Drupal Commerce - Persistent Data Storage within the Cart

Question

My objective is to build an commerce site that attributes 'tokens' (integer values) to products and than keeps a running total of the complete token value within the cart. The idea is to check against how many tokens the user has before allowing a purchase, allowing a product to be added to cart, etc. etc. So far my strategy has been to do this:

1. Hook_entity_info_alter on the line item product type 'token-based-products' to add a persistent data field for the token value which is required and accessible within views. This seems pretty straight forward.
2. My Question. How do I keep persistent data storage about tokens within the cart for validation? The objective for this is to create a few hooks that check the running total token value of the cart before allowing/disallowing a product being added AND before allowing products to be checked out.

Answer 1

I discovered that the wise thing to do was to attribute tokens per user and do either a custom module validation or rules before the product being approved for checkout. Due to the fact that quantities can change in the cart, the validation would also trigger on deletes, or quantity changes in the cart.