// Only knows about rates
// `pallet-interest-accrual` only implement this trait
trait InterestAccrual {
    type RateData;

    fn get_rate(rate_per_year) -> RateData; // RateData will be (Rate, Rate) for the current impl.
    fn reference_rate(rate_per_year);
    fn unreference_rate(rate_per_year);
}

// Knows about debt.
// Nobody implemented this. 
// Adds a new layer of debt for free to any InterestAccrual.
trait DebtAccrual: InterestAccrual {
    fn current_debt(rate_per_year, norm_debt) -> Balance {
        // Default impl at the trait level
    }
    fn adjust_debt(rate_per_year, norm_debt, value) -> Balance {
        // Default impl at the trait level
    }
    fn normalize(rate_per_year, norm_debt, value) -> Balance {
        // Default impl at the trait level
    }
}

// This trait comes free
impl<T: InterestAccrual> DebtAccrual for T {}