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

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

@@ -1,5 +1,7 @@
 package dev.openfeature.sdk;
 
+import dev.openfeature.sdk.exceptions.GeneralError;
+import dev.openfeature.sdk.exceptions.OpenFeatureError;
 import dev.openfeature.sdk.internal.TriConsumer;
 
 /**
@@ -16,21 +18,56 @@
  */
 public abstract class EventProvider implements FeatureProvider {
 
+    private ProviderState providerState = ProviderState.NOT_READY;
+
     /**
      * {@inheritDoc}
      */
     @Override
-    public abstract ProviderState getState();
+    public final ProviderState getState() {
+        return providerState;
+    }
+
+    @Override
+    public final void initialize(EvaluationContext evaluationContext) throws Exception {
+        try {
+            doInitialization(evaluationContext);
+            providerState = ProviderState.READY;
+        } catch (OpenFeatureError openFeatureError) {
+            if (ErrorCode.PROVIDER_FATAL.equals(openFeatureError.getErrorCode())) {
+                providerState = ProviderState.FATAL;
+            } else {
+                providerState = ProviderState.ERROR;
+            }
+            throw openFeatureError;
+        } catch (Exception e) {
+            providerState = ProviderState.ERROR;
+            throw new GeneralError(e);
+        }
+    }
+
+    protected void doInitialization(EvaluationContext evaluationContext) throws Exception {
+        // Intentionally left blank, to be implemented by inheritors
+    }
+
+    @Override
+    public final void shutdown() {
+        providerState = ProviderState.NOT_READY;
+        doShutdown();
+    }
+
+    protected void doShutdown() {
+        // Intentionally left blank, to be implemented by inheritors
+    }
 
     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 +87,18 @@ 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 (ProviderEvent.PROVIDER_ERROR.equals(event)) {
+            providerState = ProviderState.ERROR;
+        } else if (ProviderEvent.PROVIDER_STALE.equals(event)) {
+            providerState = ProviderState.STALE;
+        } else if (ProviderEvent.PROVIDER_READY.equals(event)) {
+            providerState = ProviderState.READY;
+        }
         if (this.onEmit != null) {
             this.onEmit.accept(this, event, details);
         }
@@ -63,7 +107,7 @@ 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 +118,7 @@ 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 +128,7 @@ 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 +138,7 @@ 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/OpenFeatureAPI.java

@@ -5,11 +5,7 @@
 import dev.openfeature.sdk.internal.AutoCloseableReentrantReadWriteLock;
 import lombok.extern.slf4j.Slf4j;
 
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.List;
-import java.util.Optional;
-import java.util.Set;
+import java.util.*;
 import java.util.function.Consumer;
 
 /**
@@ -86,7 +82,7 @@ public Client getClient() {
      * Multiple clients can be used to segment feature flag configuration.
      * If there is already a provider bound to this domain, this provider will be used.
      * Otherwise, the default provider is used until a provider is assigned to that domain.
-     * 
+     *
      * @param domain an identifier which logically binds clients with providers
      * @return a new client instance
      */
@@ -100,15 +96,18 @@ public Client getClient(String domain) {
      * Multiple clients can be used to segment feature flag configuration.
      * If there is already a provider bound to this domain, this provider will be used.
      * Otherwise, the default provider is used until a provider is assigned to that domain.
-     * 
-     * @param domain a identifier which logically binds clients with providers
+     *
+     * @param domain  a identifier which logically binds clients with providers
      * @param version a version identifier
      * @return a new client instance
      */
     public Client getClient(String domain, String version) {
-        return new OpenFeatureClient(this,
+        return new OpenFeatureClient(
+                () -> providerRepository.getProvider(domain),
+                this,
                 domain,
-                version);
+                version
+        );
     }
 
     /**
@@ -193,8 +192,8 @@ public void setProvider(FeatureProvider provider) {
     /**
      * Add a provider for a domain.
      *
-     * @param domain     The domain to bind the provider to.
-     * @param provider   The provider to set.
+     * @param domain   The domain to bind the provider to.
+     * @param provider The provider to set.
      */
     public void setProvider(String domain, FeatureProvider provider) {
         try (AutoCloseableLock __ = lock.writeLockAutoCloseable()) {
@@ -226,8 +225,8 @@ public void setProviderAndWait(FeatureProvider provider) throws OpenFeatureError
     /**
      * Add a provider for a domain and wait for initialization to finish.
      *
-     * @param domain     The domain to bind the provider to.
-     * @param provider   The provider to set.
+     * @param domain   The domain to bind the provider to.
+     * @param provider The provider to set.
      */
     public void setProviderAndWait(String domain, FeatureProvider provider) throws OpenFeatureError {
         try (AutoCloseableLock __ = lock.writeLockAutoCloseable()) {
@@ -300,6 +299,7 @@ public void addHooks(Hook... hooks) {
 
     /**
      * Fetch the hooks associated to this client.
+     *
      * @return A list of {@link Hook}s.
      */
     public List<Hook> getHooks() {
@@ -404,7 +404,7 @@ void addHandler(String domain, ProviderEvent event, Consumer<EventDetails> handl
 
     /**
      * Runs the handlers associated with a particular provider.
-     * 
+     *
      * @param provider the provider from where this event originated
      * @param event    the event type
      * @param details  the event details