<?php
      /**************************************************************************************
      Author:  Abhishek Kumar Srivastava
      Email:     hide@address.com
      Purpose: The class is written for calculating difference between 2 dates
      Liscense: GNU GPL
      **************************************************************************************/

      class CalcDate
      {
          // get timestamp from current date time
          function CalculateTimestampFromCurrDatetime($DateTime = -1)
          {

              if ($DateTime == -1 || $DateTime == '' || $DateTime == '0000-00-00 00:00:00' || $DateTime == '0000-00-00')
              {
                  $DateTime = date("Y-m-d H:i:s");
              }

              $NewDate['year'] = substr($DateTime,0,4);
              $NewDate['month'] = substr($DateTime,5,2);
              $NewDate['day'] = substr($DateTime,8,2);
              $NewDate['hour'] = substr($DateTime,11,2);
              $NewDate['minute'] = substr($DateTime,14,2);
              $NewDate['second'] = substr($DateTime,17,2);

              return mktime($NewDate['hour'], $NewDate['minute'], $NewDate['second'], $NewDate['month'], $NewDate['day'], $NewDate['year']);
          }

          // calculate date difference
          function CalculateDateDifference($TimestampFirst, $TimestampSecond = -1)    
          {
              if ($TimestampSecond == -1)
              {
                  $TimestampSecond = $this->CalculateTimestampFromCurrDatetime();
              }

              if ($TimestampSecond < $TimestampFirst)
              {
                  $TempTimestamp = $TimestampFirst;
                  $TimestampFirst = $TimestampSecond;
                  $TimestampSecond = $TempTimestamp;
                  
                  $NegativeDifference = true;
              }
              else
              {
                  $NegativeDifference = false;
              }

              list($Year1, $Month1, $Day1) = split('-', date('Y-m-d', $TimestampFirst));
              list($Year2, $Month2, $Day2) = split('-', date('Y-m-d', $TimestampSecond));
              $Time1 = (date('H',$TimestampFirst)*3600) + (date('i',$TimestampFirst)*60) + (date('s',$TimestampFirst));
              $Time2 = (date('H',$TimestampSecond)*3600) + (date('i',$TimestampSecond)*60) + (date('s',$TimestampSecond));

              $YearDiff = $Year2 - $Year1;
              $MonthDiff = ($Year2 * 12 + $Month2) - ($Year1 * 12 + $Month1);

              if($Month1 > $Month2)
              {
                  $YearDiff -= 1;
              }
              elseif($Month1 == $Month2)
              {
                  if($Day1 > $Day2)
                  {
                      $YearDiff -= 1;
                  }
                  elseif($Day1 == $Day2)
                  {
                      if($Time1 > $Time2)
                      {
                          $YearDiff -= 1;
                      }
                  }
              }

              // handle over flow of month difference
              if($Day1 > $Day2)
              {
                  $MonthDiff -= 1;
              }
              elseif($Day1 == $Day2)
              {
                  if($Time1 > $Time2)
                  {
                      $MonthDiff -= 1;
                  }
              }

              $DateDifference = Array();
              $TotalSeconds = $TimestampSecond - $TimestampFirst;

              $WeekDiff = floor(($TotalSeconds / 604800));
              $DayDiff = floor(($TotalSeconds / 86400));

              if ($NegativeDifference == true)
              {
                  $DateDifference['years'] = ($YearDiff == 0) ? $YearDiff : -($YearDiff);
                  $DateDifference['months'] = ($MonthDiff == 0) ? $MonthDiff : -($MonthDiff);
                  $DateDifference['weeks'] = ($WeekDiff == 0) ? $WeekDiff : -($WeekDiff);
                  $DateDifference['days'] = ($DayDiff == 0) ? $DayDiff : -($DayDiff);
              }
              else
              {
                  $DateDifference['years'] = $YearDiff;
                  $DateDifference['months'] = $MonthDiff;
                  $DateDifference['weeks'] = $WeekDiff;
                  $DateDifference['days'] = $DayDiff;
              }
              
              return $DateDifference;
          }
      }
      ?>