perf: skip geocoding on list endpoints, add in-memory cache

- GetAllDeviceDetails, GetDevicesWithoutConnections, GetDevicesWithoutTowers
  now pass nil geocoder to avoid Nominatim calls on list requests.
  This reduces GET /device-details response time from ~2 minutes to <1s.
- Added sync.Map cache to nominatimGeocoder so repeated calls for the
  same coordinates (e.g. GetDeviceDetailsByID) hit cache instead of
  Nominatim, preventing HTTP 429 rate limit errors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

usecase/device_details.go

@@ -91,7 +91,7 @@ func (u *deviceDetailsUseCase) GetDevicesWithoutConnections(deviceTypes []string
         return nil, err
     }
     
-    responses, err := helper.ConvertToDeviceDetailsResponses(devices, u.geocoder)
+    responses, err := helper.ConvertToDeviceDetailsResponses(devices, nil)
     if err != nil {
         return nil, err
     }
@@ -184,7 +184,7 @@ func (u *deviceDetailsUseCase) GetDevicesWithoutTowers(deviceTypes []string) ([]
         return nil, err
     }
     
-    responses, err := helper.ConvertToDeviceDetailsResponses(devices, u.geocoder)
+    responses, err := helper.ConvertToDeviceDetailsResponses(devices, nil)
     if err != nil {
         return nil, err
     }
@@ -477,7 +477,9 @@ func (u *deviceDetailsUseCase) GetAllDeviceDetails() ([]res.DeviceDetailsRespons
         return nil, err
     }
     
-    return helper.ConvertToDeviceDetailsResponses(devices, u.geocoder)
+    // Skip geocoding on list endpoint to avoid Nominatim rate limiting.
+    // Geocoding is only performed on single-device GET (GetDeviceDetailsByID).
+    return helper.ConvertToDeviceDetailsResponses(devices, nil)
 }
 
 func (u *deviceDetailsUseCase) GetDeviceDetailsByID(id uuid.UUID) (res.DeviceDetailsResponse, error) {

utils/service/geo_service.go

@@ -6,39 +6,42 @@ import (
 	"io/ioutil"
 	"log"
 	"net/http"
+	"sync"
 	"time"
 )
 
 type GeocodingService interface {
-    GetAddressFromCoordinates(latitude, longitude float64) (string, error)
+	GetAddressFromCoordinates(latitude, longitude float64) (string, error)
 }
 
 type nominatimGeocoder struct {
-    client *http.Client
+	client *http.Client
+	cache  sync.Map // key: "lat,lon" → string address
 }
 
-
 func NewGeocodingService() GeocodingService {
-    client := &http.Client{
-        Timeout: 10 * time.Second,
-    }
-    return &nominatimGeocoder{
-        client: client,
-    }
+	client := &http.Client{
+		Timeout: 10 * time.Second,
+	}
+	return &nominatimGeocoder{
+		client: client,
+	}
 }
 
 type NominatimResponse struct {
 	DisplayName string `json:"display_name"`
-	Error 	 string `json:"error"`
+	Error       string `json:"error"`
 }
 
-
 func (g *nominatimGeocoder) GetAddressFromCoordinates(latitude, longitude float64) (string, error) {
-
-
 	if latitude < -90 || latitude > 90 || longitude < -180 || longitude > 180 {
-		errMsg := fmt.Sprintf("Invalid coordinates: lat=%f, lon=%f", latitude, longitude)
-		return "", fmt.Errorf(errMsg)
+		return "", fmt.Errorf("invalid coordinates: lat=%f, lon=%f", latitude, longitude)
+	}
+
+	// Check in-memory cache first — avoids repeated Nominatim calls for same device
+	cacheKey := fmt.Sprintf("%.6f,%.6f", latitude, longitude)
+	if cached, ok := g.cache.Load(cacheKey); ok {
+		return cached.(string), nil
 	}
 
 	url := fmt.Sprintf(
@@ -46,7 +49,6 @@ func (g *nominatimGeocoder) GetAddressFromCoordinates(latitude, longitude float6
 		latitude, longitude,
 	)
 
-
 	req, err := http.NewRequest("GET", url, nil)
 	if err != nil {
 		log.Printf("Request creation error: %v", err)
@@ -66,7 +68,6 @@ func (g *nominatimGeocoder) GetAddressFromCoordinates(latitude, longitude float6
 		return "", fmt.Errorf("geocoding service returned status %d", resp.StatusCode)
 	}
 
-	// Read full response body
 	bodyBytes, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
 		log.Printf("Error reading response body: %v", err)
@@ -84,18 +85,18 @@ func (g *nominatimGeocoder) GetAddressFromCoordinates(latitude, longitude float6
 		return "", err
 	}
 
-	// Detailed error checking
 	if result.Error != "" {
 		log.Printf("Nominatim API Error: %s", result.Error)
 		return "", fmt.Errorf("geocoding error: %s", result.Error)
 	}
 
-	// Check for empty display name
 	if result.DisplayName == "" {
 		log.Printf("No address found for coordinates: %f, %f", latitude, longitude)
 		return "", fmt.Errorf("no address found for these coordinates")
 	}
 
-	return result.DisplayName, nil
-}
+	// Store in cache for future calls
+	g.cache.Store(cacheKey, result.DisplayName)
 
+	return result.DisplayName, nil
+}