use std::fs::read_to_string;

fn main() {
    let (password, _) = read_to_string("../input.txt")
        .expect("failed to open input file")
        .lines()
        .fold((0u32, 50), |(zero_count, position), rotation| {
            let (direction, distance) = rotation.split_at(1);
            let distance = distance.parse::<u16>().expect("failed to parse distance");
            let modulo_distance = distance % 100;
            let (new_position, overflow) = match direction {
                "L" => {
                    if modulo_distance > position {
                        (100 - (modulo_distance - position), position != 0)
                    } else {
                        (position - modulo_distance, position == modulo_distance)
                    }
                }
                "R" => {
                    let turned = position + modulo_distance;
                    (turned % 100, turned >= 100)
                }
                other => panic!("unexpected direction {other}"),
            };
            let new_count = zero_count + (u32::from(distance) / 100) + if overflow { 1 } else { 0 };
            (new_count, new_position)
        });
    println!("The door password is {password}!");
}