/**
   * @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. `[gimuy]*`: optional regexp flags
  5. `$`: fix the match at the end of the string
  */
  var regex = /^\/([^\\[]|\\.|\[([^\\\]]|\\.)+\])*\/[gimuy]*$/;
  
  //------------------------------------------------------------------------------
  // 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.");
              }
          }
  
      };
  
  };
  
  module.exports.schema = [];