chore: add support to set screen name to all event

posthog-android/src/main/java/com/posthog/android/PostHogAndroid.kt

@@ -4,6 +4,7 @@ import android.app.Application
 import android.content.Context
 import com.posthog.PostHog
 import com.posthog.PostHogInterface
+import com.posthog.PostHogScreenProcessor
 import com.posthog.android.internal.MainHandler
 import com.posthog.android.internal.PostHogActivityLifecycleCallbackIntegration
 import com.posthog.android.internal.PostHogAndroidContext
@@ -88,6 +89,10 @@ public class PostHogAndroid private constructor() {
                 if (config.captureDeepLinks || config.captureScreenViews || config.sessionReplay) {
                     config.addIntegration(PostHogActivityLifecycleCallbackIntegration(context, config))
                 }
+                // if the processor depends on captureScreenViews, only adds if its enabled
+                if (config.captureScreenViews) {
+                    config.addProcessor(PostHogScreenProcessor())
+                }
             }
             if (config.captureApplicationLifecycleEvents) {
                 config.addIntegration(PostHogAppInstallIntegration(context, config))

posthog-android/src/main/java/com/posthog/android/internal/PostHogActivityLifecycleCallbackIntegration.kt

@@ -6,6 +6,7 @@ import android.app.Application.ActivityLifecycleCallbacks
 import android.os.Bundle
 import com.posthog.PostHog
 import com.posthog.PostHogIntegration
+import com.posthog.ScreenTracker
 import com.posthog.android.PostHogAndroidConfig
 
 /**
@@ -47,6 +48,7 @@ internal class PostHogActivityLifecycleCallbackIntegration(
 
             if (!screenName.isNullOrEmpty()) {
                 PostHog.screen(screenName)
+                ScreenTracker.setCurrentScreen(screenName)
             }
         }
     }

posthog/api/posthog.api

@@ -75,6 +75,7 @@ public class com/posthog/PostHogConfig {
 	public fun <init> (Ljava/lang/String;Ljava/lang/String;ZZZZIIIILcom/posthog/PostHogEncryption;Lcom/posthog/PostHogOnFeatureFlags;ZLcom/posthog/PostHogPropertiesSanitizer;Lkotlin/jvm/functions/Function1;Lcom/posthog/PersonProfiles;)V
 	public synthetic fun <init> (Ljava/lang/String;Ljava/lang/String;ZZZZIIIILcom/posthog/PostHogEncryption;Lcom/posthog/PostHogOnFeatureFlags;ZLcom/posthog/PostHogPropertiesSanitizer;Lkotlin/jvm/functions/Function1;Lcom/posthog/PersonProfiles;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun addIntegration (Lcom/posthog/PostHogIntegration;)V
+	public final fun addProcessor (Lcom/posthog/PostHogPropertiesProcessor;)V
 	public final fun getApiKey ()Ljava/lang/String;
 	public final fun getCachePreferences ()Lcom/posthog/internal/PostHogPreferences;
 	public final fun getContext ()Lcom/posthog/internal/PostHogContext;
@@ -95,6 +96,7 @@ public class com/posthog/PostHogConfig {
 	public final fun getOptOut ()Z
 	public final fun getPersonProfiles ()Lcom/posthog/PersonProfiles;
 	public final fun getPreloadFeatureFlags ()Z
+	public final fun getProcessors ()Ljava/util/List;
 	public final fun getPropertiesSanitizer ()Lcom/posthog/PostHogPropertiesSanitizer;
 	public final fun getReplayStoragePrefix ()Ljava/lang/String;
 	public final fun getSdkName ()Ljava/lang/String;
@@ -236,13 +238,28 @@ public abstract interface class com/posthog/PostHogOnFeatureFlags {
 	public abstract fun loaded ()V
 }
 
+public abstract interface class com/posthog/PostHogPropertiesProcessor {
+	public abstract fun process (Ljava/util/Map;)Ljava/util/Map;
+}
+
 public abstract interface class com/posthog/PostHogPropertiesSanitizer {
 	public abstract fun sanitize (Ljava/util/Map;)Ljava/util/Map;
 }
 
+public final class com/posthog/PostHogScreenProcessor : com/posthog/PostHogPropertiesProcessor {
+	public fun <init> ()V
+	public fun process (Ljava/util/Map;)Ljava/util/Map;
+}
+
 public abstract interface annotation class com/posthog/PostHogVisibleForTesting : java/lang/annotation/Annotation {
 }
 
+public final class com/posthog/ScreenTracker {
+	public static final field INSTANCE Lcom/posthog/ScreenTracker;
+	public final fun getCurrentScreenName ()Ljava/lang/String;
+	public final fun setCurrentScreen (Ljava/lang/String;)V
+}
+
 public abstract interface class com/posthog/internal/PostHogContext {
 	public abstract fun getDynamicContext ()Ljava/util/Map;
 	public abstract fun getSdkInfo ()Ljava/util/Map;

posthog/src/main/java/com/posthog/PostHog.kt

@@ -441,8 +441,14 @@ public class PostHog private constructor(
                     appendGroups = !groupIdentify,
                 )
 
