wc_maybe_reduce_stock_levels()
Function: When a payment is complete, we can reduce stock levels for items within an order.
Source: includes/wc-stock-functions.php:92
wc_maybe_increase_stock_levels()
Function: When a payment is cancelled, restore stock.
Source: includes/wc-stock-functions.php:123
wc_update_product_stock()
Function: Update a product’s stock amount.
Source: includes/wc-stock-functions.php:26