CoinbaseRxJava2CallAdapterFactory.kt

/**
 * A [CallAdapter.Factory] which allows [CoinbaseResponse] objects to be 
 * returned from RxJava streams. For the type 
 * [Observable<CoinbaseResponse<SuccessBody, ErrorBody>>], the following 
 * semantics are provided:
 *
 * 1. 2xx responses call onNext with the deserialized body set as 
 * [CoinbaseResponse.body]
 * 2. non-2xx responses call onNext with the deserialized error body set as
 * [CoinbaseResponse.errorBody]
 * 3. Calls that fail due to network issues call onNext with network errors set as
 * [CoinbaseResponse.networkError]
 */
class CoinbaseRxJava2CallAdapterFactory : CallAdapter.Factory() {

   override fun get(
        returnType: Type,
        annotations: Array<Annotation>,
        retrofit: Retrofit
    ): CallAdapter<*, *>? {
        val rawType = getRawType(returnType) // ie Single

        // Check if we support this type, must be Rx stream of CoinbaseResponse.
        val supportedType = SupportedType.create(rawType) ?: return null

        val observableEmissionType = getParameterUpperBound( // ie CoinbaseResponse
            0,
            returnType as ParameterizedType
        )
        val successBodyType = getParameterUpperBound( // ie AccessToken
            0, observableEmissionType as ParameterizedType
        )
        val delegateType = Types.newParameterizedType( // ie Single<Response<AccessToken>>
            getRawType(returnType),
            Types.newParameterizedType(Response::class.java, successBodyType)
        )
        val delegateAdapter = retrofit.nextCallAdapter(
            this,
            delegateType,
            annotations
        )

        val errorBodyType = getParameterUpperBound( // ie OAuthError
           1, 
           observableEmissionType)
        val errorBodyConverter = retrofit.nextResponseBodyConverter<Any?>(
            null,
            errorBodyType,
            annotations
        )

        return CoinbaseRxJava2CallAdapter(
            successBodyType,
            delegateAdapter as CallAdapter<Any, Any>,
            errorBodyConverter,
            supportedType as SupportedType<Any, Any>
        )
    }
}