fix(alerts): Provide all applicable service ranges when only given start time (#3440)

Author: jlucytan

lib/dotcom/utils/service_date_time.ex

@@ -244,12 +244,17 @@ defmodule Dotcom.Utils.ServiceDateTime do
 
   @doc """
   Returns service ranges between two datetimes, inclusive.
-  One datetime can be given, which will return only the service range for the given datetime.
+  If only the stop datetime is provided, returns the service range for that datetime.
+  If only the start datetime is provided, returns all service ranges from that datetime onward.
   """
   @spec service_range_range(DateTime.t() | nil, DateTime.t() | nil) :: [named_service_range()]
   def service_range_range(nil, nil), do: []
-  def service_range_range(start, nil) when not is_nil(start), do: [service_range(start)]
-  def service_range_range(nil, stop) when not is_nil(stop), do: [service_range(stop)]
+  def service_range_range(nil, stop), do: [service_range(stop)]
+
+  def service_range_range(start, nil) do
+    all_service_ranges()
+    |> Enum.drop_while(&(&1 != service_range(start)))
+  end
 
   def service_range_range(start, stop) do
     start_index = service_range_index(start)

test/dotcom/utils/service_date_time_test.exs

@@ -241,20 +241,20 @@ defmodule Dotcom.Utils.ServiceDateTimeTest do
       assert service_range_range(today, next_week) == [:today, :this_week, :next_week]
     end
 
-    test "returns one service range when given only one start datetime" do
+    test "returns one service range when given only one stop datetime" do
       # Setup
       next_week = service_range_next_week() |> random_time_range_date_time()
 
       # Exercise / Verify
-      assert service_range_range(next_week, nil) == [:next_week]
+      assert service_range_range(nil, next_week) == [:next_week]
     end
 
-    test "returns one service range when given only one stop datetime" do
+    test "returns all service ranges from the start datetime onward when given only one start datetime" do
       # Setup
       next_week = service_range_next_week() |> random_time_range_date_time()
 
       # Exercise / Verify
-      assert service_range_range(nil, next_week) == [:next_week]
+      assert service_range_range(next_week, nil) == [:next_week, :after_next_week]
     end
   end