extern crate crypto;


use std::u64;

use crypto::md5::Md5;
use crypto::digest::Digest;


fn main() {
    println!("{:?}", process("ckczppom", "000000"));
}

fn process(secret: &str, starts_with: &str) -> Option<u64> {
    let mut md5 = Md5::new();

    for i in 1..u64::MAX {
        let input = format!("{}{}", secret, i);

        md5.input(input.as_bytes());

        let result = md5.result_str();

        if result.starts_with(starts_with) {
            return Some(i);
        }

        md5.reset();
    }

    None
}


#[cfg(test)]
mod tests {
    use super::process;

    #[test]
    fn example_01() {
        assert_eq!(Some(609043), process("abcdef", "00000"));
    }

    #[test]
    fn example_02() {
        assert_eq!(Some(1048970), process("pqrstuv", "00000"));
    }
}