chore: add new classes for logging

- Add FlutterLogbackAppender.java for logging events in the Flutter app
- Integrate OptimizelyFlutterSdkPlugin with FlutterLogbackAppender
- Update Constants.swift, SwiftOptimizelyFlutterSdkPlugin.swift, and related classes

Author: muzahidul-opti

android/src/main/java/com/optimizely/optimizely_flutter_sdk/FlutterLogbackAppender.java

@@ -0,0 +1,42 @@
+package com.optimizely.optimizely_flutter_sdk;
+
+import android.os.Handler;
+import android.os.Looper;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.AppenderBase;
+import io.flutter.plugin.common.MethodChannel;
+
+public class FlutterLogbackAppender extends AppenderBase<ILoggingEvent> {
+
+    public static final String CHANNEL_NAME = "optimizely_flutter_sdk_logger";
+    public static MethodChannel channel;
+    private static final Handler mainThreadHandler = new Handler(Looper.getMainLooper());
+
+    public static void setChannel(MethodChannel channel) {
+        FlutterLogbackAppender.channel = channel;
+    }
+
+    @Override
+    protected void append(ILoggingEvent event) {
+        if (channel == null) {
+            return;
+        }
+
+        String message = event.getFormattedMessage();
+        int level = event.getLevel().toInt();
+
+        Map<String, Object> logData = new HashMap<>();
+        logData.put("level", level);
+        logData.put("message", message);
+
+        mainThreadHandler.post(() -> {
+            if (channel != null) {
+                channel.invokeMethod("log", logData);
+            }
+        });
+    }
+}

android/src/main/java/com/optimizely/optimizely_flutter_sdk/OptimizelyFlutterSdkPlugin.java

@@ -32,10 +32,19 @@
 
 import io.flutter.embedding.engine.plugins.activity.ActivityAware;
 
+import org.slf4j.LoggerFactory;
+
+import ch.qos.logback.classic.Logger;
+import ch.qos.logback.classic.LoggerContext;
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.Appender;
+
+
 /** OptimizelyFlutterSdkPlugin */
 public class OptimizelyFlutterSdkPlugin extends OptimizelyFlutterClient implements FlutterPlugin, ActivityAware, MethodCallHandler {
 
   public static MethodChannel channel;
+  private Appender<ILoggingEvent> flutterLogbackAppender;
 
   @Override
   public void onMethodCall(@NonNull MethodCall call, @NonNull Result result) {
@@ -157,11 +166,31 @@ public void onAttachedToEngine(@NonNull FlutterPluginBinding binding) {
     channel = new MethodChannel(binding.getBinaryMessenger(), "optimizely_flutter_sdk");
     channel.setMethodCallHandler(this);
     context = binding.getApplicationContext();
+
+    MethodChannel loggerChannel = new MethodChannel(binding.getBinaryMessenger(), FlutterLogbackAppender.CHANNEL_NAME);
+    FlutterLogbackAppender.setChannel(loggerChannel);
+
+    // Add appender to logback
+    flutterLogbackAppender = new FlutterLogbackAppender();
+    LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();
+    flutterLogbackAppender.setContext(lc);
+    flutterLogbackAppender.start();
+    Logger rootLogger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
+    rootLogger.addAppender(flutterLogbackAppender);
   }
 
   @Override
   public void onDetachedFromEngine(@NonNull FlutterPluginBinding binding) {
     channel.setMethodCallHandler(null);
+    // Stop and detach the appender
+    if (flutterLogbackAppender != null) {
+        Logger rootLogger = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
+        rootLogger.detachAppender(flutterLogbackAppender);
+        flutterLogbackAppender.stop();
+        flutterLogbackAppender = null;
+    }
+    // Clean up the channel
+    FlutterLogbackAppender.setChannel(null);
   }
 
   @Override

ios/Classes/HelperClasses/Constants.swift

@@ -91,7 +91,6 @@ struct RequestParameterKey {
     static let reasons = "reasons"
     static let decideOptions = "optimizelyDecideOption"
     static let defaultLogLevel = "defaultLogLevel"
-    static let useCustomLogger = "useCustomLogger"
     static let eventBatchSize = "eventBatchSize"
     static let eventTimeInterval = "eventTimeInterval"
     static let eventMaxQueueSize = "eventMaxQueueSize"

ios/Classes/SwiftOptimizelyFlutterSdkPlugin.swift

@@ -172,15 +172,10 @@ public class SwiftOptimizelyFlutterSdkPlugin: NSObject, FlutterPlugin {
         notificationIdsTracker.removeValue(forKey: sdkKey)
         optimizelyClientsTracker.removeValue(forKey: sdkKey)
 
-        // Check if custom logger is requested
-        var logger: OPTLogger?
-        if let useCustomLogger = parameters[RequestParameterKey.useCustomLogger] as? Bool, useCustomLogger {
-            // OptimizelyFlutterLogger bridges iOS logs to Flutter via Method Channel
-            // When useCustomLogger = true:
-            // iOS SDK log → OptimizelyFlutterLogger → Flutter Method Channel → Flutter console
-            logger = OptimizelyFlutterLogger()
-        }
-
+        // OptimizelyFlutterLogger bridges iOS logs to Flutter via Method Channel
+        // iOS SDK log → OptimizelyFlutterLogger → Flutter Method Channel → Flutter console
+        var logger: OPTLogger = OptimizelyFlutterLogger()
+        
         // Creating new instance
         let optimizelyInstance = OptimizelyClient(
             sdkKey:sdkKey, 

lib/optimizely_flutter_sdk.dart

@@ -73,11 +73,6 @@ class OptimizelyFlutterSdk {
   final OptimizelyLogLevel _defaultLogLevel;
   final SDKSettings _sdkSettings;
   static OptimizelyLogger? _customLogger;
-  /// Set a custom logger for the SDK
-  static void setLogger(OptimizelyLogger logger) {
-    _customLogger = logger;
-    LoggerBridge.initialize(logger);
-  }
   /// Get the current logger
   static OptimizelyLogger? get logger {
     return _customLogger;
@@ -97,11 +92,8 @@ class OptimizelyFlutterSdk {
       _defaultLogLevel = defaultLogLevel,
       _sdkSettings = sdkSettings {
       // Set the logger if provided
-      if (logger != null) {
-        setLogger(logger);
-      } else {
-        logWarning("Logger not provided.");
-      }
+      _customLogger = logger ?? DefaultOptimizelyLogger();
+      LoggerBridge.initialize(_customLogger);
   }
 
   /// Starts Optimizely SDK (Synchronous) with provided sdkKey.

lib/src/optimizely_client_wrapper.dart

@@ -80,7 +80,6 @@ class OptimizelyClientWrapper {
       Constants.eventBatchSize: eventOptions.batchSize,
       Constants.eventTimeInterval: eventOptions.timeInterval,
       Constants.eventMaxQueueSize: eventOptions.maxQueueSize,
-      Constants.useCustomLogger: logger != null,
     };
 
     // Odp Request params

lib/src/utils/constants.dart

@@ -86,7 +86,6 @@ class Constants {
   static const String optimizelyDecideOption = "optimizelyDecideOption";
   static const String optimizelySegmentOption = "optimizelySegmentOption";
   static const String optimizelySdkSettings = "optimizelySdkSettings";
-  static const String useCustomLogger = 'useCustomLogger';
   static const String defaultLogLevel = "defaultLogLevel";
   static const String payload = "payload";
   static const String value = "value";