const INPUT_FILE: &str = "input";

#[derive(PartialEq, Clone, Copy)]
enum Direction {
    Up,
    Down,
    Unknown,
}
use Direction::*;

fn is_safe(levels: &[u32]) -> bool {
    let mut direction = Unknown;
    for i in 0..levels.len() - 1 {
        let [x, y] = levels[i..=i + 1] else {
            unreachable!()
        };
        let (diff, d) = if x > y { (x - y, Down) } else { (y - x, Up) };
        if direction == Unknown {
            direction = d;
        }
        if diff == 0 || diff > 3 || direction != d {
            return false;
        }
    }
    return true;
}

fn main() {
    let input = std::fs::read_to_string(INPUT_FILE).unwrap();

    let mut total = 0;
    for report in input.lines() {
        let levels: Vec<u32> = report
            .split_whitespace()
            .map(|l| l.parse().unwrap())
            .collect();
        if is_safe(&levels) {
            total += 1;
        }
    }
    println!("Levels! {:?}", total);
}