/*
 * Copyright (c) 2011-2019 Contributors to the Eclipse Foundation
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
 * which is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
 */

package io.vertx.core;

import io.vertx.codegen.annotations.Fluent;
import io.vertx.codegen.annotations.GenIgnore;
import io.vertx.codegen.annotations.Nullable;
import io.vertx.codegen.annotations.VertxGen;
import io.vertx.core.impl.VertxThread;
import io.vertx.core.json.JsonObject;

import java.util.List;

The execution context of a Handler execution. 
 When Vert.x provides an event to a handler or calls the start or stop methods of a Verticle, the execution is associated with a Context. 

Usually a context is an *event-loop context* and is tied to a specific event loop thread. So executions for that
context always occur on that exact same event loop thread.

In the case of worker verticles and running inline blocking code a worker context will be associated with the execution
which will use a thread from the worker thread pool.

When a handler is set by a thread associated with a specific context, the Vert.x will guarantee that when that handler
is executed, that execution will be associated with the same context.

If a handler is set by a thread not associated with a context (i.e. a non Vert.x thread). Then a new context will
be created for that handler.

In other words, a context is propagated.

This means that when a verticle is deployed, any handlers it sets will be associated with the same context - the context
of the verticle.

This means (in the case of a standard verticle) that the verticle code will always be executed with the exact same
thread, so you don't have to worry about multi-threaded acccess to the verticle state and you can code your application
as single threaded.
 This class also allows arbitrary data to be put and get on the context so it can be shared easily amongst different handlers of, for example, a verticle instance. 
 This class also provides runOnContext which allows an action to be executed asynchronously using the same context. 
Author:
Tim Fox/**
 * The execution context of a {@link io.vertx.core.Handler} execution.
 * <p>
 * When Vert.x provides an event to a handler or calls the start or stop methods of a {@link io.vertx.core.Verticle},
 * the execution is associated with a {@code Context}.
 * <p>
 * Usually a context is an *event-loop context* and is tied to a specific event loop thread. So executions for that
 * context always occur on that exact same event loop thread.
 * <p>
 * In the case of worker verticles and running inline blocking code a worker context will be associated with the execution
 * which will use a thread from the worker thread pool.
 * <p>
 * When a handler is set by a thread associated with a specific context, the Vert.x will guarantee that when that handler
 * is executed, that execution will be associated with the same context.
 * <p>
 * If a handler is set by a thread not associated with a context (i.e. a non Vert.x thread). Then a new context will
 * be created for that handler.
 * <p>
 * In other words, a context is propagated.
 * <p>
 * This means that when a verticle is deployed, any handlers it sets will be associated with the same context - the context
 * of the verticle.
 * <p>
 * This means (in the case of a standard verticle) that the verticle code will always be executed with the exact same
 * thread, so you don't have to worry about multi-threaded acccess to the verticle state and you can code your application
 * as single threaded.
 * <p>
 * This class also allows arbitrary data to be {@link #put} and {@link #get} on the context so it can be shared easily
 * amongst different handlers of, for example, a verticle instance.
 * <p>
 * This class also provides {@link #runOnContext} which allows an action to be executed asynchronously using the same context.
 *
 * @author <a href="http://tfox.org">Tim Fox</a>
 */
@VertxGen
public interface Context {

  
Is the current thread a worker thread?
 NOTE! This is not always the same as calling isWorkerContext. If you are running blocking code from an event loop context, then this will return true but isWorkerContext will return false. 
Returns:
true if current thread is a worker thread, false otherwise/**
   * Is the current thread a worker thread?
   * <p>
   * NOTE! This is not always the same as calling {@link Context#isWorkerContext}. If you are running blocking code
   * from an event loop context, then this will return true but {@link Context#isWorkerContext} will return false.
   *
   * @return true if current thread is a worker thread, false otherwise
   */
  static boolean isOnWorkerThread() {
    Thread t = Thread.currentThread();
    return t instanceof VertxThread && ((VertxThread) t).isWorker();
  }

  
Is the current thread an event thread?
 NOTE! This is not always the same as calling isEventLoopContext. If you are running blocking code from an event loop context, then this will return false but isEventLoopContext will return true. 
Returns:
true if current thread is an event thread, false otherwise/**
   * Is the current thread an event thread?
   * <p>
   * NOTE! This is not always the same as calling {@link Context#isEventLoopContext}. If you are running blocking code
   * from an event loop context, then this will return false but {@link Context#isEventLoopContext} will return true.
   *
   * @return true if current thread is an event thread, false otherwise
   */
  static boolean isOnEventLoopThread() {
    Thread t = Thread.currentThread();
    return t instanceof VertxThread && !((VertxThread) t).isWorker();
  }

  
Is the current thread a Vert.x thread? That's either a worker thread or an event loop thread
Returns:
true if current thread is a Vert.x thread, false otherwise/**
   * Is the current thread a Vert.x thread? That's either a worker thread or an event loop thread
   *
   * @return true if current thread is a Vert.x thread, false otherwise
   */
  static boolean isOnVertxThread() {
    return Thread.currentThread() instanceof VertxThread;
  }

  
Run the specified action asynchronously on the same context, some time after the current execution has completed.
Params:
action –  the action to run/**
   * Run the specified action asynchronously on the same context, some time after the current execution has completed.
   *
   * @param action  the action to run
   */
  void runOnContext(Handler<Void> action);

  
Safely execute some blocking code.
 Executes the blocking code in the handler blockingCodeHandler using a thread from the worker pool. 
 When the code is complete the handler resultHandler will be called with the result on the original context (e.g. on the original event loop of the caller). 
 A Future instance is passed into blockingCodeHandler. When the blocking code successfully completes, the handler should call the Promise.complete or Promise.complete(Object) method, or the Promise.fail method if it failed. 

