/**
 * @fileoverview Rule to flag the use of empty character classes in regular expressions
 * @author Ian Christian Myers
 */

"use strict";

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

/*
plain-English description of the following regexp:
0. `^` fix the match at the beginning of the string
1. `\/`: the `/` that begins the regexp
2. `([^\\[]|\\.|\[([^\\\]]|\\.)+\])*`: regexp contents; 0 or more of the following
  2.0. `[^\\[]`: any character that's not a `\` or a `[` (anything but escape sequences and character classes)
  2.1. `\\.`: an escape sequence
  2.2. `\[([^\\\]]|\\.)+\]`: a character class that isn't empty
3. `\/` the `/` that ends the regexp
4. `[gimy]*`: optional regexp flags
5. `$`: fix the match at the end of the string
*/
var regex = /^\/([^\\[]|\\.|\[([^\\\]]|\\.)+\])*\/[gimy]*$/;

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

module.exports = function(context) {

    return {

        "Literal": function(node) {
            var token = context.getFirstToken(node);
            if (token.type === "RegularExpression" && !regex.test(token.value)) {
                context.report(node, "Empty class.");
            }
        }

    };

};