use std::ops::Mul;

trait Volume {
    /// Returns the volume in SI units (cubic metres).
    fn si(self) -> CubicMetre;
}

#[derive(Debug, PartialEq)]
struct CubicMetre(f64);

#[derive(Debug, PartialEq)]
struct Litre(f64);

impl Volume for Litre {
    fn si(self) -> CubicMetre {
        CubicMetre(self.0 * 10_f64.powf(-3.))
    }
}

impl From<i32> for Litre {
    fn from(value: i32) -> Self {
        Self(value as f64)
    }
}

impl From<CubicMetre> for Litre {
    fn from(value: CubicMetre) -> Self {
        Self(value.0 * 10_f64.powf(3.))
    }
}

impl Mul<f64> for Litre {
    type Output = Self;

    fn mul(self, rhs: f64) -> Self::Output {
        Self(self.0 * rhs)
    }
}

#[cfg(test)]
mod tests {
    use crate::volume::{CubicMetre, Litre, Volume};

    #[test]
    fn litre_to_cubic_metre() {
        assert_eq!(Litre(1000.).si(), CubicMetre(1.))
    }

    #[test]
    fn cubic_metre_to_litre() {
        assert_eq!(Litre::from(CubicMetre(1.)), Litre(1000.))
    }
}