Adding product to cart on Add to Cart click

aaptc_add_product_to_cart.php

<?php

/*
* Automatically adding the product to the cart.
*/

function aaptc_add_product_to_cart( $item_key, $product_id ) {

	$product_category_id 	= 123; // cricket bat category id

	$product_cats_ids 	= wc_get_product_term_ids( $product_id, 'product_cat' );

    if ( ! is_admin() && in_array( $product_category_id, $product_cats_ids ) ) {
        $free_product_id = 12989;  // 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() == $free_product_id )
                    $found = true;
                
            }
            // if product not found, add it
            if ( ! $found )
                WC()->cart->add_to_cart( $free_product_id );
        } else {
            // if no products in cart, add it
            WC()->cart->add_to_cart( $free_product_id );
        }        
    }    
}

add_action( 'woocommerce_add_to_cart', 'aaptc_add_product_to_cart', 10, 2 );

Hi kartikparmar,
Thanks very much for your sharing of the code and it is really helpful.
However, may I ask a very newbie question about --- $product_category_id = 123; // cricket bat category id
I''m just wondering if I can add multiple product_category_id (Rather than only a single category ID like"123")?
If yes, what is the correct way to do it?
Much appreciated in advance!
Regards
Graham

Did you found a solution for multiply categories?

Yes. Please check out the below link and let me know if that works for you or not.
Link: https://gist.github.com/kartikparmar/409969d947edb06a91387b6d840d7c01

Hi. I'm trying to implement your code to another case but can't figure out what am I doing wrong.

I need to add extra cost (with $multiplier) to user selected shipping method based on product catogory.

So, I need to check if any of products in cart is on $product_category_id
And if so then I need to multiply selected shipping cost to $multiplier value.

This $multiplier should be applied to total shipping cost calculated by shipping method (not to every item in cart).
Can you please help?
Thanks.

<?php
add_filter( 'woocommerce_package_rates','overwrite_shipping_cost', 100, 2 );
function overwrite_shipping_cost($rates, $package ) {
    global $woocommerce;

        if ( get_field( 'multiplier', 'option' ) ) :
            $multiplier = get_field( 'multiplier', 'option' );
        else :
            $multiplier = 1;
        endif;

        $product_category_id 	= array( 86, 21, 47 ); 
        $product_cats_ids 		= wc_get_product_term_ids( $product_id, 'product_cat' ); 
        $product_category_id_check = false;
        
        foreach( $products as $cart_item ){
            $product_id = $cart_item['product_id'];
        }
                
        foreach ( $product_category_id as $key => $value ) {
            if ( in_array( $value, $product_cats_ids ) ) { 
                $product_category_id_check = true;
            }
        }
        
        if ( ! is_admin() && $product_category_id_check ) {
                    // If Shiptor 1
                    if ( isset( $rates['shiptor-shiptor:14:delivery-point_shiptor_terminal'] )) {
                        $rates['shiptor-shiptor:14:delivery-point_shiptor_terminal']->cost = $rates['shiptor-shiptor:14:delivery-point_shiptor_terminal']->cost * $multiplier;
                    } 

                    // If Shiptor 2
                    if ( isset( $rates['shiptor-shiptor:14:to-door_shiptor_courier'] )) {
                        $rates['shiptor-shiptor:14:to-door_shiptor_courier']->cost = $rates['shiptor-shiptor:14:to-door_shiptor_courier']->cost * $multiplier;
                    }

                    //If anothee shipping method
                    if ( isset( $rates['rpaefw_post_calc:16'] )) {
                        $rates['rpaefw_post_calc:16']->cost = $rates['rpaefw_post_calc:16']->cost * $multiplier;
                    }
        }


    return $rates;
}

Thank you for sharing the code.
Please check the code at the below link. I have modified it based on your requirements but I haven't tested it. Hopefully, that will work for you. Please let me know the result.
https://gist.github.com/kartikparmar/5f8a969d9261e010b0645a8ace9f500e

hi, could you tell me, how to implement this code to my source code with woocommerce ? thank you so much. I really like this code

hi, could you tell me, how to implement this code to my source code with woocommerce ? thank you so much. I really like this code

You can add this in your currently active theme's functions.php file and change the product ids according to your requirements.