Feature/unified cache

[Shiva205101]

🚀 Summary

This PR introduces a high-performance, pluggable caching module to the GoFr framework. It allows seamless injection and usage of either in-memory or Redis-based cache implementations across application layers with support for future observability and middleware extensibility.

This implements Phase 1 of the "Unified Cache Layer" as proposed in the GoFr Summer of Code framework extensions.

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🎯 Motivation

GoFr previously lacked a unified caching abstraction, which led developers to implement manual and inconsistent caching logic. This PR standardizes cache usage via:

• A consistent Cache interface
• Centralized injection using app.Container.Set("cache", ...)
• Swappable backend support (in-memory or Redis)
• Clean handler/service/store integration without tight coupling

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🧩 What's Implemented

• Cache interface: defines Get, Set, Delete, and WrapQuery
• In-memory implementation with TTL & thread safety
• Redis-based implementation using go-redis/v9
• Container-based cache injection via Container.Set()
• Developer-friendly usage examples and structure

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📦 Example Usage

Registering the cache in main.go

cache := inmemory.New() // or redis.New(redisClient)
app.Container.Set("cache", cache)

Using it in application logic (service or store layer)

func (s *UserService) GetCachedUser(id string) (string, error) {
    cache := s.cache

    val, err := cache.Get("user:" + id)
    if err == nil {
        return val, nil
    }

    // Fallback to DB or compute logic
    val = "some-value"
    _ = cache.Set("user:"+id, val, 5*time.Minute)
    return val, nil
}

Optional: WrapQuery (Phase 2 Preview)

result, err := cache.WrapQuery("user:123", 5*time.Minute, func() (string, error) {
    return fetchUserFromDB()
})

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🧪 Tests

• ✅ Manual tests for in-memory and Redis integration
• ✅ Sample usage validated in Handler → Service → Store stack

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📂 Affected Files

pkg/cache/cache.go           # Interface definition
pkg/cache/inmemory.go        # In-memory backend
pkg/cache/redis.go           # Redis backend
pkg/cache/container.go       # Optional helper for container registration
examples/main.go             # Demonstration of registration and use

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📊 Observability (Planned)

• Prometheus metrics: cache_hits_total, cache_misses_total, cache_errors_total
• OpenTelemetry spans: cache.Get, cache.Set, cache.WrapQuery
• Logging middleware: WithLogging(cache, logger) wrapper

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🗒 Related

Closes issue: TBD by maintainers
Proposal: Unified Cache Layer – Phase 1 (Application-level injection)

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🙌 Notes for Reviewers

• This PR focuses solely on Phase 1: registration and basic cache operations.
• Context is intentionally not passed to cache operations for simplicity.
• Backend choice (Redis vs Memory) is fully up to the app developer.
• All implementations are thread-safe.

Future PRs will extend this with query wrapping logic, metrics, and trace hooks.

Note: The Container is a struct. We use app.Container.Set("cache", cache) to register dependencies.