use std::collections::HashSet;
use std::error::Error;
use std::fs::File;
use std::io::BufReader;
use std::io::SeekFrom;
use std::io::prelude::*;

fn main() -> std::io::Result<()> {
    let mut file = match File::open("input") {
        // The `description` method of `io::Error` returns a string that describes the error
        Err(why) => panic!("couldn't open input: {}", Error::description(&why)),
        Ok(file) => file,
    };

    let mut repeat = true;
    let mut total: i128 = 0;
    let mut seen = HashSet::<i128>::new();
    seen.insert(0);

    while repeat {
        file.seek(SeekFrom::Start(0));
        let reader = BufReader::new(&file);
        let lines = reader.lines();

        for result in lines {
            let l = result.unwrap();
            let offset:i128 = i128::from_str_radix(&l, 10).unwrap();

            total = total + offset;
            println!("{} => {}", offset, total);

            if seen.contains(&total) {
                println!("seen {} before", total);
                repeat = false;
                break;
            }

            seen.insert(total);
       }
   }

    println!("{}", total);

    Ok(())
}