From c1bf9f51d9592f4eee4c6e48cd01fef78068ded4 Mon Sep 17 00:00:00 2001
From: Shota Iguchi <shota-iguchi@cookpad.com>
Date: Sat, 24 Sep 2016 00:22:59 +0900
Subject: [PATCH] Add next occur and previous occurred day of week API

---
 activesupport/CHANGELOG.md                    |  4 ++++
 .../core_ext/date_and_time/calculations.rb    | 16 ++++++++++++++
 .../test/core_ext/date_time_ext_test.rb       | 22 +++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index bb578d81dc917..63061302426ad 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add `Date#prev_occurring` and `Date#next_occurring` to return specified next/previous occurring day of week.
+
+    *Shota Iguchi*
+
 *   Add default option to class_attribute. Before:
 
       class_attribute :settings
diff --git a/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb b/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb
index f2ba7fdda51a0..e2e1d3e359147 100644
--- a/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb
+++ b/activesupport/lib/active_support/core_ext/date_and_time/calculations.rb
@@ -320,6 +320,22 @@ def all_year
       beginning_of_year..end_of_year
     end
 
+    # Returns specific next occurring day of week
+    def next_occurring(day_of_week)
+      current_day_number = wday != 0 ? wday - 1 : 6
+      from_now = DAYS_INTO_WEEK.fetch(day_of_week) - current_day_number
+      from_now += 7 unless from_now > 0
+      since(from_now.days)
+    end
+
+    # Returns specific previous occurring day of week
+    def prev_occurring(day_of_week)
+      current_day_number = wday != 0 ? wday - 1 : 6
+      ago = current_day_number - DAYS_INTO_WEEK.fetch(day_of_week)
+      ago += 7 unless ago > 0
+      ago(ago.days)
+    end
+
     private
       def first_hour(date_or_time)
         date_or_time.acts_like?(:time) ? date_or_time.beginning_of_day : date_or_time
diff --git a/activesupport/test/core_ext/date_time_ext_test.rb b/activesupport/test/core_ext/date_time_ext_test.rb
index be7c14e9b4ffb..276fa2bfd3aac 100644
--- a/activesupport/test/core_ext/date_time_ext_test.rb
+++ b/activesupport/test/core_ext/date_time_ext_test.rb
@@ -28,6 +28,28 @@ def test_to_s
     end
   end
 
+  def test_next_occur
+    datetime = DateTime.new(2016, 9, 24, 0, 0) # saturday
+    assert_equal datetime.next_occurring(:monday), datetime.since(2.days)
+    assert_equal datetime.next_occurring(:tuesday), datetime.since(3.days)
+    assert_equal datetime.next_occurring(:wednesday), datetime.since(4.days)
+    assert_equal datetime.next_occurring(:thursday), datetime.since(5.days)
+    assert_equal datetime.next_occurring(:friday), datetime.since(6.days)
+    assert_equal datetime.next_occurring(:saturday), datetime.since(1.week)
+    assert_equal datetime.next_occurring(:sunday), datetime.since(1.day)
+  end
+
+  def test_prev_occur
+    datetime = DateTime.new(2016, 9, 24, 0, 0) # saturday
+    assert_equal datetime.prev_occurring(:monday), datetime.ago(5.days)
+    assert_equal datetime.prev_occurring(:tuesday), datetime.ago(4.days)
+    assert_equal datetime.prev_occurring(:wednesday), datetime.ago(3.days)
+    assert_equal datetime.prev_occurring(:thursday), datetime.ago(2.days)
+    assert_equal datetime.prev_occurring(:friday), datetime.ago(1.day)
+    assert_equal datetime.prev_occurring(:saturday), datetime.ago(1.week)
+    assert_equal datetime.prev_occurring(:sunday), datetime.ago(6.days)
+  end
+
   def test_readable_inspect
     datetime = DateTime.new(2005, 2, 21, 14, 30, 0)
     assert_equal "Mon, 21 Feb 2005 14:30:00 +0000", datetime.readable_inspect