add budget investment stats

app/controllers/admin/stats_controller.rb

@@ -52,9 +52,29 @@ class Admin::StatsController < Admin::BaseController
     @users_who_have_sent_message = DirectMessage.select(:sender_id).distinct.count
   end
 
+  def budget_investments
+    votes = Vote.for_budget_investments(Budget::Investment.all)
+    @vote_count = votes.count
+    @participant_count = votes.select(:voter_id).distinct.count
+
+    @voters_in_heading = {}
+    budget = Budget.last
+    budget.headings.each do |heading|
+      @voters_in_heading[heading] = voters_in_heading(heading)
+    end
+  end
+
   def polls
     @polls = ::Poll.current
     @participants = ::Poll::Voter.where(poll: @polls)
   end
 
+  private
+
+    def voters_in_heading(heading)
+      Vote.where(votable_type: "Budget::Investment").
+      includes(:budget_investment).
+      where(budget_investments: { heading_id: heading.id }).
+      select("votes.voter_id").distinct.count
+    end
 end