Event and State Management

/**
 * Returns the listenable interface for events
 * @return listenable
 */
Listenable<CuratorListener> getCuratorListenable();

/**
 * Returns the listenable interface for unhandled errors
 * @return listenable
 */
Listenable<UnhandledErrorListener> getUnhandledErrorListenable();

/**
 * Represents ZooKeeper events and background operation results
 */
public interface CuratorEvent {
    /**
     * Get the event type
     * @return event type
     */
    CuratorEventType getType();
    
    /**
     * Get the ZooKeeper result code
     * @return result code (0 = success)
     */
    int getResultCode();
    
    /**
     * Get the path associated with this event
     * @return path or null
     */
    String getPath();
    
    /**
     * Get the background context object
     * @return context or null
     */
    Object getContext();
    
    /**
     * Get stat information
     * @return stat or null
     */
    Stat getStat();
    
    /**
     * Get data associated with the event
     * @return data bytes or null
     */
    byte[] getData();
    
    /**
     * Get the name (for create operations with sequential modes)
     * @return name or null
     */
    String getName();
    
    /**
     * Get children list (for getChildren operations)
     * @return children list or null
     */
    List<String> getChildren();
    
    /**
     * Get ACL list (for getACL/setACL operations)
     * @return ACL list or null
     */
    List<ACL> getACLList();
    
    /**
     * Get transaction results (for transaction operations)
     * @return transaction results or null
     */
    List<CuratorTransactionResult> getOpResults();
    
    /**
     * Get the watched event (for watcher callbacks)
     * @return watched event or null
     */
    WatchedEvent getWatchedEvent();
}

/**
 * Types of curator events
 */
public enum CuratorEventType {
    CREATE, DELETE, EXISTS, GET_DATA, SET_DATA, CHILDREN,
    SYNC, GET_ACL, SET_ACL, TRANSACTION, GET_CONFIG, RECONFIG,
    WATCHED, REMOVE_WATCHES, ADD_WATCH, CLOSING
}

/**
 * Listener for background events and errors
 */
public interface CuratorListener {
    /**
     * Called when a background event occurs
     * @param client the client
     * @param event the event
     * @throws Exception errors
     */
    void eventReceived(CuratorFramework client, CuratorEvent event) throws Exception;
}

/**
 * Listener for unhandled errors
 */
public interface UnhandledErrorListener {
    /**
     * Called when an unhandled error occurs
     * @param message error message
     * @param e the exception
     */
    void unhandledError(String message, Throwable e);
}

/**
 * Callback for background operations
 */
public interface BackgroundCallback {
    /**
     * Called when a background operation completes
     * @param client the client
     * @param event the event
     * @throws Exception errors
     */
    void processResult(CuratorFramework client, CuratorEvent event) throws Exception;
}

// Add general curator listener
client.getCuratorListenable().addListener(new CuratorListener() {
    @Override
    public void eventReceived(CuratorFramework client, CuratorEvent event) throws Exception {
        System.out.println("Event: " + event.getType() + " Path: " + event.getPath());
        
        // Handle different event types
        switch (event.getType()) {
            case CREATE:
                System.out.println("Node created: " + event.getPath());
                break;
            case DELETE:
                System.out.println("Node deleted: " + event.getPath());
                break;
            case GET_DATA:
                byte[] data = event.getData();
                System.out.println("Got data: " + new String(data));
                break;
            case CHILDREN:
                List<String> children = event.getChildren();
                System.out.println("Children: " + children);
                break;
            case TRANSACTION:
                List<CuratorTransactionResult> results = event.getOpResults();
                System.out.println("Transaction completed with " + results.size() + " operations");
                break;
        }
    }
});

// Add unhandled error listener
client.getUnhandledErrorListenable().addListener(new UnhandledErrorListener() {
    @Override
    public void unhandledError(String message, Throwable e) {
        System.err.println("Unhandled error: " + message);
        e.printStackTrace();
    }
});

