use base64::Engine;
use base64::engine::general_purpose::URL_SAFE_NO_PAD;
use rand::Rng;
use rand::rngs::OsRng;
use sha2::{Digest, Sha256};

pub fn generate_numeric_code(len: usize) -> String {
    let mut rng = OsRng;
    (0..len)
        .map(|_| rng.gen_range(0..10u32).to_string())
        .collect()
}

pub fn sha256_b64url(data: &[u8]) -> String {
    URL_SAFE_NO_PAD.encode(Sha256::digest(data))
}

pub fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
    if a.len() != b.len() {
        return false;
    }
    let mut diff = 0u8;
    for (x, y) in a.iter().zip(b.iter()) {
        diff |= x ^ y;
    }
    diff == 0
}