feat: make provider interface "stateless"; SDK maintains provider state

README.md

@@ -317,11 +317,6 @@ public class MyProvider implements FeatureProvider {
         return () -> "My Provider";
     }
 
-    @Override
-    public ProviderState getState() {
-        // optionally indicate your provider's state (assumed to be READY if not implemented)
-    }
-
     @Override
     public void initialize(EvaluationContext evaluationContext) throws Exception {
         // start up your provider
@@ -368,11 +363,6 @@ class MyEventProvider extends EventProvider {
         return () -> "My Event Provider";
     }
 
-    @Override
-    public ProviderState getState() {
-        // indicate your provider's state (required for EventProviders)
-    }
-
     @Override
     public void initialize(EvaluationContext evaluationContext) throws Exception {
         // emit events when flags are changed in a hypothetical REST API
@@ -391,6 +381,13 @@ class MyEventProvider extends EventProvider {
 }
 ```
 
+Providers no longer need to manage their own state, this is done by the SDK itself. If desired, the state of a provider 
+can be queried through the client that uses the provider.
+
+```java
+OpenFeatureAPI.getInstance().getClient().getProviderState();
+```
+
 > Built a new provider? [Let us know](https://github.com/open-feature/openfeature.dev/issues/new?assignees=&labels=provider&projects=&template=document-provider.yaml&title=%5BProvider%5D%3A+) so we can add it to the docs!
 
 ### Develop a hook

src/main/java/dev/openfeature/sdk/Client.java

@@ -33,4 +33,10 @@ public interface Client extends Features, EventBus<Client> {
      * @return A list of {@link Hook}s.
      */
     List<Hook> getHooks();
+
+    /**
+     * Returns the current state of the associated provider.
+     * @return the provider state
+     */
+    ProviderState getProviderState();
 }

src/main/java/dev/openfeature/sdk/ErrorCode.java

@@ -2,5 +2,6 @@
 
 @SuppressWarnings("checkstyle:MissingJavadocType")
 public enum ErrorCode {
-    PROVIDER_NOT_READY, FLAG_NOT_FOUND, PARSE_ERROR, TYPE_MISMATCH, TARGETING_KEY_MISSING, INVALID_CONTEXT, GENERAL
+    PROVIDER_NOT_READY, FLAG_NOT_FOUND, PARSE_ERROR, TYPE_MISMATCH, TARGETING_KEY_MISSING, INVALID_CONTEXT, GENERAL,
+    PROVIDER_FATAL
 }

src/main/java/dev/openfeature/sdk/EventProvider.java

@@ -2,6 +2,7 @@
 
 import dev.openfeature.sdk.internal.TriConsumer;
 
+
 /**
  * Abstract EventProvider. Providers must extend this class to support events.
  * Emit events with {@link #emit(ProviderEvent, ProviderEventDetails)}. Please
@@ -15,22 +16,20 @@
  * @see FeatureProvider
  */
 public abstract class EventProvider implements FeatureProvider {
+    private EventProviderListener eventProviderListener;
 
-    /**
-     * {@inheritDoc}
-     */
-    @Override
-    public abstract ProviderState getState();
+    void setEventProviderListener(EventProviderListener eventProviderListener) {
+        this.eventProviderListener = eventProviderListener;
+    }
 
     private TriConsumer<EventProvider, ProviderEvent, ProviderEventDetails> onEmit = null;
 
     /**
      * "Attach" this EventProvider to an SDK, which allows events to propagate from this provider.
-     * No-op if the same onEmit is already attached. 
+     * No-op if the same onEmit is already attached.
      *
      * @param onEmit the function to run when a provider emits events.
      * @throws IllegalStateException if attempted to bind a new emitter for already bound provider
-     *
      */
     void attach(TriConsumer<EventProvider, ProviderEvent, ProviderEventDetails> onEmit) {
         if (this.onEmit != null && this.onEmit != onEmit) {
@@ -50,11 +49,14 @@ void detach() {
 
     /**
      * Emit the specified {@link ProviderEvent}.
-     * 
+     *
      * @param event   The event type
      * @param details The details of the event
      */
     public void emit(ProviderEvent event, ProviderEventDetails details) {
+        if (eventProviderListener != null) {
+            eventProviderListener.onEmit(event, details);
+        }
         if (this.onEmit != null) {
             this.onEmit.accept(this, event, details);
         }
@@ -63,7 +65,7 @@ public void emit(ProviderEvent event, ProviderEventDetails details) {
     /**
      * Emit a {@link ProviderEvent#PROVIDER_READY} event.
      * Shorthand for {@link #emit(ProviderEvent, ProviderEventDetails)}
-     * 
+     *
      * @param details The details of the event
      */
     public void emitProviderReady(ProviderEventDetails details) {
@@ -74,7 +76,7 @@ public void emitProviderReady(ProviderEventDetails details) {
      * Emit a
      * {@link ProviderEvent#PROVIDER_CONFIGURATION_CHANGED}
      * event. Shorthand for {@link #emit(ProviderEvent, ProviderEventDetails)}
-     * 
+     *
      * @param details The details of the event
      */
     public void emitProviderConfigurationChanged(ProviderEventDetails details) {
@@ -84,7 +86,7 @@ public void emitProviderConfigurationChanged(ProviderEventDetails details) {
