Add payment structure

app/models/list_payment.rb

@@ -0,0 +1,16 @@
+class ListPayment
+  include SimplyStored::Couch
+  include ActiveModel::SerializerSupport
+  property :amount
+  property :source # bitcoin, apple_pay, etc...
+  belongs_to :list
+  belongs_to :user
+
+  after_save :close_list_when_is_paid
+  validates :list_id, presence: true
+
+  def close_list_when_is_paid
+    amount_paid = list.list_payments.inject(0.0){|sum, payment| sum + payment.amount}
+    list.close! if amount_paid >= list.price
+  end
+end