//! Day 3: Gear Ratios

use std::collections::{HashMap, HashSet};

use itertools::Itertools;
use once_cell::sync::Lazy;
use regex::Regex;

use crate::util::grid::{NeighborsCfg, Pos};

pub const DAY: u8 = 3;
pub const TITLE: &str = "Gear Ratios";

const NCFG: NeighborsCfg = NeighborsCfg {
    diag: true,
    tl: Some(Pos::usize(0, 0)),
    br: None,
};
static NUMBERS: Lazy<Regex> = Lazy::new(|| Regex::new(r"\d+").unwrap());

pub fn part1(input: Vec<String>) -> String {
    let mut symbol_neighbors = HashSet::new();

    for (y, line) in input.iter().enumerate() {
        for (x, c) in line.chars().enumerate() {
            if c != '.' && c.is_ascii_punctuation() {
                let p = Pos::usize(x, y);
                p.neighbors(&NCFG).for_each(|p| {
                    symbol_neighbors.insert(p);
                });
            }
        }
    }

    let mut sum = 0;
    for (y, line) in input.iter().enumerate() {
        for m in NUMBERS.captures_iter(line) {
            let m = m.get(0).unwrap();
            for x in m.range() {
                let p = Pos::usize(x, y);
                if symbol_neighbors.contains(&p) {
                    sum += m.as_str().parse::<u64>().unwrap();
                    break;
                }
            }
        }
    }

    sum.to_string()
}

pub fn part2(input: Vec<String>) -> String {
    let mut numbers = HashMap::new();

    for (y, line) in input.iter().enumerate() {
        for m in NUMBERS.captures_iter(line) {
            let m = m.get(0).unwrap();
            let n = m.as_str().parse::<u64>().unwrap();
            for x in m.range() {
                let p = Pos::usize(x, y);
                numbers.insert(p, n);
            }
        }
    }

    let mut gears = 0;
    for (y, line) in input.iter().enumerate() {
        for (x, c) in line.chars().enumerate() {
            if c == '*' {
                let p = Pos::usize(x, y);
                let nx = p
                    .neighbors(&NCFG)
                    .filter_map(|p| numbers.get(&p))
                    .dedup()
                    .collect_vec();
                if nx.len() == 2 {
                    gears += nx[0] * nx[1];
                }
            }
        }
    }

    gears.to_string()
}

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

    #[test]
    fn t_example1() {
        assert_eq!(part1(crate::read_example(DAY, 1)), "4361");
    }

    #[test]
    fn t_part1() {
        assert_eq!(part1(crate::read_input(DAY)), "520135");
    }

    #[test]
    fn t_example2() {
        assert_eq!(part2(crate::read_example(DAY, 2)), "467835");
    }

    #[test]
    fn t_part2() {
        assert_eq!(part2(crate::read_input(DAY)), "72514855");
    }
}