Add Products to user’s ID Woocommerce

/* Add to cart product api */
add_action( 'rest_api_init', function () {
    register_rest_route( 'wp/v2', 'add_to_cart_product', array(
        'methods' => array('GET','POST'),
        'callback' => 'add_to_cart_product',
    ) );
} );

function add_to_cart_product(){

    //wp_set_current_user($_POST['user_id']);
    /*wp_set_auth_cookie($_POST['user_id']);*/

    /* Required Parameters
    $_POST['user_id']
    $_POST['product_id'] */

    global $woocommerce,$wpdb;

    $array = $wpdb->get_results("select meta_value from ".$wpdb->prefix."usermeta where meta_key='_woocommerce_persistent_cart_1' and user_id = ".$_POST['user_id']);
    $data =$array[0]->meta_value;
    $cart_data=unserialize($data);

    $flag = 0;
    foreach($cart_data['cart'] as $key => $val) {
        //$_product = $val['data'];
        if($val['product_id'] != $_POST['product_id']){
            $flag = 0;
        }
        elseif($val['product_id'] == $_POST['product_id']) {
            $flag = 2;

        }
    }
    if($flag == 2){
        $cart_data['cart'][$key]['quantity']++;
    }
    else{
        $string = $woocommerce->cart->generate_cart_id( $_POST['product_id'], 0, array(), $cart_data['cart'] );
        $product = wc_get_product( $_POST['product_id'] );
        $cart_data['cart'][$string] = array(
            'key' => $string,
            'product_id' => $_POST['product_id'],
            'variation_id' => 0,
            'variation' => array(),
            'quantity' => 1,
            'line_tax_data' => array(
                'subtotal' => array(),
                'total' => array()
            ),
            'line_subtotal' => $product->get_price(),
            'line_subtotal_tax' => 0,
            'line_total' => $product->get_price(),
            'line_tax' => 0,
        );



    //echo "<pre>";
    //print_r($cart_data);
    //exit;
    //$serialize_data = serialize($cart_data);
    //$woocommerce->cart->add_to_cart( $_POST['product_id'] );
    update_user_meta($_POST['user_id'],'_woocommerce_persistent_cart_1',$cart_data);
    return cart_items(); // API response whatever you want
}