Adding product to cart on website visit

aaptc_add_product_to_cart.php

<?php
/*
* Automatically adding the product to the cart.
*/

function aaptc_add_product_to_cart() {

    if ( ! is_admin() ) {
        $product_id = 12986;  // Product Id of the free product which will get added to cart
        $found 	= false;

        //check if product already in cart
        if ( sizeof( WC()->cart->get_cart() ) > 0 ) {
            foreach ( WC()->cart->get_cart() as $cart_item_key => $values ) {
                $_product = $values['data'];
                if ( $_product->get_id() == $product_id )
                    $found = true;
            }
            // if product not found, add it
            if ( ! $found )
                WC()->cart->add_to_cart( $product_id );
        } else {
            // if no products in cart, add it
            WC()->cart->add_to_cart( $product_id );
        }
    }    
}

add_action( 'init', 'aaptc_add_product_to_cart' );
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