file uploading multiple times in codeigniter - codeigniter

Question

i am trying to upload files in codeigniter.but my files are uploading multiple times.this is my controller code.
public function savedocument() {
if (isset($_FILES) && !empty($_FILES)) {
$category_id = $_POST['category'];
$category_name = $_POST['category_name'];
$config = array();
$config['upload_path'] = 'uploadpath';
$config['allowed_types'] = 'gif|jpg|png|pdf|doc|docx';
$config['max_size'] = '20480';
$config['overwrite'] = FALSE;
$this->load->library('upload', $config);
$files = $_FILES;
for($i=0; $i< count($_FILES['files']['name']); $i++)
{
$_FILES['files']['name']= $files['files']['name'][$i];
$_FILES['files']['type']= $files['files']['type'][$i];
$_FILES['files']['tmp_name']= $files['files']['tmp_name'][$i];
$_FILES['files']['error']= $files['files']['error'][$i];
$_FILES['files']['size']= $files['files']['size'][$i];
$this->upload->initialize($config);
if (!$this->upload->do_upload('files')) {
$response['message'] = $this->upload->display_errors();
}
else {
$this->upload->do_upload('files');
$file_details = $this->upload->data();
//print_r($file_details);
$user_id = $this->session->userdata('user_id');
$uploaded_file_details = array(
'tmp_name' => $file_details["file_name"],
'file_name' => $file_details["orig_name"],
'size' => $file_details["file_size"],
'type' => $file_details["file_type"],
'category_name' => $category_name,
'category_id' => $category_id,
'upload_at' => date("Y-m-d H:i:s"),
'uploaded_by' => $user_id
);
$document_id = $this->document->CraeteNewDocument($uploaded_file_details);
}
redirect('admin/documents', 'refresh');
}
}
}
can anyone point out the issue.how to make if there is only one file to upload upload it once and if multiple files are selected.have to upload it.