/*
 * Copyright (c) 2011-2016 The original author or authors
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Apache License v2.0 which accompanies this distribution.
 *
 *      The Eclipse Public License is available at
 *      http://www.eclipse.org/legal/epl-v10.html
 *
 *      The Apache License v2.0 is available at
 *      http://www.opensource.org/licenses/apache2.0.php
 *
 * You may elect to redistribute this code under either of these licenses.
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package io.vertx.circuitbreaker;

import io.vertx.circuitbreaker.impl.CircuitBreakerImpl;
import io.vertx.codegen.annotations.CacheReturn;
import io.vertx.codegen.annotations.Fluent;
import io.vertx.codegen.annotations.VertxGen;
import io.vertx.core.AsyncResult;
import io.vertx.core.Future;
import io.vertx.core.Handler;
import io.vertx.core.Promise;
import io.vertx.core.Vertx;

import java.util.function.Function;

An implementation of the circuit breaker pattern for Vert.x
Author:
Clement Escoffier/**
 * An implementation of the circuit breaker pattern for Vert.x
 *
 * @author <a href="http://escoffier.me">Clement Escoffier</a>
 */
@VertxGen
public interface CircuitBreaker {

  
Creates a new instance of CircuitBreaker. 
Params:
name –    the name
vertx –   the Vert.x instance
options – the configuration option
Returns:
the created instance/**
   * Creates a new instance of {@link CircuitBreaker}.
   *
   * @param name    the name
   * @param vertx   the Vert.x instance
   * @param options the configuration option
   * @return the created instance
   */
  static CircuitBreaker create(String name, Vertx vertx, CircuitBreakerOptions options) {
    return new CircuitBreakerImpl(name, vertx, options == null ? new CircuitBreakerOptions() : options);
  }

  
Creates a new instance of CircuitBreaker, with default options. 
Params:
name –  the name
vertx – the Vert.x instance
Returns:
the created instance/**
   * Creates a new instance of {@link CircuitBreaker}, with default options.
   *
   * @param name  the name
   * @param vertx the Vert.x instance
   * @return the created instance
   */
  static CircuitBreaker create(String name, Vertx vertx) {
    return new CircuitBreakerImpl(name, vertx, new CircuitBreakerOptions());
  }

  
Closes the circuit breaker. It stops sending events on its state on the event bus. This method is not related to the close state of the circuit breaker. To set the circuit breaker in the close state, use reset(). /**
   * Closes the circuit breaker. It stops sending events on its state on the event bus.
   * This method is not related to the {@code close} state of the circuit breaker. To set the circuit breaker in the
   * {@code close} state, use {@link #reset()}.
   */
  @Fluent
  CircuitBreaker close();

  
Sets a Handler invoked when the circuit breaker state switches to open. 
Params:
handler – the handler, must not be null
Returns:
the current CircuitBreaker/**
   * Sets a {@link Handler} invoked when the circuit breaker state switches to open.
   *
   * @param handler the handler, must not be {@code null}
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  CircuitBreaker openHandler(Handler<Void> handler);

  
Sets a Handler invoked when the circuit breaker state switches to half-open. 
Params:
handler – the handler, must not be null
Returns:
the current CircuitBreaker/**
   * Sets a {@link Handler} invoked when the circuit breaker state switches to half-open.
   *
   * @param handler the handler, must not be {@code null}
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  CircuitBreaker halfOpenHandler(Handler<Void> handler);

  
Sets a Handler invoked when the circuit breaker state switches to close. 
Params:
handler – the handler, must not be null
Returns:
the current CircuitBreaker/**
   * Sets a {@link Handler} invoked when the circuit breaker state switches to close.
   *
   * @param handler the handler, must not be {@code null}
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  CircuitBreaker closeHandler(Handler<Void> handler);

  
Executes the given operation with the circuit breaker control. The operation is generally calling an
external system. The operation receives a Promise object as parameter and must call Promise.complete(Object) when the operation has terminated successfully. The operation must also call Promise.fail(Throwable) in case of failure. 

