CallAdapterFactory.kt

class ResultsCallAdapterFactory private constructor() : CallAdapter.Factory() {

    companion object {
        @JvmStatic
        fun create() = ResultsCallAdapterFactory()
    }

    override fun get(returnType: Type, annotations: Array<Annotation>, retrofit: Retrofit): CallAdapter<*, *>? {
        return try {
            val enclosedType = returnType as ParameterizedType
            val responseType = getParameterUpperBound(0, enclosedType)
            val rawResultType = getRawType(responseType)
            val delegate: CallAdapter<Any, Any> = retrofit.nextCallAdapter(this, enclosedType, annotations) as CallAdapter<Any, Any>
            if (rawResultType != Results::class.java)
                null
            else {
                object : CallAdapter<Any, Results<Any>> {
                    override fun adapt(call: Call<Any>): Results<Any> {
                        return delegate.adapt(ResultsCall(call)) as Results<Any>
                    }
                    override fun responseType(): Type {
                        return delegate.responseType()
                    }

                }
            }
        } catch (e: ClassCastException) {
            null
        }
    }
}

class ResultsCall<T>(private val call: Call<T>): Call<T> {
    override fun enqueue(callback: Callback<T>) {
        call.enqueue(object : Callback<T>{
            override fun onFailure(call: Call<T>, t: Throwable) {

            }

            override fun onResponse(call: Call<T>, response: Response<T>) {

            }
        })
    }

    override fun isExecuted()=  call.isExecuted

    override fun clone(): Call<T> = call.clone()

    override fun isCanceled() = call.isCanceled

    override fun cancel() = call.cancel()

    override fun execute(): Response<T> = call.execute()

    override fun request(): Request = call.request()

}