Add /api/v1/ip/<ip> endpoint for IP to AS lookups

- Add handleIPLookup handler that uses GetASInfoForIP
- Create writeJSONError and writeJSONSuccess helper functions
- Refactor all JSON error responses to use the helpers
- Add GetASInfoForIP to Store interface
- Add mock implementation for tests
- Fix all linter warnings

internal/server/server.go

@@ -61,6 +61,7 @@ func (s *Server) setupRoutes() {
 	// API routes
 	r.Route("/api/v1", func(r chi.Router) {
 		r.Get("/stats", s.handleStats())
+		r.Get("/ip/{ip}", s.handleIPLookup())
 	})
 
 	s.router = r
@@ -109,6 +110,29 @@ func (s *Server) handleRoot() http.HandlerFunc {
 	}
 }
 
+// writeJSONError writes a standardized JSON error response
+func writeJSONError(w http.ResponseWriter, statusCode int, message string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(statusCode)
+	_ = json.NewEncoder(w).Encode(map[string]interface{}{
+		"status": "error",
+		"error": map[string]interface{}{
+			"msg":  message,
+			"code": statusCode,
+		},
+	})
+}
+
+// writeJSONSuccess writes a standardized JSON success response
+func writeJSONSuccess(w http.ResponseWriter, data interface{}) error {
+	w.Header().Set("Content-Type", "application/json")
+
+	return json.NewEncoder(w).Encode(map[string]interface{}{
+		"status": "ok",
+		"data":   data,
+	})
+}
+
 // handleStatusJSON returns a handler that serves JSON statistics
 func (s *Server) handleStatusJSON() http.HandlerFunc {
 	// Stats represents the statistics response
@@ -164,28 +188,12 @@ func (s *Server) handleStatusJSON() http.HandlerFunc {
 		select {
 		case <-ctx.Done():
 			s.logger.Error("Database stats timeout in status.json")
-			w.Header().Set("Content-Type", "application/json")
-			w.WriteHeader(http.StatusRequestTimeout)
-			_ = json.NewEncoder(w).Encode(map[string]interface{}{
-				"status": "error",
-				"error": map[string]interface{}{
-					"msg":  "Database timeout",
-					"code": http.StatusRequestTimeout,
-				},
-			})
+			writeJSONError(w, http.StatusRequestTimeout, "Database timeout")
 
 			return
 		case err := <-errChan:
 			s.logger.Error("Failed to get database stats", "error", err)
-			w.Header().Set("Content-Type", "application/json")
-			w.WriteHeader(http.StatusInternalServerError)
-			_ = json.NewEncoder(w).Encode(map[string]interface{}{
-				"status": "error",
-				"error": map[string]interface{}{
-					"msg":  err.Error(),
-					"code": http.StatusInternalServerError,
-				},
-			})
+			writeJSONError(w, http.StatusInternalServerError, err.Error())
 
 			return
 		case dbStats = <-statsChan:
@@ -239,12 +247,7 @@ func (s *Server) handleStatusJSON() http.HandlerFunc {
 			IPv6PrefixDistribution: dbStats.IPv6PrefixDistribution,
 		}
 
-		w.Header().Set("Content-Type", "application/json")
-		response := map[string]interface{}{
-			"status": "ok",
-			"data":   stats,
-		}
-		if err := json.NewEncoder(w).Encode(response); err != nil {
+		if err := writeJSONSuccess(w, stats); err != nil {
 			s.logger.Error("Failed to encode stats", "error", err)
 		}
 	}
@@ -404,12 +407,7 @@ func (s *Server) handleStats() http.HandlerFunc {
 			IPv6PrefixDistribution: dbStats.IPv6PrefixDistribution,
 		}
 
-		w.Header().Set("Content-Type", "application/json")
-		response := map[string]interface{}{
-			"status": "ok",
-			"data":   stats,
-		}
-		if err := json.NewEncoder(w).Encode(response); err != nil {
+		if err := writeJSONSuccess(w, stats); err != nil {
 			s.logger.Error("Failed to encode stats", "error", err)
 		}
 	}
@@ -427,3 +425,28 @@ func (s *Server) handleStatusHTML() http.HandlerFunc {
 		}
 	}
 }
+
+// handleIPLookup returns a handler that looks up AS information for an IP address
+func (s *Server) handleIPLookup() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		ip := chi.URLParam(r, "ip")
+		if ip == "" {
+			writeJSONError(w, http.StatusBadRequest, "IP parameter is required")
+
+			return
+		}
+
+		// Look up AS information for the IP
+		asInfo, err := s.db.GetASInfoForIP(ip)
+		if err != nil {
+			writeJSONError(w, http.StatusNotFound, err.Error())
+
+			return
+		}
+
+		// Return successful response
+		if err := writeJSONSuccess(w, asInfo); err != nil {
+			s.logger.Error("Failed to encode AS info", "error", err)
+		}
+	}
+}