How to set a maximum stock level for total WooCommerce variations sold, disregarding individual variation stock levels - variables

Question

I'm wondering if we are able to hook into WooCommerce to set a maximum amount of stock that can be purchased for a variable product. Disregarding the individual variation stock levels once this maximum amount is reached.
For example, I have a variable product selling workshop groups. There are 4 variations, each with a stock level set at 100. This is because no group can have more than 100 people in. However, only 250 tickets are available for sale (not 400 that we might expect because of the 4x100 quantity).
So this works as far as the max 100 places per workshop group. We just need to somehow be able to limit the total stock level of all 4 variations to 250.
I had hoped enabling the parent product "Manage stock" option and setting this to 250 would work. But obviously, variations must override this. If we can hook into that and turn that back on even when variation stock management is in use that might be a nice way of solving this.
Thanks for any help.

Answer 1

I came up with a solution to my problem by doing the following:
Add 2 custom fields to the WooCommerce product page, which will store the max quantity of the total variations we can sell and also the max quantity of an individual variation. The code for this is:
// Modify WooCommerce Product Settings
add_action('woocommerce_product_options_inventory_product_data', 'wc_add_custom_field' );
function wc_add_custom_field() {
$fields = array('Total quantity' => 'total_quantity','Variation quantity' => 'variation_quantity');
$field_description = array('total_quantity' ='description','variation_quantity' ='description');
$field_placeholder = array('total_quantity' =>'e.g. 300','variation_quantity' =>'e.g. 100');
foreach ($fields as $key => $value) {
woocommerce_wp_text_input( array(
'id' => $value,
'label' => $key,
'description' => $field_description[$value],
'desc_tip' => 'true',
'placeholder' => $field_placeholder[$value]
) );
}
}
// Save Fields
add_action( 'save_post_product', 'woo_add_custom_general_fields_save' );
function woo_add_custom_general_fields_save( $post_id ){
update_post_meta( $post_id, 'total_quantity', $_POST['total_quantity'] );
update_post_meta( $post_id, 'variation_quantity', $_POST['variation_quantity'] );
}
Add cart/basket validation rules to stop customers being able to purchase products that exceed the value of the custom "total_quantity" field added above:
add_action( "woocommerce_add_to_cart_validation","sc_woocommerce_add_to_cart_validation", 1, 5 );
function sc_woocommerce_add_to_cart_validation( $passed, $product_id, $quantity, $variation_id, $variations ) {
// Iterate through each variation and get the total stock remaining
$product_variable = new WC_Product_Variable($product_id);
$product_variations = $product_variable->get_available_variations();
settype($variation_stock_availability, "integer");
foreach ($product_variations as $variation) {
$variation_stock_availability = +(int)$variation['max_qty'];
}
$count_variations = count($product_variations);
$total_quantity = get_post_meta( $product_id, 'total_quantity', true );
$variation_quantity = get_post_meta( $product_id, 'variation_quantity', true );
// formula to test if any stock remaining based on sold variations
$formula = $count_variations * $variation_quantity;
$formula1 = (int)$formula + (int)$quantity;
$formula1 = $formula1 - $variation_stock_availability;
// Iterating through each cart item and use the current running quantity in the cart in the forumula
foreach (WC()->cart->get_cart() as $cart_item_key=>$cart_item ){
// count(selected category) quantity
$running_qty += (int) $cart_item['quantity'];
$formula2 = (int)$formula + (int)$running_qty;
$formula2 = $formula2 - $variation_stock_availability;
// More than allowed products in the cart is not allowed
if ($formula2 >= $total_places) {
wc_add_notice( sprintf( __( "Unfortunately there is no availability based on your selection", "donaheys" )), 'error' );
$passed = false;
return $passed;
}
}
// More than allowed products in the cart is not allowed
if ($formula1 >= $total_places) {
// Add the error
wc_add_notice( sprintf( __( "Unfortunately there is no availability based on your selection", "donaheys" )), 'error' );
$passed = false;
return $passed;
} else {
$passed = true;
return $passed;
}
$running_qty = 0;
}
The result of the above code ensures we are can set a maximum amount of stock that can be purchased for a variable product, disregarding the individual variation stock levels once this maximum amount is reached.