/// Number of trailing zeros tells us which bit is set and there should only be one set
/// Do some math to convert to the needed priority
fn bits_to_priority(b: u64) -> u32 {
    let trailing = b.trailing_zeros();
    match trailing {
        0..=25 => trailing + 27,
        32..=57 => trailing - 31,
        _ => unreachable!(""),
    }
}

/// For each byte in the string offset it towards 0
/// to make it fit in u64 and set a bit at the position of its value
fn to_bits(s: &str) -> u64 {
    s.bytes().fold(0, |a, v| a | 1 << (v - 65))
}

pub fn part1(input: &str) -> impl std::fmt::Display {
    input
        .lines()
        .map(|l| l.split_at(l.len() / 2))
        .map(|(l, r)| bits_to_priority(to_bits(l) & to_bits(r)))
        .sum::<u32>()
}

pub fn part2(input: &str) -> impl std::fmt::Display {
    let mut lines = input.lines();
    let mut sum = 0;

    while let Some(l1) = lines.next() {
        let l2 = lines.next().expect("second is guaranteed to be there");
        let l3 = lines.next().expect("third is guaranteed to be there");

        sum += bits_to_priority(to_bits(l1) & to_bits(l2) & to_bits(l3));
    }
    sum
}

#[test]
fn test_part1() {
    assert_eq!("15", part1("A Y\nB X\nC Z").to_string())
}

#[test]
fn test_part2() {
    assert_eq!("12", part2("A Y\nB X\nC Z").to_string())
}