use rand::RngCore;
use sha2::{Digest, Sha256};

pub struct CodeGenerator {
    counter: u64,
    salt: [u8; 32],
}

impl CodeGenerator {
    pub fn generate(&mut self) -> String {
        let count = self.counter;
        self.counter += 1;

        let mut hasher = Sha256::new();
        hasher.update(self.salt);
        hasher.update(count.to_be_bytes());

        format!("{:x}", hasher.finalize())[..6].to_string()
    }
}

impl Default for CodeGenerator {
    fn default() -> Self {
        let mut salt = [0; 32];
        rand::thread_rng().fill_bytes(&mut salt);

        CodeGenerator { counter: 0, salt }
    }
}

#[cfg(test)]
mod test {
    use super::*;
    #[test]
    fn test_generate() {
        let code = CodeGenerator::default().generate();
        assert_eq!(code.len(), 6);
    }
}