// === Lageränderungen mitschreiben ===
add_action('woocommerce_product_set_stock', function($product){
    global $wpdb;
    $table = $wpdb->prefix . 'stock_log';

    // Tabelle einmalig anlegen
    if ($wpdb->get_var("SHOW TABLES LIKE '{$table}'") != $table) {
        $charset_collate = $wpdb->get_charset_collate();
        $sql = "CREATE TABLE $table (
            id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
            product_id bigint(20) unsigned NOT NULL,
            old_stock int NOT NULL,
            new_stock int NOT NULL,
            changed_at datetime NOT NULL,
            PRIMARY KEY (id)
        ) $charset_collate;";
        require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
        dbDelta($sql);
    }

    // alten und neuen Bestand abholen
    $old_stock = $product->get_changes()['stock_quantity'] ?? $product->get_stock_quantity();
    $new_stock = $product->get_stock_quantity();

    if ($old_stock != $new_stock) {
        $wpdb->insert($table, [
            'product_id' => $product->get_id(),
            'old_stock'  => intval($old_stock),
            'new_stock'  => intval($new_stock),
            'changed_at' => current_time('mysql')
        ]);
    }
}, 10, 1);

// === Admin-Menü: Log anzeigen ===
add_action('admin_menu', function(){
    add_menu_page(
        'Bestands-Log',
        'Bestands-Log',
        'manage_woocommerce',
        'stock-log',
        function(){
            global $wpdb;
            $table = $wpdb->prefix . 'stock_log';
            $rows = $wpdb->get_results("SELECT * FROM $table ORDER BY changed_at DESC LIMIT 50");
            echo '<div class="wrap"><h1>Letzte Bestandsänderungen</h1><table class="widefat"><thead><tr><th>ID</th><th>Produkt</th><th>Alt</th><th>Neu</th><th>Zeit</th></tr></thead><tbody>';
            foreach($rows as $r){
                $product = wc_get_product($r->product_id);
                echo '<tr>';
                echo '<td>' . $r->id . '</td>';
                echo '<td>' . ($product ? $product->get_name() : $r->product_id) . '</td>';
                echo '<td>' . $r->old_stock . '</td>';
                echo '<td>' . $r->new_stock . '</td>';
                echo '<td>' . $r->changed_at . '</td>';
                echo '</tr>';
            }
            echo '</tbody></table></div>';
        }
    );
});