use aoc_runner_derive::{aoc, aoc_generator};
use nom::character::complete::multispace0;
use nom::multi::many1;
use nom::{character::complete::u64 as parse_u64, IResult};

#[aoc_generator(day1)]
pub fn generator(input: &str) -> Vec<(u64, u64)> {
    many1(parse_line)(input).unwrap().1
}

fn parse_line(input: &str) -> IResult<&str, (u64, u64)> {
    let (input, left) = parse_u64(input)?;
    let (input, _) = multispace0(input)?;
    let (input, right) = parse_u64(input)?;
    let (input, _) = multispace0(input)?;
    Ok((input, (left, right)))
}

#[aoc(day1, part1)]
pub fn part1(input: &[(u64, u64)]) -> u64 {
    let (mut left, mut right): (Vec<u64>, Vec<u64>) = input.iter().copied().unzip();
    left.sort();
    right.sort();
    left.iter()
        .zip(right.iter())
        .map(|(l, r)| (*l).abs_diff(*r))
        .sum()
}

#[aoc(day1, part2)]
pub fn part2(input: &[(u64, u64)]) -> usize {
    let (mut left, mut right): (Vec<u64>, Vec<u64>) = input.iter().copied().unzip();
    left.sort();
    right.sort();

    let mut l;
    let mut r = 0;
    let mut score = 0usize;
    for value in left {
        l = r;
        while l < right.len() && right[l] < value {
            l += 1
        }
        r = l;
        while r < right.len() && right[r] <= value {
            r += 1
        }
        score += (value as usize) * (r - l);
        if r == right.len() - 1 {
            break;
        };
    }
    score
}