     /**
      * Emit a {@link ProviderEvent#PROVIDER_STALE} event.
      * Shorthand for {@link #emit(ProviderEvent, ProviderEventDetails)}
-     * 
+     *
      * @param details The details of the event
      */
     public void emitProviderStale(ProviderEventDetails details) {
@@ -94,7 +96,7 @@ public void emitProviderStale(ProviderEventDetails details) {
     /**
      * Emit a {@link ProviderEvent#PROVIDER_ERROR} event.
      * Shorthand for {@link #emit(ProviderEvent, ProviderEventDetails)}
-     * 
+     *
      * @param details The details of the event
      */
     public void emitProviderError(ProviderEventDetails details) {

src/main/java/dev/openfeature/sdk/EventProviderListener.java

@@ -0,0 +1,6 @@
+package dev.openfeature.sdk;
+
+@FunctionalInterface
+interface EventProviderListener {
+    void onEmit(ProviderEvent event, ProviderEventDetails details);
+}

src/main/java/dev/openfeature/sdk/FeatureProvider.java

@@ -60,11 +60,13 @@ default void shutdown() {
      * If the provider needs to be initialized, it should return {@link ProviderState#NOT_READY}.
      * If the provider is in an error state, it should return {@link ProviderState#ERROR}.
      * If the provider is functioning normally, it should return {@link ProviderState#READY}.
-     * 
+     *
      * <p><i>Providers which do not implement this method are assumed to be ready immediately.</i></p>
-     * 
+     *
      * @return ProviderState
+     * @deprecated The state is handled by the SDK internally. Query the state from the {@link Client} instead.
      */
+    @Deprecated
     default ProviderState getState() {
         return ProviderState.READY;
     }

src/main/java/dev/openfeature/sdk/FeatureProviderStateManager.java

@@ -0,0 +1,82 @@
+package dev.openfeature.sdk;
+
+import dev.openfeature.sdk.exceptions.OpenFeatureError;
+import lombok.Getter;
+import lombok.experimental.Delegate;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+class FeatureProviderStateManager implements EventProviderListener {
+
+    private interface ExcludeFromDelegate {
+        void initialize(EvaluationContext evaluationContext) throws Exception;
+
+        void shutdown();
+
+        ProviderState getState();
+    }
+
+    @Delegate(excludes = ExcludeFromDelegate.class)
+    private final FeatureProvider delegate;
+    private final AtomicBoolean isInitialized = new AtomicBoolean();
+    @Getter
+    private ProviderState state = ProviderState.NOT_READY;
+
+    public FeatureProviderStateManager(FeatureProvider delegate) {
+        this.delegate = delegate;
+        if (delegate instanceof EventProvider) {
+            ((EventProvider) delegate).setEventProviderListener(this);
+        }
+    }
+
+    public void initialize(EvaluationContext evaluationContext) throws Exception {
+        if (isInitialized.getAndSet(true)) {
+            return;
+        }
+        try {
+            delegate.initialize(evaluationContext);
+            state = ProviderState.READY;
+        } catch (OpenFeatureError openFeatureError) {
+            if (ErrorCode.PROVIDER_FATAL.equals(openFeatureError.getErrorCode())) {
+                state = ProviderState.FATAL;
+            } else {
+                state = ProviderState.ERROR;
+            }
+            isInitialized.set(false);
+            throw openFeatureError;
+        } catch (Exception e) {
+            state = ProviderState.ERROR;
+            isInitialized.set(false);
+            throw e;
+        }
+    }
+
+    public void shutdown() {
+        delegate.shutdown();
+        state = ProviderState.NOT_READY;
+        isInitialized.set(false);
+    }
+
+    @Override
+    public void onEmit(ProviderEvent event, ProviderEventDetails details) {
+        if (ProviderEvent.PROVIDER_ERROR.equals(event)) {
+            if (details != null && details.getErrorCode() == ErrorCode.PROVIDER_FATAL) {
+                state = ProviderState.FATAL;
+            } else {
+                state = ProviderState.ERROR;
+            }
+        } else if (ProviderEvent.PROVIDER_STALE.equals(event)) {
+            state = ProviderState.STALE;
+        } else if (ProviderEvent.PROVIDER_READY.equals(event)) {
+            state = ProviderState.READY;
+        }
+    }
+
+    FeatureProvider getProvider() {
+        return delegate;
+    }
+
+    public boolean hasSameProvider(FeatureProvider featureProvider) {
+        return this.delegate.equals(featureProvider);
+    }
+}

src/main/java/dev/openfeature/sdk/NoOpProvider.java

@@ -59,7 +59,7 @@ public ProviderEvaluation<Double> getDoubleEvaluation(String key, Double default
 
     @Override
     public ProviderEvaluation<Value> getObjectEvaluation(String key, Value defaultValue,
-        EvaluationContext invocationContext) {
+                                                         EvaluationContext invocationContext) {
         return ProviderEvaluation.<Value>builder()
                 .value(defaultValue)
                 .variant(PASSED_IN_DEFAULT)