Implement branching in SnapshotProvider

lib/tfw/components/snapshot_provider.py

@@ -17,16 +17,36 @@ class SnapshotProvider:
             'GIT_COMMITTER_EMAIL': ''
         }
 
+        self._head_detached = False
+        self._branch = 'master'
+        self._branches = [self._branch]
+
     def init_repo(self):
         self._run(('git', 'init'))
 
     def take_snapshot(self):
+        if self._head_detached:
+            self._checkout_branch_from_head()
         self._run(('git', 'add', '-A'))
         self._run(('git', 'commit', '-m', 'Snapshot'))
 
+    def _checkout_branch_from_head(self):
+        head_hash = self._get_head_hash()
+        self._run((
+            'git', 'checkout',
+            '-b', head_hash, head_hash
+        ))
+        self._branches.append(head_hash)
+        self._branch = head_hash
+        self._head_detached = False
+
+    def _get_head_hash(self):
+        return self._get_stdout(('git', 'rev-parse', 'HEAD'))
+
     def restore_snapshot(self, date):
         commit = self._get_commit_from_timestamp(date)
         self._checkout_commit(commit)
+        self._head_detached = True
 
     def _get_commit_from_timestamp(self, date):
         return self._get_stdout((
@@ -34,7 +54,7 @@ class SnapshotProvider:
             '--date=iso',
             '-n', '1',
             f'--before="{date.isoformat()}"',
-            'master'
+            self._branch
         ))
 
     def _checkout_commit(self, commit):