use rand::TryRngCore;
use rand::rngs::OsRng;

fn gen_psswd(len: usize) -> Result<String, Box<dyn std::error::Error>> {
    const CHARSET: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
                             abcdefghijklmnopqrstuvwxyz\
                             0123456789\
                             !@#$%^&*()-_=+[]{}|;:,.<>?";

    let mut rng = OsRng;
    let mut password = String::with_capacity(len);

    for _ in 0..len {
        let rand_index = rng.try_next_u32()? as usize % CHARSET.len();
        password.push(CHARSET[rand_index] as char);
    }

    Ok(password)
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let password = gen_psswd(16)?;
    println!("Generated secure password: {}", password);
    Ok(())
}