Coupon Usage & Condition Handling

[RealMrHex]

Hi again @Safemood,

I've implemented your package in our system and encountered a few scenarios that raise some concerns. I have a couple of questions regarding coupon usage and condition handling:

1. Undoing Coupon Usage

How can we revert a coupon usage in specific scenarios? Here's our issue:

• Users apply a coupon at checkout, see the discounted total, and proceed to the payment gateway.
• If they close the checkout page after applying the coupon, the coupon is consumed (burned).
• If they proceed to the payment gateway but cancel the payment or the invoice expires, the coupon is still considered used.

For single-use coupons, this behavior causes problems since the coupon is effectively lost even if no payment occurs.

Proposed Solution:
A way to verify coupon usage, perhaps with usingBy and usedBy attributes in the coupon's JSON data, could help. A verifyUsage method might allow the system to associate the coupon with a user temporarily and finalize its usage only upon successful payment.

2. Preventing Multiple Usages in Parallel Sessions

Another issue arises when a user opens multiple checkout pages:

• Suppose we create a single-use coupon.
• The user opens three checkout pages simultaneously and applies the coupon to all three.
• Since the coupon usage isn't finalized yet, all three carts receive the discount.
• The user can then proceed to payment for all three carts, effectively bypassing the single-use restriction.

This creates a serious issue where single-use coupons can be exploited.

3. Applying Conditions to Coupons

We also need a way to apply conditions based on specific products/items. For example, we may want to:

• Restrict a coupon to only apply to certain products.
• Define conditions like a minimum quantity, category-based discounts, etc.

Currently, I couldn't find a built-in way to set such conditions. Do you have any suggestions on how we can achieve this?

Looking forward to your thoughts! Thanks for your time.

[Safemood]

Hi @RealMrHex!

Unfortunately, we cannot revert a coupon once it’s used (you can recreate it).

I recommend that instead of applying the coupon immediately, you use Coupon::get('code') and apply it during the successful payment operation. This will return the discount value, allowing you to use it on your frontend.

To address the race condition issue, we can implement a "Pessimistic Locking" mechanism to prevent multiple uses in parallel sessions. This will avoid the exploit where a user can use the coupon across multiple checkout pages. Even I believe that, in the current API, if the user applies the coupon to multiple carts, they can only proceed with the discount once.

As for the conditions, the current API doesn’t support product-specific restrictions, but this could definitely be a useful feature to add in the future.