// The `From` trait is used for value-to-value conversions. If `From` is
// implemented, an implementation of `Into` is automatically provided.
// You can read more about it in the documentation:
// https://doc.rust-lang.org/std/convert/trait.From.html
//
// Representing units of measurements with separate types is a common practice.
// It avoids accidentally mixing up values of different units of measurement.

struct Celsius(f64);

struct Fahrenheit(f64);

impl From<Celsius> for Fahrenheit {
    fn from(Celsius(celsius): Celsius) -> Self {
        Fahrenheit(celsius * 1.8 + 32.0)
    }
}

impl From<Fahrenheit> for Celsius {
    fn from(Fahrenheit(fahrenheit): Fahrenheit) -> Self {
        Celsius((fahrenheit - 32.0) / 1.8)
    }
}

fn main() {
    // You can optionally experiment here.
}

#[cfg(test)]
mod tests {
    use super::*;

    const CASES: [(f64, f64); 6] = [
        (-50.0, -58.0),
        (0.0, 32.0),
        (20.0, 68.0),
        (100.0, 212.0),
        (400.0, 752.0),
        (1000.0, 1832.0),
    ];

    #[test]
    fn celsius_to_fahrenheit() {
        for (celsius, fahrenheit) in CASES {
            let Fahrenheit(actual) = Celsius(celsius).into();
            assert_eq!(actual.round(), fahrenheit);
        }
    }

    #[test]
    fn fahrenheit_to_celsius() {
        for (celsius, fahrenheit) in CASES {
            let Celsius(actual) = Fahrenheit(fahrenheit).into();
            assert_eq!(actual.round(), celsius);
        }
    }
}