Add SAN discount for upgrades

[tspenov]

Changes

Ticket

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have tried to find clearer solution before commenting hard-to-understand parts of code
• I have added tests that prove my fix is effective or that my feature works

Summary by CodeRabbit

• New Features

  • SAN token holders with 1,000+ tokens now automatically receive the SAN_HOLDER_1000 discount on subscription upgrade if they don't already have an active discount.

• Behavior

  • Improved handling of existing discounts during upgrades to avoid incorrectly reapplying or removing coupons.

• Tests

  • Added comprehensive tests covering SAN-based discount application and edge cases during subscription upgrades.

[coderabbitai]

📝 Walkthrough

Walkthrough

Modify subscription upgrade flow to first retrieve the Stripe subscription, remove any 100% discount when moving to basic, optionally add SAN_HOLDER_1000 coupon based on DB SAN balance and existing Stripe discount, then update the Stripe subscription. New private helper added and tests covering these scenarios included.

Changes

Cohort / File(s)	Summary
Stripe subscription logic lib/sanbase/stripe/stripe_api.ex	Refactor upgrade_downgrade/2 pipeline to fetch Stripe subscription early, change maybe_remove_coupon/3 → maybe_remove_coupon/4 to accept the stripe_subscription, add new private maybe_add_san_coupon(params, db_subscription, stripe_subscription) that applies SAN_HOLDER_1000 when user SAN ≥1000 and no existing Stripe discount, then update subscription with resulting params. Variable renamed to updated_stripe_subscription in pipeline.
Subscription upgrade tests test/sanbase/billing/subscription_test.exs	Add tests under "update_subscription - SAN discount on upgrade" to verify: coupon applied for ≥1000 SAN and no existing discount; coupon not applied if Stripe subscription already has a discount; not applied if SAN <1000; and upgrade success paths. Uses Stripe mocks and test helpers.

Sequence Diagram

sequenceDiagram
    participant Client
    participant API as upgrade_downgrade/2
    participant DB as Database
    participant Stripe as Stripe API

    Client->>API: Request subscription upgrade
    API->>Stripe: Retrieve Stripe subscription
    Stripe-->>API: Stripe subscription (discount info)
    API->>DB: Read subscription / user SAN balance
    DB-->>API: Return SAN balance
    API->>API: maybe_remove_coupon(params, db_sub, _plan, stripe_sub)
    API->>API: maybe_add_san_coupon(params, db_sub, stripe_sub)
    API->>Stripe: Update subscription with final params
    Stripe-->>API: Update confirmation
    API-->>Client: Upgrade result

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Poem

🐇 I nibble code and count my SAN,
A thousand hops — a coupon's plan.
Remove the old, add one that's new,
Upgrade done with carrot-chew! ✨

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Add SAN discount for upgrades' is clear, specific, and directly matches the core changes shown in the summary: new SAN-based discount logic (SAN_HOLDER_1000 coupon) applied during subscription upgrades.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix-san-discount-upgrades

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@lib/sanbase/stripe/stripe_api.ex`:
- Around line 283-295: The duplicate Stripe call happens because both
maybe_remove_coupon/3 and maybe_add_san_coupon/2 call
retrieve_subscription(db_subscription.stripe_id); refactor the flow to call
retrieve_subscription once (e.g., in the upgrade pipeline before those helpers)
and pass the returned stripe_subscription into both helpers by changing their
signatures to maybe_remove_coupon(..., stripe_subscription) and
maybe_add_san_coupon(..., stripe_subscription), updating all call sites to
supply the fetched stripe_subscription and removing the internal
retrieve_subscription calls from those functions.

🧹 Nitpick comments (1)

lib/sanbase/stripe/stripe_api.ex (1)

290-290: Consider extracting the coupon ID to a module attribute.

The coupon ID "SAN_HOLDER_1000" is hardcoded. Extracting it to a module attribute would improve maintainability and make it easier to change or reference consistently.

♻️ Suggested refactor

 defmodule Sanbase.StripeApi do
   `@moduledoc` """
   Module wrapping communication with Stripe.
   """
+
+  `@san_holder_coupon` "SAN_HOLDER_1000"

Then reference as @san_holder_coupon in the function.