NativeModule_NoEvents_Conditional_Logic.ts

import { NativeModules, Platform } from 'react-native';
import { Consumer } from '../models';

// declare a type for the native module explicitly and assign to that variable:
const AuthenticationServiceNativeModule: AuthenticationServiceNativeModule =
  NativeModules.AuthenticationService;

// all common methods that have same signature between IOS/Android:
interface AuthenticationServiceNativeModule {
  initialize(awsdkBundleId: string, awsdkUrl: string, awsdkKey: string): Promise<string>;
  authenticateConsumer(userName: string, password: string): Promise<Consumer>;
}

// if we have android-specific calls, we extend interface and cast later:
interface AndroidAuthenticationService extends AuthenticationServiceNativeModule {
  androidOnlyCall(): Promise<string>;
}

// if we have ios-specific calls, we extend interface and cast later:
// TypeScript Rule complains if you start interface with "I"
// eslint-disable-next-line @typescript-eslint/interface-name-prefix
interface IOSAuthenticationService extends AuthenticationServiceNativeModule {
  iosOnlyCall(): Promise<string>;
}

export interface AuthenticationService extends AuthenticationServiceNativeModule {
  platformAgnosticMethod(): Promise<string>;
}

// re-export strongly-typed interface with conditional platform logic encapsulated:
export const AuthenticationService: AuthenticationService = {
  // spread native module methods at top level:
  ...AuthenticationServiceNativeModule,

  // encapsulate conditional platform logic here so callers don't have to know this:
  platformAgnosticMethod() {
    if (Platform.OS === 'ios') {
      // cast to the android service interface and make call:
      return (AuthenticationServiceNativeModule as IOSAuthenticationService).iosOnlyCall();
    } else {
      // cast to the ios service interface and make call:
      return (AuthenticationServiceNativeModule as AndroidAuthenticationService).androidOnlyCall();
    }
  },
};