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

/// Parses a string & returns its effect on the horizontal & vertical position/aim
pub fn parse_ins(s: &str) -> (i32, i32) {
    let mut parts = s.split_ascii_whitespace();
    let command = parts.next().unwrap();
    let num: i32 = parts.next().unwrap().parse().unwrap();

    match command {
        "forward" => (num, 0),
        "down" => (0, num),
        "up" => (0, -num),
        _ => unimplemented!(),
    }
}

pub fn part1() -> io::Result<i32> {
    let file = File::open("input/day2")?;
    let reader = BufReader::new(file);

    let mut forward = 0;
    let mut depth = 0;

    for line in reader.lines() {
        let (f, d) = parse_ins(&line.unwrap());

        forward += f;
        depth += d;
    }

    Ok(forward * depth)
}

pub fn part2() -> io::Result<i32> {
    let file = File::open("input/day2")?;
    let reader = BufReader::new(file);

    let mut forward = 0;
    let mut depth = 0;
    let mut aim = 0;

    for line in reader.lines() {
        let (f, a) = parse_ins(&line.unwrap());

        aim += a;
        forward += f;
        depth += aim * f;
    }

    Ok(forward * depth)
}