# The Expense class is an account type used to represents assets or services consumed in the generation of revenue.
#
# === Normal Balance
# The normal balance on Expense accounts is a *Debit*. 
#
# @see http://en.wikipedia.org/wiki/Expense Expenses
#
# @author Michael Bulat
class Expense < Account
  
  # The credit balance for the account.
  # 
  # @example
  #   >> expense.credits_balance
  #   => #<BigDecimal:103259bb8,'0.1E4',4(12)> 
  #
  # @return [BigDecimal] The decimal value credit balance
  def credits_balance
    credits_balance = BigDecimal.new('0')
    credit_transactions.each do |credit_transaction|
      credits_balance = credits_balance + credit_transaction.amount
    end
    return credits_balance
  end

  # The debit balance for the account.
  # 
  # @example
  #   >> expense.debits_balance
  #   => #<BigDecimal:103259bb8,'0.3E4',4(12)> 
  #
  # @return [BigDecimal] The decimal value credit balance
  def debits_balance
    debits_balance = BigDecimal.new('0')
    debit_transactions.each do |debit_transaction|
      debits_balance = debits_balance + debit_transaction.amount
    end
    return debits_balance
  end
  
  # The balance of the account.
  #
  # Expenses have normal debit balances, so the credits are subtracted from the debits
  # unless this is a contra account, in which debits are subtracted from credits
  # 
  # @example
  #   >> expense.balance
  #   => #<BigDecimal:103259bb8,'0.2E4',4(12)> 
  #
  # @return [BigDecimal] The decimal value balance
  def balance
    unless contra
      debits_balance - credits_balance
    else
      credits_balance - debits_balance
    end
  end  
  
  # This class method is used to return
  # the balance of all Expense accounts.
  #
  # Contra accounts are automatically subtracted from the balance.
  #
  # @example
  #   >> Expense.balance
  #   => #<BigDecimal:1030fcc98,'0.82875E5',8(20)>
  #
  # @return [BigDecimal] The decimal value balance
  def self.balance
    accounts_balance = BigDecimal.new('0') 
    accounts = self.find(:all)
    accounts.each do |expense|
      unless expense.contra
        accounts_balance += expense.balance
      else
        accounts_balance -= expense.balance
      end
    end
    accounts_balance
  end  
end