gistfile1.rb

module Ledger::Balance
 
  def balance(transaction=nil)
    sum_of_credits(transaction) - sum_of_debits(transaction)
  end
 
  def amount_available(transaction=nil)
    self.balance(transaction)
  end
 
  def spent
    sum_of_debits
  end
 
protected
 
  def sum_of_credits(transaction=nil)
    credits_sum = Ledger::Credit.select('COALESCE(SUM(credit),0) as credit').where(destination: self)
    credits_sum = credits_sum.where('transaction_id <= ?', transaction) if transaction
    
    credits_sum.first.credit
  end
 
  def sum_of_debits(transaction=nil)
    debits_sum = Ledger::Debit.select('COALESCE(SUM(debit),0) as debit').where(destination: self)
    debits_sum = credits_sum.where('transaction_id <= ?', transaction) if transaction
    
    debits_sum.first.debit
  end
end