use std::borrow::Cow;

/// Processes a string: trims whitespace and capitalizes if needed.
/// Uses Cow to avoid cloning if the input does not require modification.
fn process_text<'a>(input: &'a str, capitalize: bool) -> Cow<'a, str> {
    let trimmed_input = input.trim(); // `trim` returns a `&str`, potentially a sub-slice.

    // If we don't need to capitalize, we can borrow the trimmed part.
    // This avoids an allocation that `to_uppercase()` would perform.
    if !capitalize {
        return Cow::Borrowed(trimmed_input);
    }

    // If capitalization is requested, we *must* produce an owned String.
    // `to_uppercase()` returns a new String, so we transition to `Cow::Owned`.
    Cow::Owned(trimmed_input.to_uppercase())
}

fn main() {
    let text1 = "  hello rust  "; // Needs trimming and capitalization
    let text2 = "WORLD";          // Already trimmed, already caps
    let text3 = "  already good  "; // Needs trimming, no caps
    let text4 = "simple";         // No trimming, no caps

    println!("'{}' (no caps): '{}'", text1, process_text(text1, false)); // Cow::Borrowed("hello rust")
    println!("'{}' (caps): '{}'", text1, process_text(text1, true));   // Cow::Owned("HELLO RUST")

    println!("'{}' (no caps): '{}'", text2, process_text(text2, false)); // Cow::Borrowed("WORLD")
    println!("'{}' (caps): '{}'", text2, process_text(text2, true));     // Cow::Owned("WORLD")

    println!("'{}' (no caps): '{}'", text3, process_text(text3, false)); // Cow::Borrowed("already good")
    println!("'{}' (caps): '{}'", text3, process_text(text3, true));     // Cow::Owned("ALREADY GOOD")

    println!("'{}' (no caps): '{}'", text4, process_text(text4, false)); // Cow::Borrowed("simple")
    println!("'{}' (caps): '{}'", text4, process_text(text4, true));     // Cow::Owned("SIMPLE")
}