public Coupon(int discount, DateTime expiry)
{
if (expiry < DateTime.Today)
{
throw new ArgumentException("Coupon must be constructed with valid expiry date");
}
_expiry = expiry;
_discount = discount;
// Because coupon states are internal, we will
// couple them with the specific states so they
// are highly cohesive. For this implementation,
// we will construct on state change.
_currentState = new ValidCouponState();
}
public void SetCouponState(ICouponState state)
{
_currentState = state;
}
