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

fn main() -> Result<(), Box<dyn Error>> {
    let file = File::open("inputs/day23.txt")?;
    let mut lines = io::BufReader::new(file).lines().map(|l| l.unwrap());
    let line = lines.nth(0).expect("No line in file.");

    let input: Vec<usize> = line
        .chars()
        .map(|c| c.to_string().parse().expect("Can't parse number"))
        .collect();

    let cup_count = 1_000_000;

    // Initilize the linked list with cup_count ordered cups
    let mut cups = Vec::with_capacity(cup_count + 1);
    for v in 0..cup_count + 1 {
        cups.push(v + 1)
    }

    // Order the first ten according to the input
    for i in 0..input.len() - 1 {
        let cup = input[i];
        let next_cup = input[i + 1];

        cups[cup] = next_cup;
    }

    // Initialize cup zero, used as the 'current cup' later
    cups[0] = input[0];

    // Connect the ends
    // The last from the input, points to the first autogenerated cup
    cups[input[input.len() - 1]] = input.len() + 1;

    let idx = cups.len() - 1;
    cups[idx] = input[0];

    for _ in 1..10_000_001 {
        let cur_cup = cups[0];

        let taken1 = cups[cur_cup];
        let taken2 = cups[taken1];
        let taken3 = cups[taken2];
        cups[cur_cup] = cups[taken3];
        cups[0] = cups[taken3];

        let mut dest = cur_cup;
        while dest == taken1 || dest == taken2 || dest == taken3 || dest == cur_cup {
            dest = if dest - 1 == 0 { cup_count } else { dest - 1 }
        }

        let cut = cups[dest];
        cups[dest] = taken1;
        cups[taken3] = cut;
    }

    let a = cups[1];
    let b = cups[a];

    println!("Cups: {} {}", a, b);

    let answer = a * b;
    println!("Answer: {}", answer);

    Ok(())
}

#[cfg(test)]
mod tests {
    use crate::*;
}