2022/src/bin/day02.rs

use std::str::FromStr;

use aoc_2022::*;

use color_eyre::eyre::Result;
use thiserror::Error;
use tracing::*;
use tracing_subscriber::EnvFilter;

#[derive(Debug, Clone, Copy)]
enum Shape {
    Rock,
    Paper,
    Scissors,
}

impl Shape {
    fn score(&self) -> i32 {
        match self {
            Shape::Rock => 1,
            Shape::Paper => 2,
            Shape::Scissors => 3,
        }
    }
}

#[derive(Error, Debug)]
enum ShapeError {
    #[error("empty string given")]
    Empty,
    
    #[error("unknown shape ‹{0}›")]
    UnknownShape(String),
}

impl FromStr for Shape {
    type Err = ShapeError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.is_empty() {
            return Err(ShapeError::Empty);
        }

        match s {
            "A" | "X" => Ok(Shape::Rock),
            "B" | "Y" => Ok(Shape::Paper),
            "C" | "Z" => Ok(Shape::Scissors),
            _ => Err(ShapeError::UnknownShape(s.to_string())),
        }
    }
}

#[derive(Debug, Clone, Copy)]
enum Outcome {
    Lose,
    Draw,
    Win,
}

#[derive(Debug, Clone, Copy)]
struct Round {
    opponent: Shape,
    me: Shape,
}

#[derive(Error, Debug)]
enum RoundError {
    #[error("invalid shape ‹{0}›")]
    InvalidShape(#[from] ShapeError),
}

impl FromStr for Round {
    type Err = RoundError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let mut split_str = s.split(' ');

        let opponent = split_str.next().unwrap().parse::<Shape>();
        let me = split_str.next().unwrap().parse::<Shape>();

        Ok(Round {
            opponent: opponent?,
            me: me?,
        })
    }
}

impl Round {
    fn score(&self) -> i32 {
        let shape_score = self.me.score();

        let result_score = match (self.me, self.opponent) {
            (Shape::Scissors, Shape::Paper) => 6,
            (Shape::Paper, Shape::Rock) => 6,
            (Shape::Rock, Shape::Scissors) => 6,
            (Shape::Paper, Shape::Scissors) => 0,
            (Shape::Rock, Shape::Paper) => 0,
            (Shape::Scissors, Shape::Rock) => 0,
            _ => 3,
        };

        shape_score + result_score
    }

    fn expected_outcome(&self) -> Outcome {
        match self.me {
            Shape::Rock => Outcome::Lose,
            Shape::Paper => Outcome::Draw,
            Shape::Scissors => Outcome::Win,
        }
    }

    fn expected_score(&self) -> i32 {
        let result_score = match self.expected_outcome() {
            Outcome::Lose => 0,
            Outcome::Draw => 3,
            Outcome::Win => 6,
        };

        let shape_score = match (self.expected_outcome(), self.opponent) {
            (Outcome::Lose, Shape::Rock) => Shape::Scissors.score(),
            (Outcome::Lose, Shape::Paper) => Shape::Rock.score(),
            (Outcome::Lose, Shape::Scissors) => Shape::Paper.score(),
            (Outcome::Win, Shape::Rock) => Shape::Paper.score(),
            (Outcome::Win, Shape::Paper) => Shape::Scissors.score(),
            (Outcome::Win, Shape::Scissors) => Shape::Rock.score(),
            _ => self.opponent.score(),
        };

        result_score + shape_score
    }
}

type Input = Vec<Round>;
type Output = i32;

fn part_1(input: &Input) -> Output {
    input.iter().map(Round::score).sum()
}

fn part_2(input: &Input) -> Output {
    input.iter().map(Round::expected_score).sum()
}

fn parse_input(pathname: &str) -> Input {
    file_to_structs(pathname)
}

fn main() -> Result<()> {
    tracing_subscriber::fmt()
        .with_env_filter(EnvFilter::from_default_env())
        .with_target(false)
        .with_file(true)
        .with_line_number(true)
        .without_time()
        .compact()
        .init();
    color_eyre::install()?;

    let input = parse_input("inputs/day02.txt");

    info!("Part 1: {}", part_1(&input));
    info!("Part 2: {}", part_2(&input));

    Ok(())
}

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

    #[test]
    fn test_part_1() {
        let sample = parse_input("samples/day02.txt");
        assert_eq!(part_1(&sample), 15);
    }

    #[test]
    fn test_part_2() {
        let sample = parse_input("samples/day02.txt");
        assert_eq!(part_2(&sample), 12);
    }
}