adventofcode2022/day02/part2.rs

// Copyright 2022 Christian Ulrich
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.
//
// usage: ./part2 < input

use std::convert::TryFrom;
use std::io;

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

enum Outcome {
    Lose = 0,
    Draw = 3,
    Win = 6,
}

struct Round {
    me: Item,
    other: Item,
}

struct Rounds {}

impl TryFrom<&str> for Item {
    type Error = &'static str;

    fn try_from(value: &str) -> Result<Self, Self::Error> {
        match value {
            "A" => Ok(Item::Rock),
            "B" => Ok(Item::Paper),
            "C" => Ok(Item::Scissors),
            _ => Err("invalid value"),
        }
    }
}

impl TryFrom<&str> for Outcome {
    type Error = &'static str;

    fn try_from(value: &str) -> Result<Self, Self::Error> {
        match value {
            "X" => Ok(Outcome::Lose),
            "Y" => Ok(Outcome::Draw),
            "Z" => Ok(Outcome::Win),
            _ => Err("invalid value"),
        }
    }
}

impl Round {
    pub fn new(me: Item, other: Item) -> Self {
        Self {
            me: me,
            other: other,
        }
    }

    pub fn with_outcome(other: Item, outcome: Outcome) -> Self {
        let me = match (other, outcome) {
            (Item::Rock, Outcome::Lose) => Item::Scissors,
            (Item::Rock, Outcome::Win) => Item::Paper,
            (Item::Paper, Outcome::Lose) => Item::Rock,
            (Item::Paper, Outcome::Win) => Item::Scissors,
            (Item::Scissors, Outcome::Lose) => Item::Paper,
            (Item::Scissors, Outcome::Win) => Item::Rock,
            _ => other,
        };
        Self::new(me, other)
    }

    fn outcome(&self) -> Outcome {
        match (self.me, self.other) {
            (Item::Rock, Item::Paper) => Outcome::Lose,
            (Item::Rock, Item::Scissors) => Outcome::Win,
            (Item::Paper, Item::Rock) => Outcome::Win,
            (Item::Paper, Item::Scissors) => Outcome::Lose,
            (Item::Scissors, Item::Rock) => Outcome::Lose,
            (Item::Scissors, Item::Paper) => Outcome::Win,
            _ => Outcome::Draw,
        }
    }

    pub fn score(&self) -> usize {
        self.outcome() as usize + self.me as usize
    }
}

impl Iterator for Rounds {
    type Item = Result<Round, &'static str>;

    fn next(&mut self) -> Option<Self::Item> {
        if let Some(line) = io::stdin().lines().next() {
            let line = line.unwrap();
            if line.len() > 0 {
                if let Some((left, right)) = line.split_once(' ') {
                    if let (Ok(item), Ok(outcome)) =
                        (Item::try_from(left), Outcome::try_from(right))
                    {
                        return Some(Ok(Round::with_outcome(item, outcome)));
                    }
                }
                return Some(Err("input file contains invalid line"));
            }
        }
        None
    }
}

fn main() -> Result<(), &'static str> {
    let rounds = Rounds {};
    let mut result = 0;
    for round in rounds {
        result += round?.score();
    }
    println!("{result}");
    Ok(())
}