Gist for Medium

Environment.kt

const val DEVELOPMENT = 1
const val STAGING = 2
const val PRODUCTION = 3

@IntDef(DEVELOPMENT, STAGING, PRODUCTION)
@Retention(AnnotationRetention.SOURCE)
annotation class Environment

EnvironmentInterceptor.kt

class EnvironmentInterceptor : Interceptor {

    private val devUrl = "dev.api.com"
    private val stagingUrl = "staging.api.com"
    private val productionUrl = "production.api.com"
  
    @Environment
    private var env = DEBUG

    override fun intercept(chain: Interceptor.Chain): Response {
        val currentRequest = chain.request()
        val host = when (env) {
            DEVELOPMENT -> devUrl
            STAGING -> stagingUrl
            else -> productionUrl
        }
        return chain.proceed(
            currentRequest.newBuilder().url(currentRequest.url.newBuilder().host(host).build())
                .build()
        )
    }

    fun setEnvironment(ctx: Context, action: () -> Unit) {
        AlertDialog.Builder(ctx).apply {
            setTitle("choose your environment")
            setItems(arrayOf("Development", "Staging", "Production")) { dialog, which ->
                env =  when(which) {
                    0 -> DEVELOPMENT
                    1 -> STAGING
                    else -> PRODUCTION
                }
                action.invoke()
                dialog.dismiss()
            }
        }.create().show()
    }
}

koinModule.kt

val yourModule = module {
  single(named("environment")) { EnvironmentInterceptor() }
  single {
        OkHttpClient.Builder().apply {
            readTimeout(120, TimeUnit.SECONDS)
            connectTimeout(120, TimeUnit.SECONDS)
            followRedirects(false)
            followSslRedirects(false)
            retryOnConnectionFailure(true)
            addInterceptor(get<Interceptor>(named("environment")))
        }.build()
    }
}

SplashScreenActivity.kt

class SplashScreenActivity : AppCompatActivity {
  private val envInterceptor by inject<EnvironmentInterceptor>(named("environment"))
  
  override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_splash_screen)
        envInterceptor.setEnvironment(this) {
          // Call your first API here
        }
    }
}