/**
 *這裡面用到的是AOP的知識點，如果不了解可以先自行補下，後面我有空把Spring的AOP原理也寫下，這樣回頭看這個就沒這麼難了
 */
@Component
@Aspect  //切入
public class GhyHystrixAspect {
    //通過執行緒池去請求
    ExecutorService executorService= Executors.newFixedThreadPool(10);
    //定義切點針對GhyHystrix進行切入
    @Pointcut(value = "@annotation(GhyHystrix)")
    public void pointCut(){}
    //切入後執行的方法
    @Around(value = "pointCut()&&@annotation(hystrixCommand)")
    public Object doPointCut(ProceedingJoinPoint joinPoint, GhyHystrix hystrixCommand) throws InterruptedException, ExecutionException, TimeoutException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        //定義超時降級
        int timeout=hystrixCommand.timeout();
        //前置的判斷邏輯
        Future future=executorService.submit(()->{
            try {
                return joinPoint.proceed(); //執行目標方法
            } catch (Throwable throwable) {
                throwable.printStackTrace();
            }
            return null;
        });
        Object result;
        try {
            //得到開始和結束時間判斷是否超時，如果超時就降級
            result=future.get(timeout, TimeUnit.MILLISECONDS);
        } catch (InterruptedException | ExecutionException | TimeoutException e) {
            e.printStackTrace();
            //超時了就取消請求
            future.cancel(true);
            // 先判斷是否為空如果空就把異常拋出去
            if(StringUtils.isBlank(hystrixCommand.fallback())){
                throw e;
            }
            //調用fallback
            result=invokeFallback(joinPoint,hystrixCommand.fallback());
        }
        return result;
    }
   //反射調用
    private Object invokeFallback(ProceedingJoinPoint joinPoint,String fallback) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        MethodSignature signature=(MethodSignature)joinPoint.getSignature();
        //拿到方法的資訊
        Method method=signature.getMethod();
        //得到參數類型
        Class<?>[] parameterTypes=method.getParameterTypes();
        //以上是獲取被代理的方法的參數和Method
        //得到fallback方法
        try {
            Method fallbackMethod=joinPoint.getTarget().getClass().getMethod(fallback,parameterTypes);
            fallbackMethod.setAccessible(true);
            //完成反射調用
            return fallbackMethod.invoke(joinPoint.getTarget(),joinPoint.getArgs());
        } catch (Exception e) {
            e.printStackTrace();
            throw e;
        }
    }
}

@Around("hystrixCommandAnnotationPointcut() ||
hystrixCollapserAnnotationPointcut()")
public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint
joinPoint) throws Throwable {
  Method method = getMethodFromTarget(joinPoint);
  //省略程式碼...
  MetaHolderFactory metaHolderFactory =
META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));
  MetaHolder metaHolder = metaHolderFactory.create(joinPoint);
  //如果是非同步，則創建GenericObservableCommand， 否則，則創建GenericCommand
  HystrixInvokable invokable =
HystrixCommandFactory.getInstance().create(metaHolder);
 
  ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?
    metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();
  Object result;
  try {
    if (!metaHolder.isObservable()) { //是否是響應式的（由於我們這些都是同步的會走
這個邏輯）
     //默認是走這裡面，用命令執行器去執行
      result = CommandExecutor.execute(invokable, executionType,
metaHolder);
   } else {
      result = executeObservable(invokable, executionType, metaHolder);
   }
 } catch (HystrixBadRequestException e) {
    throw e.getCause();
 } catch (HystrixRuntimeException e) {
    throw hystrixRuntimeExceptionToThrowable(metaHolder, e);
}
  return result;
}

    public static Object execute(HystrixInvokable invokable, ExecutionType executionType, MetaHolder metaHolder) throws RuntimeException {
        Validate.notNull(invokable);
        Validate.notNull(metaHolder);
         
