use rand::Rng;
pub fn generate(rng: &mut rand::rngs::ThreadRng) -> String {
let mut digits: Vec<u8> = (0..rng.gen_range(1..9))
.map(|_| rng.gen_range(0..=9))
.collect();
if digits.is_empty() {
digits.push(rng.gen_range(1..=9));
}
let mut sum: i32 = 0;
for (i, &d) in digits.iter().rev().enumerate() {
sum += (i as i32 + 2) * d as i32;
}
let check = ((-(sum) % 11).rem_euclid(11) % 10) as u8;
digits.push(check);
digits.iter().map(|d| (b'0' + d) as char).collect()
}
pub fn validate(code: &str) -> bool {
let clean: String = code.chars().filter(|c| c.is_ascii_digit()).collect();
if clean.is_empty() || clean.len() > 9 {
return false;
}
let digits: Vec<u8> = clean.bytes().map(|b| b - b'0').collect();
let n = digits.len();
let mut sum: i32 = 0;
for (i, &d) in digits[..n - 1].iter().rev().enumerate() {
sum += (i as i32 + 2) * d as i32;
}
let expected = ((-(sum) % 11).rem_euclid(11) % 10) as u8;
expected == digits[n - 1]
}