The operation is not invoked if the circuit breaker is open, and the given fallback is called immediately. The
circuit breaker also monitor the completion of the operation before a configure timeout. The operation is
considered as failed if it does not terminate in time.
 This method returns a Future object to retrieve the status and result of the operation, with the status being a success or a failure. If the fallback is called, the returned future is successfully completed with the value returned from the fallback. If the fallback throws an exception, the returned future is marked as failed. 
Params:
command –  the operation
fallback – the fallback function. It gets an exception as parameter and returns the fallback result
Type parameters:
<T> –      the type of result
Returns:
a future object completed when the operation or its fallback completes/**
   * Executes the given operation with the circuit breaker control. The operation is generally calling an
   * <em>external</em> system. The operation receives a {@link Promise} object as parameter and <strong>must</strong>
   * call {@link Promise#complete(Object)} when the operation has terminated successfully. The operation must also
   * call {@link Promise#fail(Throwable)} in case of failure.
   * <p>
   * The operation is not invoked if the circuit breaker is open, and the given fallback is called immediately. The
   * circuit breaker also monitor the completion of the operation before a configure timeout. The operation is
   * considered as failed if it does not terminate in time.
   * <p>
   * This method returns a {@link Future} object to retrieve the status and result of the operation, with the status
   * being a success or a failure. If the fallback is called, the returned future is successfully completed with the
   * value returned from the fallback. If the fallback throws an exception, the returned future is marked as failed.
   *
   * @param command  the operation
   * @param fallback the fallback function. It gets an exception as parameter and returns the <em>fallback</em> result
   * @param <T>      the type of result
   * @return a future object completed when the operation or its fallback completes
   */
  <T> Future<T> executeWithFallback(Handler<Promise<T>> command, Function<Throwable, T> fallback);

  
Same as executeWithFallback(Handler<Promise<Object>>, Function<Throwable,Object>) but using a callback. 
Params:
command –  the operation
fallback – the fallback
handler –  the completion handler receiving either the operation result or the fallback result. The parameter is an AsyncResult because if the fallback is not called, the error is passed to the handler.
Type parameters:
<T> –      the type of result/**
   * Same as {@link #executeWithFallback(Handler, Function)} but using a callback.
   *
   * @param command  the operation
   * @param fallback the fallback
   * @param handler  the completion handler receiving either the operation result or the fallback result. The
   *                 parameter is an {@link AsyncResult} because if the fallback is not called, the error is passed
   *                 to the handler.
   * @param <T>      the type of result
   */
  default <T> void executeWithFallback(Handler<Promise<T>> command, Function<Throwable, T> fallback,
                                              Handler<AsyncResult<T>> handler) {
    Future<T> fut = executeWithFallback(command, fallback);
    fut.onComplete(handler);
  }

  
Same as executeWithFallback(Handler<Promise<Object>>, Function<Throwable,Object>) but using the circuit breaker default fallback. 
Params:
command – the operation
Type parameters:
<T> –     the type of result
Returns:
a future object completed when the operation or its fallback completes/**
   * Same as {@link #executeWithFallback(Handler, Function)} but using the circuit breaker default fallback.
   *
   * @param command the operation
   * @param <T>     the type of result
   * @return a future object completed when the operation or its fallback completes
   */
  <T> Future<T> execute(Handler<Promise<T>> command);

  
Same as executeWithFallback(Handler<Promise<Object>>, Function<Throwable,Object>) but using the circuit breaker default fallback. 
Params:
command – the operation
handler –  the completion handler receiving either the operation result or the fallback result. The parameter is an AsyncResult because if the fallback is not called, the error is passed to the handler.
Type parameters:
<T> –     the type of result/**
   * Same as {@link #executeWithFallback(Handler, Function)} but using the circuit breaker default fallback.
   *
   * @param command the operation
   * @param handler  the completion handler receiving either the operation result or the fallback result. The
   *                 parameter is an {@link AsyncResult} because if the fallback is not called, the error is passed
   *                 to the handler.
   * @param <T>     the type of result
   */
  default <T> void execute(Handler<Promise<T>> command, Handler<AsyncResult<T>> handler) {
    Future<T> fut = execute(command);
    fut.onComplete(handler);
  }

