aoc22/day10/src/main.rs

use std::num;
use std::env;
use std::process;
use std::fs::File;
use std::io::{self, BufRead};

#[derive(Debug)]
enum Inst{
    AddX(i64),
    Noop,
}

#[derive(Debug)]
struct ParseError(String);
impl From<num::ParseIntError> for ParseError {
    fn from(e: num::ParseIntError) -> Self {
        ParseError(e.to_string())
    }
}

fn parse_line(line: String) -> Result<Inst, ParseError> {
    match &line[..4] {
        "noop" => Ok(Inst::Noop),
        "addx" => Ok(Inst::AddX(line[5..].parse::<i64>()?)),
        _ => Err(ParseError(String::from("bad instruction"))),
    }
}

fn main() {
    let file = File::open(&env::args().nth(1).unwrap()).unwrap();
    let reader = io::BufReader::new(file);
    let mut xs: Vec<i64> = vec![1];

    for line in reader.lines().flatten() {
        let last_x = *xs.last().unwrap();
        match parse_line(line) {
            Ok(Inst::Noop) => { xs.push(last_x) },
            Ok(Inst::AddX(x)) => { xs.push(last_x); xs.push(last_x + x) },
            Err(e) => { eprintln!("error: {:?}", e); process::exit(1) },
        }
    }

    let screen: Vec<_> = xs.iter().enumerate()
        .map(|(i, &x)| if ((i as i64) % 40 - x).abs() <= 1 { '#' } else { '.' })
        .collect();
    for i in 0..6 {
        println!("{}", screen[(i*40)..((i+1)*40)].iter().collect::<String>());
    }
}