From da74aa7a4736d174039a979727e7dba1e9224ded Mon Sep 17 00:00:00 2001
From: Mark Magnusson <mark@2600hz.com>
Date: Tue, 17 Mar 2020 14:46:08 -0400
Subject: [PATCH] [4.3] Add previous_day method to kz_date (#6383)

* Add previous_day method to kz_date
    kz_date:previous_day/1 will correctly handle month/year boundries
when calculating the previous day

* add some leap-year tests
---
 core/kazoo_stdlib/src/kz_date.erl        | 16 ++++++++++++++++
 core/kazoo_stdlib/test/kz_date_tests.erl |  8 ++++++++
 2 files changed, 24 insertions(+)

diff --git a/core/kazoo_stdlib/src/kz_date.erl b/core/kazoo_stdlib/src/kz_date.erl
index f922f0ba77d..c0f351675de 100644
--- a/core/kazoo_stdlib/src/kz_date.erl
+++ b/core/kazoo_stdlib/src/kz_date.erl
@@ -15,6 +15,7 @@
         ,to_iso_week/1
 
         ,find_next_weekday/2
+        ,previous_day/1
         ,normalize/1
         ,relative_difference/2
 
@@ -132,6 +133,21 @@ find_next_weekday({Y, M, D}, Weekday) ->
             normalize({Y, M, D + ( 7 - DOW ) + RefDOW})
     end.
 
+%%------------------------------------------------------------------------------
+%% @doc Calculates the date of the previous day, while also handling the situation
+%% where that day falls on the previous month or previous year.
+%% @end
+%%------------------------------------------------------------------------------
+-spec previous_day(kz_time:date()) -> kz_time:date().
+previous_day({Y, 1, 1}) ->
+    {Y-1, 12, days_in_month(Y-1, 12)};
+
+previous_day({Y, M, 1}) ->
+    {Y, M-1, days_in_month(Y, M-1)};
+
+previous_day({Y, M, D}) ->
+    {Y, M, D-1}.
+
 -spec from_iso8601(binary()) -> kz_time:date() | 'error'.
 from_iso8601(<<Year:4/binary, Month:2/binary, Day:2/binary>>) ->
     {kz_term:to_integer(Year), kz_term:to_integer(Month), kz_term:to_integer(Day)};
diff --git a/core/kazoo_stdlib/test/kz_date_tests.erl b/core/kazoo_stdlib/test/kz_date_tests.erl
index e4228273c74..a11d3f41267 100644
--- a/core/kazoo_stdlib/test/kz_date_tests.erl
+++ b/core/kazoo_stdlib/test/kz_date_tests.erl
@@ -14,6 +14,14 @@
 
 -include_lib("eunit/include/eunit.hrl").
 
+prev_date_test_() ->
+    [?_assertEqual({2020,02,02}, kz_date:previous_day({2020,02,03}))
+    ,?_assertEqual({2020,01,31}, kz_date:previous_day({2020,02,01}))
+    ,?_assertEqual({2019,12,31}, kz_date:previous_day({2020,01,01}))
+    ,?_assertEqual({2020,02,29}, kz_date:previous_day({2020,03,01}))
+    ,?_assertEqual({2019,02,28}, kz_date:previous_day({2019,03,01}))
+    ].
+
 pad_month_test_() ->
     [?_assertEqual(<<"10">>, kz_date:pad_month(10))
     ,?_assertEqual(<<"10">>, kz_date:pad_month(<<"10">>))