        switch (executionType) {

            case SYNCHRONOUS: {
                return castToExecutable(invokable, executionType).execute();
            }
            case ASYNCHRONOUS: {
                HystrixExecutable executable = castToExecutable(invokable, executionType);
                if (metaHolder.hasFallbackMethodCommand()
                        && ExecutionType.ASYNCHRONOUS == metaHolder.getFallbackExecutionType()) {
                    return new FutureDecorator(executable.queue());
                }
                return executable.queue();
            }
            case OBSERVABLE: {
                HystrixObservable observable = castToObservable(invokable);
                return ObservableExecutionMode.EAGER == metaHolder.getObservableExecutionMode() ? observable.observe() : observable.toObservable();
            }
            default:
                throw new RuntimeException("unsupported execution type: " + executionType);
        }
    }

  public R execute() {
        try {
            return queue().get();
        } catch (Exception e) {
            throw Exceptions.sneakyThrow(decomposeException(e));
        }
    }

public Future<R> queue() {
  /*
    * The Future returned by Observable.toBlocking().toFuture() does not
implement the
    * interruption of the execution thread when the "mayInterrupt" flag of
Future.cancel(boolean) is set to true;
    * thus, to comply with the contract of Future, we must wrap around it.
    */
  final Future<R> delegate = toObservable().toBlocking().toFuture();
  final Future<R> f = new Future<R>() {
    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
      if (delegate.isCancelled()) {
        return false;
     }
      if
(HystrixCommand.this.getProperties().executionIsolationThreadInterruptOnFutureCa
ncel().get()) {
        /*
          * The only valid transition here is false -> true. If there
are two futures, say f1 and f2, created by this command
          * (which is super-weird, but has never been prohibited),
and calls to f1.cancel(true) and to f2.cancel(false) are
          * issued by different threads, it's unclear about what
value would be used by the time mayInterruptOnCancel is checked.
          * The most consistent way to deal with this scenario is to
say that if *any* cancellation is invoked with interruption,
          * than that interruption request cannot be taken back.
          */
        interruptOnFutureCancel.compareAndSet(false,
mayInterruptIfRunning);
     }
      final boolean res = delegate.cancel(interruptOnFutureCancel.get());
      if (!isExecutionComplete() && interruptOnFutureCancel.get()) {
        final Thread t = executionThread.get();
        if (t != null && !t.equals(Thread.currentThread())) {
t.interrupt();
       }
     }
      return res;
   }
    @Override
    public boolean isCancelled() {
      return delegate.isCancelled();
   }
    @Override
    public boolean isDone() {
      return delegate.isDone();
   }
    //最終會調用此方法
    @Override
    public R get() throws InterruptedException, ExecutionException {
      return delegate.get();
   }
    @Override
    public R get(long timeout, TimeUnit unit) throws InterruptedException,
ExecutionException, TimeoutException {
      return delegate.get(timeout, unit);
   }
 };
  /* special handling of error states that throw immediately */
  if (f.isDone()) {
    try {
      f.get();
      return f;
   } catch (Exception e) {
      Throwable t = decomposeException(e);
      if (t instanceof HystrixBadRequestException) {
        return f;
     } else if (t instanceof HystrixRuntimeException) {
        HystrixRuntimeException hre = (HystrixRuntimeException) t;
        switch (hre.getFailureType()) {
          case COMMAND_EXCEPTION:
          case TIMEOUT:
            // we don't throw these types from queue() only from
queue().get() as they are execution errors
            return f;
          default:
            // these are errors we throw from queue() as they as
rejection type errors
            throw hre;
       }
     } else {
        throw Exceptions.sneakyThrow(t);
     }
   }
 }
return f;
}

   public Observable<R> toObservable() {
        final AbstractCommand<R> _cmd = this;

        //doOnCompleted handler already did all of the SUCCESS work
        //doOnError handler already did all of the FAILURE/TIMEOUT/REJECTION/BAD_REQUEST work
        final Action0 terminateCommandCleanup = new Action0() {

            @Override
            public void call() {
                if (_cmd.commandState.compareAndSet(CommandState.OBSERVABLE_CHAIN_CREATED, CommandState.TERMINAL)) {
                    handleCommandEnd(false); //user code never ran
                } else if (_cmd.commandState.compareAndSet(CommandState.USER_CODE_EXECUTED, CommandState.TERMINAL)) {
                    handleCommandEnd(true); //user code did run
                }
            }
        };

