Extract model to handle chart data

We're adding it inside the Ahoy module because the Ahoy::DataSource
class is also in that module. We might move it to a different place in
the future.

app/controllers/admin/api/stats_controller.rb

@@ -10,7 +10,7 @@ class Admin::Api::StatsController < Admin::Api::BaseController
     ds = Ahoy::DataSource.new
 
     if params[:event].present?
-      ds.add params[:event].titleize, Ahoy::Event.where(name: params[:event]).group_by_day(:time).count
+      ds.add params[:event].titleize, Ahoy::Chart.new(params[:event]).group_by_day(:time).count
     end
 
     if params[:visits].present?

app/controllers/admin/stats_controller.rb

@@ -1,6 +1,6 @@
 class Admin::StatsController < Admin::BaseController
   def show
-    @event_names = Ahoy::Event.distinct.order(:name).pluck(:name)
+    @event_names = Ahoy::Chart.active_event_names
 
     @visits    = Visit.count
     @debates   = Debate.with_hidden.count
@@ -34,7 +34,7 @@ class Admin::StatsController < Admin::BaseController
     @event = params[:event]
 
     if params[:event]
-      @count = Ahoy::Event.where(name: params[:event]).count
+      @count = Ahoy::Chart.new(params[:event]).count
     else
       @count = params[:count]
     end

app/models/ahoy/chart.rb

@@ -0,0 +1,20 @@
+module Ahoy
+  class Chart
+    attr_reader :event_name
+    delegate :count, :group_by_day, to: :events
+
+    def initialize(event_name)
+      @event_name = event_name
+    end
+
+    def self.active_event_names
+      Ahoy::Event.distinct.order(:name).pluck(:name)
+    end
+
+    private
+
+      def events
+        Ahoy::Event.where(name: event_name)
+      end
+  end
+end