Add PaymentService implementation and related support classes

app/src/main/java/com/deliveryhero/android/braintreesample/BraintreeSampleApplication.kt

@@ -2,12 +2,34 @@ package com.deliveryhero.android.braintreesample
 
 import android.app.Application
 import android.widget.TextView
+import com.deliveryhero.android.braintreesample.service.ApiClientRequestInterceptor
+import com.deliveryhero.android.braintreesample.service.PaymentService
+import okhttp3.OkHttpClient
+import okhttp3.logging.HttpLoggingInterceptor
+import retrofit2.Retrofit
+import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory
+import retrofit2.converter.gson.GsonConverterFactory
 import timber.log.Timber
 
 class BraintreeSampleApplication : Application() {
 
   companion object {
 
+    private val okhttp by lazy {
+      OkHttpClient.Builder()
+          .addInterceptor(HttpLoggingInterceptor().setLevel(HttpLoggingInterceptor.Level.BODY))
+          .addInterceptor(ApiClientRequestInterceptor)
+          .build()
+    }
+    private val retrofit by lazy {
+      Retrofit.Builder().baseUrl("https://braintree-sample-merchant.herokuapp.com")
+          .client(okhttp)
+          .addConverterFactory(GsonConverterFactory.create())
+          .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
+          .build()
+    }
+    val paymentService by lazy { retrofit.create(PaymentService::class.java) }
+
     fun initializeTrees(outputTo: TextView) {
       Timber.plant(Timber.DebugTree())
       Timber.plant(OutputTree(outputTo))

app/src/main/java/com/deliveryhero/android/braintreesample/feature/payment/RetrieveToken.kt

@@ -0,0 +1,9 @@
+package com.deliveryhero.android.braintreesample.feature.payment
+
+import com.deliveryhero.android.braintreesample.model.ClientToken
+import io.reactivex.Single
+
+interface RetrieveToken {
+
+  operator fun invoke(): Single<ClientToken>
+}

app/src/main/java/com/deliveryhero/android/braintreesample/feature/payment/RetrieveTokenImpl.kt

@@ -0,0 +1,8 @@
+package com.deliveryhero.android.braintreesample.feature.payment
+
+import com.deliveryhero.android.braintreesample.BraintreeSampleApplication.Companion.paymentService
+
+class RetrieveTokenImpl : RetrieveToken {
+
+  override operator fun invoke() = paymentService.getClientToken(null, null)
+}

app/src/main/java/com/deliveryhero/android/braintreesample/model/PaymentModels.kt

@@ -0,0 +1,5 @@
+package com.deliveryhero.android.braintreesample.model
+
+import com.google.gson.annotations.SerializedName
+
+data class ClientToken(@SerializedName("client_token") val value: String = "")

app/src/main/java/com/deliveryhero/android/braintreesample/service/PaymentService.kt

@@ -0,0 +1,28 @@
+package com.deliveryhero.android.braintreesample.service
+
+import com.deliveryhero.android.braintreesample.model.ClientToken
+import io.reactivex.Single
+import okhttp3.Interceptor
+import okhttp3.Response
+import retrofit2.http.GET
+import retrofit2.http.Query
+
+interface PaymentService {
+
+  @GET("/client_token")
+  fun getClientToken(@Query("customer_id") customerId: String?,
+                     @Query("merchant_account_id") merchantAccountId: String?)
+      : Single<ClientToken>
+}
+
+object ApiClientRequestInterceptor : Interceptor {
+
+  override fun intercept(chain: Interceptor.Chain): Response {
+    val request = chain.request()
+        .newBuilder()
+        .addHeader("User-Agent", "braintree/android-demo-app/2.5.5-SNAPSHOT")
+        .addHeader("Accept", "application/json")
+        .build()
+    return chain.proceed(request)
+  }
+}