From 5359c91a64e4da5d7988a18d022be5e22038013f Mon Sep 17 00:00:00 2001
From: "Rohit R. Abbadi" <rohit@flackon.com>
Date: Wed, 5 Aug 2020 01:40:51 +0530
Subject: [PATCH] optimize filtering on streams

https://github.com/ably/ably-flutter/pull/21#discussion_r464578211
---
 lib/src/impl/realtime/channels.dart   | 43 ++++++---------------------
 lib/src/impl/realtime/connection.dart | 20 +++----------
 2 files changed, 13 insertions(+), 50 deletions(-)

diff --git a/lib/src/impl/realtime/channels.dart b/lib/src/impl/realtime/channels.dart
index 835ebc954..22d9e420d 100644
--- a/lib/src/impl/realtime/channels.dart
+++ b/lib/src/impl/realtime/channels.dart
@@ -113,21 +113,9 @@ class RealtimePlatformChannel extends PlatformObject implements spec.RealtimeCha
 
   @override
   Stream<ChannelStateChange> on([ChannelEvent channelEvent]) {
-    Stream<ChannelStateChange> stream = listen(PlatformMethod.onRealtimeChannelStateChanged, _payload).transform<ChannelStateChange>(
-      StreamTransformer.fromHandlers(
-        handleData: (dynamic value, EventSink<ChannelStateChange> sink){
-          ChannelStateChange stateChange = value as ChannelStateChange;
-          if (channelEvent!=null) {
-            if (stateChange.event==channelEvent) {
-              sink.add(stateChange);
-            }
-          } else {
-            sink.add(stateChange);
-          }
-        }
-      )
-    );
-    return stream;
+    return listen(PlatformMethod.onRealtimeChannelStateChanged, _payload)
+      .map((stateChange) => stateChange as ChannelStateChange)
+      .where((stateChange) => channelEvent==null || stateChange.event==channelEvent);
   }
 
   @override
@@ -135,25 +123,12 @@ class RealtimePlatformChannel extends PlatformObject implements spec.RealtimeCha
     String name,
     List<String> names
   }) {
-    Stream<spec.Message> stream = listen(PlatformMethod.onRealtimeChannelMessage, _payload).transform<spec.Message>(
-      StreamTransformer.fromHandlers(
-        handleData: (dynamic value, EventSink<spec.Message> sink){
-          spec.Message message = value as spec.Message;
-          if (names!=null){
-            if(names.contains(message.name)){
-              sink.add(message);
-            }
-          } else if (name!=null) {
-            if(message.name==name){
-              sink.add(message);
-            }
-          } else {
-            sink.add(message);
-          }
-        }
-      )
-    );
-    return stream;
+    final subscribedNames = {name, ...?names}.where((n) => n != null).toList();
+    return listen(PlatformMethod.onRealtimeChannelMessage, _payload)
+      .map((message) => message as spec.Message)
+      .where((message) =>
+          subscribedNames.isEmpty ||
+          subscribedNames.any((n) => n == message.name));
   }
 
 }
diff --git a/lib/src/impl/realtime/connection.dart b/lib/src/impl/realtime/connection.dart
index c82d4bab2..14ef5ed59 100644
--- a/lib/src/impl/realtime/connection.dart
+++ b/lib/src/impl/realtime/connection.dart
@@ -42,22 +42,10 @@ class ConnectionPlatformObject extends PlatformObject implements Connection {
 
   @override
   Stream<ConnectionStateChange> on([ConnectionEvent connectionEvent]) {
-    Stream<ConnectionStateChange> stream = listen(PlatformMethod.onRealtimeConnectionStateChanged).transform<ConnectionStateChange>(
-        StreamTransformer.fromHandlers(
-            handleData: (dynamic value, EventSink<ConnectionStateChange> sink){
-              ConnectionStateChange stateChange = value as ConnectionStateChange;
-              if (connectionEvent!=null) {
-                if (stateChange.event==connectionEvent) {
-                  sink.add(stateChange);
-                }
-              } else {
-                sink.add(stateChange);
-              }
-
-            }
-        )
-    );
-    return stream;
+    return listen(PlatformMethod.onRealtimeConnectionStateChanged)
+      .map((connectionEvent) => connectionEvent as ConnectionStateChange)
+      .where((connectionStateChange) =>
+        connectionEvent==null || connectionStateChange.event==connectionEvent);
   }
 
   @override