use crate::utils;
use std::collections::{HashMap, HashSet};

pub fn task1() {
    let input = utils::read_file("input/day07.txt");
    let mut tasks: HashSet<char> = HashSet::new();
    let dependencies: Vec<(char, char)> = input
        .lines()
        .map(|line| (line.chars().nth(5).unwrap(), line.chars().nth(36).unwrap()))
        .collect();

    let mut depends_on: HashMap<char, HashSet<char>> = HashMap::new();
    for (a, b) in dependencies {
        depends_on.entry(b).or_insert(HashSet::new()).insert(a);
        tasks.insert(a);
        tasks.insert(b);
    }

    let mut open: HashSet<char> = tasks
        .iter()
        .filter(|task| !depends_on.contains_key(task))
        .map(|c| *c)
        .collect();

    let mut result = String::new();
    while open.len() > 0 {
        let next = open.iter().min().unwrap().clone();
        open.remove(&next);
        result.push(next);
        let newly_open: HashSet<char> = depends_on
            .iter()
            .filter(|(_task, deps)| deps.iter().all(|dep| result.chars().any(|c| c == *dep)))
            .map(|(task, _)| *task)
            .collect();
        open = open.union(&newly_open).map(|c| *c).collect();
        for c in newly_open {
            depends_on.remove(&c);
        }
    }

    println!("{}", result);
}