use crate::solvers::Solver;
use std::io::BufRead;

pub struct SecretEntrance {}

impl SecretEntrance {
    const START_POSITION: i32 = 50;
    const DIAL_SIZE: i32 = 100;
    const ZERO_POSITION: i32 = 0;
    const POSITIVE_SIGN_CHAR: char = 'R';
    const NEGATIVE_SIGN_CHAR: char = 'L';

    fn update_position(
        position: i32,
        distance: i32,
        mut zero_hits: u64,
        mut zero_passes: u64,
    ) -> (i32, u64, u64) {
        let mut new_position = position + distance;
        let rounds = new_position.div_euclid(Self::DIAL_SIZE);
        zero_passes += u64::try_from(rounds.abs()).unwrap();
        new_position -= Self::DIAL_SIZE * rounds;
        if new_position == Self::ZERO_POSITION {
            zero_hits += 1;
            if position != Self::ZERO_POSITION && distance < 0 {
                zero_passes += 1;
            }
        } else if position == Self::ZERO_POSITION && distance < 0 {
            zero_passes -= 1;
        }
        (new_position, zero_hits, zero_passes)
    }
}

impl Solver for SecretEntrance {
    const PUZZLE_INDEX: u8 = 1;
    const PUZZLE_NAME: &'static str = "Secret Entrance";

    fn process_data<R: BufRead>(&self, reader: R) -> (u64, u64) {
        let mut position = Self::START_POSITION;
        let mut zero_hits = 0;
        let mut zero_passes = 0;
        let format: String = format!(
            "{{[{}{}]}}{{d}}",
            Self::POSITIVE_SIGN_CHAR,
            Self::NEGATIVE_SIGN_CHAR
        );
        for line in reader.lines().map_while(Result::ok) {
            let (sign, distance) = scan_fmt!(&line, &format, char, i32).unwrap();
            (position, zero_hits, zero_passes) = Self::update_position(
                position,
                if sign == Self::POSITIVE_SIGN_CHAR {
                    distance
                } else {
                    -distance
                },
                zero_hits,
                zero_passes,
            );
        }
        (zero_hits, zero_passes)
    }
}