// Use background callback for specific operations
client.create()
      .creatingParentsIfNeeded()
      .inBackground(new BackgroundCallback() {
          @Override
          public void processResult(CuratorFramework client, CuratorEvent event) throws Exception {
              if (event.getResultCode() == 0) {
                  System.out.println("Successfully created: " + event.getPath());
              } else {
                  System.err.println("Failed to create: " + event.getResultCode());
              }
          }
      })
      .forPath("/background/path", "data".getBytes());

// Lambda-style callback
client.getData()
      .inBackground((curatorFramework, curatorEvent) -> {
          if (curatorEvent.getResultCode() == 0) {
              byte[] data = curatorEvent.getData();
              System.out.println("Data retrieved: " + new String(data));
          }
      })
      .forPath("/some/path");

/**
 * Returns the listenable interface for the Connect State
 * @return listenable
 */
Listenable<ConnectionStateListener> getConnectionStateListenable();

/**
 * Return the configured error policy
 * @return error policy
 */
ConnectionStateErrorPolicy getConnectionStateErrorPolicy();

/**
 * Represents connection states to ZooKeeper
 */
public enum ConnectionState {
    /**
     * Sent for the first successful connection to the server
     */
    CONNECTED,
    
    /**
     * There has been a loss of connection. Leaders, locks, etc. should suspend
     * until the connection is re-established
     */
    SUSPENDED,
    
    /**
     * A suspended or lost connection has been re-established
     */
    RECONNECTED,
    
    /**
     * The connection is confirmed to be lost. Close any locks, leaders, etc. and
     * attempt to re-create them
     */
    LOST,
    
    /**
     * The connection has gone into read-only mode. This can only happen if you pass true
     * for canBeReadOnly() in the builder
     */
    READ_ONLY;
    
    /**
     * Check if this state represents a connection
     * @return true if connected
     */
    public boolean isConnected() {
        return (this == CONNECTED) || (this == RECONNECTED) || (this == READ_ONLY);
    }
}

/**
 * Listener for connection state changes
 */
public interface ConnectionStateListener {
    /**
     * Called when the connection state changes
     * @param client the client
     * @param newState the new state
     */
    void stateChanged(CuratorFramework client, ConnectionState newState);
}

/**
 * Policy for handling connection errors
 */
public interface ConnectionStateErrorPolicy {
    /**
     * Return true if this the given state represents an error
     * @param state the state
     * @return true/false
     */
    boolean isErrorState(ConnectionState state);
    
    /**
     * Return the timeout to use when checking error states
     * @return timeout in milliseconds
     */
    int getErrorThresholdMs();
}

/**
 * Default error policy implementation
 */
public class StandardConnectionStateErrorPolicy implements ConnectionStateErrorPolicy {
    // Default implementation considers SUSPENDED and LOST as error states
}

/**
 * Session-based error policy implementation
 */
public class SessionConnectionStateErrorPolicy implements ConnectionStateErrorPolicy {
    // Session-based error handling with different thresholds
}

// Add connection state listener
client.getConnectionStateListenable().addListener(new ConnectionStateListener() {
    @Override
    public void stateChanged(CuratorFramework client, ConnectionState newState) {
        System.out.println("Connection state changed to: " + newState);
        
        switch (newState) {
            case CONNECTED:
                System.out.println("Connected to ZooKeeper");
                // Initialize application state
                break;
                
            case SUSPENDED:
                System.out.println("Connection suspended - pausing operations");
                // Pause non-critical operations
                break;
                
            case RECONNECTED:
                System.out.println("Reconnected to ZooKeeper");
                // Resume operations, refresh state if needed
                break;
                
            case LOST:
                System.out.println("Connection lost - cleaning up");
                // Clean up ephemeral nodes, release locks, etc.
                break;
                
            case READ_ONLY:
                System.out.println("In read-only mode");
                // Only perform read operations
                break;
        }
    }
});

// Use custom executor for connection state callbacks
Executor customExecutor = Executors.newSingleThreadExecutor(r -> {
    Thread t = new Thread(r, "ConnectionStateHandler");
    t.setDaemon(true);
    return t;
});

client.getConnectionStateListenable().addListener(connectionStateListener, customExecutor);

