Feat/caching strategy

[A6dulmalik]

Linked Issue

Closes #200

---

What does this PR do?

Implements a comprehensive Redis-based caching strategy to reduce database load and improve response times. The implementation includes a core caching service with Redis backend, cache decorators for method-level caching, automatic cache invalidation via event emitters, cache warming for critical data on startup, and analytics tracking for hit/miss rates. Services (Courses, Users, Search) are integrated with appropriate TTL strategies per data type.

---

Type of change

• ✨ New feature (non-breaking change that adds functionality)

---

Pre-merge checklist (required)

Branch & metadata

• Branch name follows feature/issue-<N>-<slug> / fix/issue-<N>-<slug> convention
• Branch is up to date with the target branch (develop or main)
• All commits and the PR title follow the Conventional Commits format with issue reference

Code quality & tests

• npm run lint:ci — zero ESLint warnings
• npm run format:check — Prettier reports no changes needed
• npm run typecheck — zero TypeScript errors
• npm run test:ci — all tests pass, coverage ≥ 70%
• New service methods have corresponding .spec.ts unit tests
• New API endpoints are covered by at least one e2e test
• No existing tests were deleted (if any were, justification is provided in the PR description)

Error handling & NestJS best practices

• All new/updated DTOs use class-validator / class-transformer decorators and are wired through NestJS pipes (e.g. global ValidationPipe or explicit)
• All controller entry points validate external input at the boundary (no unvalidated raw any/unknown reaching the domain)
• Controllers/services throw appropriate NestJS HTTP exceptions (e.g. BadRequestException, UnauthorizedException, ForbiddenException, NotFoundException) instead of generic Error
• Any new error shapes are handled by existing exception filters or the filters have been updated accordingly
• Logging goes through the shared logging abstraction (e.g. Nest Logger or central logger service) with meaningful, structured messages
• Authentication/authorization guards (e.g. AuthGuard, role/permissions guards, custom guards) are applied to all new/modified endpoints where appropriate
• If an endpoint is intentionally public, this is explicitly mentioned in the PR description with rationale

API documentation / Swagger

• Swagger / OpenAPI decorators are added or updated for all new/changed controller endpoints (including DTOs, responses, and error schemas)
• I have started the app locally and confirmed the /api (or Swagger UI) reflects new/changed endpoints correctly
• If there are no API surface changes, this is explicitly stated in the PR description

Breaking changes

• This PR does not introduce a breaking API change

---

Breaking change description (if applicable)

N/A

---

Test evidence (required)

Commands run locally

npm run lint:ci          ✅ Passed (0 errors, 0 warnings)
npm run format:check     ✅ Passed
git commit -m "feat(caching): implement comprehensive Redis caching strategy"  ✅ Passed

Manual / API verification

New admin endpoints available at /cache/*:

• GET /cache/stats — Cache statistics (Redis + Analytics)
• GET /cache/analytics — Detailed cache metrics
• GET /cache/metrics/prometheus — Prometheus-compatible metrics
• GET /cache/strategies — All cache strategies
• DELETE /cache/clear — Clear all cache
• DELETE /cache/clear/:pattern — Clear by pattern
• POST /cache/warm — Trigger cache warming

---

Screenshots / recordings (if applicable)

N/A — Backend service implementation only

---

Note: You'll need to check/uncheck the items based on your actual verification. The unchecked items (typecheck, test:ci, unit tests, e2e tests, branch naming) require you to run those commands locally.

[drips-wave]

@A6dulmalik Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits