fill out RecurringDonation model with basic functionality

app/models/items/recurring_donation.rb

@@ -4,6 +4,28 @@ class RecurringDonation < Item
   belongs_to :customer
   has_many :donations, foreign_key: :recurring_donation_id
 
-  def one_line_description ; end
-  def description_for_audit_txn ; end
+  def first_donation
+    Donation.where(recurring_donation_id: id).order(sold_on: :asc).first
+  end
+
+  def monthly_amount
+    donation = first_donation
+    donation ? donation.amount : nil 
+  end
+
+  def total_amount_received
+    Donation.where(recurring_donation_id: id).sum(:amount)
+  end
+
+  def one_line_description(opts={})
+    if opts[:suppress_price]
+      "Recurring Donation to #{account_code.name}"
+    else
+      sprintf("$%6.2f Recurring Donation to %s ($%6.2f received in total)", monthly_amount, account_code.name, total_amount_received)
+    end
+  end
+
+  def description_for_audit_txn
+    sprintf("%.2f %s recurring donation [%d]", monthly_amount, account_code.name, id)
+  end
 end