Refactor date lookup

lib/day.rb

@@ -3,23 +3,17 @@
 class Day < Sequel::Model
   dataset_module do
     def latest(date = Date.today)
-      where(date: select(:date).where(Sequel[:date] <= date)
-                               .order(Sequel.desc(:date))
-                               .limit(1))
+      where(date: _nearest_date_with_rates(date))
     end
 
-    # Returns rates for a given date interval
-    #
-    # If the start date falls on a holiday/weekend, rates start from the closest preceding business day.
     def between(interval)
       return where(false) if interval.begin > Date.today
 
-      previous_date = select(:date)
-        .where(Sequel[:date] <= interval.begin)
-        .order(Sequel.desc(:date))
-        .limit(1)
-
-      where(Sequel.expr(:date) >= Sequel.function(:coalesce, previous_date, interval.begin))
+      where(Sequel.expr(:date) >= Sequel.function(
+        :coalesce,
+        _nearest_date_with_rates(interval.begin),
+        interval.begin,
+      ))
         .where(Sequel.expr(:date) <= interval.end)
     end
 
@@ -31,5 +25,12 @@ class Day < Sequel::Model
       )
         .join(Sequel.function(:jsonb_each, :rates).lateral.as(:rates), true)
     end
+
+    def _nearest_date_with_rates(date)
+      select(:date)
+        .where(Sequel[:date] <= date)
+        .order(Sequel.desc(:date))
+        .limit(1)
+    end
   end
 end