part of conversation: https://www.reddit.com/r/androiddev/comments/7owabf/reactive_apps_architecture_design_asymnetry_that/

ColdComplexishReactiveComponent.kt

data class SearchByTagRequest(val tag: String)

data class ImageColor(val hexValue: String) //some validation on the value here

data class SearchByColorRequest(val includedColors: List<ImageColor>, val excludedColors: List<ImageColor>)

interface ImageSearcher {
  fun searchForImageByTag(requests: Observable<SearchByTagRequest>): Observable<SearchResults> 
  fun searchForImageByColors(requests: Observable<SearchByColorRequest>): Observable<SearchResults>
}

class GoogleImageSearcher(val googleImagesApi: GoogleImagesApi, val analyticsClient: AnalyticsThing): ImageSearcher {
  
  override fun searchForImageByTag(searchRequests: Observable<SearchByTagRequest>) {
    return searchRequests.filter {
      it.length > 3 //google doesn't search for less than three characters for this example
    }.switchMap {
      googleImagesApi.searchForImageByTag(it.tag)
    }.map(this::apiResultToGeneralSearchResults)
  }
    
  override fun searchForImageByColors(searchRequests: Observable<SearchByColorRequest>) {
    return searchRequests
    .doOnNext { 
      //some logging perhaps or analytics around most searched for colors,  I dunno.
      //you can see here with this component, you can do whatever RX-y stuff you want, 
      //because you pass in a stream, get back a stream.
      //and nothing happens until you subscribe
      analyticsClient.trackIncludedColorsSearchRequest(it.includedColors)
    } .switchMap {
      googleImagesApi.searchForByColors(mapColorsToGoogleApiColors(it.includedColors, it.excludedColors) 
    }.map(this::apiResultToGeneralSearchResults)
  }
                                          
  private fun apiResultToGeneralSearchResults(response: GoogleImagesApiResponse) {
    //blah blah whatever you need to do
  }
                                          
  private fun mapColorsToGoogleApiColors(included: List<ImageColor>, excluded: List<ImageColor> {
    //blah blah transform to the way the google image api expects these to be, like maybe a comma separated string, whatever..
  }
  
}