/** Solution for Advent of Code 2022 day 3.
 * https://adventofcode.com/2022/day/3
 */
use aoc2022::StdError;
use std::collections::HashSet;
use std::fs::File;
use std::io::{BufRead, BufReader};

fn main() -> StdError<()> {
    // Open the input file and split all the lines.
    let lines: Vec<_> = BufReader::new(File::open("input/day3.txt")?)
        .lines()
        .collect::<Result<_, _>>()?; // "Short circuit" any Errors in the iterator

    let sum: u32 = lines
        .iter()
        .map(|l| {
            assert!(l.len() % 2 == 0); // We won't be able to evenly split a odd-length line!
            let (one, two) = (&l[0..l.len() / 2], &l[l.len() / 2..]);

            // Make sets out of the characters in each compartment...
            HashSet::<char>::from_iter(one.chars())
                // ... then calculate the intersection, giving us the "items" (chars) in common
                .intersection(&HashSet::from_iter(two.chars()))
                .map(|c| match c {
                    // Now, we map our "items" to their "priorities".
                    // Fortunately we can cast all chars to u32, which makes this a matter of some
                    // simple arithmetic.
                    'a'..='z' => (*c as u32) - 'a' as u32 + 1,
                    'A'..='Z' => (*c as u32) - 'A' as u32 + 27,
                    _ => panic!("Got non-ascii alphabetic char!"),
                })
                .sum::<u32>() // Sum the priorities of items in common in each "rucksack"
        })
        .sum(); // Sum all the rucksacks' priorities
    println!("Part 1: {}", sum);
    Ok(())
}