feat: add books APIs

internal/middleware/ratelimit.go

@@ -0,0 +1,81 @@
+package middleware
+
+import (
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/prabhupadasays/spsays-bff/pkg/response"
+)
+
+// RateLimiter is a simple in-memory token bucket rate limiter.
+// In production, replace with DragonflyDB/Redis-based limiter.
+type RateLimiter struct {
+	mu       sync.Mutex
+	visitors map[string]*visitor
+	rate     int           // tokens per interval
+	interval time.Duration // refill interval
+}
+
+type visitor struct {
+	tokens   int
+	lastSeen time.Time
+}
+
+// NewRateLimiter creates a new in-memory rate limiter.
+func NewRateLimiter(rate int, interval time.Duration) *RateLimiter {
+	rl := &RateLimiter{
+		visitors: make(map[string]*visitor),
+		rate:     rate,
+		interval: interval,
+	}
+	// Clean up stale visitors every minute
+	go rl.cleanup()
+	return rl
+}
+
+// Limit returns a middleware that rate-limits requests by IP.
+func (rl *RateLimiter) Limit(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ip := r.RemoteAddr
+
+		rl.mu.Lock()
+		v, exists := rl.visitors[ip]
+		if !exists {
+			v = &visitor{tokens: rl.rate, lastSeen: time.Now()}
+			rl.visitors[ip] = v
+		}
+
+		// Refill tokens
+		elapsed := time.Since(v.lastSeen)
+		refill := int(elapsed / rl.interval)
+		if refill > 0 {
+			v.tokens = min(v.tokens+refill*rl.rate, rl.rate)
+			v.lastSeen = time.Now()
+		}
+
+		if v.tokens <= 0 {
+			rl.mu.Unlock()
+			response.Error(w, http.StatusTooManyRequests, "rate limit exceeded")
+			return
+		}
+
+		v.tokens--
+		rl.mu.Unlock()
+
+		next.ServeHTTP(w, r)
+	})
+}
+
+func (rl *RateLimiter) cleanup() {
+	for {
+		time.Sleep(time.Minute)
+		rl.mu.Lock()
+		for ip, v := range rl.visitors {
+			if time.Since(v.lastSeen) > 3*time.Minute {
+				delete(rl.visitors, ip)
+			}
+		}
+		rl.mu.Unlock()
+	}
+}