use nom::{
    bytes::complete::tag,
    character::complete::{line_ending, space1, u32 as nom_u32},
    combinator::map,
    multi::separated_list1,
    sequence::tuple,
    IResult,
};
use std::{collections::BTreeSet, fs};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let input = fs::read_to_string("inputs/day_4.txt")?;
    let parsed = Scratchcards::parser(&input).unwrap().1;
    dbg!(&parsed.points());
    dbg!(&parsed.scratchcard_explosion_sum());

    Ok(())
}

#[derive(Debug)]
struct Scratchcards(Vec<Scratchcard>);

#[derive(Debug)]
struct Scratchcard {
    winning: BTreeSet<u32>,
    owned: BTreeSet<u32>,
}

impl Scratchcards {
    fn parser(input: &str) -> IResult<&str, Self> {
        map(
            separated_list1(line_ending, Scratchcard::parser),
            Scratchcards,
        )(input)
    }

    fn points(&self) -> usize {
        self.0.iter().map(|card| card.points()).sum()
    }

    fn scratchcard_explosion_sum(&self) -> u64 {
        let mut scratchcard_pile = vec![1_u64.into(); self.0.len()];

        for i in 0..scratchcard_pile.len() {
            let points = self.0[i].winning_numbers();
            let new_scratchcards: u64 = scratchcard_pile[i];
            for offset in 0..points {
                if let Some(pile) = scratchcard_pile.get_mut(i + 1 + offset) {
                    *pile += new_scratchcards;
                }
            }
        }

        scratchcard_pile.into_iter().sum()
    }
}

impl Scratchcard {
    fn parser(input: &str) -> IResult<&str, Self> {
        map(
            tuple((
                tag("Card"),
                space1,
                nom_u32,
                tag(":"),
                space1,
                separated_list1(space1, nom_u32),
                space1,
                tag("|"),
                space1,
                separated_list1(space1, nom_u32),
            )),
            |(_, _, _, _, _, winning, _, _, _, owned)| Scratchcard {
                winning: winning.into_iter().collect(),
                owned: owned.into_iter().collect(),
            },
        )(input)
    }

    fn winning_numbers(&self) -> usize {
        self.winning.intersection(&self.owned).count()
    }

    fn points(&self) -> usize {
        let winning_numbers = self.winning_numbers();
        if winning_numbers > 0 {
            2_usize.pow(winning_numbers as u32 - 1)
        } else {
            0
        }
    }
}