Refactor to prepare for getting monthly overview

app/models/reading.rb

@@ -76,6 +76,14 @@ class Reading < ActiveRecord::Base
       @@max_charge_kwh
     end
     
+    # do not make distinction between high and low consumption/production
+    def consumed_and_produced_for_diff(d)
+
+      usage_kwh = (d[:total_kwh_consumed_high].nil? || d[:total_kwh_consumed_low].nil?) ? nil :  d[:total_kwh_consumed_high] + d[:total_kwh_consumed_low] 
+      return_kwh = (d[:total_kwh_produced_high].nil? || d[:total_kwh_produced_low].nil?) ? nil : d[:total_kwh_produced_high] + d[:total_kwh_produced_low]
+
+      return usage_kwh, return_kwh
+    end
     
     def diff_on(date)
       readings_on = day(date)
@@ -87,5 +95,16 @@ class Reading < ActiveRecord::Base
         { :total_kwh_consumed_high => 0, :total_kwh_consumed_low => 0, :total_kwh_produced_high => 0, :total_kwh_produced_low => 0, :total_m3_gas_consumed => 0 }
       end
     end
+
+    def diff_between(from_date, to_date)
+      readings_on_days = days(from_date, to_date)
+      first = readings_on_days.first
+      last = readings_on_days.last
+      if last
+        last.diff(first)
+      else
+        { :total_kwh_consumed_high => 0, :total_kwh_consumed_low => 0, :total_kwh_produced_high => 0, :total_kwh_produced_low => 0, :total_m3_gas_consumed => 0 }
+      end
+    end
   end
 end