Building SDKs with clean architecture babylon Londroid April 2018 Joao Alves and Sakis Kaliakoudas 

Babylon Services 

● Partner agreement to ship babylon services as SDKs ● 2 months to ship initial versions ● 5 months for them to integrate ● 3 months of going through a multi phase QA Lift off 

● Initial discussion ● Many parallel streams ● Usually 2 developers per SDK ● At most 4 teams working in parallel in different SDKs Planning 

How many SDKs? 

Babylon SDKs Appointments SDK Authentication SDK Consultation SDK User SDK NHS GP SDK Maps SDK Clinical Records SDK Payment SDK AI Chatbot SDK Monitor SDK Notifications SDK Common SDK Wrapper 

What did the code look like? 

Views Presenters Interactors Gateways/ Repositories Retrofit Services Clean architecture layers 

Views Presenters Interactors Gateways/ Repositories Retrofit Services What to ship? 

View related Domain Views Presenters Interactors Gateways/ Repositories Retrofit Services What to ship? 

Views Presenters Interactors Gateways/ Repositories Retrofit Services Legacy 

Views Presenters Interactors Gateways/ Repositories Retrofit Services MVP 

Views Presenters Interactors Gateways/ Repositories Retrofit Services MVP + Clean 

Moving stuff around App Gateways/ Repositories Interactors Entities SDK 1 SDK 2 SDK N App Non-SDK Interactors Non-SDK Gateways SDK Gateways Entities 

Moving stuff around App Gateways/ Repositories Interactors Entities App Non-SDK Interactors Non-SDK Gateways SDK Gateways Entities SDK 1 SDK 2 SDK N 

Moving stuff around App Gateways/ Repositories Interactors Entities App Non-SDK Interactors Non-SDK Gateways SDK Gateways Entities SDK 1 SDK 2 SDK N 

Gateways and entities sharing SDK Gateways Entities SDK 1 SDK 2 SDK N 

Splitting it up Gateways 1 Gateways 2 Gateways N Entities SDK 1 SDK 2 SDK N 

class DoSomethingInteractor{ private Gateway gateway; @Inject public DoSomethingInteractor(Gateway gateway){ this.gateway = gateway; } Disposable execute(Request request, Callback callback){ ... } } But what does it look like 

interface Callback{ void onSuccess(Result result); void onError(Exception exception); } class Request { String someField1; String someField2; } class Result { String someField3; String someField4; } But what does it look like 

class DoSomethingInteractor{ private Gateway gateway; @Inject public DoSomethingInteractor(Gateway gateway){ this.gateway = gateway; } Disposable execute(Request request, Callback callback){ ... } } But what does it look like 

Client Clinical Records SDK Wrapping the interactors ClinicalRecordsApi clinicalRecordsApi = ClinicalRecordsSdk.getApiInstance(); clinicalRecordsApi.doSomething(request, callback); Client requests an instance of the API 

Clinical Records API Client Clinical Records SDK Wrapping the interactors ClinicalRecordsApi clinicalRecordsApi = ClinicalRecordsSdk.getApiInstance(); clinicalRecordsApi.doSomething(request, callback); The SDK class instantiates the API 

Clinical Records API Client Clinical Records SDK Wrapping the interactors ClinicalRecordsApi clinicalRecordsApi = ClinicalRecordsSdk.getApiInstance(); clinicalRecordsApi.doSomething(request, callback); Returns it to the client 

Clinical Records API Interactors Interactors Interactors Gateways Interactors Entities Client Clinical Records SDK Wrapping the interactors ClinicalRecordsApi clinicalRecordsApi = ClinicalRecordsSdk.getApiInstance(); clinicalRecordsApi.doSomething(request, callback); Client can access all the SDK interactors via the API 

SDK API Interface /** * Get list of appointments for the main user and its registered children * (if any). * * @param request the request object that contains the required information * to get the user appointments. * @param output the callback through which the results are returned. * * @return an RxJava 2 {@link Disposable} resource to manage this request. */ Disposable getAppointments(GetAppointmentsRequest request, GetAppointmentsOutput output); 

String patientId = "patientId"; GetAppointmentsRequest request = GetAppointmentsRequest.create(AppointmentType.UPCOMING, patientId); babylonAppointmentApi.getAppointments(request, new GetAppointmentsOutput() { @Override public void onFetchAppointmentsSuccess(List appointments) { if (appointments.isEmpty()) { getView().showNoAppointments(); } else { getView().showAppointments(appointments); } }}); Presenter using the SDK: 

Dog fooding ● Using the SDKs inside our Apps ● Local development with local gradle module dependencies ● CI builds the SDKs, publishes them, then builds the app using artifact dependencies 

Build and deploy Local Maven Repo Artifactory Single Gradle Task ● ~25 releases in 10 months (excluding hotfixes) ● Releases around every 10 days a day an hour a minute 

Security ● No sensitive information stored locally ● Encryption with Android keystore ● Using Dexguard ● Logging based on environment ● Timber Wrapper 

Uniquely identifying clients via their public certificate Offline: ● Get certificate hash ● Merge it together with the application id to generate a new hash ● Save this hash inside the SDKs Runtime: ● Calculate the same hash ● Match it against the precomputed value 

Activities in the SDKs? 

Kotlin? 

SDK size ● Trimming all dependencies ● Native libraries ● Dexguard 

Documentation ● JavaDoc with CheckStyle ● Release notes - from git diff to git code owners ● Sample App ● Wiki page 

Support ● Slack support ● Dedicated JIRA board ● Daily/Weekly calls 

Finish line ● Improved code quality ● Much less legacy code ● Modularized project ● Loads of knowledge ● Much bigger user base 

What does the code look like now? 

Lessons learned ● Planning + Planning + Planning ● Don’t create silos - merge often ● More logging ● Version controlled documentation 

● Problems are bound to happen and trust us they will happen. And they don’t come on their own they come in herds. ● Work your way through them and you’ll eventually get to the finish line. Don’t Panic 

Questions? Presented by Joao Alves and Sakis Kaliakoudas Say hi on Twitter & Medium: @jcmsalves & @skaliakoudas PS: we’re hiring, come and talk to us to know more 

Useful links ● SDK class example: (https://tinyurl.com/MyBossMadeMeDoThis) ● Getting a certificate hash (https://tinyurl.com/tralalatralalo) ● Merging a certificate hash with an application id to generate a new hash (https://tinyurl.com/we-r-hiringgg) ● Calculating the same hash at runtime (https://tinyurl.com/PleaseDontAskQuestions)