use criterion::{criterion_group, criterion_main, Criterion};

fn load_input() -> Vec<Vec<i32>> {
    let data = std::fs::read_to_string("src/bin/part09.txt")
        .expect("Could not read file")
        .lines()
        .map(|l| {
            l.split_whitespace().map(|s| s.parse::<i32>().unwrap()).collect::<Vec<_>>()
        })
        .collect::<Vec<_>>();

    data
}

fn extrapolate_next_value(series: &[i32]) -> i32 {
    let differences = forward_differences(series);
    let mut next_value = *series.last().unwrap();

    //next_value += differences.iter().skip(1).map(|d| d.last().unwrap()).sum::<i32>();

    for diff in differences.iter().skip(1) {
        next_value += diff.last().unwrap();
    }

    next_value
}

fn forward_differences(series: &[i32]) -> Vec<Vec<i32>> {
    let mut differences = vec![series.to_vec()];
    
    while differences.last().unwrap().iter().any(|d| *d != 0) {
        let last = differences.last().unwrap();
        let next = last.windows(2).map(|w| w[1] - w[0]).collect();
        differences.push(next);
    }

    differences
}


fn bench_extrapolate_next_value(c: &mut Criterion) {
    let data = load_input();
    c.bench_function("extrapolate_next_value", |b| b.iter(|| extrapolate_next_value(&data[0])));
}

criterion_group!(benches, bench_extrapolate_next_value);
criterion_main!(benches);