use regex::Regex;
use std::collections::HashMap;
use std::fs;

/// One remembered Aunt Sue: her number and whatever compounds were noted.
#[derive(Debug)]
struct Sue {
    number: u32,
    properties: HashMap<String, u32>,
}

/// Parses the puzzle input into a list of `Sue`s.
///
/// Each line looks like `Sue 1: goldfish: 9, cars: 0, samoyeds: 9`. The
/// number of properties varies per line, so we pull out the `name: count`
/// pairs with a regex rather than assuming a fixed format.
fn parse_sues(input: &str) -> Vec<Sue> {
    let line_re = Regex::new(r"^Sue (\d+): (.+)$").unwrap();
    let property_re = Regex::new(r"(\w+): (\d+)").unwrap();

    input
        .lines()
        .filter_map(|line| {
            let caps = line_re.captures(line)?;
            let number = caps[1].parse().unwrap();
            let properties = property_re
                .captures_iter(&caps[2])
                .map(|prop| (prop[1].to_string(), prop[2].parse().unwrap()))
                .collect();

            Some(Sue { number, properties })
        })
        .collect()
}

/// The exact readings from the MFCSAM.
fn target_properties() -> HashMap<&'static str, u32> {
    HashMap::from([
        ("children", 3),
        ("cats", 7),
        ("samoyeds", 2),
        ("pomeranians", 3),
        ("akitas", 0),
        ("vizslas", 0),
        ("goldfish", 5),
        ("trees", 3),
        ("cars", 2),
        ("perfumes", 1),
    ])
}

/// A Sue matches if every compound she's remembered for equals the target
/// reading exactly. Properties she isn't remembered for are simply skipped,
/// per the puzzle's "missing things aren't zero" rule.
fn matches_target(sue: &Sue, target: &HashMap<&str, u32>) -> bool {
    sue.properties
        .iter()
        .all(|(name, &count)| target.get(name.as_str()) == Some(&count))
}

fn main() {
    let input = fs::read_to_string("input.txt").expect("failed to read input.txt");
    let sues = parse_sues(&input);
    let target = target_properties();

    let real_sue = sues
        .iter()
        .find(|sue| matches_target(sue, &target))
        .expect("no Sue matched the MFCSAM readings");

    println!("Sue {} gave the gift.", real_sue.number);
}