Create a Python function named "hyphenate_words" that takes a single string argument and returns a modified version of the string with all spaces replaced by hyphens. The function should remove all leading and trailing white spaces and convert all letters to lowercase. The output string should not contain any punctuation or special characters. Only letters, numbers, and hyphens are allowed. If the input string is empty or contains only whitespaces, the function should return an empty string.
This prompt doesn't seem malicious.