AoC-2022/day2/src/main.rs

use std::fs::File;
use std::io::BufRead;
use std::io::BufReader;
use std::io::Lines;

use clap::Arg;
use clap::Command;

struct Accumulator<B> {
    lines: Lines<B>,
    current: u32,
}

trait Elvish<B> {
    fn elf(self) -> Accumulator<B>;
}

impl<B> Elvish<B> for Lines<B> {
    fn elf(self) -> Accumulator<B> {
        Accumulator {
            lines: self,
            current: 0,
        }
    }
}

impl<B: BufRead> Iterator for Accumulator<B> {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        while let Some(Ok(line)) = self.lines.next() {
            let line = line.trim();
            if line.is_empty() {
                let result = self.current;
                self.current = 0;
                return Some(result);
            } else {
                self.current += line.parse::<u32>().unwrap();
            }
        }
        None
    }
}

fn main() {
    let matches = Command::new("Day1").arg(Arg::new("filename")).get_matches();
    let filename = matches
        .get_one::<String>("filename")
        .expect("Need a filename");
    println!("Processing {}...", filename);

    let file = File::open(filename).expect("Can't read file");
    let reader = BufReader::new(file);

    let mut calories = reader.lines().elf().collect::<Vec<u32>>();
    calories.sort_by(|a, b| b.cmp(a));
    println!("Sum: {:?}", calories.iter().take(3).sum::<u32>())
}