Adding a traits injector plugin sample. (#126)

Adding a traits injector plugin sample.

Author: didiergarcia

samples/kotlin-android-app/src/main/java/com/segment/analytics/next/plugins/InjectTraitsPlugin.kt

@@ -0,0 +1,39 @@
+package com.segment.analytics.next.plugins
+
+import com.segment.analytics.kotlin.core.*
+import com.segment.analytics.kotlin.core.platform.Plugin
+import com.segment.analytics.kotlin.core.utilities.updateJsonObject
+import kotlinx.serialization.json.JsonObject
+
+class InjectTraitsPlugin: Plugin {
+    override val type: Plugin.Type = Plugin.Type.Enrichment
+    override lateinit var analytics: Analytics
+
+    /*
+    NOTE: This object acts as a cache for the traits object; We update it as we get
+    identify events. Given its role as a cache, however, it should live as a global
+    static object. Moving it to your Application class is a good solution.
+     */
+    var cachedTraits: Traits = emptyJsonObject
+
+    override fun execute(event: BaseEvent): BaseEvent? {
+
+        if (event.type == EventType.Identify) {
+
+            // Grab trait related info from the identify event
+            // and update the cache
+            val jsonTraits= event.context.get("traits") as? JsonObject ?: emptyJsonObject
+
+            cachedTraits = updateJsonObject(cachedTraits) {
+                it.putAll(jsonTraits)
+            }
+        } else {
+            // All other events get the traits added to them.
+            event.context = updateJsonObject(event.context) {
+                it["traits"] = cachedTraits
+            }
+        }
+
+        return event
+    }
+}