(SP: 5) [Quiz] Redis caching + guest session fix + cleanup

[LesiaUKR]

Summary

Closes #260
Closes #261
Closes #262

• Implement Redis caching for quiz answer verification (replaces AES-256-GCM encryption)
• Fix guest language switch on result screen
• Remove redundant files after Redis migration
• Improve accessibility with WCAG-compliant color contrast

Issues Closed

Issue	SP	Description
#260	3	Redis cache for quiz answer verification
#261	1	Guest language switch fix
#262	1	Codebase cleanup

Changes

Redis Cache (#260)

• Cache correct answers per quiz in Redis (12h TTL)
• Replace AES decryption with O(1) Redis lookup
• Single DB query per cache miss (shared by all users)
• Add initializeQuizCache server action

Guest Language Switch Fix (#261)

• Guest result screen survives language switch
• Session with completed status is now restored

Codebase Cleanup (#262)

Deleted	Reason
PendingResultHandler.tsx	Never runs (auth → dashboard)
start-session/route.ts	Broken import, unused
quiz-crypto.ts	AES replaced by Redis
quiz-crypto.test.ts	Tests dead code

WCAG Accessibility

• Improved color contrast for quiz UI elements
• Compliant with WCAG 2.1 AA standards

Known Limitations (documented)

• Server-side time enforcement deferred (low priority)
• Hydration flash on refresh (~100-300ms)

Test Results

• All 66 quiz tests pass
• verify-answer.test.ts rewritten for Redis API

Test plan

• Authenticated user: quiz flow with points
• Guest user: quiz flow with "Login to save"
• Guest → auth sync: pending result saved on dashboard
• Language switch mid-quiz: progress preserved
• Language switch on guest result: result preserved

Summary by CodeRabbit

• New Features

  • Debug endpoints to inspect and clear quiz answer cache in development.

• Improvements

  • Accessibility enhancements (aria-hidden for decorative icons).
  • Quiz start now initializes server-side cache to reduce verification latency.
  • Dashboard and layout utility refinements.

• Bug Fixes

  • More reliable session restoration (completed sessions load correctly).
  • Simplified answer verification flow with clearer success/error responses.

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Project	Deployment	Actions	Updated (UTC)
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[coderabbitai]

📝 Walkthrough

Walkthrough

Migrates quiz answer verification from client-side encryption to a Redis-backed server cache. Adds cache utilities and initialization action, updates verify-answer API and quiz components to use cached answers, removes crypto module and PendingResultHandler, adds Redis debug routes, and performs widespread import/formatting cleanup.

Changes

Cohort / File(s)	Summary
Redis quiz cache & API frontend/lib/quiz/quiz-answers-redis.ts, frontend/actions/quiz.ts, frontend/app/api/quiz/verify-answer/route.ts	Added Redis-backed quiz answer cache (getOrCreateQuizAnswersCache, getCorrectAnswer); new initializeQuizCache action; verify-answer now queries cache (payload: quizId, questionId, selectedAnswerId) and returns { success, isCorrect }.
Debug endpoints frontend/app/api/debug/redis/route.ts, frontend/app/api/debug/redis-clear/route.ts	New dev-only GET/DELETE endpoints to inspect and clear quiz:answers:* keys from Redis.
Removed crypto & tests frontend/lib/quiz/quiz-crypto.ts, frontend/lib/tests/quiz/quiz-crypto.test.ts	Deleted AES-based quiz encryption/decryption module and its test suite.
Quiz components & props frontend/components/quiz/QuizContainer.tsx, frontend/components/quiz/QuizResult.tsx, frontend/components/quiz/QuizQuestion.tsx, frontend/components/quiz/QuizProgress.tsx, frontend/components/quiz/CountdownTimer.tsx, frontend/components/quiz/QuizCard.tsx	Removed encryptedAnswers prop; initialize cache on start; verify requests updated; replaced AlertTriangle→TriangleAlert; accessibility additions (aria-hidden, shrink-0); removed quizSlug from QuizResult; minor UI/class updates.
Pending result flow frontend/components/quiz/PendingResultHandler.tsx, frontend/components/auth/PostAuthQuizSync.tsx	Deleted PendingResultHandler component; PostAuthQuizSync removed router usage and uses window.location.reload() after successful sync.
Quiz page & session frontend/app/[locale]/quiz/[slug]/page.tsx, frontend/lib/quiz/quiz-session.ts	Redirect when missing/invalid seed; removed encrypted blob creation and PendingResultHandler render; session restore logic relaxed to allow completed to be loaded.
Verification tests & mocks frontend/lib/tests/quiz/verify-answer.test.ts, frontend/lib/tests/quiz/quiz-session.test.ts	Updated verify-answer tests to mock Redis/getCorrectAnswer and new request shape; removed crypto tests; adjusted quiz-session expectations for completed sessions.
Seed & db scripts frontend/db/seed-quiz-react.ts, other seed files	Renamed cleanupReactQuiz to _cleanupReactQuiz and removed its invocation; small import spacing fixes.
Formatting & imports 50+ files (components, tests, db queries, services, utils) e.g., frontend/app/[locale]/dashboard/page.tsx, frontend/components/**, frontend/db/..., frontend/lib/...	Widespread import spacing and formatting changes, minor Tailwind utility renames/sizing updates, and removal of unused imports (cosmetic).
Config updates frontend/eslint.config.mjs, frontend/tsconfig.json	Added _dev-notes/** to ESLint globalIgnores; added "node" to TypeScript types.