        //mark the command as CANCELLED and store the latency (in addition to standard cleanup)
        final Action0 unsubscribeCommandCleanup = new Action0() {
            @Override
            public void call() {
                if (_cmd.commandState.compareAndSet(CommandState.OBSERVABLE_CHAIN_CREATED, CommandState.UNSUBSCRIBED)) {
                    if (!_cmd.executionResult.containsTerminalEvent()) {
                        _cmd.eventNotifier.markEvent(HystrixEventType.CANCELLED, _cmd.commandKey);
                        try {
                            executionHook.onUnsubscribe(_cmd);
                        } catch (Throwable hookEx) {
                            logger.warn("Error calling HystrixCommandExecutionHook.onUnsubscribe", hookEx);
                        }
                        _cmd.executionResultAtTimeOfCancellation = _cmd.executionResult
                                .addEvent((int) (System.currentTimeMillis() - _cmd.commandStartTimestamp), HystrixEventType.CANCELLED);
                    }
                    handleCommandEnd(false); //user code never ran
                } else if (_cmd.commandState.compareAndSet(CommandState.USER_CODE_EXECUTED, CommandState.UNSUBSCRIBED)) {
                    if (!_cmd.executionResult.containsTerminalEvent()) {
                        _cmd.eventNotifier.markEvent(HystrixEventType.CANCELLED, _cmd.commandKey);
                        try {
                            executionHook.onUnsubscribe(_cmd);
                        } catch (Throwable hookEx) {
                            logger.warn("Error calling HystrixCommandExecutionHook.onUnsubscribe", hookEx);
                        }
                        _cmd.executionResultAtTimeOfCancellation = _cmd.executionResult
                                .addEvent((int) (System.currentTimeMillis() - _cmd.commandStartTimestamp), HystrixEventType.CANCELLED);
                    }
                    handleCommandEnd(true); //user code did run
                }
            }
        };

        final Func0<Observable<R>> applyHystrixSemantics = new Func0<Observable<R>>() {
            @Override
            public Observable<R> call() {
                if (commandState.get().equals(CommandState.UNSUBSCRIBED)) {
                    return Observable.never();
                }
                return applyHystrixSemantics(_cmd);
            }
        };

        final Func1<R, R> wrapWithAllOnNextHooks = new Func1<R, R>() {
            @Override
            public R call(R r) {
                R afterFirstApplication = r;

                try {
                    afterFirstApplication = executionHook.onComplete(_cmd, r);
                } catch (Throwable hookEx) {
                    logger.warn("Error calling HystrixCommandExecutionHook.onComplete", hookEx);
                }

                try {
                    return executionHook.onEmit(_cmd, afterFirstApplication);
                } catch (Throwable hookEx) {
                    logger.warn("Error calling HystrixCommandExecutionHook.onEmit", hookEx);
                    return afterFirstApplication;
                }
            }
        };

