use aoc_runner_derive::aoc;

// PROBLEM 1 solution
#[aoc(day1, part1)]
pub fn part1(input: &str) -> u64 {
    let mut val = 50u64;
    let mut pass = 0u64;
    let mod_val = 100;
    for line in input.lines() {
        let line = line.trim();
        let (sign, num) = line.split_at(1);
        let num_val = num.parse::<u64>().unwrap();

        let add_val = match sign.as_bytes()[0] {
            b'R' => num_val,
            b'L' => mod_val - (num_val % mod_val),
            c => panic!("Invalid direction {c}"),
        };
        val = (val + add_val) % mod_val;
        if val == 0 {
            pass += 1
        }
    }
    pass
}

// PROBLEM 2 solution

fn advance<const N: i64>(mut start: i64, mut n: i64) -> (i64, i64) {
    let mut zero_crossings = 0;
    while n != 0 {
        if n > 0 {
            start += 1;
            if start == 100 {
                start = 0;
                zero_crossings += 1;
            }
            n -= 1
        } else {
            start -= 1;
            if start == 0 {
                zero_crossings += 1;
            }
            if start == -1 {
                start = 99;
            }
            n += 1
        }
    }
    (start, zero_crossings)
}

#[aoc(day1, part2)]
pub fn part2(input: &str) -> i64 {
    let mut val = 50;
    let mut pass = 0i64;

    for line in input.lines() {
        let line = line.trim();
        let (sign, num) = line.split_at(1);
        let num_val = num.parse::<i64>().unwrap();

        let (new_val, add_pass) = match sign.as_bytes()[0] {
            b'R' => advance::<100>(val, num_val),
            b'L' => advance::<100>(val, -num_val),
            c => panic!("Invalid direction {c}"),
        };
        val = new_val;
        pass += add_pass;
    }
    pass
}

#[cfg(test)]
mod tests {
    use crate::day1::*;

    const EXAMPLE: &str = "L68
    L30
    R48
    L5
    R60
    L55
    L1
    L99
    R14
    L82";

    #[test]
    fn problem1_example() {
        assert_eq!(part1(EXAMPLE), 3);
    }

    #[test]
    fn problem2_example() {
        assert_eq!(part2(EXAMPLE), 6);
    }
}