Sequence Diagram

sequenceDiagram
    participant Client as Quiz Client
    participant Server as API Server
    participant Redis as Redis Cache
    participant DB as Database

    rect rgba(100,150,200,0.5)
    Note over Client,DB: Old Flow (Encryption-Based)
    Client->>Client: Encrypt correct answers (client-side)
    Client->>Server: POST /verify-answer with encryptedAnswers
    Server->>Server: Decrypt encryptedAnswers
    Server->>Server: Compare decrypted answer with submission
    Server->>Client: Return isCorrect
    end

    rect rgba(150,200,100,0.5)
    Note over Client,DB: New Flow (Redis-Cached)
    Client->>Server: POST /quiz/[slug] (start)
    Server->>Server: initializeQuizCache(quizId)
    Server->>DB: Query correct answers for quizId
    Server->>Redis: Cache answers (TTL: 12h)
    Server->>Client: Quiz initialized

    Client->>Server: POST /verify-answer { quizId, questionId, selectedAnswerId }
    Server->>Redis: getCorrectAnswer(quizId, questionId)
    Redis->>Server: Return correctAnswerId
    Server->>Server: Compare selectedAnswerId === correctAnswerId
    Server->>Client: Return { success, isCorrect }
    end

Loading

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~65 minutes

Possibly related issues

• (SP: 1) [Frontend] Remove redundant quiz files after Redis migration #262: Matches removal of quiz-crypto and PendingResultHandler and migration to Redis-backed verification.
• (SP: 3) [Backend] Implement Redis caching for quiz answer verification (per-quiz strategy) #260: Implements the Redis-backed per-quiz answer cache and initialization flow that this PR adds.

Possibly related PRs

• (SP: 10) [Frontend] Quiz flow: Security encryption + session persistence + UX fixes #131: Alters the same verify-answer flow and quiz props but with an alternate (encryption) approach — likely overlapping or conflicting.
• feat(quiz): replace emojis with lucide-react icons #139: Touches the same quiz UI components (icons/markup) updated here.
• (SP: 2) [Frontend][Backend] Sync guest quiz results after authentication across all login methods #147: Related to guest-result / post-auth quiz synchronization and PendingResultHandler/PostAuthQuizSync changes.

Suggested labels

refactor

Suggested reviewers

• AM1007
• ViktorSvertoka

Poem

🐰
I cached the answers in a stash so neat,
Redis hums and keeps them quick and sweet.
No more secrets wrapped in crypto's art,
The quiz runs smooth — a rabbit's work of heart.
Hop on, test it — watch the refactor beat!

🚥 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 clearly summarizes the main changes: Redis caching for quiz verification, a guest session fix, and cleanup work. It accurately reflects the primary objectives outlined in the PR.

