Add method to check state of canWrite permission

Author: andrewhavens

android/src/main/java/com/devstepbcn/wifi/AndroidWifiModule.java

@@ -36,6 +36,8 @@
 import org.json.JSONException;
 import org.json.JSONObject;
 
+import com.facebook.react.bridge.Promise;
+
 public class AndroidWifiModule extends ReactContextBaseJavaModule {
 
 	//WifiManager Instance
@@ -91,6 +93,20 @@ public void loadWifiList(Callback successCallback, Callback errorCallback) {
 		}
 	}
 
+	//Returns a promise that resolves a boolean of wether or not the canWrite
+	//permission has been granted
+	@ReactMethod
+	public void checkCanWrite(Promise promise) {
+		boolean canWrite = true;
+		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N || Build.VERSION.RELEASE.toString().equals("6.0.1")) {
+			// In versions >= 6.0.1, we no longer need to request permission to write to settings.
+		else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+			// In version 6.0.0, we need to request permission to write to settings in order to forceWifi.
+			canWrite = Settings.System.canWrite(reactContext);
+		}
+		promise.resolve(canWrite);
+	}
+
 	//Method to force wifi usage if the user needs to send requests via wifi
 	//if it does not have internet connection. Useful for IoT applications, when
 	//the app needs to communicate and send requests to a device that have no