fn trim_me(input: &str) -> &str {
    // TODO: Remove whitespace from both ends of a string
    // can find the 1st not whitespace and last not whitespace and then return slice
    let f = input
        .find(|c: char| !c.is_whitespace())
        .unwrap_or(input.len());
    let r = input.rfind(|c: char| !c.is_whitespace()).unwrap_or(0);
    if f < r {
        &input[f..r + 1]
    } else {
        &input[..input.len() - f]
    }
    // input.trim()
}

fn compose_me(input: &str) -> String {
    // TODO: Add " world!" to the string! There are multiple ways to do this.
    input.to_owned() + " world!"
}

fn replace_me(input: &str) -> String {
    // TODO: Replace "cars" in the string with "balloons".
    input.to_owned().replace("cars", "balloons")
}

fn main() {
    // You can optionally experiment here.
}

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

    #[test]
    fn trim_a_string() {
        assert_eq!(trim_me("   "), "");
        assert_eq!(trim_me("Hello!     "), "Hello!");
        assert_eq!(trim_me("  What's up!"), "What's up!");
        assert_eq!(trim_me("   Hola!  "), "Hola!");
        assert_eq!(trim_me("Hi!"), "Hi!");
    }

    #[test]
    fn compose_a_string() {
        assert_eq!(compose_me("Hello"), "Hello world!");
        assert_eq!(compose_me("Goodbye"), "Goodbye world!");
    }

    #[test]
    fn replace_a_string() {
        assert_eq!(
            replace_me("I think cars are cool"),
            "I think balloons are cool",
        );
        assert_eq!(
            replace_me("I love to look at cars"),
            "I love to look at balloons",
        );
    }
}