_{✏️ 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 sl/feat/quiz

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[coderabbitai]

Actionable comments posted: 3

🤖 Fix all issues with AI agents

In `@frontend/app/`[locale]/quiz/[slug]/page.tsx:
- Around line 30-36: The code currently uses parseInt(seedParam, 10) without
validating the result, which can yield NaN and break
getQuizQuestionsRandomized/randomizeQuizQuestions; update the logic around
seedParam/parseInt to detect non-numeric or NaN seeds and handle them the same
way as a missing seed (i.e., perform the redirect to
`/${locale}/quiz/${slug}?seed=${Date.now()}`) so only a valid numeric seed is
passed into the seed variable and into getQuizQuestionsRandomized; ensure any
check covers empty string, non-digits, and NaN after parseInt.

In `@frontend/app/api/quiz/verify-answer/route.ts`:
- Around line 3-28: The handler POST currently returns 404 when
getCorrectAnswer(quizId, questionId) yields null even if the cache was evicted;
import and call getOrCreateQuizAnswersCache(quizId) as a fallback to rehydrate
the cache, then retry getCorrectAnswer(quizId, questionId) before returning the
404 via NextResponse; update imports to include getOrCreateQuizAnswersCache and
ensure behavior remains identical if the retry still returns null.

In `@frontend/lib/quiz/quiz-answers-redis.ts`:
- Around line 22-84: getCorrectAnswer returns null on cache miss (or when Redis
is disabled) causing the verify-answer route to 404 even though
getOrCreateQuizAnswersCache allowed the quiz to start; add a DB fallback or
cache rehydration so answer verification works. Update getCorrectAnswer (or the
verify-answer handler) to, on cache miss, either call
getOrCreateQuizAnswersCache(quizId) and re-read redis, or run the same DB query
used in getOrCreateQuizAnswersCache
(db.select(...).from(quizAnswers).innerJoin(quizQuestions,
eq(quizAnswers.quizQuestionId,
quizQuestions.id)).where(and(eq(quizQuestions.quizId, quizId),
eq(quizAnswers.isCorrect, true)))) to find the correct answer for questionId,
populate the answers map and (optionally) set the redis key via
getRedisClient()/getCacheKey with QUIZ_CACHE_TTL_SECONDS; return the found
answerId or null if none. Ensure to reference getOrCreateQuizAnswersCache,
getCorrectAnswer, quizAnswers, quizQuestions, getRedisClient, getCacheKey, and
QUIZ_CACHE_TTL_SECONDS when making the change.

🧹 Nitpick comments (3)

frontend/components/quiz/QuizResult.tsx (1)

15-27: Unused prop quizSlug in interface.

The quizSlug prop is declared in QuizResultProps (line 22) but is no longer destructured or used in the component. This appears to be leftover from the redirect URL change.

🧹 Remove unused prop from interface

 interface QuizResultProps {
   score: number;
   total: number;
   percentage: number;
   answeredCount: number;
   violationsCount?: number;
   isGuest?: boolean;
-  quizSlug?: string;
   pointsAwarded?: number | null;
   isIncomplete?: boolean;
   onRestart: () => void;
   onBackToTopics: () => void;
 }

frontend/components/quiz/QuizQuestion.tsx (1)

58-67: Redundant border class in conditional styling.

Line 59 already includes border in the base class. Lines 64-65 add border border-green-500 and border border-red-500, resulting in duplicate border declarations.

🧹 Remove redundant border class

                 isSelected &&
                   isAnswering &&
                   'border-blue-500 bg-blue-50 dark:bg-blue-950',
-                showCorrect && 'border border-green-500',
-                showIncorrect && 'border border-red-500',
+                showCorrect && 'border-green-500',
+                showIncorrect && 'border-red-500',
                 !isAnswering && 'cursor-default'

frontend/lib/quiz/quiz-session.ts (1)

48-52: Comment is now outdated.

The comment "Only restore in_progress sessions" no longer accurately describes the behavior. The condition now allows both in_progress and completed sessions to be restored (only rules status is cleared).

📝 Update comment to reflect actual behavior

-    // Only restore in_progress sessions
+    // Discard sessions that haven't started yet
     if (data.status === 'rules') {
       clearQuizSession(quizId);
       return null;
     }