Simplify discount budget calculation

lib/planet_express_express/discount_budget.rb

@@ -5,59 +5,15 @@ module PlanetExpressExpress
     end
 
     def limit_discounts(shipments)
-      keys = shipments.keys
-      positions = Array.new(keys.length, 0)
+      shipments[:all].each do |month|
+        available_budget = @limit_per_month
 
-      # We expect all keys to have the same length
-      total_length = shipments[keys.first].length
-
-      for month in 0..(total_length - 1) do
-        reset_positions(positions)
-        budget = @limit_per_month
-
-        while true
-          # Find the next shipment
-          min_index = Float::INFINITY
-          next_val = nil # key_index
-
-          for key_index in 0..(keys.length - 1) do
-            current_position = positions[key_index]
-
-            shipment = shipments[keys[key_index]][month][current_position]
-            next if shipment.nil?
-
-            if shipment[:id] < min_index
-              next_val = key_index
-              min_index = shipment[:id]
-            end
-          end
-
-          break if next_val.nil?
-          # End find the next shipment
-
-          shipment = shipments[keys[next_val]][month][positions[next_val]]
-          positions[next_val] = positions[next_val] + 1
-
-          budget = apply_discount(budget, shipment)
-        end
-      end
-    end
-
-    private
-
-    attr_reader :limit_per_month
-
-    def apply_discount(available_budget, shipment)
+        month.each do |shipment|
           if shipment[:discount] > available_budget
             shipment[:discount] = available_budget
-        return 0
           end
-      available_budget - shipment[:discount]
+          available_budget = available_budget - shipment[:discount]
         end
-
-    def reset_positions(positions)
-      for i in 0..(positions.length - 1) do
-        positions[i] = 0
       end
     end
   end