Change order status just after payment in WooCommerce

Question

I need to change automatically an order status for completed after receiving payment, but only if the order status is "processing". I found that snippet, what makes orders status completed in every case, but my payments plugins after successful payment changes returns data and changes the order status for "processing". I would like to change it into "completed" after success and don't change it if the status isn't "processing". The main problem I met is I don't know how to get the received status order.

Here is my code:

add_filter( 'woocommerce_thankyou', 'update_order_status', 10, 2 );

function update_order_status( $order_id ) {
   $order = new WC_Order( $order_id );
   $order_status = $order->get_status();    
   if ('processing' == $order_status) {    
       $order->update_status( 'completed' );    
    }    
 //return $order_status;
}

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Edit:

I figured it out already. Here's the code that works for me:

add_filter( 'woocommerce_thankyou', 'update_order_status', 10, 1 );

function update_order_status( $order_id ) {
  if ( !$order_id ){
    return;
  }
  $order = new WC_Order( $order_id );
  if ( 'processing' == $order->status) {
    $order->update_status( 'completed' );
  }
  return;
}

Answer 1

Update 2 - 2019: Use WooCommerce: Auto complete paid orders (updated thread)

So the right hook to use is woocommerce_payment_complete_order_status filter returning complete

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Update 1: Compatibility with WooCommerce version 3+

I have changed the answer

Based on: WooCommerce - Auto Complete paid virtual Orders (depending on Payment methods), you will be able to handle also all payment methods in conditionals:

// => not a filter (an action hook)
add_action( 'woocommerce_thankyou', 'custom_woocommerce_auto_complete_paid_order', 10, 1 );
function custom_woocommerce_auto_complete_paid_order( $order_id ) {
    if ( ! $order_id )
        return;

    $order = new WC_Order( $order_id );

    // No updated status for orders delivered with Bank wire, Cash on delivery and Cheque payment methods.
    if ( get_post_meta($order_id, '_payment_method', true) == 'bacs' || get_post_meta($order_id, '_payment_method', true) == 'cod' || get_post_meta($order_id, '_payment_method', true) == 'cheque' ) {
        return;
     }
    // "completed" updated status for paid "processing" Orders (with all others payment methods)
    elseif ( $order->has_status( 'processing' ) ) {
        $order->update_status( 'completed' );
    }
    else {
        return;
    }
}