tab/app/models/transaction.rb

# == Schema Information
#
# Table name: transactions
#
#  id           :integer          not null, primary key
#  debtor_id    :integer          not null
#  creditor_id  :integer          not null
#  issuer_id    :integer          not null
#  issuer_type  :string           not null
#  amount       :integer          default(0), not null
#  message      :string
#  created_at   :datetime         not null
#  updated_at   :datetime         not null
#  id_at_client :integer
#

class Transaction < ActiveRecord::Base
  include BaseTransaction
  include TransactionHelpers

  after_save    :recalculate_balances!
  after_destroy :recalculate_balances!

  validates :id_at_client, presence: true, uniqueness: { scope: :issuer_id }, if: :is_client_transaction?

  def signed_amount_for(user)
    return -amount if user == debtor
    return amount if user == creditor
  end

  def reverse
    self.creditor, self.debtor = self.debtor, self.creditor
    self.amount *= -1
  end

  private

  def recalculate_balances!
    creditor.calculate_balance!
    debtor.calculate_balance!
  end
end