/*
** check a date
** dd.mm.yyyy || mm/dd/yyyy || dd-mm-yyyy || yyyy-mm-dd 
*/

function check_date($date) {
    if(strlen($date) == 10) {
        $pattern = '/\.|\/|-/i';    // . or / or -
        preg_match($pattern, $date, $char);
        
        $array = preg_split($pattern, $date, -1, PREG_SPLIT_NO_EMPTY); 
        
        if(strlen($array[2]) == 4) {
            // dd.mm.yyyy || dd-mm-yyyy
            if($char[0] == "."|| $char[0] == "-") {
                $month = $array[1];
                $day = $array[0];
                $year = $array[2];
            }
            // mm/dd/yyyy    # Common U.S. writing
            if($char[0] == "/") {
                $month = $array[0];
                $day = $array[1];
                $year = $array[2];
            }
        }
        // yyyy-mm-dd    # iso 8601
        if(strlen($array[0]) == 4 && $char[0] == "-") {
            $month = $array[1];
            $day = $array[2];
            $year = $array[0];
        }
        if(checkdate($month, $day, $year)) {    //Validate Gregorian date
            return TRUE;
        
        } else {
            return FALSE;
        }
    }else {
        return FALSE;    // more or less 10 chars
    }
}

check_date('21.02.1983');
check_date('21-02-1983');
check_date('02/21/1983'); // Common U.S. writing
check_date('1983-02-21'); // iso 8601