<?php

  /**
   * Parses the given datetime string and changes it to the given format. This uses strtotime()
   * to convert the datetime to timestamp, then changes format using date()
   *
   * @param string $dateStr String representing the datetime. If empty current datetime is used.
   * @param string $format  The desired format. Default: d/m/Y
   * @param string $defaultIfInvalid A value to be returned if the given datetime is invalid
   *
   * @return string
   */

  public static function formatDate($dateStr = '',$format = 'd/m/Y',$defaultIfInvalid = '-') {

      $dateStr = trim($dateStr);

      if(!$dateStr) {
          $dateStr = date( 'Y-m-d H:i:s' );
      }

      $format = trim($format);

      if(!$format) {
          $format = 'd/m/Y';
      }

      $ts = strtotime($dateStr);

      if(!$ts) {
          return $defaultIfInvalid;
      }

      return date($format,$ts);

  }