use std::{
    fs::File,
    io::{BufRead, BufReader},
};

fn main() -> () {
    let path = "input.txt";

    let input = File::open(path).unwrap();
    let buf = BufReader::new(input);

    let score: i32 = buf
        .lines()
        .map(|line| {
            let line = line.unwrap();
            let opponent: i32 = match &line[0..1] {
                "A" => 0,
                "B" => 1,
                "C" => 2,
                _ => panic!("Invalid input"),
            };
            let you: i32 = match &line[2..3] {
                "X" => 0,
                "Y" => 1,
                "Z" => 2,
                _ => panic!("Invalid input"),
            };
            pick_score(you) + win_score(opponent, you)
        })
        .sum();

    println!("{}", score);
}

/// Transforms the "wrapping" cases of RPS into the trivial "middle" case where A wins if A > B
fn normalise_mod3(opponent: i32, you: i32) -> (i32, i32) {
    let i = match opponent {
        0 => 1,
        2 => 2,
        _ => 0,
    };
    ((opponent + i) % 3, (you + i) % 3)
}

/// Get score component for losing (0 points), drawing (3 points) or winning (6 points) the round
fn win_score(opponent: i32, you: i32) -> i32 {
    let (opponent, you) = normalise_mod3(opponent, you);
    let is_won = you - opponent.signum() + 1; // 0 on loss, 1 on draw, 2 on win}
    3 * is_won
}

/// Get score component for your pick (trivial)
fn pick_score(you: i32) -> i32 {
    you + 1
}