package storage

import (
	"sync"
	"time"
)

// HoldCache caches hold endpoints for (DID, repository) pairs
// This avoids expensive ATProto lookups on every blob request during pulls
//
// NOTE: This is a simple in-memory cache for MVP. For production deployments:
// - Use Redis or similar for distributed caching
// - Consider implementing cache size limits
// - Monitor memory usage under high load
type HoldCache struct {
	mu    sync.RWMutex
	cache map[string]*holdCacheEntry
}

type holdCacheEntry struct {
	holdEndpoint string
	expiresAt    time.Time
}

var globalHoldCache = &HoldCache{
	cache: make(map[string]*holdCacheEntry),
}

func init() {
	// Start background cleanup goroutine
	go func() {
		ticker := time.NewTicker(5 * time.Minute)
		defer ticker.Stop()
		for range ticker.C {
			globalHoldCache.Cleanup()
		}
	}()
}

// GetGlobalHoldCache returns the global hold cache instance
func GetGlobalHoldCache() *HoldCache {
	return globalHoldCache
}

// Set stores a hold endpoint for a (DID, repository) pair with a TTL
func (c *HoldCache) Set(did, repository, holdEndpoint string, ttl time.Duration) {
	c.mu.Lock()
	defer c.mu.Unlock()

	key := did + ":" + repository
	c.cache[key] = &holdCacheEntry{
		holdEndpoint: holdEndpoint,
		expiresAt:    time.Now().Add(ttl),
	}
}

// Get retrieves a hold endpoint for a (DID, repository) pair
// Returns empty string and false if not found or expired
func (c *HoldCache) Get(did, repository string) (string, bool) {
	c.mu.RLock()
	defer c.mu.RUnlock()

	key := did + ":" + repository
	entry, ok := c.cache[key]
	if !ok {
		return "", false
	}

	// Check if expired
	if time.Now().After(entry.expiresAt) {
		// Don't delete here (would need write lock), let cleanup handle it
		return "", false
	}

	return entry.holdEndpoint, true
}

// Cleanup removes expired entries (called automatically every 5 minutes)
func (c *HoldCache) Cleanup() {
	c.mu.Lock()
	defer c.mu.Unlock()

	now := time.Now()
	removed := 0
	for key, entry := range c.cache {
		if now.After(entry.expiresAt) {
			delete(c.cache, key)
			removed++
		}
	}

	// Log cleanup stats for monitoring
	if removed > 0 || len(c.cache) > 100 {
		// Log if we removed entries OR if cache is growing large
		// This helps identify if cache size is becoming a concern
		println("Hold cache cleanup: removed", removed, "entries, remaining", len(c.cache))
	}
}