Add stock qty and status to variation dropdown

add_filter( 'woocommerce_dropdown_variation_attribute_options_html', 'variations_options_html_callback', 10, 2);

function variations_options_html_callback( $html, $args ){

$args = wp_parse_args( apply_filters( 'woocommerce_dropdown_variation_attribute_options_args', $args ), array(
'options' => false,
'attribute' => false,
'product' => false,
'selected' => false,
'name' => '',
'id' => '',
'class' => '',
'show_option_none' => __( 'Choose an option', 'woocommerce' ),
) );

$options = $args['options'];
$product = $args['product'];
$attribute = $args['attribute'];
$name = $args['name'] ? $args['name'] : 'attribute_' . sanitize_title( $attribute );
$id = $args['id'] ? $args['id'] : sanitize_title( $attribute );
$class = $args['class'];
$show_option_none = $args['show_option_none'] ? true : false;
$show_option_none_text = $args['show_option_none'] ? $args['show_option_none'] : __( 'Choose an option', 'woocommerce' ); // We'll do our best to hide the placeholder, but we'll need to show something when resetting options.

if ( empty( $options ) && ! empty( $product ) && ! empty( $attribute ) ) {
$attributes = $product->get_variation_attributes();
$options = $attributes[ $attribute ];
}

$html = '<select id="' . esc_attr( $id ) . '" class="' . esc_attr( $class ) . '" name="' . esc_attr( $name ) . '" data-attribute_name="attribute_' . esc_attr( sanitize_title( $attribute ) ) . '" data-show_option_none="' . ( $show_option_none ? 'yes' : 'no' ) . '">';
$html .= '<option value="">' . esc_html( $show_option_none_text ) . '</option>';

if ( ! empty( $options ) ) {
if ( $product && taxonomy_exists( $attribute ) ) {
// Get terms if this is a taxonomy - ordered. We need the names too.
$terms = wc_get_product_terms( $product->get_id(), $attribute, array( 'fields' => 'all' ) );

foreach ( $terms as $term ) {
if ( in_array( $term->slug, $options ) ) {

$stock_status = get_variation_stock_status( $product, $name, $term->slug );

$html .= '<option value="' . esc_attr( $term->slug ) . '" ' . selected( sanitize_title( $args['selected'] ), $term->slug, false ) . '>' . esc_html( apply_filters( 'woocommerce_variation_option_name', $term->name ).$stock_status ) . '</option>';
}
}
} else {
foreach ( $options as $option ) {
// This handles < 2.4.0 bw compatibility where text attributes were not sanitized.
$selected = sanitize_title( $args['selected'] ) === $args['selected'] ? selected( $args['selected'], sanitize_title( $option ), false ) : selected( $args['selected'], $option, false );
$html .= '<option value="' . esc_attr( $option ) . '" ' . $selected . '>' . esc_html( apply_filters( 'woocommerce_variation_option_name', $option ) ) . '</option>';
}
}
}

$html .= '</select>';

return $html;
}

function get_variation_stock_status( $product, $name, $term_slug ){
foreach ( $product->get_available_variations() as $variation ){
if($variation['attributes'][$name] == $term_slug ){
$variation_obj = wc_get_product( $variation['variation_id'] );
$stock_qty = $variation_obj->get_stock_quantity();
break;
}
}

return $stock_qty == 0 ? ' - (Niet op voorraad)' : ' - ' . $stock_qty . ' op voorraad';

}