SugarLogic Custom Function subDate()

<?php
/*
 * File Location:
 * /custom/include/Expressions/Expression/Date/psi_SubDateExpression.php
 */
require_once('include/Expressions/Expression/Date/DateExpression.php');

/**
 * <b>psi_subDate($date1, $date2)</b><br>
 * Returns an absolute value integer of the number of days between <em>$date1</em> and <em>$date2</em>
 * ex: <em>psi_subDate(date("1/1/2010"), date("1/5/2010"))</em> = "4"
 **/
class psi_SubDateExpression extends DateExpression{

  static function getOperationName() {
    return "psi_subDays";
  }

  static function getParameterTypes() {
    return array("date", "date");
  }

  static function getParamCount() {
    return 2;
  }

  function toString() {

  }

  function evaluate() {
    $params = $this->getParameters();
    $date1 = DateExpression::parse($params[0]->evaluate());
    $date2 = DateExpression::parse($params[1]->evaluate());
    if(!$date1) {
      return false;
    }
    if(!$date2){
      return false;
    }

    $date1_string = $date1->format('U');
    $date2_string = $date2->format('U');
    $diff = $date1_string - $date2_string;
    $diff = abs($diff);

    if(is_int($diff)){
      $seconds = $diff;
      $minutes = $diff/60;
      $hours = $minutes/60;
      $days = $hours/24;
      return $days;
    } else {
      return false;
    }


  }


  static function getJSEvaluate() {
  return <<<EOQ
  var params = this.getParameters();
  var date1 = SUGAR.util.DateUtils.parse(params[0].evaluate(), 'user');
  var date2 = SUGAR.util.DateUtils.parse(params[1].evaluate(), 'user');

  /*
   * heavily derived from this SO posting...
   * http://stackoverflow.com/a/12004010
   * -- Matt Poer
   */
  var datediff = date1.getTime() - date2.getTime(); //store the getTime diff - or +
  return (datediff / (24*60*60*1000)); //Convert values to -/+ days and return value
EOQ;
  }

}