rock-paper-scissors.rs

use std::error::Error;

#[derive(PartialEq)]
enum MyGameResult {
    Win,
    Lose,
    Tie
}

#[derive(Debug, PartialEq, Clone, Copy)]
enum Shape {
    Rock = 0,
    Paper = 1,
    Scissors = 2,
}

impl Shape {

    fn get_winning_move_for_opponent(&self) -> Self {
        let self_u8 = *self as u8;
        Shape::try_from((&self_u8 + 2) % 3).unwrap()
    }

    fn get_losing_move_for_opponent(&self) -> Self {
        let self_u8 = *self as u8;
        Shape::try_from((self_u8 + 1) % 3).unwrap()
    }

}

impl std::convert::TryFrom<u8> for Shape {
    type Error = Box<dyn Error>;

    fn try_from(value: u8) -> Result<Self, Self::Error>{
        match value {
            0 => Ok(Shape::Rock),
            1 => Ok(Shape::Paper),
            2 => Ok(Shape::Scissors),
            _ => Err(format!("invalid shape: {}", value).into()),
        }
    }
}

fn vs(me: Shape, opponent: Shape) -> MyGameResult {

    let winning_move_for_opponent = me.get_winning_move_for_opponent();
    let losing_move_for_opponent = me.get_losing_move_for_opponent();

    println!("me: {me:?}, opponent: {opponent:?}, winning_move_for_opponent: {winning_move_for_opponent:?}, losing_move_for_opponent: {losing_move_for_opponent:?}");

    match opponent {
        x if x == losing_move_for_opponent => MyGameResult::Lose,
        x if x == winning_move_for_opponent => MyGameResult::Win,
        x if x == me => MyGameResult::Tie,
        _ => unreachable!()
    }
}

fn main() {

    // Wins
    assert!(vs(Shape::Scissors, Shape::Paper) == MyGameResult::Win); // "Scissors cuts Paper"
    assert!(vs(Shape::Paper, Shape::Rock) == MyGameResult::Win); // "Paper covers Rock"
    assert!(vs(Shape::Rock, Shape::Scissors) == MyGameResult::Win); // "Rock crushes Scissors"

    // Ties
    assert!(vs(Shape::Rock, Shape::Rock) == MyGameResult::Tie);
    assert!(vs(Shape::Paper, Shape::Paper) == MyGameResult::Tie);
    assert!(vs(Shape::Scissors, Shape::Scissors) == MyGameResult::Tie);

    // One Example Loss
    assert!(vs(Shape::Scissors, Shape::Rock) == MyGameResult::Lose);

}