+            var currentProperties = mergedProperties
+            // has to run before the sanitizer so people can remove stuff processors add
+            config?.processors?.forEach {
+                currentProperties = it.process(currentProperties.toMutableMap())
+            }
+
             // sanitize the properties or fallback to the original properties
-            val sanitizedProperties = config?.propertiesSanitizer?.sanitize(mergedProperties.toMutableMap()) ?: mergedProperties
+            val sanitizedProperties = config?.propertiesSanitizer?.sanitize(currentProperties.toMutableMap()) ?: currentProperties
 
             val postHogEvent =
                 PostHogEvent(

posthog/src/main/java/com/posthog/PostHogConfig.kt

@@ -156,6 +156,9 @@ public open class PostHogConfig(
     private val integrationsList: MutableList<PostHogIntegration> = mutableListOf()
     private val integrationLock = Any()
 
+    private val processorsList: MutableList<PostHogPropertiesProcessor> = mutableListOf()
+    private val processorsLock = Any()
+
     /**
      * The integrations list
      */
@@ -188,6 +191,21 @@ public open class PostHogConfig(
         }
     }
 
+    public val processors: List<PostHogPropertiesProcessor>
+        get() {
+            val list: List<PostHogPropertiesProcessor>
+            synchronized(processorsLock) {
+                list = processorsList.toList()
+            }
+            return list
+        }
+
+    public fun addProcessor(processor: PostHogPropertiesProcessor) {
+        synchronized(processorsLock) {
+            processorsList.add(processor)
+        }
+    }
+
     public companion object {
         public const val DEFAULT_HOST: String = "https://us.i.posthog.com"
     }

posthog/src/main/java/com/posthog/PostHogPropertiesProcessor.kt

@@ -0,0 +1,5 @@
+package com.posthog
+
+public fun interface PostHogPropertiesProcessor {
+    public fun process(properties: MutableMap<String, Any>): Map<String, Any>
+}

posthog/src/main/java/com/posthog/PostHogScreenProcessor.kt

@@ -0,0 +1,15 @@
+package com.posthog
+
+public class PostHogScreenProcessor : PostHogPropertiesProcessor {
+    override fun process(properties: MutableMap<String, Any>): Map<String, Any> {
+        if (properties.containsKey("\$screen_name")) {
+            return properties
+        }
+
+        val currentScreen = ScreenTracker.getCurrentScreenName()
+
+        properties["\$screen_name"] = currentScreen
+
+        return properties
+    }
+}

posthog/src/main/java/com/posthog/ScreenTracker.kt

@@ -0,0 +1,13 @@
+package com.posthog
+
+public object ScreenTracker {
+    @Volatile private lateinit var currentScreen: String
+
+    public fun setCurrentScreen(screenName: String) {
+        currentScreen = screenName
+    }
+
+    public fun getCurrentScreenName(): String {
+        return currentScreen
+    }
+}

posthog/src/test/java/com/posthog/PostHogTest.kt

@@ -45,6 +45,7 @@ internal class PostHogTest {
         reloadFeatureFlags: Boolean = true,
         sendFeatureFlagEvent: Boolean = true,
         integration: PostHogIntegration? = null,
+        processor: PostHogPropertiesProcessor? = null,
         cachePreferences: PostHogMemoryPreferences = PostHogMemoryPreferences(),
         propertiesSanitizer: PostHogPropertiesSanitizer? = null,
     ): PostHogInterface {
@@ -58,6 +59,9 @@ internal class PostHogTest {
                 if (integration != null) {
                     addIntegration(integration)
                 }
+                if (processor != null) {
+                    addProcessor(processor)
+                }
                 this.sendFeatureFlagEvent = sendFeatureFlagEvent
                 this.cachePreferences = cachePreferences
                 this.propertiesSanitizer = propertiesSanitizer
@@ -1128,4 +1132,61 @@ internal class PostHogTest {
 
         sut.close()
     }
+
+    @Test
+    fun `processor does not override existing screen_name in event properties`() {
+        val http = mockHttp()
+        val url = http.url("/")
+
+        val sut = getSut(url.toString(), preloadFeatureFlags = false, reloadFeatureFlags = false, processor = PostHogScreenProcessor())
+
+        ScreenTracker.setCurrentScreen("CurrentScreen")
+
+        sut.capture(
+            "Test Event",
+            properties =
+                mapOf(
+                    "test_prop" to "test_value",
+                    "\$screen_name" to "ProvidedScreen",
+                ),
+        )
+
+        queueExecutor.shutdownAndAwaitTermination()
+
+        val request = http.takeRequest()
+
+        val content = request.body.unGzip()
+        val batch = serializer.deserialize<PostHogBatchEvent>(content.reader())
+
+        val theEvent = batch.batch.first()
+
+        assertEquals("ProvidedScreen", theEvent.properties?.get("\$screen_name"))
+
+        sut.close()
+    }
+
+    @Test
+    fun `processor adds screen_name to event properties`() {
+        val http = mockHttp()
+        val url = http.url("/")
+
+        val sut = getSut(url.toString(), preloadFeatureFlags = false, reloadFeatureFlags = false, processor = PostHogScreenProcessor())
+
+        ScreenTracker.setCurrentScreen("TestScreen")
+
+        sut.capture("Test Event", properties = mapOf("test_prop" to "test_value"))
+
+        queueExecutor.shutdownAndAwaitTermination()
+
+        val request = http.takeRequest()
+
+        val content = request.body.unGzip()
+        val batch = serializer.deserialize<PostHogBatchEvent>(content.reader())
+
+        val theEvent = batch.batch.first()
+
+        assertEquals("TestScreen", theEvent.properties?.get("\$screen_name"))
+
+        sut.close()
+    }
 }