use std::collections::HashMap;
use std::collections::HashSet;
use std::error::Error;
use std::fs::File;
use std::io::{self, BufRead};
use std::vec::Vec;

fn enumerate_ways(
    start: &str,
    end: &str,
    vertices: &HashMap<String, HashSet<String>>,
    mut path: Vec<String>,
    mut allow_twice: bool,
) -> u64 {
    if start == end {
        return 1;
    }

    if start.chars().all(|c| c.is_lowercase()) {
        if path.iter().filter(|n| n == &&start).count() > 0 {
            if !allow_twice {
                return 0;
            } else {
                allow_twice = false;
            }
        }
    }

    path.push(start.to_string());

    let mut ways = 0;

    for neighbor in vertices[start].iter() {
        if neighbor != "start" {
            ways += enumerate_ways(neighbor, end, vertices, path.clone(), allow_twice);
        }
    }

    ways
}

fn main() -> Result<(), Box<dyn Error>> {
    let file = File::open("inputs/day12.txt")?;
    let links: Vec<(String, String)> = io::BufReader::new(file)
        .lines()
        .map(|l| l.unwrap())
        .map(|l| {
            let mut ends = l.split('-');
            (
                ends.next().unwrap().to_string(),
                ends.next().unwrap().to_string(),
            )
        })
        .collect();

    let mut vertices: HashMap<String, HashSet<String>> = HashMap::new();
    for link in links.iter() {
        if vertices.contains_key(&link.0) {
            let mut set = vertices[&link.0].clone();
            set.insert(link.1.clone());
            vertices.insert(link.0.clone(), set);
        } else {
            let mut set: HashSet<String> = HashSet::new();
            set.insert(link.1.clone());
            vertices.insert(link.0.clone(), set);
        }

        if vertices.contains_key(&link.1) {
            let mut set = vertices[&link.1].clone();
            set.insert(link.0.clone());
            vertices.insert(link.1.clone(), set);
        } else {
            let mut set: HashSet<String> = HashSet::new();
            set.insert(link.0.clone());
            vertices.insert(link.1.clone(), set);
        }
    }

    let ways1 = enumerate_ways("start", "end", &vertices, Vec::new(), false);

    println!("Answer1: {}", ways1);
    println!("");

    let ways2 = enumerate_ways("start", "end", &vertices, Vec::new(), true);

    println!("Answer2: {}", ways2);

    Ok(())
}