  
Same as executeAndReportWithFallback(Promise<Object>, Handler<Promise<Object>>, Function<Throwable,Object>) but using the circuit breaker default fallback. 
Params:
resultPromise – the promise on which the operation result is reported
command –      the operation
Type parameters:
<T> –          the type of result
Returns:
the current CircuitBreaker/**
   * Same as {@link #executeAndReportWithFallback(Promise, Handler, Function)} but using the circuit breaker default
   * fallback.
   *
   * @param resultPromise the promise on which the operation result is reported
   * @param command      the operation
   * @param <T>          the type of result
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  <T> CircuitBreaker executeAndReport(Promise<T> resultPromise, Handler<Promise<T>> command);

  
Executes the given operation with the circuit breaker control. The operation is generally calling an
external system. The operation receives a Promise object as parameter and must call Promise.complete(Object) when the operation has terminated successfully. The operation must also call Promise.fail(Throwable) in case of failure. 

The operation is not invoked if the circuit breaker is open, and the given fallback is called immediately. The
circuit breaker also monitor the completion of the operation before a configure timeout. The operation is
considered as failed if it does not terminate in time.
 Unlike executeWithFallback(Handler<Promise<Object>>, Function<Throwable,Object>), this method does return a Future object, but let the caller pass a Future object on which the result is reported. If the fallback is called, the future is successfully completed with the value returned by the fallback function. If the fallback throws an exception, the future is marked as failed. 
Params:
resultPromise – the promise on which the operation result is reported
command –      the operation
fallback –     the fallback function. It gets an exception as parameter and returns the fallback result
Type parameters:
<T> –          the type of result
Returns:
the current CircuitBreaker/**
   * Executes the given operation with the circuit breaker control. The operation is generally calling an
   * <em>external</em> system. The operation receives a {@link Promise} object as parameter and <strong>must</strong>
   * call {@link Promise#complete(Object)} when the operation has terminated successfully. The operation must also
   * call {@link Promise#fail(Throwable)} in case of failure.
   * <p>
   * The operation is not invoked if the circuit breaker is open, and the given fallback is called immediately. The
   * circuit breaker also monitor the completion of the operation before a configure timeout. The operation is
   * considered as failed if it does not terminate in time.
   * <p>
   * Unlike {@link #executeWithFallback(Handler, Function)},  this method does return a {@link Future} object, but
   * let the caller pass a {@link Future} object on which the result is reported. If the fallback is called, the future
   * is successfully completed with the value returned by the fallback function. If the fallback throws an exception,
   * the future is marked as failed.
   *
   * @param resultPromise the promise on which the operation result is reported
   * @param command      the operation
   * @param fallback     the fallback function. It gets an exception as parameter and returns the <em>fallback</em> result
   * @param <T>          the type of result
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  <T> CircuitBreaker executeAndReportWithFallback(Promise<T> resultPromise, Handler<Promise<T>> command,
                                                  Function<Throwable, T> fallback);

  
Sets a default Function invoked when the bridge is open to handle the "request", or on failure if CircuitBreakerOptions.isFallbackOnFailure() is enabled. 

The function gets the exception as parameter and returns the fallback result.
Params:
handler – the handler
Returns:
the current CircuitBreaker/**
   * Sets a <em>default</em> {@link Function} invoked when the bridge is open to handle the "request", or on failure
   * if {@link CircuitBreakerOptions#isFallbackOnFailure()} is enabled.
   * <p>
   * The function gets the exception as parameter and returns the <em>fallback</em> result.
   *
   * @param handler the handler
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  <T> CircuitBreaker fallback(Function<Throwable, T> handler);

  
Resets the circuit breaker state (number of failure set to 0 and state set to closed).
Returns:
the current CircuitBreaker/**
   * Resets the circuit breaker state (number of failure set to 0 and state set to closed).
   *
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  CircuitBreaker reset();

  
Explicitly opens the circuit.
Returns:
the current CircuitBreaker/**
   * Explicitly opens the circuit.
   *
   * @return the current {@link CircuitBreaker}
   */
  @Fluent
  CircuitBreaker open();

  
Returns:
the current state./**
   * @return the current state.
   */
  CircuitBreakerState state();

  
Returns:
the current number of failures./**
   * @return the current number of failures.
   */
  long failureCount();

  
Returns:
the name of the circuit breaker./**
   * @return the name of the circuit breaker.
   */
  @CacheReturn
  String name();

  @Fluent
  CircuitBreaker retryPolicy(Function<Integer, Long> retryPolicy);
}