Add Next cleanup time header (#48)

internal/middleware/ratelimiter.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"net/http"
+	"server/config"
 	"server/internal/db"
 	"server/internal/server/utils"
 	mock "server/internal/tests/dbmocks"
@@ -18,6 +19,8 @@ import (
 
 // RateLimiter middleware to limit requests based on a specified limit and duration
 func RateLimiter(client *db.DiceDB, next http.Handler, limit int64, window float64) http.Handler {
+	configValue := config.LoadConfig()
+	cronFrequencyInterval := configValue.Server.CronCleanupFrequency
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if handleCors(w, r) {
 			return
@@ -78,28 +81,40 @@ func RateLimiter(client *db.DiceDB, next http.Handler, limit int64, window float
 			}
 		}
 
-		// Get the cron last cleanup run time
-		var lastCronCleanupTime int64
-		resp := client.Client.Get(ctx, utils.LastCronCleanupTimeUnixMs)
-		if resp.Err() != nil && !errors.Is(resp.Err(), dicedb.Nil) {
-			slog.Error("Failed to get last cron cleanup time for headers", slog.Any("err", resp.Err().Error()))
-		}
-
-		if resp.Val() != "" {
-			lastCronCleanupTime, err = strconv.ParseInt(resp.Val(), 10, 64)
-			if err != nil {
-				slog.Error("Error converting last cron cleanup time", "error", err)
-			}
+		secondsDifference, err := calculateNextCleanupTime(ctx, client, cronFrequencyInterval)
+		if err != nil {
+			slog.Error("Error calculating next cleanup time", "error", err)
 		}
 
 		addRateLimitHeaders(w, limit, limit-(requestCount+1), requestCount+1, currentWindow+int64(window),
-			lastCronCleanupTime)
+			secondsDifference)
 
 		slog.Info("Request processed", "count", requestCount+1)
 		next.ServeHTTP(w, r)
 	})
 }
 
+func calculateNextCleanupTime(ctx context.Context, client *db.DiceDB, cronFrequencyInterval time.Duration) (int64, error) {
+	var lastCronCleanupTime int64
+	resp := client.Client.Get(ctx, utils.LastCronCleanupTimeUnixMs)
+	if resp.Err() != nil && !errors.Is(resp.Err(), dicedb.Nil) {
+		return -1, resp.Err()
+	}
+
+	if resp.Val() != "" {
+		var err error
+		lastCronCleanupTime, err = strconv.ParseInt(resp.Val(), 10, 64) // directly assign here
+		if err != nil {
+			return -1, err
+		}
+	}
+
+	lastCleanupTime := time.UnixMilli(lastCronCleanupTime)
+	nextCleanupTime := lastCleanupTime.Add(cronFrequencyInterval)
+	timeDifference := nextCleanupTime.Sub(time.Now())
+	return int64(timeDifference.Seconds()), nil
+}
+
 func MockRateLimiter(client *mock.DiceDBMock, next http.Handler, limit int64, window float64) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if handleCors(w, r) {
@@ -170,14 +185,14 @@ func MockRateLimiter(client *mock.DiceDBMock, next http.Handler, limit int64, wi
 	})
 }
 
-func addRateLimitHeaders(w http.ResponseWriter, limit, remaining, used, resetTime, cronLastCleanupTime int64) {
+func addRateLimitHeaders(w http.ResponseWriter, limit, remaining, used, resetTime, secondsLeftForCleanup int64) {
 	w.Header().Set("x-ratelimit-limit", strconv.FormatInt(limit, 10))
 	w.Header().Set("x-ratelimit-remaining", strconv.FormatInt(remaining, 10))
 	w.Header().Set("x-ratelimit-used", strconv.FormatInt(used, 10))
 	w.Header().Set("x-ratelimit-reset", strconv.FormatInt(resetTime, 10))
-	w.Header().Set("x-last-cleanup-time", strconv.FormatInt(cronLastCleanupTime, 10))
+	w.Header().Set("x-next-cleanup-time", strconv.FormatInt(secondsLeftForCleanup, 10))
 
 	// Expose the rate limit headers to the client
 	w.Header().Set("Access-Control-Expose-Headers", "x-ratelimit-limit, x-ratelimit-remaining,"+
-		"x-ratelimit-used, x-ratelimit-reset, x-last-cleanup-time")
+		"x-ratelimit-used, x-ratelimit-reset, x-next-cleanup-time")
 }