Convert some more core classes to kotlin

core/src/main/java/io/plaidapp/core/data/DataLoadingSubject.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2019 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.plaidapp.core.data
+
+/**
+ * An interface for classes offering data loading state to be observed.
+ */
+interface DataLoadingSubject {
+    fun registerCallback(callbacks: DataLoadingCallbacks)
+
+    interface DataLoadingCallbacks {
+        fun dataStartedLoading()
+        fun dataFinishedLoading()
+    }
+}

core/src/main/java/io/plaidapp/core/data/PlaidItem.kt

@@ -18,7 +18,7 @@ package io.plaidapp.core.data
 
 /**
  * Base class for all model types.
- * // TODO - make the item immutable
+ * // TODO - make the item immutable (https://github.com/android/plaid/issues/795)
  */
 abstract class PlaidItem(
     @Transient open val id: Long,

core/src/main/java/io/plaidapp/core/data/api/DeEnvelopingConverter.kt

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2019 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.plaidapp.core.data.api
+
+import com.google.gson.Gson
+import com.google.gson.TypeAdapter
+import com.google.gson.reflect.TypeToken
+import okhttp3.ResponseBody
+import retrofit2.Converter
+import retrofit2.Retrofit
+import java.lang.reflect.Type
+import javax.inject.Inject
+
+/**
+ * A [retrofit2.Converter.Factory] which removes unwanted wrapping envelopes from API responses.
+ */
+class DeEnvelopingConverter @Inject constructor(internal val gson: Gson) : Converter.Factory() {
+
+    override fun responseBodyConverter(
+        type: Type,
+        annotations: Array<Annotation>,
+        retrofit: Retrofit
+    ): Converter<ResponseBody, Any>? {
+
+        // This converter requires an annotation providing the name of the payload in the envelope;
+        // if one is not supplied then return null to continue down the converter chain.
+        val payloadName = getPayloadName(annotations) ?: return null
+
+        val adapter: TypeAdapter<*> = gson.getAdapter(TypeToken.get(type))
+        return Converter { body: ResponseBody ->
+            gson.newJsonReader(body.charStream()).use { jsonReader ->
+                jsonReader.beginObject()
+                while (jsonReader.hasNext()) {
+                    if (payloadName == jsonReader.nextName()) {
+                        return@use adapter.read(jsonReader)
+                    } else {
+                        jsonReader.skipValue()
+                    }
+                }
+                return@use null
+            }
+        }
+    }
+
+    private fun getPayloadName(annotations: Array<Annotation>?): String? {
+        val annotation = annotations?.firstOrNull { it is EnvelopePayload }
+        return if (annotation != null) {
+            (annotation as EnvelopePayload).value
+        } else {
+            null
+        }
+    }
+}

core/src/main/java/io/plaidapp/core/data/api/EnvelopePayload.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2019 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.plaidapp.core.data.api
+
+import kotlin.annotation.AnnotationRetention.RUNTIME
+
+/**
+ * An annotation for identifying the payload that we want to extract from an API response wrapped in
+ * an envelope object.
+ */
+@Target(
+    AnnotationTarget.FUNCTION,
+    AnnotationTarget.PROPERTY_GETTER,
+    AnnotationTarget.PROPERTY_SETTER
+)
+@Retention(RUNTIME)
+annotation class EnvelopePayload(val value: String = "")