// Check current connection state
ConnectionState currentState = client.getZookeeperClient().getZooKeeper().getState();
System.out.println("Current ZK state: " + currentState);

// Wait for connection
if (!client.getZookeeperClient().blockUntilConnectedOrTimedOut()) {
    throw new RuntimeException("Failed to connect to ZooKeeper");
}

/**
 * Factory for creating connection state listener managers
 */
public class ConnectionStateListenerManagerFactory {
    /**
     * Standard factory instance
     */
    public static final ConnectionStateListenerManagerFactory standard;
    
    /**
     * Create a circuit breaking factory
     * @param retryPolicy retry policy for circuit breaking
     * @return circuit breaking factory
     */
    public static ConnectionStateListenerManagerFactory circuitBreaking(RetryPolicy retryPolicy);
}

/**
 * Circuit breaker for connection management
 */
public interface CircuitBreaker {
    /**
     * Check if the circuit is open (failing)
     * @return true if circuit is open
     */
    boolean isOpen();
    
    /**
     * Get the current retry count
     * @return retry count
     */
    int getRetryCount();
}

/**
 * Connection state listener with circuit breaking capability
 */
public class CircuitBreakingConnectionStateListener implements ConnectionStateListener {
    /**
     * Get the circuit breaker instance
     * @return circuit breaker
     */
    public CircuitBreaker getCircuitBreaker();
}

/**
 * Manager for circuit breaking functionality
 */
public class CircuitBreakingManager {
    /**
     * Check if circuit breaking is active
     * @return true if active
     */
    public boolean isActive();
    
    /**
     * Get the current circuit breaker
     * @return circuit breaker or null
     */
    public CircuitBreaker getCircuitBreaker();
}

// Configure client with circuit breaking connection state management
CuratorFramework clientWithCircuitBreaker = CuratorFrameworkFactory.builder()
    .connectString("localhost:2181")
    .retryPolicy(new ExponentialBackoffRetry(1000, 3))
    .connectionStateListenerManagerFactory(
        ConnectionStateListenerManagerFactory.circuitBreaking(
            new ExponentialBackoffRetry(1000, 5)
        )
    )
    .build();

// Custom error policy
ConnectionStateErrorPolicy customPolicy = new ConnectionStateErrorPolicy() {
    @Override
    public boolean isErrorState(ConnectionState state) {
        return state == ConnectionState.LOST || state == ConnectionState.SUSPENDED;
    }
    
    @Override
    public int getErrorThresholdMs() {
        return 30000; // 30 seconds
    }
};

CuratorFramework clientWithCustomPolicy = CuratorFrameworkFactory.builder()
    .connectString("localhost:2181")
    .retryPolicy(new ExponentialBackoffRetry(1000, 3))
    .connectionStateErrorPolicy(customPolicy)
    .build();

/**
 * Generic interface for managing listeners
 */
public interface Listenable<T> {
    /**
     * Add a listener with the default executor
     * @param listener listener to add
     */
    void addListener(T listener);
    
    /**
     * Add a listener with custom executor
     * @param listener listener to add
     * @param executor executor for listener callbacks
     */
    void addListener(T listener, Executor executor);
    
    /**
     * Remove a listener
     * @param listener listener to remove
     */
    void removeListener(T listener);
}

/**
 * Container for listener and its executor
 */
public class ListenerEntry<T> {
    /**
     * Get the listener
     * @return listener
     */
    public T getListener();
    
    /**
     * Get the executor
     * @return executor
     */
    public Executor getExecutor();
}

// Add listeners with custom executors
ExecutorService backgroundExecutor = Executors.newCachedThreadPool();
ExecutorService priorityExecutor = Executors.newSingleThreadExecutor();

// High priority connection state listener
client.getConnectionStateListenable().addListener(criticalConnectionListener, priorityExecutor);

// Background event processing
client.getCuratorListenable().addListener(backgroundEventListener, backgroundExecutor);

// Remove listeners when done
client.getConnectionStateListenable().removeListener(criticalConnectionListener);
client.getCuratorListenable().removeListener(backgroundEventListener);

// Clean up executors
backgroundExecutor.shutdown();
priorityExecutor.shutdown();