refactor: restructure network module using DI and separate interfaces per entity API

This refactor is based on using the NIA project as a base project. Improves code
structure without changing functionality, and makes it easier to extend when
working with multiple API methods.

Author: morz

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/api/NewsResourceApi.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * 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
+ *
+ *     https://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 com.google.samples.apps.nowinandroid.core.network.api
+
+import com.google.samples.apps.nowinandroid.core.network.model.NetworkChangeList
+import com.google.samples.apps.nowinandroid.core.network.model.NetworkNewsResource
+import com.google.samples.apps.nowinandroid.core.network.retrofit.NetworkResponse
+import retrofit2.http.GET
+import retrofit2.http.Query
+
+/**
+ * Retrofit API declaration for News Resource API
+ */
+internal interface NewsResourceApi {
+    @GET(value = "newsresources")
+    suspend fun getNewsResources(
+        @Query("id") ids: List<String>?,
+    ): NetworkResponse<List<NetworkNewsResource>>
+
+    @GET(value = "changelists/newsresources")
+    suspend fun getNewsResourcesChangeList(
+        @Query("after") after: Int?,
+    ): List<NetworkChangeList>
+}

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/api/TopicApi.kt

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2025 The Android Open Source Project
+ *
+ * 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
+ *
+ *     https://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 com.google.samples.apps.nowinandroid.core.network.api
+
+import com.google.samples.apps.nowinandroid.core.network.model.NetworkChangeList
+import com.google.samples.apps.nowinandroid.core.network.model.NetworkTopic
+import com.google.samples.apps.nowinandroid.core.network.retrofit.NetworkResponse
+import retrofit2.http.GET
+import retrofit2.http.Query
+
+/**
+ * Retrofit API declaration for Topic API
+ */
+internal interface TopicApi {
+    @GET(value = "topics")
+    suspend fun getTopics(
+        @Query("id") ids: List<String>?,
+    ): NetworkResponse<List<NetworkTopic>>
+
+    @GET(value = "changelists/topics")
+    suspend fun getTopicChangeList(
+        @Query("after") after: Int?,
+    ): List<NetworkChangeList>
+}

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/di/ApiModule.kt

@@ -0,0 +1,33 @@
+package com.google.samples.apps.nowinandroid.core.network.di
+
+import androidx.tracing.trace
+import com.google.samples.apps.nowinandroid.core.network.api.NewsResourceApi
+import com.google.samples.apps.nowinandroid.core.network.api.TopicApi
+import dagger.Module
+import dagger.Provides
+import dagger.hilt.InstallIn
+import dagger.hilt.components.SingletonComponent
+import retrofit2.Retrofit
+import javax.inject.Singleton
+import kotlin.jvm.java
+
+@Module
+@InstallIn(SingletonComponent::class)
+internal object ApiModule {
+
+    @Provides
+    @Singleton
+    internal fun providesTopicApi(retrofit: Retrofit): TopicApi {
+        trace("RetrofitNiaNetwork") {
+            return retrofit.create(TopicApi::class.java)
+        }
+    }
+
+    @Provides
+    @Singleton
+    internal fun providesNewsResourceApi(retrofit: Retrofit): NewsResourceApi {
+        trace("RetrofitNiaNetwork") {
+            return retrofit.create(NewsResourceApi::class.java)
+        }
+    }
+}

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/di/NetworkModule.kt

@@ -23,15 +23,19 @@ import coil.decode.SvgDecoder
 import coil.util.DebugLogger
 import com.google.samples.apps.nowinandroid.core.network.BuildConfig
 import com.google.samples.apps.nowinandroid.core.network.demo.DemoAssetManager
+import com.google.samples.apps.nowinandroid.core.network.retrofit.NIA_BASE_URL
 import dagger.Module
 import dagger.Provides
 import dagger.hilt.InstallIn
 import dagger.hilt.android.qualifiers.ApplicationContext
 import dagger.hilt.components.SingletonComponent
 import kotlinx.serialization.json.Json
 import okhttp3.Call
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.OkHttpClient
 import okhttp3.logging.HttpLoggingInterceptor
+import retrofit2.Retrofit
+import retrofit2.converter.kotlinx.serialization.asConverterFactory
 import javax.inject.Singleton
 
