#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum Play {
    Rock = 1,
    Paper = 2,
    Scissors = 3,
}

#[derive(Debug, PartialEq, Eq)]
pub struct Strategy {
    pub elf: Play,
    pub you: Play,
}

pub fn calc_score(input: &Strategy) -> usize {
    //an enum wins if (you-elf)%3 = 1, looses if it = 2
    (match (input.you as i8 - input.elf as i8).rem_euclid(3) {
        1 => 6,
        2 => 0,
        0 => 3,
        _ => unreachable!("you were {}, elf was {}", input.you as i8, input.elf as i8),
    }) + input.you as usize //play enum has value corresponding to its score.
}

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

    #[test]
    fn test_calc_score() {
        let input = Strategy {
            elf: Play::Scissors,
            you: Play::Scissors,
        };
        assert_eq!(calc_score(&input), 6);
    }
}