fix pig latin with empty string

src/pig_latin.rs

@@ -7,6 +7,7 @@ pub fn showroom() {
     let uppercase = String::from("UPPERCASE");
     let accent = String::from("école");
     let accent_multiples_char = String::from("église");
+    let empty = String::from("");
 
     let consonant = to_pig_latin(consonant);
     println!("And the suffix to add is: {}", consonant);
@@ -20,6 +21,8 @@ pub fn showroom() {
     println!("And the suffix to add is: {}", accent);
     let accent_multiples_char = to_pig_latin(accent_multiples_char);
     println!("And the suffix to add is: {}", accent_multiples_char);
+    let empty = to_pig_latin(empty);
+    println!("And the suffix to add is: {}", empty);
 
     println!();
 }
@@ -29,16 +32,24 @@ pub fn to_pig_latin(mut s: String) -> String {
 
     // FIXME: is there something better than removing the 1st char like this ?
     // Since 2 of the 3 branches need to reform the word.
-    let first_letter = s.remove(0);
+    let first_letter = s.chars().next();
+
+    let first_letter = if let Some(first) = first_letter {
+        first
+    } else {
+        println!("Your string is empty, impossible to transform this string to pig latin.");
+        return s;
+    };
 
     if !first_letter.is_alphabetic() {
-        // Not starting with a letter, ignore and reset the letter
-        format!("{}{}", first_letter, s)
+        println!("Not starting with a letter, impossible to transform this string to pig latin.");
+        s
     } else if vowels.contains(&first_letter.to_ascii_lowercase()) {
         // Starting with a vowel, reform the word and place add "-hay"
-        format!("{}{}-hay", first_letter, s)
+        format!("{}-hay", s)
     } else {
         // Starting with a consonant, place the consonant at the end of the word followed by "ay"
+        s.remove(0);
         format!("{}-{}ay", s, first_letter)
     }
 }