 @Module
@@ -92,4 +96,23 @@ internal object NetworkModule {
             }
             .build()
     }
+
+    @Provides
+    @Singleton
+    fun provideRetrofit(
+        networkJson: Json,
+        okhttpCallFactory: dagger.Lazy<Call.Factory>,
+    ): Retrofit {
+        trace("RetrofitNiaNetwork") {
+            return Retrofit.Builder()
+                .baseUrl(NIA_BASE_URL)
+                // We use callFactory lambda here with dagger.Lazy<Call.Factory>
+                // to prevent initializing OkHttp on the main thread.
+                .callFactory { okhttpCallFactory.get().newCall(it) }
+                .addConverterFactory(
+                    networkJson.asConverterFactory("application/json".toMediaType()),
+                )
+                .build()
+        }
+    }
 }

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/retrofit/RetrofitNiaNetwork.kt

@@ -16,55 +16,25 @@
 
 package com.google.samples.apps.nowinandroid.core.network.retrofit
 
-import androidx.tracing.trace
 import com.google.samples.apps.nowinandroid.core.network.BuildConfig
 import com.google.samples.apps.nowinandroid.core.network.NiaNetworkDataSource
+import com.google.samples.apps.nowinandroid.core.network.api.NewsResourceApi
+import com.google.samples.apps.nowinandroid.core.network.api.TopicApi
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkChangeList
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkNewsResource
 import com.google.samples.apps.nowinandroid.core.network.model.NetworkTopic
 import kotlinx.serialization.Serializable
-import kotlinx.serialization.json.Json
-import okhttp3.Call
-import okhttp3.MediaType.Companion.toMediaType
 import retrofit2.Retrofit
-import retrofit2.converter.kotlinx.serialization.asConverterFactory
-import retrofit2.http.GET
-import retrofit2.http.Query
 import javax.inject.Inject
 import javax.inject.Singleton
 
-/**
- * Retrofit API declaration for NIA Network API
- */
-private interface RetrofitNiaNetworkApi {
-    @GET(value = "topics")
-    suspend fun getTopics(
-        @Query("id") ids: List<String>?,
-    ): NetworkResponse<List<NetworkTopic>>
-
-    @GET(value = "newsresources")
-    suspend fun getNewsResources(
-        @Query("id") ids: List<String>?,
-    ): NetworkResponse<List<NetworkNewsResource>>
-
-    @GET(value = "changelists/topics")
-    suspend fun getTopicChangeList(
-        @Query("after") after: Int?,
-    ): List<NetworkChangeList>
-
-    @GET(value = "changelists/newsresources")
-    suspend fun getNewsResourcesChangeList(
-        @Query("after") after: Int?,
-    ): List<NetworkChangeList>
-}
-
-private const val NIA_BASE_URL = BuildConfig.BACKEND_URL
+internal const val NIA_BASE_URL = BuildConfig.BACKEND_URL
 
 /**
  * Wrapper for data provided from the [NIA_BASE_URL]
  */
 @Serializable
-private data class NetworkResponse<T>(
+internal data class NetworkResponse<T>(
     val data: T,
 )
 
@@ -73,32 +43,19 @@ private data class NetworkResponse<T>(
  */
 @Singleton
 internal class RetrofitNiaNetwork @Inject constructor(
-    networkJson: Json,
-    okhttpCallFactory: dagger.Lazy<Call.Factory>,
+    val newsResourceApi: NewsResourceApi,
+    val topicApi: TopicApi
 ) : NiaNetworkDataSource {
 
-    private val networkApi = trace("RetrofitNiaNetwork") {
-        Retrofit.Builder()
-            .baseUrl(NIA_BASE_URL)
-            // We use callFactory lambda here with dagger.Lazy<Call.Factory>
-            // to prevent initializing OkHttp on the main thread.
-            .callFactory { okhttpCallFactory.get().newCall(it) }
-            .addConverterFactory(
-                networkJson.asConverterFactory("application/json".toMediaType()),
-            )
-            .build()
-            .create(RetrofitNiaNetworkApi::class.java)
-    }
-
     override suspend fun getTopics(ids: List<String>?): List<NetworkTopic> =
-        networkApi.getTopics(ids = ids).data
+        topicApi.getTopics(ids = ids).data
 
     override suspend fun getNewsResources(ids: List<String>?): List<NetworkNewsResource> =
-        networkApi.getNewsResources(ids = ids).data
+        newsResourceApi.getNewsResources(ids = ids).data
 
     override suspend fun getTopicChangeList(after: Int?): List<NetworkChangeList> =
-        networkApi.getTopicChangeList(after = after)
+        topicApi.getTopicChangeList(after = after)
 
     override suspend fun getNewsResourceChangeList(after: Int?): List<NetworkChangeList> =
-        networkApi.getNewsResourcesChangeList(after = after)
+        newsResourceApi.getNewsResourcesChangeList(after = after)
 }