From 93562172eb2552f6c791bd1efed2f1eb55bc5df2 Mon Sep 17 00:00:00 2001
From: Ed Page <eopage@byu.net>
Date: Wed, 23 Feb 2011 22:12:19 -0600
Subject: [PATCH] Pulling in from skeleton

---
 src/util/time_utils.py |   94 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 src/util/time_utils.py

diff --git a/src/util/time_utils.py b/src/util/time_utils.py
new file mode 100644
index 0000000..90ec84d
--- /dev/null
+++ b/src/util/time_utils.py
@@ -0,0 +1,94 @@
+from datetime import tzinfo, timedelta, datetime
+
+ZERO = timedelta(0)
+HOUR = timedelta(hours=1)
+
+
+def first_sunday_on_or_after(dt):
+	days_to_go = 6 - dt.weekday()
+	if days_to_go:
+		dt += timedelta(days_to_go)
+	return dt
+
+
+# US DST Rules
+#
+# This is a simplified (i.e., wrong for a few cases) set of rules for US
+# DST start and end times. For a complete and up-to-date set of DST rules
+# and timezone definitions, visit the Olson Database (or try pytz):
+# http://www.twinsun.com/tz/tz-link.htm
+# http://sourceforge.net/projects/pytz/ (might not be up-to-date)
+#
+# In the US, since 2007, DST starts at 2am (standard time) on the second
+# Sunday in March, which is the first Sunday on or after Mar 8.
+DSTSTART_2007 = datetime(1, 3, 8, 2)
+# and ends at 2am (DST time; 1am standard time) on the first Sunday of Nov.
+DSTEND_2007 = datetime(1, 11, 1, 1)
+# From 1987 to 2006, DST used to start at 2am (standard time) on the first
+# Sunday in April and to end at 2am (DST time; 1am standard time) on the last
+# Sunday of October, which is the first Sunday on or after Oct 25.
+DSTSTART_1987_2006 = datetime(1, 4, 1, 2)
+DSTEND_1987_2006 = datetime(1, 10, 25, 1)
+# From 1967 to 1986, DST used to start at 2am (standard time) on the last
+# Sunday in April (the one on or after April 24) and to end at 2am (DST time;
+# 1am standard time) on the last Sunday of October, which is the first Sunday
+# on or after Oct 25.
+DSTSTART_1967_1986 = datetime(1, 4, 24, 2)
+DSTEND_1967_1986 = DSTEND_1987_2006
+
+
+class USTimeZone(tzinfo):
+
+	def __init__(self, hours, reprname, stdname, dstname):
+		self.stdoffset = timedelta(hours=hours)
+		self.reprname = reprname
+		self.stdname = stdname
+		self.dstname = dstname
+
+	def __repr__(self):
+		return self.reprname
+
+	def tzname(self, dt):
+		if self.dst(dt):
+			return self.dstname
+		else:
+			return self.stdname
+
+	def utcoffset(self, dt):
+		return self.stdoffset + self.dst(dt)
+
+	def dst(self, dt):
+		if dt is None or dt.tzinfo is None:
+			# An exception may be sensible here, in one or both cases.
+			# It depends on how you want to treat them.  The default
+			# fromutc() implementation (called by the default astimezone()
+			# implementation) passes a datetime with dt.tzinfo is self.
+			return ZERO
+		assert dt.tzinfo is self
+
+		# Find start and end times for US DST. For years before 1967, return
+		# ZERO for no DST.
+		if 2006 < dt.year:
+			dststart, dstend = DSTSTART_2007, DSTEND_2007
+		elif 1986 < dt.year < 2007:
+			dststart, dstend = DSTSTART_1987_2006, DSTEND_1987_2006
+		elif 1966 < dt.year < 1987:
+			dststart, dstend = DSTSTART_1967_1986, DSTEND_1967_1986
+		else:
+			return ZERO
+
+		start = first_sunday_on_or_after(dststart.replace(year=dt.year))
+		end = first_sunday_on_or_after(dstend.replace(year=dt.year))
+
+		# Can't compare naive to aware objects, so strip the timezone from
+		# dt first.
+		if start <= dt.replace(tzinfo=None) < end:
+			return HOUR
+		else:
+			return ZERO
+
+
+Eastern  = USTimeZone(-5, "Eastern",  "EST", "EDT")
+Central  = USTimeZone(-6, "Central",  "CST", "CDT")
+Mountain = USTimeZone(-7, "Mountain", "MST", "MDT")
+Pacific  = USTimeZone(-8, "Pacific",  "PST", "PDT")
-- 
1.7.9.5