Implement restore_snapshot latest commit on branch detection

lib/tfw/components/snapshot_provider.py

@@ -10,6 +10,7 @@ from uuid import uuid4
 from dateutil import parser as dateparser
 
 
+# TODO: gitignore
 class SnapshotProvider:
     def __init__(self, directory, git_dir):
         self._classname = self.__class__.__name__
@@ -125,6 +126,9 @@ class SnapshotProvider:
 
     def restore_snapshot(self, date):
         commit = self._get_commit_from_timestamp(date)
+        branch = self._last_valid_branch
+        if commit == self._latest_commit_on_branch(branch):
+            commit = branch
         self._checkout(commit)
 
     def _get_commit_from_timestamp(self, date):
@@ -153,6 +157,14 @@ class SnapshotProvider:
             self.__last_valid_branch = self._branch
         return self.__last_valid_branch
 
+    def _latest_commit_on_branch(self, branch):
+        return self._get_stdout((
+            'git', 'log',
+            '-n', '1',
+            '--pretty=format:%H',
+            branch
+        ))
+
     @property
     def all_timelines(self):
         return self._branches