# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1438121939 -7200
# Node ID 3e15d39530663c418346bca4ab200564aea05457
# Parent  1d28f68285a3b832f7d0aca533c29f8935889b97
Introduced a dedicated function for getting time zones/regimes from datetimes.
Changed the get_datetime_item and get_datetime_attributes functions to provide
time zone attributes using the datetime primarily, falling back on any provided
zone/regime information only if necessary.
Added fallback time zones/regimes when getting period start and end item
details.

diff -r 1d28f68285a3 -r 3e15d3953066 imiptools/data.py
--- a/imiptools/data.py	Tue Jul 28 19:27:27 2015 +0200
+++ b/imiptools/data.py	Wed Jul 29 00:18:59 2015 +0200
@@ -22,9 +22,9 @@
 from bisect import bisect_left
 from datetime import date, datetime, timedelta
 from email.mime.text import MIMEText
-from imiptools.dates import format_datetime, get_datetime, get_duration, \
-                            get_freebusy_period, get_period, get_tzid, \
-                            to_timezone, to_utc_datetime
+from imiptools.dates import format_datetime, get_datetime, get_datetime_tzid, \
+                            get_duration, get_freebusy_period, get_period, \
+                            get_tzid, to_timezone, to_utc_datetime
 from imiptools.period import Period, RecurringPeriod, period_overlaps
 from vCalendar import iterwrite, parse, ParseError, to_dict, to_node
 from vRecurrence import get_parameters, get_rule
@@ -367,8 +367,9 @@
     else:
         value, attr = t
         dt = get_datetime(value, attr)
-        if dt.tzname() == "UTC":
-            attr["TZID"] = "UTC"
+        tzid = get_datetime_tzid(dt)
+        if tzid:
+            attr["TZID"] = tzid
         return dt, attr
 
 # Conversion functions.
diff -r 1d28f68285a3 -r 3e15d3953066 imiptools/dates.py
--- a/imiptools/dates.py	Tue Jul 28 19:27:27 2015 +0200
+++ b/imiptools/dates.py	Wed Jul 29 00:18:59 2015 +0200
@@ -260,6 +260,19 @@
     else:
         return dt + timedelta(1)
 
+def get_datetime_tzid(dt):
+
+    "Return the time zone identifier from 'dt' or None if unknown."
+
+    if not isinstance(dt, datetime):
+        return None
+    elif dt.tzname() == "UTC":
+        return "UTC"
+    elif dt.tzinfo and hasattr(dt.tzinfo, "zone"):
+        return dt.tzinfo.zone
+    else:
+        return None
+
 def to_date(dt):
 
     "Return the date of 'dt'."
@@ -295,15 +308,15 @@
     else:
         return dt
 
-def to_timezone(dt, name):
+def to_timezone(dt, tzid):
 
     """
     Return a datetime corresponding to 'dt' in the time regime having the given
-    'name'.
+    'tzid'.
     """
 
     try:
-        tz = name and timezone(name) or None
+        tz = tzid and timezone(tzid) or None
     except UnknownTimeZoneError:
         tz = None
     return to_tz(dt, tz)
@@ -328,6 +341,9 @@
     (start, end) tuple containing datetimes in the UTC time zone, where dates
     are converted to points in time so that each day has a specific start and
     end point defined in UTC.
+
+    Here, 'tzid' is used to "project" dates into a time zone of interest before
+    then being converted into UTC start and end datetimes.
     """
 
     start = to_utc_datetime(start, tzid)
@@ -362,14 +378,16 @@
 
 def get_datetime_attributes(dt, tzid=None):
 
-    "Return attributes for 'dt' and 'tzid'."
+    """
+    Return attributes for the 'dt' date or datetime object with 'tzid'
+    indicating the time zone if not otherwise defined.
+    """
 
     if isinstance(dt, datetime):
         attr = {"VALUE" : "DATE-TIME"}
+        tzid = get_datetime_tzid(dt) or tzid
         if tzid:
             attr["TZID"] = tzid
-        elif dt.tzname() == "UTC":
-            attr["TZID"] = "UTC"
         return attr
     else:
         return {"VALUE" : "DATE"}
@@ -380,12 +398,13 @@
 
     """
     Return an iCalendar-compatible string and attributes for 'dt' using any
-    specified 'tzid' to assert a particular time zone.
+    specified 'tzid' to assert a particular time zone if not otherwise defined.
     """
 
     if not dt:
         return None, None
-    dt = to_timezone(dt, tzid)
+    if not get_datetime_tzid(dt):
+        dt = to_timezone(dt, tzid)
     value = format_datetime(dt)
     attr = get_datetime_attributes(dt, tzid)
     return value, attr
diff -r 1d28f68285a3 -r 3e15d3953066 imiptools/period.py
--- a/imiptools/period.py	Tue Jul 28 19:27:27 2015 +0200
+++ b/imiptools/period.py	Wed Jul 29 00:18:59 2015 +0200
@@ -83,10 +83,10 @@
         return self.tzid
 
     def get_start_item(self):
-        return self.start, get_datetime_attributes(self.start)
+        return self.start, get_datetime_attributes(self.start, self.get_tzid())
 
     def get_end_item(self):
-        return self.end, get_datetime_attributes(self.end)
+        return self.end, get_datetime_attributes(self.end, self.get_tzid())
 
     def get_start_point(self):
         return to_utc_datetime(self.get_start(), self.get_tzid())