use crate::input::Input;

pub fn solve(input: &mut Input) -> Result<usize, String> {
    let snake_len = input.part_values(2, 10);
    let mut snake = vec![(0_i32, 0_i32); snake_len];
    let mut visited = Vec::with_capacity(input.text.len());
    visited.push((0_i32, 0_i32));

    for line in input.text.lines().filter(|line| line.len() > 2) {
        let direction = line.as_bytes()[0];
        let steps = i32::from(
            line[2..]
                .parse::<u8>()
                .map_err(|_| "Not an integer for steps".to_string())?,
        );

        match direction {
            b'U' => snake[0].1 -= steps,
            b'R' => snake[0].0 += steps,
            b'D' => snake[0].1 += steps,
            _ => snake[0].0 -= steps,
        };

        for _ in 0..steps {
            for i in 1..snake_len {
                if snake[i - 1].0.abs_diff(snake[i].0) > 1
                    || snake[i - 1].1.abs_diff(snake[i].1) > 1
                {
                    snake[i].0 += (snake[i - 1].0 - snake[i].0).signum();
                    snake[i].1 += (snake[i - 1].1 - snake[i].1).signum();
                    if i + 1 == snake_len {
                        visited.push(snake[i]);
                    }
                }
            }
        }
    }

    visited.sort_unstable();
    Ok(visited.windows(2).filter(|w| w[0] != w[1]).count() + 1)
}

#[test]
pub fn tests() {
    use crate::input::{test_part_one, test_part_two};

    let test_input = "R 4\nU 4\nL 3\nD 1\nR 4\nD 1\nL 5\nR 2";
    test_part_one!(test_input => 13);
    test_part_two!(test_input => 1);

    let test_input = "R 5\nU 8\nL 8\nD 3\nR 17\nD 10\nL 25\nU 20";
    test_part_two!(test_input => 36);

    let real_input = include_str!("day09_input.txt");
    test_part_one!(real_input => 6081);
    test_part_two!(real_input => 2487);
}