Fix caching of winning alternative

lib/split/dashboard/views/_experiment.erb

@@ -4,9 +4,7 @@
   <% experiment_class = "experiment" %>
 <% end %>
 
-<% unless experiment.calc_time == Time.now.day %>
-  <% experiment.estimate_winning_alternative %>
-<% end %>
+<% experiment.calc_winning_alternatives %>
 
 <div class="<%= experiment_class %>">
   <div class="experiment-header">

lib/split/experiment.rb

@@ -274,17 +274,22 @@ def load_from_redis
     end
 
     def calc_winning_alternatives
-      if goals.empty?
-        self.estimate_winning_alternative
-      else
-        goals.each do |goal|
-          self.estimate_winning_alternative(goal)
+      # Super simple cache so that we only recalculate winning alternatives once per day
+      days_since_epoch = Time.now.utc.to_i / 86400
+
+      if self.calc_time != days_since_epoch
+        if goals.empty?
+          self.estimate_winning_alternative
+        else
+          goals.each do |goal|
+            self.estimate_winning_alternative(goal)
+          end
         end
-      end
 
-      calc_time = Time.now.day
+        self.calc_time = days_since_epoch
 
-      self.save
+        self.save
+      end
     end
 
     def estimate_winning_alternative(goal = nil)
@@ -390,7 +395,7 @@ def calc_time=(time)
     end
 
     def calc_time
-      Split.redis.hget(experiment_config_key, :calc_time)
+      Split.redis.hget(experiment_config_key, :calc_time).to_i
     end
 
     def jstring(goal = nil)

spec/experiment_spec.rb

@@ -428,6 +428,13 @@ def same_but_different_goals
       p_goal2 = alt.p_winner(goal2)
       expect(p_goal1).not_to be_within(0.04).of(p_goal2)
     end
+
+    it "should return nil and not re-calculate probabilities if they have already been calculated today" do
+      experiment = Split::ExperimentCatalog.find_or_create({'link_color3' => ["purchase", "refund"]}, 'blue', 'red', 'green')
+      experiment_calc_time = Time.now.utc.to_i / 86400
+      experiment.calc_time = experiment_calc_time
+      expect(experiment.calc_winning_alternatives).to be nil
+    end
   end
 
 end