feat: Implement RtcEngine plugin feature (#470)

* feat: Implement RtcEngine plugin feature

* Remove unnecessary comments

* Remove unnecessary comments

* Resolve PR comment

android/src/main/java/io/agora/rtc/base/RtcEngine.kt

@@ -371,8 +371,20 @@ class IRtcEngine {
   }
 }
 
-class RtcEngineManager(
-  private val emit: (methodName: String, data: Map<String, Any?>?) -> Unit
+open class RtcEngineFactory {
+  open fun create(params: Map<String, *>, rtcEngineEventHandler: RtcEngineEventHandler): RtcEngine? {
+    val engine = RtcEngineEx.create(mapToRtcEngineConfig(params["config"] as Map<*, *>).apply {
+      mContext = params["context"] as Context
+      mEventHandler = rtcEngineEventHandler
+    })
+
+    return engine
+  }
+}
+
+open class RtcEngineManager(
+  private val emit: (methodName: String, data: Map<String, Any?>?) -> Unit,
+  private val rtcEngineFactory: RtcEngineFactory = RtcEngineFactory()
 ) : IRtcEngine.RtcEngineInterface {
   var engine: RtcEngine? = null
     private set
@@ -385,17 +397,20 @@ class RtcEngineManager(
   }
 
   override fun create(params: Map<String, *>, callback: Callback) {
-    engine = RtcEngineEx.create(mapToRtcEngineConfig(params["config"] as Map<*, *>).apply {
-      mContext = params["context"] as Context
-      mEventHandler = RtcEngineEventHandler { methodName, data ->
-        emit(methodName, data)
-      }
+    engine = rtcEngineFactory.create(params, RtcEngineEventHandler { methodName, data ->
+      emit(methodName, data)
     })
-    callback.code((engine as RtcEngineEx).setAppType((params["appType"] as Number).toInt()))
+    callback.code((engine as RtcEngineEx).setAppType((params["appType"] as Number).toInt())) {
+      RtcEngineRegistry.instance.onRtcEngineCreated(engine)
+      it
+    }
   }
 
   override fun destroy(callback: Callback) {
-    callback.resolve(engine) { release() }
+    callback.resolve(engine) {
+      release()
+      RtcEngineRegistry.instance.onRtcEngineDestroyed()
+    }
   }
 
   override fun setChannelProfile(params: Map<String, *>, callback: Callback) {

android/src/main/java/io/agora/rtc/base/RtcEnginePlugin.kt

@@ -0,0 +1,44 @@
+package io.agora.rtc.base
+
+import io.agora.rtc.RtcEngine
+
+/**
+ * A [RtcEnginePlugin] allows developers to interact with the [RtcEngine] which created from flutter
+ * side.
+ */
+interface RtcEnginePlugin {
+
+  /**
+   * This callback will be called when the [RtcEngine] is created by
+   * [RtcEngine.createWithContext](https://docs.agora.io/cn/Video/API%20Reference/flutter/agora_rtc_engine/RtcEngine/createWithContext.html)
+   * function from flutter.
+   *
+   * @param rtcEngine The same [RtcEngine] used by flutter side
+   */
+  fun onRtcEngineCreated(rtcEngine: RtcEngine?)
+
+  /**
+   * This callback will be called when the [RtcEngine.destroy](https://docs.agora.io/cn/Video/API%20Reference/flutter/v4.0.7/rtc_channel/RtcChannel/destroy.html)
+   * function is called from flutter.
+   */
+  fun onRtcEngineDestroyed()
+
+  companion object Registrant {
+    /**
+     * Register a [RtcEnginePlugin]. The [plugin] will be called when the [RtcEngine] is created from
+     * flutter side.
+     */
+    fun register(plugin: RtcEnginePlugin) {
+      RtcEngineRegistry.instance.add(plugin = plugin)
+    }
+
+    /**
+     * Unregister a previously registered [RtcEnginePlugin].
+     */
+    fun unregister(plugin: RtcEnginePlugin) {
+      RtcEngineRegistry.instance.remove(pluginClass = plugin.javaClass)
+    }
+  }
+}
+
+

android/src/main/java/io/agora/rtc/base/RtcEngineRegistry.kt

@@ -0,0 +1,43 @@
+package io.agora.rtc.base
+
+import io.agora.rtc.RtcEngine
+import java.util.HashMap
+
+/**
+ * The [RtcEngineRegistry] is response to add, remove and notify the callback when [RtcEngine] is created
+ * from flutter side.
+ */
+internal class RtcEngineRegistry private constructor() : RtcEnginePlugin {
+  companion object {
+    val instance: RtcEngineRegistry by lazy { RtcEngineRegistry() }
+  }
+
+  private val plugins: MutableMap<Class<out RtcEnginePlugin>, RtcEnginePlugin> = HashMap()
+
+  /**
+   * Add a [RtcEnginePlugin].
+   */
+  fun add(plugin: RtcEnginePlugin) {
+    if (plugins.containsKey(plugin.javaClass)) return
+    plugins[plugin.javaClass] = plugin
+  }
+
+  /**
+   * Remove the previously added [RtcEnginePlugin].
+   */
+  fun remove(pluginClass: Class<out RtcEnginePlugin>) {
+    plugins.remove(pluginClass)
+  }
+
+  override fun onRtcEngineCreated(rtcEngine: RtcEngine?) {
+    for (plugin in plugins.values) {
+      plugin.onRtcEngineCreated(rtcEngine)
+    }
+  }
+
+  override fun onRtcEngineDestroyed() {
+    for (plugin in plugins.values) {
+      plugin.onRtcEngineDestroyed()
+    }
+  }
+}

android/src/main/kotlin/io/agora/agora_rtc_engine/AgoraRtcEnginePlugin.kt

@@ -6,6 +6,7 @@ import android.os.Looper
 import androidx.annotation.NonNull
 import io.agora.rtc.RtcEngine
 import io.agora.rtc.base.RtcEngineManager
+import io.agora.rtc.base.RtcEngineRegistry
 import io.flutter.embedding.engine.plugins.FlutterPlugin
 import io.flutter.plugin.common.*
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler
@@ -27,7 +28,7 @@ class AgoraRtcEnginePlugin : FlutterPlugin, MethodCallHandler, EventChannel.Stre
   private lateinit var eventChannel: EventChannel
 
   private var eventSink: EventChannel.EventSink? = null
-  private val manager = RtcEngineManager { methodName, data -> emit(methodName, data) }
+  private val manager = RtcEngineManager(emit = { methodName, data -> emit(methodName, data) })
   private val handler = Handler(Looper.getMainLooper())
   private val rtcChannelPlugin = AgoraRtcChannelPlugin(this)
 

android/src/main/kotlin/io/agora/agora_rtc_engine/AgoraSurfaceViewFactory.kt

@@ -29,7 +29,7 @@ class AgoraSurfaceViewFactory(
   }
 }
 
-class AgoraSurfaceView(
+internal class AgoraSurfaceView(
   context: Context,
   messenger: BinaryMessenger,
   viewId: Int,

example/android/app/build.gradle

@@ -30,6 +30,7 @@ android {
 
     sourceSets {
         main.java.srcDirs += 'src/main/kotlin'
+        test.java.srcDirs += 'src/test/kotlin'
     }
 
     lintOptions {
@@ -66,4 +67,7 @@ dependencies {
     androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
 
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
+
+    testImplementation 'junit:junit:4.13.2'
+    testImplementation 'org.mockito:mockito-core:3.3.3'
 }