pub fn pig_latin(string: &str) -> String {
    let s = String::from(string);
    let mut portion = String::new();
    let mut latinised = String::new();
    let mut starts_with_vowel = false;
    let vowels = ['a', 'e', 'i', 'o', 'u'];

    if s.is_empty() {
        return s;
    }

    let first_character = s.chars().next().unwrap();

    if vowels.contains(&first_character) {
        portion.push_str("-hay");
        starts_with_vowel = true;
    } else {
        portion = format!("-{}ay", &first_character);
    }
    for (pos, char) in s.char_indices() {
        if pos == 0 && !starts_with_vowel {
            continue;
        }
        latinised.push(char);
    }
    latinised.push_str(&portion);
    latinised
}

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

    #[test]
    fn test_pig_latin_start_with_vowel() {
        let string = "apple";
        let result = pig_latin(string);
        assert_eq!(result, "apple-hay");
    }

    #[test]
    fn test_pig_latin_start_with_consonant() {
        let string = "first";
        let result = pig_latin(string);
        assert_eq!(result, "irst-fay");
    }

    #[test]
    fn test_pig_latin_empty_string() {
        let string = "";
        let result = pig_latin(string);
        assert_eq!(result, string)
    }
}