use std::fs::File;
use std::io::{BufRead, BufReader, Lines};

use lazy_regex::{lazy_regex, Lazy, Regex};

// --- Day 4: Scratchcards ---

// The gondola takes you up. Strangely, though, the ground doesn't seem to be coming
// with you; you're not climbing a mountain. As the circle of Snow Island recedes below
// you, an entire new landmass suddenly appears above you! The gondola carries you to
// the surface of the new island and lurches into the station.

// As you exit the gondola, the first thing you notice is that the air here is much
// warmer than it was on Snow Island. It's also quite humid. Is this where the water
// source is?

// The next thing you notice is an Elf sitting on the floor across the station in what
// seems to be a pile of colorful square cards.

// "Oh! Hello!" The Elf excitedly runs over to you. "How may I be of service?" You ask
// about water sources.

// "I'm not sure; I just operate the gondola lift. That does sound like something we'd
// have, though - this is Island Island, after all! I bet the gardener would know. He's
// on a different island, though - er, the small kind surrounded by water, not the
// floating kind. We really need to come up with a better naming scheme. Tell you what:
// if you can help me with something quick, I'll let you borrow my boat and you can go
// visit the gardener. I got all these scratchcards as a gift, but I can't figure out
// what I've won."

// The Elf leads you over to the pile of colorful cards. There, you discover dozens of
// scratchcards, all with their opaque covering already scratched off. Picking one up,
// it looks like each card has two lists of numbers separated by a vertical bar (|): a
// list of winning numbers and then a list of numbers you have. You organize the
// information into a table (your puzzle input).

// BOILERPLATE
type InputIter = Lines<BufReader<File>>;

fn get_input() -> InputIter {
    let f = File::open("input").unwrap();
    let br = BufReader::new(f);
    br.lines()
}

fn main() {
    println!("Problem 1 solution: {}", problem1(get_input()));
    println!("Problem 2 solution: {}", problem2(get_input()));
}

// PARSING

const CARD_REGEX: Lazy<Regex> = lazy_regex!(r"^Card\s+([0-9]+):(.+)\|(.+)$");

fn num_list(s: &str) -> Vec<u32> {
    s.split_whitespace()
        .map(|s_num| s_num.parse().unwrap())
        .collect()
}

pub struct Card {
    id: usize,
    winning_numbers: Vec<u32>,
    our_numbers: Vec<u32>,
}

impl Card {
    fn score(&self) -> u64 {
        let match_count = self
            .winning_numbers
            .iter()
            .filter(|win| self.our_numbers.contains(win))
            .count();
        if match_count > 0 {
            1 << (match_count - 1)
        } else {
            0
        }
    }
    // Return the number of copies won
    fn win_copies(&self) -> usize {
        self.winning_numbers
            .iter()
            .filter(|win| self.our_numbers.contains(win))
            .count()
    }
}

impl From<&str> for Card {
    fn from(s: &str) -> Self {
        let parts = CARD_REGEX.captures(s).unwrap();
        Card {
            id: parts.get(1).unwrap().as_str().parse().unwrap(),
            winning_numbers: num_list(parts.get(2).unwrap().as_str()),
            our_numbers: num_list(parts.get(3).unwrap().as_str()),
        }
    }
}

// PROBLEM 1 solution

// As far as the Elf has been able to figure out, you have to figure out which of the
// numbers you have appear in the list of winning numbers. The first match makes the
// card worth one point and each match after the first doubles the point value of that
// card.

// For example:

// Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
// Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
// Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
// Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
// Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
// Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11

// In the above example, card 1 has five winning numbers (41, 48, 83, 86, and 17) and
// eight numbers you have (83, 86, 6, 31, 17, 9, 48, and 53). Of the numbers you have,
// four of them (48, 83, 17, and 86) are winning numbers! That means card 1 is worth 8
// points (1 for the first match, then doubled three times for each of the three matches
// after the first).

//     Card 2 has two winning numbers (32 and 61), so it is worth 2 points. Card 3 has
//     two winning numbers (1 and 21), so it is worth 2 points. Card 4 has one winning
//     number (84), so it is worth 1 point. Card 5 has no winning numbers, so it is
//     worth no points. Card 6 has no winning numbers, so it is worth no points.

