From d2da07a2f6782f065f23337cb0eb42eb7fad6800 Mon Sep 17 00:00:00 2001
From: Erik Stein <erik@classlibrary.net>
Date: Fri, 3 Feb 2017 17:49:03 +0100
Subject: [PATCH] Added date related calculation helpers.

---
 requirements.txt |  2 ++
 utils/dates.py   | 84 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 requirements.txt

diff --git a/requirements.txt b/requirements.txt
new file mode 100644
index 0000000..bb38adb
--- /dev/null
+++ b/requirements.txt
@@ -0,0 +1,2 @@
+Django<2
+python-dateutil
diff --git a/utils/dates.py b/utils/dates.py
index 9fb760e..3b5c5a3 100644
--- a/utils/dates.py
+++ b/utils/dates.py
@@ -4,8 +4,92 @@ from __future__ import unicode_literals
 
 
 import calendar
+from collections import namedtuple
+from dateutil import rrule
+from datetime import date, datetime
+
+
+def force_date(d):
+    if type(d) == datetime:
+        return d.date()
+    else:
+        return d
+
+
+def first_of_month(d):
+    return d.replace(day=1)
 
 
 def get_last_of_month(d):
+    """
+    >>> get_last_of_month(date(2000, 2, 1))
+    datetime.date(2000, 2, 29)
+    >>> get_last_of_month(date(2004, 2, 1))
+    datetime.date(2004, 2, 29)
+    >>> get_last_of_month(date(2004, 12, 1))
+    datetime.date(2004, 12, 31)
+    """
     day = calendar.monthrange(d.year, d.month)[1]
     return d.replace(day=day)
+
+
+def as_month(d):
+    """
+    >>> as_month(datetime(2007, 1, 13, 14, 0))
+    datetime.date(2007, 1, 1)
+    """
+    return force_date(first_of_month(d))
+
+
+#
+# Date Range Calculations
+
+
+DateRange = namedtuple('Range', ['start', 'end'])
+
+
+def months_for_daterange(daterange):
+    """
+    Returns all months for a given date range.
+    A month is represented by a datetime.date object of the first day of the month
+
+    >>> daterange = DateRange(date(2015, 3, 5), date(2015, 8, 25))
+    >>> months_for_daterange(daterange)
+    [datetime.date(2015, 3, 1), datetime.date(2015, 4, 1), datetime.date(2015, 5, 1), datetime.date(2015, 6, 1), datetime.date(2015, 7, 1), datetime.date(2015, 8, 1)]
+
+    """
+    return map(
+        as_month,
+        rrule.rrule(rrule.MONTHLY, dtstart=daterange.start, until=daterange.end)
+    )
+
+
+def months_for_daterange_list(daterange_list):
+    """
+    >>> range_list = [DateRange(date(2015, 2, 25), date(2015, 2, 25)), DateRange(date(2015, 3, 13), date(2015, 3, 13)), DateRange(date(2015, 5, 3), date(2015, 5, 3)), DateRange(date(2015, 5, 7), date(2015, 7, 7)), DateRange(date(2015, 6, 28), date(2015, 6, 28)), DateRange(date(2015, 7, 5), date(2015, 7, 5)), DateRange(date(2015, 10, 14), date(2015, 10, 14)), DateRange(date(2015, 11, 11), date(2015, 12, 11))]
+    >>> months_for_daterange_list(range_list)
+    [datetime.date(2015, 2, 1), datetime.date(2015, 3, 1), datetime.date(2015, 5, 1), datetime.date(2015, 6, 1), datetime.date(2015, 7, 1), datetime.date(2015, 10, 1), datetime.date(2015, 11, 1), datetime.date(2015, 12, 1)]
+    """
+    all_months = set()
+    for dr in daterange_list:
+        all_months.update(months_for_daterange(dr))
+    return sorted(list(all_months))
+
+
+"""
+# >>> from datetime import datetime
+# >>> from collections import namedtuple
+# >>> Range = namedtuple('Range', ['start', 'end'])
+# >>> r1 = Range(start=datetime(2012, 1, 15), end=datetime(2012, 5, 10))
+# >>> r2 = Range(start=datetime(2012, 3, 20), end=datetime(2012, 9, 15))
+# >>> latest_start = max(r1.start, r2.start)
+# >>> earliest_end = min(r1.end, r2.end)
+# >>> overlap = (earliest_end - latest_start).days + 1
+# >>> overlap
+52
+"""
+
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()