Retrofit Singleton Factory

RetrofitSingleton.kt

companion object Factory {
        @Volatile
        private var retrofit : Retrofit? = null

        @Synchronized
        fun getInstance(baseUrl: String, tokenStorage: TokenStorage): FireResponseService? {
            retrofit = retrofit ?: synchronized(this) {
                retrofit ?: buildRetrofit(baseUrl, tokenStorage)
            }

            return retrofit?.create(FireResponseService::class.java)
        }

        private fun buildRetrofit(baseUrl: String, tokenStorage: TokenStorage): Retrofit {
            val httpClientBuilder = OkHttpClient.Builder()

            val gsonBuilder = GsonBuilder()
                    .excludeFieldsWithoutExposeAnnotation()

            val builder = Retrofit.Builder()
                    .baseUrl(baseUrl)
                    .addConverterFactory(GsonConverterFactory.create(gsonBuilder.create()))

            if (BuildConfig.DEBUG) {
                val loggingInterceptor = HttpLoggingInterceptor()
                loggingInterceptor.level = HttpLoggingInterceptor.Level.HEADERS
                loggingInterceptor.level = HttpLoggingInterceptor.Level.BODY

                httpClientBuilder.addInterceptor(loggingInterceptor)
            }

            httpClientBuilder.addInterceptor { chain ->
                val request = chain.request()

                val requestBuilder = request.newBuilder()
                        .header("Authorization", tokenStorage.getAuthorization().authorization)

                chain.proceed(requestBuilder.build())
            }

            builder.client(httpClientBuilder.build())

            return builder.build()
        }
    }