Resizing images while uploading via File Manager

<?php
// Options
$ext_pics = array(".jpg", ".jpeg", ".gif", ".png");
$max_x="1000";
$max_y="800";

// Change picture`s pixel size 
function create_small($name_big,$name_small,$max_x="800", $max_y="600")
{
  list($x, $y, $t, $attr) = getimagesize($name_big);
  if ($x > 1000)
  {
    if ($t == IMAGETYPE_GIF)
      $big=imagecreatefromgif($name_big);
    else if ($t == IMAGETYPE_JPEG)
      $big=imagecreatefromjpeg($name_big);
    else if ($t == IMAGETYPE_PNG)
      $big=imagecreatefrompng($name_big); 
    else 
      return;    
    
    if ($x > $y)
    {
      $xs=$max_x;
      $ys=$max_x/($x/$y);
    }
    else 
    {
      $ys=$max_y;
      $xs=$max_y/($y/$x);
    }
    $small=imagecreatetruecolor ($xs,$ys);
    $res = imagecopyresampled($small,$big,0,0,0,0,$xs,$ys,$x,$y);
    imagedestroy($big);
    imagejpeg($small,$name_small);
    imagedestroy($small);
  }       
}

$currentdoc = $modx->newObject('modResource');
foreach($files as $file)
{
    $full_filename=$file['name'];
    foreach($ext_pics as $ext_pic)
    {
      $pos = strpos($full_filename, $ext_pic);
      if ($pos === false) {
        // not picture  
      } else {
        if($file['error'] == 0)
        {
          $pathInfo = pathinfo($file['name']);
          $oldPath = $directory.$file['name'];
          $final_name=$pathInfo['filename']).substr(md5(time()), 11).'-'.date("Y-m-d-h-s");
          $newPath = $currentdoc->cleanAlias($final_name.'.'.$pathInfo['extension'];
          $source->renameObject($oldPath, $newPath);
          create_small($newPath,$newPath,$max_x,$max_y);
        }
      }  
    }    
}

      
?>