WooCommerce add stock filter to WordPress Admin (Products)

woocommerce-stock-filter-for-wordpress-admin.php

/**
 * @snippet      Add Stock Filter to Products page in WordPress admin | WooCommerce
 * @comment      Localization is automatic if you have localized WooCommerce to your language
 * @source       https://gist.github.com/vyskoczilova/fbc9dd818af20ff514cdb2d50eab410a
 * @updatedversionof    https://popoleodesigns.com/add-inout-of-stock-filter-to-wordpress-admin/
 * @author       Karolína Vyskočilová
 * @testedwith   WooCommerce 3.0.7
 */
// -------------------

add_action( 'restrict_manage_posts', 'my_theme_admin_posts_filter_restrict_manage_posts' );
function my_theme_admin_posts_filter_restrict_manage_posts(){

    $type = 'product';
    if (isset($_GET['post_type'])) {
        $type = $_GET['post_type'];
    }

    //only add filter to post type you want
    if ('product' == $type){
        //change this to the list of values you want to show
        //in 'label' => 'value' format
        $values = array(
            __('Out of stock', 'woocommerce') => 'outofstock', 
            __('In stock', 'woocommerce') => 'instock',
        );
        ?>
        <select name="Stock">
        <option value="">-- <?php _e('Stock', 'woocommerce'); ?> --</option>
        <?php
            $current_v = isset($_GET['Stock'])? $_GET['Stock']:'';
            foreach ($values as $label => $value) {
                printf
                    (
                        '<option value="%s"%s>%s</option>',
                        $value,
                        $value == $current_v? ' selected="selected"':'',
                        $label
                    );
                }
        ?>
        </select>
        <?php
    }
}


add_filter( 'parse_query', 'my_theme_posts_filter' );

function my_theme_posts_filter( $query ){
    global $pagenow;
    $type = 'product';
    if (isset($_GET['post_type'])) {
        $type = $_GET['post_type'];
    }
    if ( 'product' == $type && is_admin() && $pagenow=='edit.php' && isset($_GET['Stock']) && $_GET['Stock'] != '') {
        $query->query_vars['meta_key'] = '_stock_status';
        $query->query_vars['meta_value'] = $_GET['Stock'];
    }
}