use aoc_runner_derive::{aoc, aoc_generator};
use itertools::Itertools;

const PREAMBLE_LEN: usize = 25;

#[aoc_generator(day9)]
fn parse(input: &str) -> Vec<u64> {
    input.lines().map(str::parse).map(Result::unwrap).collect_vec()
}

#[aoc(day9, part1)]
fn part1(input: &Vec<u64>) -> u64 {
    for i in PREAMBLE_LEN..input.len() {
        if let None = input[i - PREAMBLE_LEN..i]
        .iter()
        .combinations(2)
        .find(|x| x.iter().cloned().sum::<u64>() == input[i]) {
            return input[i];
        }
    }
    unreachable!()
}

#[aoc(day9, part2)]
fn part2(input: &Vec<u64>) -> u64 {
    let to_find = part1(input);

    for len in 2..input.len() {
        if let Some(nums) = input
        .windows(len)
        .find(|x| x.iter().cloned().sum::<u64>() == to_find) {
            return nums.iter().min().unwrap() + nums.iter().max().unwrap();
        }
    }
    unreachable!()
}


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

const EX: &str = r"35
20
15
25
47
40
62
55
65
95
102
117
150
182
127
219
299
277
309
576";

    #[test]
    fn part1_example() {
        assert_eq!(part1(&parse(EX)), 127);
    }

    #[test]
    fn part2_example() {
        assert_eq!(part2(&parse(EX)), 62);
    }
}