use std::time::Instant;

fn distribute_presents(street: &mut [usize], start_index: usize) -> (usize, usize) {
    let street_length = street.len();

    let mut presents = street[start_index];
    street[start_index] = 0;
    let steps = presents;

    if presents > street_length - 1 {
        let number_of_presents = presents.div_euclid(street_length);
        presents -= number_of_presents * street_length;
        street.iter_mut().for_each(|p| *p += number_of_presents);
    }
    // Check rest of presents:
    let mut index = (start_index + 1) % street_length;
    for _ in 0..presents {
        street[index] += 1;
        index = (index + 1) % street_length;
    }
    (steps, index)
}

fn puzzle1() {
    let mut street: Vec<usize> = include_str!("../../data/tweakers.input")
        .split_whitespace()
        .map(|s| s.parse::<usize>().expect("Invalid input"))
        .collect();
    println!("Start processing input... ");

    let start = Instant::now();
    let mut total_steps = 0;
    let mut start_index = 0;
    loop {
        let (steps, index) = distribute_presents(&mut street, start_index);
        total_steps += steps + 1;
        start_index = index;
        if steps == 0 {
            break;
        }
    }
    println!("{:?}", total_steps - 1);

    let elapsed = start.elapsed();
    println!("total time elapsed: {:?}", elapsed);
}

fn puzzle2() {
    let mut street: Vec<usize> = include_str!("../../data/tweakers.input")
        .split_whitespace()
        .map(|s| s.parse::<usize>().expect("Invalid input") * 2025)
        .collect();
    println!("Start processing input... ");

    let start = Instant::now();
    let mut total_steps = 0;
    let mut start_index = 0;
    loop {
        let (steps, index) = distribute_presents(&mut street, start_index);
        total_steps += steps + 1;
        start_index = index;
        if steps == 0 {
            break;
        }
    }
    println!("{:?}", total_steps - 1);

    let elapsed = start.elapsed();
    println!("total time elapsed: {:?}", elapsed);
}

fn main() {
    puzzle1();
    puzzle2();
}