main.rs

use std::{fs::File, io::Read};

use rayon::iter::{IntoParallelIterator, ParallelIterator};

fn checksum_part(part: String) -> Option<u16> {
    if part.is_empty() {
        return None;
    } else {
        return Some(part.chars().fold(0, |acc, c| acc | c as u16));
    }
}

const EXPECTED_HEADER: &str = "WASMER";

fn main() {
    let f = File::open(dbg!(std::env::args().next().unwrap())).expect("file path checked");
    let mut data = String::new();
    f.read_to_string(&mut data);

    if &data[..EXPECTED_HEADER.len()] != EXPECTED_HEADER {
        eprintln!("Missing header");
    }

    let length = data.len() / 2;
    let parts = vec![data[..length].to_string(), data[length + 1..].to_string()];

    let checksum_parts: Vec<_> = parts
        .into_par_iter()
        .map(|part| checksum_part(part).unwrap())
        .collect();

    let checksum = checksum_parts.iter().fold(0, |acc, x| acc + x);
    println!("{checksum}");
}