misc: small refactoring regarding caching and event stores

app/services/events/stores/base_store.rb

@@ -71,13 +71,25 @@ def prorated_sum(period_duration:, persisted_duration: nil)
         raise NotImplementedError
       end
 
+      def grouped_prorated_sum(period_duration:, persisted_duration: nil)
+        raise NotImplementedError
+      end
+
       # NOTE: returns the breakdown of the sum grouped by date
       #       The result format will be an array of hash with the format:
       #       [{ date: Date.parse('2023-11-27'), value: 12.9 }, ...]
       def sum_date_breakdown
         raise NotImplementedError
       end
 
+      def weighted_sum(initial_value: 0)
+        raise NotImplementedError
+      end
+
+      def grouped_weighted_sum(initial_values: [])
+        raise NotImplementedError
+      end
+
       def from_datetime
         boundaries[:from_datetime]
       end

app/services/invoices/customer_usage_service.rb

@@ -115,12 +115,7 @@ def compute_amounts
     end
 
     def charge_cache_key(charge)
-      [
-        'charge-usage',
-        charge.id,
-        subscription.id,
-        charge.updated_at.iso8601,
-      ].join('/')
+      Subscriptions::ChargeCacheService.new(subscription:, charge:).cache_key
     end
 
     def charge_cache_expiration