Fix tickets turnover calculation

app/models/ticket.rb

@@ -61,12 +61,10 @@ class Ticket < ApplicationRecord
   end
 
   def tickets_turnover_total(id)
-    tickets = TicketPurchase.where(ticket_id: id).paid
-    if tickets.blank?
-      Money.new(0, Ticket.find(id).price_currency)
-    else
-      tickets.inject(Money.new(0, tickets.first.price_currency)){ |sum, ticket| sum + (ticket.amount_paid * ticket.quantity) }
-    end
+    ticket = Ticket.find(id)
+    return Money.new(0, 'USD') unless ticket
+    sum = ticket.ticket_purchases.paid.total
+    Money.new(sum, ticket.price_currency)
   end
 
   def tickets_sold

app/models/ticket_purchase.rb

@@ -69,6 +69,11 @@ class TicketPurchase < ApplicationRecord
     purchase
   end
 
+  # Total amount
+  def self.total
+    sum('amount_paid * quantity')
+  end
+
   def pay(payment)
     update_attributes(paid: true, payment: payment)
     PhysicalTicket.transaction do

spec/models/ticket_spec.rb

@@ -65,6 +65,17 @@ describe Ticket do
     end
   end
 
+  describe '#tickets_turnover_total' do
+    let!(:purchase1) { create :ticket_purchase, ticket: ticket, amount_paid: 5_000, quantity: 1, paid: true, user: user }
+    let!(:purchase2) { create :ticket_purchase, ticket: ticket, amount_paid: 5_000, quantity: 2, paid: true, user: user }
+    let!(:purchase3) { create :ticket_purchase, ticket: ticket, amount_paid: 5_000, quantity: 10, paid: false, user: user }
+    subject { ticket.tickets_turnover_total ticket.id }
+
+    it 'returns turnover as Money with ticket\'s currency' do
+      is_expected.to eq Money.new(5_000 * 3, ticket.price_currency)
+    end
+  end
+
   describe '#unpaid?' do
     let!(:ticket_purchase) { create(:ticket_purchase, user: user, ticket: ticket) }