Add a Summary and Ranking

app/controllers/summaries_controller.rb

@@ -0,0 +1,11 @@
+class SummariesController < ApplicationController
+  def show
+    @summary = Summary.new summary_params
+  end
+
+  private
+
+  def summary_params
+    params.require(:summary).permit(talk_ids: [])
+  end
+end

app/models/ranking.rb

@@ -0,0 +1,45 @@
+RankingEntry = Struct.new :talk_id, :votes, :place
+
+class Ranking
+  include ActiveModel::Model
+
+  attr_accessor :talk_ids
+
+  def ranking
+    @ranking ||= ranking_data.map do |talk_id, votes, place|
+      RankingEntry.new talk_id, votes, place
+    end
+  end
+
+  def [](talk_id)
+    ranking[talk_id]
+  end
+
+  def talk_ids
+    @talk_ids ||= []
+  end
+
+  private
+
+  def ranking_data
+    vote_data.sort_by { |_, votes| -votes }
+             .group_by { |_, votes| votes }
+             .each_with_index.map do |votes, placement|
+               votes.last.map {|talk_vote_data| talk_vote_data << placement + 1 }
+             end.flatten(1)
+  end
+
+  def vote_data
+    blank_vote_data.merge(database_vote_data)
+  end
+
+  def blank_vote_data
+    talk_ids.map do |talk_id|
+      [talk_id, 0]
+    end.to_h
+  end
+
+  def database_vote_data
+    SelectedTalk.group(:talk_id).where(talk_id: @talk_ids).count
+  end
+end

app/models/summary.rb

@@ -0,0 +1,15 @@
+class Summary
+  include ActiveModel::Model
+
+  attr_accessor :talk_ids
+
+  def number_of_ballots
+    @number_of_ballots ||= TalkPreference.joins(:selected_talks)
+                                         .where(selected_talks: {talk_id: @talk_ids})
+                                         .uniq.count
+  end
+
+  def ranking
+    @ranking ||= Ranking.new(talk_ids: talk_ids).ranking
+  end
+end

app/views/summaries/show.json.jbuilder

@@ -0,0 +1 @@
+json.extract! @summary, :number_of_ballots, :ranking

config/routes.rb

@@ -1,5 +1,6 @@
 Rails.application.routes.draw do
   resources :talk_preferences, only: [:index, :show, :create, :update]
   root to: 'home#index'
+  resource :summary, only: :show
   # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
 end