Allowing Subscriptions & Products to be purchased in the same checkout.

products-plus-subscriptions.md

Things that will need to be done:

1. Unhook the WC_Subscriptions::maybe_empty_cart() and replace it with a similar function that doesn't empty the cart when a subscription is added (but does still call WC_Subscriptions::remove_subscriptions_from_cart() if the cart contains a subscription (WC_Subscriptions_Cart::cart_contains_subscription())
2. You probably also want to remove the redirection to the checkout page immediately after a subscription is added to the cart. To do that, remove the WC_Subscriptions::add_to_cart_redirect() function from the 'add_to_cart_redirect' hook, or if you want to redirect to the cart page, use similar code to this: https://gist.github.com/thenbrent/7254424
3. Make sure the totals are calculated correctly. This is the hard part. More details below.
4. Make sure order line items show up correctly after purchase - I don't think you'll need to change anything here, hopefully it will just work.

To understand how totals are calculated, refer to the following functions:

• WC_Subscriptions_Cart::add_calculation_price_filter() hooked to 'woocommerce_before_calculate_totals'
• WC_Subscriptions_Cart::set_subscription_prices_for_calculation() hooked to 'woocommerce_get_price'
• WC_Subscriptions_Cart::remove_calculation_price_filter() hooked to 'woocommerce_calculate_totals'
• WC_Subscriptions_Cart::calculate_subscription_totals() hooked to 'woocommerce_calculated_total'
• WC_Subscriptions_Cart::set_calculated_total() hooked to 'woocommerce_calculated_total'

Each of these has pretty good inline documentation to explain their purpose, but it will take a bit to get your head around the system as a whole and how it hooks in and where/when.

The most important thing is to understand the WC_Subscriptions_Cart::$calculation_type flag and that multiple calculations are completed for each of a subscription's pricing elements.

Hopefully, it will be possible to set the $sign_up_fee in WC_Subscriptions_Cart::set_subscription_prices_for_calculation() to be: any sign up fee on the subscription in the cart plus the total base price for all the products in the cart. That way, Subscriptions/WooCommerce should run all the appropriate calculations correctly. It's a complex area though so it may be more complicated than that.

You'll need a new filter in WC_Subscriptions_Cart::set_subscription_prices_for_calculation() for setting the sign-up fee, so I've added a 'woocommerce_subscriptions_cart_get_price' filter (woothemes/woocommerce-subscriptions@734397c).

Other considerations:

• Let me know if you need any additional hooks and I can add them in
• Although this will start as a plugin, I'd like to merge into the main code base for 1.5 a few months down the track, so please take general usage into consideration (like supporting free trials with no sign-up fee etc.)