move model validation into pattern classes and link from recurring_todo model

app/models/recurring_todos/monthly_repeat_pattern.rb

@@ -6,12 +6,49 @@ module RecurringTodos
       super user
     end
 
+    def recurrence_selector
+      get :recurrence_selector
+    end
+
     def every_x_day?
-      @recurring_todo.recurrence_selector == 0
+      get(:recurrence_selector) == 0
     end
 
     def every_xth_day?
-      @recurring_todo.recurrence_selector == 1
+      get(:recurrence_selector) == 1
+    end
+
+    def every_x_month
+      # in case monthly pattern is every day x, return every_other2 otherwise
+      # return a default value
+      get(:recurrence_selector) == 0 ? get(:every_other2) : 1
+    end
+
+    def every_x_month2
+      # in case monthly pattern is every xth day, return every_other2 otherwise
+      # return a default value
+      get(:recurrence_selector) == 1 ? get(:every_other2) : 1
+    end
+
+    def every_xth_day(default=nil)
+      get(:every_other3) || default
+    end
+
+    def day_of_week
+      get :every_count
+    end
+
+    def validate
+      super
+      case recurrence_selector
+      when 0 # 'monthly_every_x_day'
+        errors[:base] << "Every other nth month may not be empty for recurrence setting" if every_x_month.blank?
+      when 1 # 'every_xth_day'
+        errors[:base] <<"Every other nth month may not be empty for recurrence setting" if every_x_month2.blank?
+        errors[:base] <<"The day of the month may not be empty for recurrence setting" if day_of_week.blank?
+      else
+        raise Exception.new, "unexpected value of recurrence selector '#{recurrence_selector}'"
+      end
     end
 
   end