class BankAccount
  def initialize(balance=0)
    check_balance balance
    @balance = balance
  end

  def withdraw(amt)
    if @balance < amt
      @balance = 0
    else
      @balance -= amt
    end
    amt
  end

  def deposit(amt)
    if amt < 0
      raise "Deposit amoount must be non-megative."
    end
    @balance += amt
  end

  # NOTE: if the getter was named "balance", it'd be better to use: 
  #       attr_reader :balance
  def get_balance
    @balance
  end

  def merge_accounts(account)
    @balance += account.get_balance()
    account.balance = 0
  end

  def to_s
    "$#{@balance.round(2)}"
  end

  protected
  

    # NOTE: could also have the following instead of explicitly defining balance=
    # attr_writer :balance
    
    # Needed to set balance of object argument in merge_accounts 
    # as a non-public method
    def balance= new_balance
      @balance = new_balance
    end

  private
    # NOTE: could use this for other methods that check 
    #       for non-negative values (just would be a less helpful error message)
    def check_balance balance
        if balance < 0
            raise "Can't have negative balance"
        end
    end
end

def use_bank_accounts
  b1 = BankAccount.new()
  b2 = BankAccount.new(25.50)
  puts "Balance of b1: " + b1.to_s
  puts "Balance of b2: " + b2.to_s
  (b3 = BankAccount.new(3.41)).merge_accounts(b2)
  puts "Balance of b3: " + b3.to_s
  puts "Balance of b2: " + b2.to_s
end