multi file upload

<form action="upload_file.php" method="post" enctype="multipart/form-data">
<label for="file">Filename:</label><br><br><br><br>
<input type="file" class="multi" name="file[]" />
<br />
   
<input type="submit" name="submit" value="Submit" />
</form>

<?php
foreach($_FILES["file"] as $key => $file){
if ((($_file["type"] == "image/gif")
|| ($_file["type"] == "image/jpeg")
|| ($_file["type"] == "image/pjpeg"))
&& ($_file["size"] < 20000000))
  {
  if ($_file["error"] > 0)
    {
    echo "Return Code: " . $_file["error"] . "<br />";
    }
  else
    {
    $datetime = date("d_m_Y_h_i_s");
    if(!is_dir("upload/".$datetime)){
         mkdir("upload/".$datetime);
     }
    $dir = $datetime."/";
    echo "Upload: " . $_file["name"] . "<br />";
    echo "Type: " . $_file["type"] . "<br />";
    echo "Size: " . ($_file["size"] / 1024) . " Kb<br />";
    echo "Temp file: " . $_file["tmp_name"] . "<br />";

    if (file_exists("upload/" . $dir . $_file["name"]))
      {
      echo $_file["name"] . " already exists. ";
      }
    else
      {
      move_uploaded_file($_file["tmp_name"],
      "upload/" . $dir . $_file["name"]);
      echo "Stored in: " . "upload/"  . $dir . $_file["name"];
      }
    }
  }
else
  {
  echo "Invalid file";
  }
}
?>