change getMetricsEnabled to return a promise

After upgrading to Android SDK 5.0, we cannot put metricsEnabled to
constants of the module. So we change getMetricsEnabled to return a
promise instead of value directly.

API.md

@@ -399,7 +399,7 @@ If you hide the attribution button, you need to provide the user with a way to
 opt-out of telemetry. For this, you need to add `MGLMapboxMetricsEnabledSettingShownInApp`
 as `YES` in `Info.plist`, then create a switch that toggles metrics.
 
-To get the current state of metrics, use `Mapbox.getMetricsEnabled()`.
+To get the current state of metrics, use `Mapbox.getMetricsEnabled()`. It will return a promise. Before using it, don't forget to set an access token with `Mapbox.setAccessToken(accessToken)`.
 
 To enable or disable metrics, use `Mapbox.setMetricsEnabled(enabled: boolean)`.
 

android/src/main/java/com/mapbox/reactnativemapboxgl/ReactNativeMapboxGLModule.java

@@ -5,6 +5,7 @@ import android.os.Handler;
 import android.util.Log;
 
 import com.facebook.react.bridge.Arguments;
+import com.facebook.react.bridge.JSApplicationCausedNativeException;
 import com.facebook.react.bridge.JSApplicationIllegalArgumentException;
 import com.facebook.react.bridge.Promise;
 import com.facebook.react.bridge.ReactApplicationContext;
@@ -130,8 +131,6 @@ public class ReactNativeMapboxGLModule extends ReactContextBaseJavaModule {
 
         // Other constants
         constants.put("unknownResourceCount", Long.MAX_VALUE);
-        // FIXME you cannot get telemetry enabled status before you set access token
-//        constants.put("metricsEnabled", MapboxTelemetry.getInstance().isTelemetryEnabled());
 
         constants.put("userTrackingMode", userTrackingMode);
         constants.put("mapStyles", mapStyles);
@@ -177,6 +176,15 @@ public class ReactNativeMapboxGLModule extends ReactContextBaseJavaModule {
 
     // Metrics
 
+    @ReactMethod
+    public void getMetricsEnabled(final Promise promise) {
+        try {
+            promise.resolve(MapboxTelemetry.getInstance().isTelemetryEnabled());
+        } catch (NullPointerException e) {
+            promise.reject(new JSApplicationCausedNativeException("You should call getMetricsEnabled after setAccessToken"));
+        }
+    }
+
     @ReactMethod
     public void setMetricsEnabled(boolean value) {
         MapboxTelemetry.getInstance().setTelemetryEnabled(value);

index.js

@@ -73,15 +73,12 @@ if (Platform.OS === 'android') {
 
 // Metrics
 
-let _metricsEnabled = MapboxGLManager.metricsEnabled;
-
 function setMetricsEnabled(enabled: boolean) {
-  _metricsEnabled = enabled;
   MapboxGLManager.setMetricsEnabled(enabled);
 }
 
 function getMetricsEnabled() {
-  return _metricsEnabled;
+  return MapboxGLManager.getMetricsEnabled();
 }
 
 // Access token

ios/RCTMapboxGL/RCTMapboxGLManager.m

@@ -111,21 +111,23 @@ RCT_CUSTOM_VIEW_PROPERTY(contentInset, UIEdgeInsetsMake, RCTMapboxGL)
                      @"complete": [NSNumber numberWithUnsignedInt:MGLOfflinePackStateComplete],
                      @"invalid": [NSNumber numberWithUnsignedInt:MGLOfflinePackStateInvalid]
                      },
-             @"unknownResourceCount": @(UINT64_MAX),
-             @"metricsEnabled": @([RCTMapboxGLManager metricsEnabled])
+             @"unknownResourceCount": @(UINT64_MAX)
              };
 };
 
 // Metrics
 
-+ (BOOL)metricsEnabled
+RCT_EXPORT_METHOD(getMetricsEnabled:(RCTPromiseResolveBlock)resolve
+                  rejecter:(RCTPromiseRejectBlock)reject)
 {
     NSUserDefaults * ud = [NSUserDefaults standardUserDefaults];
     NSNumber * nr = [ud valueForKey:@"MGLMapboxMetricsEnabled"];
     if (!nr || ![nr isKindOfClass:[NSNumber class]]) {
-        return YES;
+        resolve(@YES);
+        return;
     }
-    return nr.boolValue;
+    
+    resolve([NSNumber numberWithBool:nr.boolValue]);
 }
 
 RCT_EXPORT_METHOD(setMetricsEnabled:(BOOL)enabled)