        final Action0 fireOnCompletedHook = new Action0() {
            @Override
            public void call() {
                try {
                    executionHook.onSuccess(_cmd);
                } catch (Throwable hookEx) {
                    logger.warn("Error calling HystrixCommandExecutionHook.onSuccess", hookEx);
                }
            }
        };
return Observable.defer(new Func0<Observable<R>>() {
  @Override
  public Observable<R> call() {
    /* this is a stateful object so can only be used once */
    /* CAS保證命令只執行一次 */
    if (!commandState.compareAndSet(CommandState.NOT_STARTED,
CommandState.OBSERVABLE_CHAIN_CREATED)) {
      IllegalStateException ex = new IllegalStateException("This instance
can only be executed once. Please instantiate a new instance.");
      //TODO make a new error type for this
      throw new HystrixRuntimeException(FailureType.BAD_REQUEST_EXCEPTION,
_cmd.getClass(), getLogMessagePrefix() + " command executed multiple times -
this is not permitted.", ex, null);
   }
   // 命令開始時間戳
    commandStartTimestamp = System.currentTimeMillis();
    // 列印日誌
    if (properties.requestLogEnabled().get()) {
      // log this command execution regardless of what happened
      if (currentRequestLog != null) {
currentRequestLog.addExecutedCommand(_cmd);
     }
   }
   // 快取開關，快取KEY（這個是Hystrix中請求快取功能，hystrix支援將一個請求結果快取起
來，下一個具有相同key的請求將直接從快取中取出結果，減少請求開銷）
    final boolean requestCacheEnabled = isRequestCachingEnabled();
    final String cacheKey = getCacheKey();
    /* try from cache first */
    if (requestCacheEnabled) {//如果開啟了快取機制，則從快取中獲取結果
      HystrixCommandResponseFromCache<R> fromCache =
(HystrixCommandResponseFromCache<R>) requestCache.get(cacheKey);
      if (fromCache != null) {
        isResponseFromCache = true;
        return handleRequestCacheHitAndEmitValues(fromCache, _cmd);
     }
   }
    // 聲明執行命令的Observable
    Observable<R> hystrixObservable =
      Observable.defer(applyHystrixSemantics)
     .map(wrapWithAllOnNextHooks);
    Observable<R> afterCache;
    //保存請求結果到快取中
    if (requestCacheEnabled && cacheKey != null) {
      // wrap it for caching
      HystrixCachedObservable<R> toCache =
HystrixCachedObservable.from(hystrixObservable, _cmd);
      HystrixCommandResponseFromCache<R> fromCache =
(HystrixCommandResponseFromCache<R>) requestCache.putIfAbsent(cacheKey,
toCache);
      if (fromCache != null) {
        // another thread beat us so we'll use the cached value instead
        toCache.unsubscribe();
        isResponseFromCache = true;
        return handleRequestCacheHitAndEmitValues(fromCache, _cmd);
     } else {
        // we just created an ObservableCommand so we cast and return it
        afterCache = toCache.toObservable();
     }
   } else {
      afterCache = hystrixObservable;
   }
    return afterCache
     .doOnTerminate(terminateCommandCleanup)   // perform cleanup once
(either on normal terminal state (this line), or unsubscribe (next line))
     .doOnUnsubscribe(unsubscribeCommandCleanup) // perform cleanup once
     .doOnCompleted(fireOnCompletedHook);
 }
});

final Func0<Observable<R>> applyHystrixSemantics = new Func0<Observable<R>>() {
  @Override
 public Observable<R> call() {
    // 當commandState處於UNSUBSCRIBED時，不執行命令
    if (commandState.get().equals(CommandState.UNSUBSCRIBED)) {
      return Observable.never();
   }
    //返回執行命令的Observable
    return applyHystrixSemantics(_cmd);
 }
};
Observable<R> hystrixObservable =
  Observable.defer(applyHystrixSemantics)
 .map(wrapWithAllOnNextHooks);

   private Observable<R> applyHystrixSemantics(final AbstractCommand<R> _cmd) {
        // mark that we're starting execution on the ExecutionHook
        // if this hook throws an exception, then a fast-fail occurs with no fallback.  No state is left inconsistent
        executionHook.onStart(_cmd);

        /* determine if we're allowed to execute */
        if (circuitBreaker.allowRequest()) {
            final TryableSemaphore executionSemaphore = getExecutionSemaphore();
            final AtomicBoolean semaphoreHasBeenReleased = new AtomicBoolean(false);
            final Action0 singleSemaphoreRelease = new Action0() {
                @Override
                public void call() {
                    if (semaphoreHasBeenReleased.compareAndSet(false, true)) {
                        executionSemaphore.release();
                    }
                }
            };

            final Action1<Throwable> markExceptionThrown = new Action1<Throwable>() {
                @Override
                public void call(Throwable t) {
                    eventNotifier.markEvent(HystrixEventType.EXCEPTION_THROWN, commandKey);
                }
            };

            if (executionSemaphore.tryAcquire()) {
                try {
                    /* used to track userThreadExecutionTime */
                    executionResult = executionResult.setInvocationStartTime(System.currentTimeMillis());
                   //跟進
                    return executeCommandAndObserve(_cmd)
                            .doOnError(markExceptionThrown)
                            .doOnTerminate(singleSemaphoreRelease)
                            .doOnUnsubscribe(singleSemaphoreRelease);
                } catch (RuntimeException e) {
                    return Observable.error(e);
                }
            } else {
                return handleSemaphoreRejectionViaFallback();
            }
        } else {
            return handleShortCircuitViaFallback();
        }
    }