added datetime_from_dir() for BackInTime dirs (and UTC conversion)

src/borg_import/helpers/timestamps.py

@@ -1,4 +1,5 @@
-from datetime import datetime
+from datetime import datetime, timedelta
+import time
 
 
 def datetime_from_mtime(path):
@@ -40,6 +41,37 @@ def datetime_from_string(s):
         raise ValueError('could not parse %r' % s)
 
 
+def datetime_from_dir(d, p=4):
+    """
+    parse datetime from part of a directory name
+
+    returns a datetime object if the format could be parsed.
+    raises ValueError if not.
+    """
+    if type(d).__name__ == 'PosixPath':
+            s = d.name
+    elif type(d) == str:
+            # in case input is just a string (for testing)
+            s = d
+    # get rid of trailing -??? numbers that BackInTime adds
+    s = s[:-p].strip()
+    for ts_format in [
+            # Back In Time format
+            '%Y%m%d-%H%M%S',
+            ]:
+        try:
+            dt = datetime.strptime(s, ts_format)
+            # adjust time zone offset to get UTC
+            tz = int(time.strftime('%z')[:-2])
+            ut = dt - timedelta(hours=tz)
+            return ut
+        except ValueError:
+            # didn't work with this format, try next
+            pass
+    else:
+        raise ValueError('could not parse %r' % s)
+
+
 def datetime_from_file(path):
     """
     discover backup timestamp from contents of a file.