Create `getDemoDataFromJson` method and use it.

Change-Id: I19336b061e74a378cc70470fbd6af8ee4c7533e0

core/network/src/main/kotlin/com/google/samples/apps/nowinandroid/core/network/demo/DemoNiaNetworkDataSource.kt

@@ -17,7 +17,8 @@
 package com.google.samples.apps.nowinandroid.core.network.demo
 
 import JvmUnitTestDemoAssetManager
-import android.os.Build
+import android.os.Build.VERSION.SDK_INT
+import android.os.Build.VERSION_CODES.N
 import com.google.samples.apps.nowinandroid.core.network.Dispatcher
 import com.google.samples.apps.nowinandroid.core.network.NiaDispatchers.IO
 import com.google.samples.apps.nowinandroid.core.network.NiaNetworkDataSource
@@ -29,6 +30,7 @@ import kotlinx.coroutines.withContext
 import kotlinx.serialization.ExperimentalSerializationApi
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.decodeFromStream
+import java.io.BufferedReader
 import javax.inject.Inject
 
 /**
@@ -40,31 +42,11 @@ class DemoNiaNetworkDataSource @Inject constructor(
     private val assets: DemoAssetManager = JvmUnitTestDemoAssetManager,
 ) : NiaNetworkDataSource {
 
-    @OptIn(ExperimentalSerializationApi::class)
     override suspend fun getTopics(ids: List<String>?): List<NetworkTopic> =
-        withContext(ioDispatcher) {
-            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
-                assets.open(TOPICS_ASSET).use(networkJson::decodeFromStream)
-            } else {
-                // Use decodeFromString to capability with API 24 below.
-                // https://github.com/Kotlin/kotlinx.serialization/issues/2457#issuecomment-1786923342
-                val topicsJsonString = assets.readText(TOPICS_ASSET)
-                networkJson.decodeFromString(topicsJsonString)
-            }
-        }
+        getDemoDataFromJson(TOPICS_ASSET)
 
-    @OptIn(ExperimentalSerializationApi::class)
     override suspend fun getNewsResources(ids: List<String>?): List<NetworkNewsResource> =
-        withContext(ioDispatcher) {
-            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
-                assets.open(NEWS_ASSET).use(networkJson::decodeFromStream)
-            } else {
-                // Use decodeFromString to capability with API 24 below.
-                // https://github.com/Kotlin/kotlinx.serialization/issues/2457#issuecomment-1786923342
-                val newsJsonString = assets.readText(NEWS_ASSET)
-                networkJson.decodeFromString(newsJsonString)
-            }
-        }
+        getDemoDataFromJson(NEWS_ASSET)
 
     override suspend fun getTopicChangeList(after: Int?): List<NetworkChangeList> =
         getTopics().mapToChangeList(NetworkTopic::id)
@@ -72,6 +54,23 @@ class DemoNiaNetworkDataSource @Inject constructor(
     override suspend fun getNewsResourceChangeList(after: Int?): List<NetworkChangeList> =
         getNewsResources().mapToChangeList(NetworkNewsResource::id)
 
+    /**
+     * Get Demo data form a [fileName] Json file.
+     */
+    @OptIn(ExperimentalSerializationApi::class)
+    private suspend inline fun <reified T> getDemoDataFromJson(fileName: String): List<T> =
+        withContext(ioDispatcher) {
+            assets.open(fileName).use { inputStream ->
+                if (SDK_INT >= N) {
+                    networkJson.decodeFromStream(inputStream)
+                } // https://github.com/Kotlin/kotlinx.serialization/issues/2457#issuecomment-1786923342
+                else {
+                    inputStream.bufferedReader().use(BufferedReader::readText)
+                        .let(networkJson::decodeFromString)
+                }
+            }
+        }
+
     companion object {
         private const val NEWS_ASSET = "news.json"
         private const val TOPICS_ASSET = "topics.json"