Add time zone helpers for converting between local IETF db time and UTC

 - Legacy-Id: 4849

Author: OleLaursen

ietf/utils/timezone.py

@@ -0,0 +1,37 @@
+import pytz
+import email.utils
+import datetime
+
+from django.conf import settings
+
+def local_timezone_to_utc(d):
+    """Takes a naive datetime in the local timezone and returns a
+    naive datetime with the corresponding UTC time."""
+    local_timezone = pytz.timezone(settings.TIME_ZONE)
+
+    d = local_timezone.localize(d).astimezone(pytz.utc)
+
+    return d.replace(tzinfo=None)
+
+def utc_to_local_timezone(d):
+    """Takes a naive datetime UTC and returns a naive datetime in the
+    local time zone."""
+    local_timezone = pytz.timezone(settings.TIME_ZONE)
+
+    d = local_timezone.normalize(d.replace(tzinfo=pytz.utc).astimezone(local_timezone))
+
+    return d.replace(tzinfo=None)
+
+def email_time_to_local_timezone(date_string):
+    """Takes a time string from an email and returns a naive datetime
+    in the local time zone."""
+
+    t = email.utils.parsedate_tz(date_string)
+    d = datetime.datetime(*t[:6])
+
+    if t[7] != None:
+        d += datetime.timedelta(seconds=t[9])
+
+    return utc_to_local_timezone(d)
+
+