Convert timestamp like Facebook and Twitter

I am fetching time from server like this: 25-07-2015 12:25:28
Now I want to show it like this:
a few second ago
1 minute ago
30 minutes ago
1 Hour ago
12 Hours ago
and after 24 Hours ago
show me the date of that day like :
25 August 2015

the following code works. But no data validation done (eg: old>new)

 <?php
$olddate = "25-08-2015 15:35:28";       //date as string
$now = time();                  //pick present time from server     
$old = strtotime( $olddate);  //create integer value of old time
$diff =  $now-$old;             //calculate difference
$old = new DateTime($olddate);
$old = $old->format('Y M d');       //format date to "2015 Aug 2015" format

    if ($diff /60 <1)                       //check the difference and do echo as required
    {
    echo intval($diff%60)."seconds ago";
    }
    else if (intval($diff/60) == 1) 
    {
    echo " 1 minute ago";
    }
    else if ($diff / 60 < 60)
    {
    echo intval($diff/60)."minutes ago";
    }
    else if (intval($diff / 3600) == 1)
    {
    echo "1 hour ago";
    }
    else if ($diff / 3600 <24)
    {
    echo intval($diff/3600) . " hours ago";
    }
    else if ($diff/86400 < 30)
    {
    echo intval($diff/86400) . " days ago";
    }
    else
    {
    echo $old;  ////format date to "2015 Aug 2015" format
    }
?>

Change the looping if you can. Logic remains same.