// So, in this example, the Elf's pile of scratchcards is worth 13 points.

// Take a seat in the large pile of colorful cards. How many points are they worth in
// total?

fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
    let cards: Vec<Card> = input
        .map(|line| Card::from(line.unwrap().as_str()))
        .collect();

    cards.iter().map(|x| x.score()).sum()
}

// PROBLEM 2 solution

// --- Part Two ---

// Just as you're about to report your findings to the Elf, one of you realizes that the
// rules have actually been printed on the back of every card this whole time.

// There's no such thing as "points". Instead, scratchcards only cause you to win more
// scratchcards equal to the number of winning numbers you have.

// Specifically, you win copies of the scratchcards below the winning card equal to the
// number of matches. So, if card 10 were to have 5 matching numbers, you would win one
// copy each of cards 11, 12, 13, 14, and 15.

// Copies of scratchcards are scored like normal scratchcards and have the same card
// number as the card they copied. So, if you win a copy of card 10 and it has 5
// matching numbers, it would then win a copy of the same cards that the original card
// 10 won: cards 11, 12, 13, 14, and 15. This process repeats until none of the copies
// cause you to win any more cards. (Cards will never make you copy a card past the end
// of the table.)

// This time, the above example goes differently:

// Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53 Card 2: 13 32 20 16 61 | 61 30 68 82
// 17 32 24 19 Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1 Card 4: 41 92 73 84 69 |
// 59 84 76 51 58  5 54 83 Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36 Card 6: 31
// 18 13 56 72 | 74 77 10 23 35 67 36 11

//     Card 1 has four matching numbers, so you win one copy each of the next four
//     cards: cards 2, 3, 4, and 5. Your original card 2 has two matching numbers, so
//     you win one copy each of cards 3 and 4. Your copy of card 2 also wins one copy
//     each of cards 3 and 4. Your four instances of card 3 (one original and three
//     copies) have two matching numbers, so you win four copies each of cards 4 and 5.
//     Your eight instances of card 4 (one original and seven copies) have one matching
//     number, so you win eight copies of card 5. Your fourteen instances of card 5 (one
//     original and thirteen copies) have no matching numbers and win no more cards.
//     Your one instance of card 6 (one original) has no matching numbers and wins no
//     more cards.

// Once all of the originals and copies have been processed, you end up with 1 instance
// of card 1, 2 instances of card 2, 4 instances of card 3, 8 instances of card 4, 14
// instances of card 5, and 1 instance of card 6. In total, this example pile of
// scratchcards causes you to ultimately have 30 scratchcards!

// Process all of the original and copied scratchcards until no more scratchcards are
// won. Including the original set of scratchcards, how many total scratchcards do you
// end up with?

fn problem2_award_copies<'a>(orig_cards: &'a Vec<Card>, card: &Card) -> Vec<&'a Card> {
    let win_copies = card.win_copies();
    let mut new_cards = Vec::new();
    if win_copies != 0 {
        for ofs in 0..win_copies {
            // card.id is 1-indexed, so would need to be card.id-1, but offset needs to
            // start at 1, which offsets this
            new_cards.push(&orig_cards[card.id + ofs]);
        }
    }

    new_cards
}

fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
    let orig_cards: Vec<Card> = input
        .map(|line| Card::from(line.unwrap().as_str()))
        .collect();

    let mut new_cards = Vec::new();
    let mut won_cards = Vec::new();

    for card in &orig_cards {
        new_cards.append(&mut problem2_award_copies(&orig_cards, card))
    }

    while let Some(card) = new_cards.pop() {
        won_cards.push(card);
        new_cards.append(&mut problem2_award_copies(&orig_cards, card))
    }

    (won_cards.len() + orig_cards.len()) as u64
}

#[cfg(test)]
mod tests {
    use crate::{problem1, problem2};
    use std::io::{BufRead, Cursor};

    const example_input: &str = "Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11";

    #[test]
    fn problem1_example_test() {
        let input = Cursor::new(example_input).lines();

        assert_eq!(problem1(input), 13);
    }

    #[test]
    fn problem2_example_test() {
        let input = Cursor::new(example_input).lines();
        assert_eq!(problem2(input), 30);
    }
}