function InputError(message){
  this.message = message;
  this.stack = (new Error()).stack;

}

  var regex1 = /(\w\W)+/;
  var regex2 = /^[a-zA-Z0-9_$]$/g;
  var nregex2 = /[^a-zA-Z0-9_$]-?/g;
  var regex4 = new RegExp("\\b(" + word + ")\\b" , "gi");
  var regex5 = /^[a-zA-Z0-9_.-]@mailbox.tu-berlin.de$/gi;

function getCharacterCount (text) {

  if(text.test(regex1)){
    return text.length;
  }
  else {
    return 0;
  }
}

function getWords (text) {
  if(text.test(regex1) && text.test(regex2)){
    return text.split(nregex2);
  } else {
    return [];
  }
}

function getLongestWords (text) {
  var array = text.getWords();
  var result = [];
  if (array.length > 0){
    for(var i = 0; i<array.length; i++){
      if (result[0].length <= array[i].length){
        result.push(array[i]);
      }
    }
    return result;
  } else {
    return [];
  }
}

function getWordFrequency (text) {
  var word;
  var result = [];
  var array = text.getWords();
  if (array.length > 0){
    for(var i = 0; i<array.length; i++){
      var count = 0;
      word = array[i];
      for(var i = 0; i<array.length; i++){
        if(array[i].test(regex4)){
          count++;
        }
      }
      result.push(word + ":" + count);
    };
    return result;
  } else {
    return {};
  }

}

function filterTUBMails (text) {
  if(text.test(regex1)){
    var array = text.split(" ");
    var result = array.filter(word => regex5);
    return result;
  } else {
    return [];
  }
}