/uni_passau/fim/seibt/gitwrapper/repo/Git.java

@@ -20,6 +20,7 @@ public class Git {
     private static final Logger LOG = Logger.getLogger(Git.class.getCanonicalName());
 
     private static final Pattern CLONING_INTO = Pattern.compile("Cloning into '(.*)'\\.\\.\\.");
+    private static final Pattern ALREADY_EXISTS = Pattern.compile("fatal: destination path '(.*)' already exists and is not an empty directory\\.");
 
     private class ExecRes {
         private int code;
@@ -37,13 +38,6 @@ public class Git {
 
         Optional<ExecRes> res = exec(parentDir, "clone", url);
         Function<ExecRes, Repository> toRepo = execRes -> {
-
-            if (execRes.code != EXIT_SUCCESS) {
-                // the repo may already exist (resulting in code 128) - pull it? delete it?
-                LOG.warning(() -> String.format("Exit code %d indicates failure while cloning '%s'.", execRes.code, url));
-                return null;
-            }
-
             Scanner sc = new Scanner(execRes.output);
 
             if (!sc.hasNextLine()) {
@@ -51,7 +45,14 @@ public class Git {
                 return null;
             }
 
-            Matcher matcher = CLONING_INTO.matcher(sc.nextLine());
+            String firstLine = sc.nextLine();
+            Matcher matcher;
+
+            if (execRes.code == EXIT_SUCCESS) {
+                matcher = CLONING_INTO.matcher(firstLine);
+            } else {
+                matcher = ALREADY_EXISTS.matcher(firstLine);
+            }
 
             if (!matcher.find()) {
                 LOG.warning(() -> String.format("Unexpected output while cloning '%s'.", url));
@@ -60,8 +61,20 @@ public class Git {
 
             String name = matcher.group(1);
             File repoDir = new File(parentDir, name);
+            String repoPath = repoDir.getAbsolutePath();
+
+            if (execRes.code == EXIT_SUCCESS) {
+                LOG.fine(() -> String.format("Cloned '%s' into '%s'.", url, repoPath));
+            } else {
+                LOG.fine(() -> String.format("Found '%s' which would be produced for '%s'", repoPath, url));
 
-            LOG.fine(() -> String.format("Cloned '%s' into '%s'.", url, repoDir.getAbsolutePath()));
+                if (!isGitDir(repoDir)) {
+                    LOG.warning(() -> String.format("'%s' is not a git repository.", repoPath));
+                    return null;
+                }
+
+                LOG.fine(() -> String.format("'%s' is a git repository. Assuming it is a clone of '%s'.", repoPath, url));
+            }
 
             return new Repository(this, url, repoDir);
         };
@@ -69,6 +82,24 @@ public class Git {
         return res.map(toRepo);
     }
 
+    /**
+     * Returns whether the given directory (or any of its parent directories) is a git repository. Returns false if
+     * <code>directory</code> is not a directory.
+     *
+     * @param directory
+     *         the directory to check
+     * @return true iff the given directory (or any of its parent directories) is a git repository
+     */
+    public boolean isGitDir(File directory) {
+
+        if (!directory.isDirectory()) {
+            return false;
+        }
+
+        Optional<ExecRes> status = exec(directory, "rev-parse", "--is-inside-git-dir");
+        return status.map(res -> res.code == EXIT_SUCCESS).orElse(false);
+    }
+
     public Optional<ExecRes> exec(File workingDirectory, String... parameters) {
         ProcessBuilder b = new ProcessBuilder();
         String[] cmdArray = new String[parameters.length + 1];