/// Encodes a String as ROT13.
/// Maintains lower/upper case, ignores all non [A-Za-z] characters.
///
/// # Examples
///
/// ```
/// use rot13::rot13;
///
/// assert_eq!("Uryyb Jbeyq!", rot13("Hello World!"));
/// assert_eq!("Test", rot13(&rot13("Test")));
/// ```

pub fn rot13(text: &str) -> String {
    text.chars().map(|c| {
        match c {
            'A' ... 'M' | 'a' ... 'm' => ((c as u8) + 13) as char,
            'N' ... 'Z' | 'n' ... 'z' => ((c as u8) - 13) as char,
            _ => c
        }
    }).collect()
}

#[cfg(test)]
mod test {
    use rot13;

    #[test]
    fn test_simple_case() {
        assert_eq!("nopq", rot13("abcd"));
    }

    #[test]
    fn test_with_non_latin_characters() {
        assert_eq!("Jöegre", rot13("Wörter"));
    }

    #[test]
    fn test_with_non_ascii_characters() {
        assert_eq!("n😋o", rot13("a😋b"));
    }

    #[test]
    fn test_can_be_reversed_by_applying_twice() {
        assert_eq!("Hello World!", rot13(&rot13("Hello World!")));
    }
}