use nom::{
    bytes::complete::{take_until, take, tag},
    character::complete::{
        newline, multispace1, alphanumeric1,
    },
    sequence::{preceded, separated_pair},
    multi::separated_list1,
    IResult,
};
use std::collections::HashMap;
use std::str::Chars;

fn parse_mapline(input: &str) -> IResult<&str, (&str, (&str, &str))> {
    let (input, start) = take(3 as usize)(input)?;
    let (input, (left, right)) = preceded(tag(" = ("), separated_pair(alphanumeric1, tag(", "), alphanumeric1))(input)?;
    Ok((input, (start, (left, right))))
}

pub fn part1(input: &str) -> String {
    let mut lines = input.lines();
    let instructions = lines.next().unwrap().chars();
    let map = lines.skip(1).map(|line| {
        parse_mapline(line).unwrap().1
    }).collect::<HashMap<&str, (&str, &str)>>();
    let mut total_steps = 0;
    let mut position = "AAA";
    for _ in 0..100 {
        for instruction in instructions.clone() {
            total_steps += 1;
            let (left, right) = map.get(position).unwrap();
            if instruction == 'L' {
                position = left;
            } else {
                position = right;
            }
            if position == "ZZZ" { return total_steps.to_string(); };
        }
    };
    total_steps.to_string()
}

pub fn part2(input: &str) -> String {
    let mut lines = input.lines();
    let instructions = lines.next().unwrap().chars();
    let map = lines.skip(1).map(|line| {
        parse_mapline(line).unwrap().1
    }).collect::<HashMap<&str, (&str, &str)>>();
    let start_nodes = map.keys().into_iter().filter(|x| x.chars().last().unwrap() == 'A').collect::<Vec<_>>();
    let mut total_steps = 0;
    let mut positions = start_nodes;
    for _ in 0..10000000 {
        for instruction in instructions.clone() {
            total_steps += 1;
            for i in 0..positions.len() {
                let (left, right) = map.get(positions[i]).unwrap();
                if instruction == 'L' {
                    positions[i] = &left;
                } else {
                    positions[i] = &right;
                }
            }
            if positions.iter().all(|x| {x.chars().last().unwrap() == 'Z'}) { return total_steps.to_string(); };
        }
    };
    total_steps.to_string()
}

pub mod prelude {
    pub use super::part1;
    pub use super::part2;
}