remove week_of_month dependency

we only used it for one thing, and honestly with all of the dynamic
method dispatch it's not clear what it's even doing, so just do the
math ourselves

Change-Id: I17b601732d7b6e5e2236eb01e9ef368fc9d1fa89
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/326665
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
Build-Review: Cody Cutrer <cody@instructure.com>

Gemfile.d/app.rb

@@ -127,10 +127,6 @@ gem "twilio-ruby", "~> 6.4", require: false
 gem "vault", "~> 0.17", require: false
 gem "vericite_api", "1.5.3"
 gem "wcag_color_contrast", "0.1.0"
-gem "week_of_month",
-    "1.2.5",
-    github: "instructure/week-of-month",
-    ref: "b3013639e9474f302b5a6f27e4e45313e8d24902"
 
 gem "faraday", "~> 2.7"
 

Gemfile.lock

@@ -6,13 +6,6 @@ GIT
     ffi-icu (0.4.0)
       ffi (~> 1.0, >= 1.0.9)
 
-GIT
-  remote: https://github.com/instructure/week-of-month.git
-  revision: b3013639e9474f302b5a6f27e4e45313e8d24902
-  ref: b3013639e9474f302b5a6f27e4e45313e8d24902
-  specs:
-    week_of_month (1.2.5)
-
 GIT
   remote: https://github.com/kreynolds/cassandra-cql.git
   revision: 02b5abbe441a345c051a180327932566fd66bb36
@@ -1368,7 +1361,6 @@ DEPENDENCIES
   vericite_api (= 1.5.3)
   wcag_color_contrast (= 0.1.0)
   webmock (~> 3.18)
-  week_of_month (= 1.2.5)!
   workflow!
   yard (~> 0.9)
   yard-appendix (= 0.1.8)

config/initializers/switchman.rb

@@ -159,23 +159,45 @@ Rails.application.config.after_initialize do
     def next_maintenance_window
       return nil unless maintenance_window_start_hour
 
-      start_day = DateTime.now
-      # This array is effectively 1 indexed
-      relevant_weeks = maintenance_window_weeks_of_month.map { |i| WeekOfMonth::Constant::WEEKS_IN_SEQUENCE[i] }
-      maintenance_days = relevant_weeks.map do |ordinal|
-        start_day.send("#{ordinal}_#{maintenance_window_weekday}_in_month".downcase)
-      end + relevant_weeks.map do |ordinal|
-        (start_day + 1.month).send("#{ordinal}_#{maintenance_window_weekday}_in_month".downcase)
+      now = Time.now.utc
+      date = nil
+      weekday = maintenance_window_weekday
+      weeks = maintenance_window_weeks_of_month
+      loop do
+        first_date = first_given_weekday_of_month(weekday, now)
+        # look at the 1st, 3rd, etc. weekday of this month, and see if it's in the future
+        weeks.each do |i|
+          new_date = first_date.advance(weeks: i - 1)
+          # make sure we didn't overrun the current month, like if there's not a 5th thursday this month
+          if new_date.future? && new_date.month == now.month
+            date = new_date
+            break
+          end
+        end
+
+        break if date
+
+        # search the next month
+        now = now.next_month
       end
 
-      next_day = maintenance_days.find(&:future?)
       # Time offsets are strange
-      start_at = next_day.utc.beginning_of_day - maintenance_window_start_hour.hours + maintenance_window_offset.minutes
+      start_at = date.beginning_of_day - maintenance_window_start_hour.hours + maintenance_window_offset.minutes
       end_at = start_at + maintenance_window_duration
 
       [start_at, end_at]
     end
 
+    # Finds the first day of the month that is a given weekday
+    #
+    # @param [Integer] which weekday we're looking for
+    # @param [Time] start_ref the month to look in
+    def first_given_weekday_of_month(weekday, start_ref)
+      date = start_ref.beginning_of_month
+      date = date.next_day until date.wday == weekday
+      date
+    end
+
     def maintenance_window_start_hour
       Setting.get("maintenance_window_start_hour", nil)&.to_i
     end
@@ -189,12 +211,15 @@ Rails.application.config.after_initialize do
       ActiveSupport::Duration.parse(Setting.get("maintenance_window_duration", "PT2H"))
     end
 
+    # @return [Integer] the weekday of the maintenance window
     def maintenance_window_weekday
-      Setting.get("maintenance_window_weekday", "thursday").downcase
+      Date::DAYNAMES.index(Setting.get("maintenance_window_weekday", "thursday").capitalize)
     end
 
+    # @return [Array<Integer>]
+    #   the weeks of the month that the maintenance window occurs on, sorted and 1-indexed
     def maintenance_window_weeks_of_month
-      Setting.get("maintenance_window_weeks_of_month", "1,3").split(",").map(&:to_i)
+      Setting.get("maintenance_window_weeks_of_month", "1,3").split(",").map(&:to_i).sort
     end
 
     def self.send_in_each_region(klass, method, enqueue_args, *args, **kwargs)