feat: onConfigChange method from common jdk (#167)

* feat: onConfigChange method from common jdk
* update for Configuration object in the callback
* chore: lint

Author: typotter

README.md

@@ -12,7 +12,7 @@ feature flagging and experimentation for Eppo customers. An API key is required
 
 ```groovy
 dependencies {
-  implementation 'cloud.eppo:android-sdk:4.6.0'
+  implementation 'cloud.eppo:android-sdk:4.7.0'
 }
 
 dependencyResolutionManagement {

eppo/build.gradle

@@ -7,7 +7,7 @@ plugins {
 }
 
 group = "cloud.eppo"
-version = "4.6.1-SNAPSHOT"
+version = "4.7.0"
 
 android {
     buildFeatures.buildConfig true
@@ -68,7 +68,7 @@ ext.versions = [
 ]
 
 dependencies {
-    api 'cloud.eppo:sdk-common-jvm:3.8.0'
+    api 'cloud.eppo:sdk-common-jvm:3.9.0'
 
     implementation 'org.slf4j:slf4j-api:2.0.17'
 

eppo/src/androidTest/java/cloud/eppo/android/EppoClientTest.java

@@ -48,8 +48,10 @@
 import java.io.InputStream;
 import java.lang.reflect.Field;
 import java.text.SimpleDateFormat;
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
@@ -352,6 +354,48 @@ private void testLoadConfigurationHelper(boolean loadAsync)
     assertTrue(eppoClient.getBooleanAssignment("bool_flag", "subject1", false));
   }
 
+  @Test
+  public void testConfigurationChangeListener() throws ExecutionException, InterruptedException {
+    List<Configuration> received = new ArrayList<>();
+
+    // Set up a changing response from the "server"
+    EppoHttpClient mockHttpClient = mock(EppoHttpClient.class);
+
+    // Mock sync get to return empty
+    when(mockHttpClient.get(anyString())).thenReturn(EMPTY_CONFIG);
+
+    // Mock async get to return empty
+    CompletableFuture<byte[]> emptyResponse = CompletableFuture.completedFuture(EMPTY_CONFIG);
+    when(mockHttpClient.getAsync(anyString())).thenReturn(emptyResponse);
+
+    setBaseClientHttpClientOverrideField(mockHttpClient);
+
+    EppoClient.Builder clientBuilder =
+        new EppoClient.Builder(DUMMY_API_KEY, ApplicationProvider.getApplicationContext())
+            .forceReinitialize(true)
+            .onConfigurationChange(received::add)
+            .isGracefulMode(false);
+
+    // Initialize and no exception should be thrown.
+    EppoClient eppoClient = clientBuilder.buildAndInitAsync().get();
+
+    verify(mockHttpClient, times(1)).getAsync(anyString());
+    assertEquals(1, received.size());
+
+    // Now, return the boolean flag config so that the config has changed.
+    when(mockHttpClient.get(anyString())).thenReturn(BOOL_FLAG_CONFIG);
+
+    // Trigger a reload of the client
+    eppoClient.loadConfiguration();
+
+    assertEquals(2, received.size());
+
+    // Reload the client again; the config hasn't changed, but Java doesn't check eTag (yet)
+    eppoClient.loadConfiguration();
+
+    assertEquals(3, received.size());
+  }
+
   @Test
   public void testPollingClient() throws ExecutionException, InterruptedException {
     EppoHttpClient mockHttpClient = mock(EppoHttpClient.class);

eppo/src/main/java/cloud/eppo/android/EppoClient.java

@@ -23,6 +23,7 @@
 import java.util.concurrent.CompletionException;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Consumer;
 
 public class EppoClient extends BaseEppoClient {
   private static final String TAG = logTag(EppoClient.class);
@@ -154,6 +155,7 @@ public static class Builder {
 
     // Assignment caching on by default. To disable, call `builder.assignmentCache(null);`
     private IAssignmentCache assignmentCache = new LRUAssignmentCache(100);
+    @Nullable private Consumer<Configuration> configChangeCallback;
 
     public Builder(@NonNull String apiKey, @NonNull Application application) {
       this.application = application;
@@ -251,6 +253,14 @@ public Builder pollingJitterMs(long pollingJitterMs) {
       return this;
     }
 
+    /**
+     * Registers a callback for when a new configuration is applied to the `EppoClient` instance.
+     */
+    public Builder onConfigurationChange(Consumer<Configuration> configChangeCallback) {
+      this.configChangeCallback = configChangeCallback;
+      return this;
+    }
+
     public CompletableFuture<EppoClient> buildAndInitAsync() {
       if (application == null) {
         throw new MissingApplicationException();
@@ -300,6 +310,10 @@ public CompletableFuture<EppoClient> buildAndInitAsync() {
               initialConfiguration,
               assignmentCache);
 
+      if (configChangeCallback != null) {
+        instance.onConfigurationChange(configChangeCallback);
+      }
+
       final CompletableFuture<EppoClient> ret = new CompletableFuture<>();
 
       AtomicInteger failCount = new AtomicInteger(0);