Add API to query district by GPS location

api/api.go

@@ -78,6 +78,39 @@ func apiAudioContentPost(w http.ResponseWriter, r *http.Request, u *models.User)
 	w.WriteHeader(http.StatusOK)
 }
 
+func apiGetDistrict(w http.ResponseWriter, r *http.Request) {
+	var latStr, lngStr string
+	err := r.ParseForm()
+	if err != nil {
+		render.Render(w, r, errRender(fmt.Errorf("Failed to parse GET form: %w", err)))
+		return
+	} else {
+		latStr = r.FormValue("lat")
+		lngStr = r.FormValue("lng")
+	}
+	lat, err := strconv.ParseFloat(latStr, 64)
+	if err != nil {
+		render.Render(w, r, errRender(fmt.Errorf("Failed to parse lat as float: %w", err)))
+		return
+	}
+	lng, err := strconv.ParseFloat(lngStr, 64)
+	if err != nil {
+		render.Render(w, r, errRender(fmt.Errorf("Failed to parse lng as float: %w", err)))
+		return
+	}
+	district, err := platform.DistrictForLocation(r.Context(), lng, lat)
+	if err != nil {
+		render.Render(w, r, errRender(fmt.Errorf("Failed to get district: %w", err)))
+		return
+	}
+	d := ResponseDistrict{
+		Agency: district.Agency.GetOr(""),
+	}
+	if err := render.Render(w, r, d); err != nil {
+		render.Render(w, r, errRender(err))
+	}
+}
+
 func handleClientIos(w http.ResponseWriter, r *http.Request, u *models.User) {
 	var sinceStr string
 	err := r.ParseForm()