pub mod day06 {
    use lazy_static::lazy_static;
    use std::collections::HashMap;
    use std::fmt::Write;
    use indextree::Arena;
    use itertools::Itertools;

    fn count_orbits(arena: &Arena<&str>, node: indextree::NodeId, depth: i32) -> i32 {
        depth + node.children(&arena).map(|child| count_orbits(arena, child, depth + 1)).sum::<i32>()
    }

    pub fn run(file_string: String) {
        // Parse input into tuple pairs (not totally necessary)
        let pairs : Vec<(&str, &str)> = file_string.lines()
            .map(|line| line.split(")").next_tuple().unwrap())
            .collect();

        // Build graph
        let mut arena = &mut Arena::new();
        let mut id_map : HashMap<&str, indextree::NodeId> = HashMap::new();

        for (center, orbit) in &pairs {
            let center_id = *id_map.entry(center).or_insert_with(|| arena.new_node(*center));
            let orbit_id = *id_map.entry(orbit).or_insert_with(|| arena.new_node(*orbit));
            center_id.append(orbit_id, &mut arena);
        }

        // Part 1 - Compute total orbits from graph
        let total_orbits = count_orbits(arena, *id_map.get("COM").unwrap(), 0);
        writeln!(&mut result, "Day 6, Problem 1 - [{}]", total_orbits).unwrap(); // 270768

        // Part 2 - Find path between two arbitrary nodes
        let you_to_com : Vec<indextree::NodeId> = id_map.get("YOU").unwrap().ancestors(&arena).collect();
        let santa_to_com : Vec<indextree::NodeId> = id_map.get("SAN").unwrap().ancestors(&arena).collect();

        // Index of last shared object
        let transfer_point = you_to_com.iter().rev()
            .zip(santa_to_com.iter().rev())
            .take_while(|pair| pair.0 == pair.1)
            .count() - 1;


        // Compute transfers
        let transfers = (you_to_com.len() - transfer_point - 2) + (santa_to_com.len() - transfer_point - 2);
        writeln!(&mut result, "Day 6, Problem 2 - [{}]", transfers).unwrap(); // 451
    }
}