[josunday002]

Summary

Handle referral code collisions in waitlist join

What was solved

#100 — waitlist.service: Hex referral code generation lacks collision retries on unique constraint conflicts

Add collision-safe referral code generation to WaitlistService::join by introducing a generateUniqueReferralCode() helper that retries generation (up to 3 attempts) and verifies absence in the repository before saving, plus a unit test in waitlist.service.spec.ts that mocks a duplicate code and asserts the retry path.

Addressed:

• Changed: backend/src/waitlist/waitlist.service.ts, backend/src/waitlist/waitlist.service.spec.ts
• Implement a generateUniqueReferralCode() helper in backend/src/waitlist/waitlist.service.ts that generates a hex referral code and verifies it does not already exist in the database before returning it.
• Retry generation up to 3 attempts on collision; only throw after exhausting retries.
• Use the helper inside WaitlistService::join so registrations do not fail on an initial random seed collision.

Changes

• backend/src/waitlist/waitlist.service.spec.ts (modify)
• backend/src/waitlist/waitlist.service.ts (modify)

Approach

1. In backend/src/waitlist/waitlist.service.ts, add a private generateUniqueReferralCode() helper that generates a hex referral code and checks the repository for an existing match, retrying up to 3 attempts before throwing.
2. Replace the inline referral code generation inside WaitlistService::join with a call to generateUniqueReferralCode().
3. In backend/src/waitlist/waitlist.service.spec.ts, add a unit test that mocks the repository to report a duplicate code on the first check and asserts the retry path produces a unique code.
4. Verify existing imports and repository method usage match the service's current patterns; keep all other waitlist logic untouched.

Issues

Closes #100

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