DateTime script

//$date_ref is in this format date('Y-m-d H:i:s')
function dateTimeDiff($date_ref){
// Get the current date
$current_date = date('Y-m-d H:i:s');

    $y1 = substr($date_ref,0,4);
    $m1 = substr($date_ref,5,2);
    $d1 = substr($date_ref,8,2);
    $h1 = substr($date_ref,11,2);
    $i1 = substr($date_ref,14,2);
    $s1 = substr($date_ref,17,2);

    $y2 = substr($current_date,0,4);
    $m2 = substr($current_date,5,2);
    $d2 = substr($current_date,8,2);
    $h2 = substr($current_date,11,2);
    $i2 = substr($current_date,14,2);
    $s2 = substr($current_date,17,2);

    $r1=date('U',mktime($h1,$i1,$s1,$m1,$d1,$y1));
    $r2=date('U',mktime($h2,$i2,$s2,$m2,$d2,$y2));

    $sDf = $r2 - $r1;
    $mDf = floor($sDf/60);
    $hDf = floor($sDf/3600);
    $dDf = floor($hDf/24);
    $mnDf = floor($dDf/30);
    $yDf = floor($mnDf/12);

    if($yDf) {
        if($yDf<2)
            echo $yDf . " year ago";
        else
            echo $yDf . " years ago";
    }
    elseif($mnDf) {
        if($mnDf<2)
            echo $mnDf . " month ago";
        else
            echo $mnDf . " months ago";
    }
    elseif($dDf) {
        if($dDf<2)
            echo "yesterday";
        else
            echo $dDf . " days ago";
    }
    elseif($hDf) {
        if($hDf<2)
            echo $hDf . " hour ago";
        else
            echo $hDf . " hours ago";
    }
    elseif($mDf) {
        if($mDf<2)
            echo $mDf . " minute ago";
        else
            echo $mDf . " minutes ago";
    }
    else {
        echo $sDf . " seconds ago";
    }
}