use rayon::prelude::*;
use sha2::{Digest, Sha256};

const N: usize = 10;
const SIZE: usize = 128 * 1024;

fn main() {
    println!("sequential");
    for checksum in Blobs::new(N).map(|x| sha256(&x)) {
        println!("{}", checksum);
    }

    println!("rayon");
    Blobs::new(N)
        .par_bridge()
        .map(|x| sha256(&x))
        .for_each(|x| println!("{}", x));
}

struct Blobs {
    n: usize,
}

impl Blobs {
    fn new(n: usize) -> Self {
        Self { n }
    }
}

struct Blob {
    data: [u8; SIZE],
}

impl Blob {
    fn new() -> Self {
        Self { data: [0; SIZE] }
    }
}

impl Iterator for Blobs {
    type Item = Blob;

    fn next(&mut self) -> Option<Self::Item> {
        if self.n > 0 {
            self.n -= 1;
            Some(Blob::new())
        } else {
            None
        }
    }
}

fn sha256(blob: &Blob) -> String {
    let mut hasher = Sha256::new();
    hasher.update(&blob.data);
    let hash = hasher.finalize();
    format!("{:x}", hash)
}