The blocking code should block for a reasonable amount of time (i.e no more than a few seconds). Long blocking operations
or polling operations (i.e a thread that spin in a loop polling events in a blocking fashion) are precluded.

When the blocking operation lasts more than the 10 seconds, a message will be printed on the console by the
blocked thread checker.
 Long blocking operations should use a dedicated thread managed by the application, which can interact with verticles using the event-bus or runOnContext(Handler<Void>) 
Params:
blockingCodeHandler –  handler representing the blocking code to run
resultHandler –  handler that will be called when the blocking code is complete
ordered –  if true then if executeBlocking is called several times on the same context, the executions
                for that context will be executed serially, not in parallel. if false then they will be no ordering
                guarantees
Type parameters:
<T> – the type of the result/**
   * Safely execute some blocking code.
   * <p>
   * Executes the blocking code in the handler {@code blockingCodeHandler} using a thread from the worker pool.
   * <p>
   * When the code is complete the handler {@code resultHandler} will be called with the result on the original context
   * (e.g. on the original event loop of the caller).
   * <p>
   * A {@code Future} instance is passed into {@code blockingCodeHandler}. When the blocking code successfully completes,
   * the handler should call the {@link Promise#complete} or {@link Promise#complete(Object)} method, or the {@link Promise#fail}
   * method if it failed.
   * <p>
   * The blocking code should block for a reasonable amount of time (i.e no more than a few seconds). Long blocking operations
   * or polling operations (i.e a thread that spin in a loop polling events in a blocking fashion) are precluded.
   * <p>
   * When the blocking operation lasts more than the 10 seconds, a message will be printed on the console by the
   * blocked thread checker.
   * <p>
   * Long blocking operations should use a dedicated thread managed by the application, which can interact with
   * verticles using the event-bus or {@link Context#runOnContext(Handler)}
   *
   * @param blockingCodeHandler  handler representing the blocking code to run
   * @param resultHandler  handler that will be called when the blocking code is complete
   * @param ordered  if true then if executeBlocking is called several times on the same context, the executions
   *                 for that context will be executed serially, not in parallel. if false then they will be no ordering
   *                 guarantees
   * @param <T> the type of the result
   */
  <T> void executeBlocking(Handler<Promise<T>> blockingCodeHandler, boolean ordered, Handler<AsyncResult<@Nullable T>> resultHandler);

  
Invoke executeBlocking(Handler<Promise<Object>>, boolean, Handler<AsyncResult<Object>>) with order = true. 
Params:
blockingCodeHandler –  handler representing the blocking code to run
resultHandler –  handler that will be called when the blocking code is complete
Type parameters:
<T> – the type of the result/**
   * Invoke {@link #executeBlocking(Handler, boolean, Handler)} with order = true.
   * @param blockingCodeHandler  handler representing the blocking code to run
   * @param resultHandler  handler that will be called when the blocking code is complete
   * @param <T> the type of the result
   */
  <T> void executeBlocking(Handler<Promise<T>> blockingCodeHandler, Handler<AsyncResult<@Nullable T>> resultHandler);

  
Same as executeBlocking(Handler<Promise<Object>>, boolean, Handler<AsyncResult<Object>>) but with an handler called when the operation completes /**
   * Same as {@link #executeBlocking(Handler, boolean, Handler)} but with an {@code handler} called when the operation completes
   */
  <T> Future<@Nullable T> executeBlocking(Handler<Promise<T>> blockingCodeHandler, boolean ordered);

  
Same as executeBlocking(Handler<Promise<Object>>, Handler<AsyncResult<Object>>) but with an handler called when the operation completes /**
   * Same as {@link #executeBlocking(Handler, Handler)} but with an {@code handler} called when the operation completes
   */
  <T> Future<T> executeBlocking(Handler<Promise<T>> blockingCodeHandler);

  
If the context is associated with a Verticle deployment, this returns the deployment ID of that deployment.
Returns:
the deployment ID of the deployment or null if not a Verticle deployment/**
   * If the context is associated with a Verticle deployment, this returns the deployment ID of that deployment.
   *
   * @return the deployment ID of the deployment or null if not a Verticle deployment
   */
  String deploymentID();

  
If the context is associated with a Verticle deployment, this returns the configuration that was specified when
the verticle was deployed.
Returns:
the configuration of the deployment or null if not a Verticle deployment/**
   * If the context is associated with a Verticle deployment, this returns the configuration that was specified when
   * the verticle was deployed.
   *
   * @return the configuration of the deployment or null if not a Verticle deployment
   */
  @Nullable JsonObject config();

  
The process args
/**
   * The process args
   */
  List<String> processArgs();

  
Is the current context an event loop context?
 NOTE! when running blocking code using Vertx.executeBlocking(Handler<Promise<Object>>, Handler<AsyncResult<Object>>) from a standard (not worker) verticle, the context will still an event loop context and this this#isEventLoopContext() will return true. 
Returns:
true if  false otherwise/**
   * Is the current context an event loop context?
   * <p>
   * NOTE! when running blocking code using {@link io.vertx.core.Vertx#executeBlocking(Handler, Handler)} from a
   * standard (not worker) verticle, the context will still an event loop context and this {@link this#isEventLoopContext()}
   * will return true.
   *
   * @return true if  false otherwise
   */
  boolean isEventLoopContext();

  
Is the current context a worker context?
 NOTE! when running blocking code using Vertx.executeBlocking(Handler<Promise<Object>>, Handler<AsyncResult<Object>>) from a standard (not worker) verticle, the context will still an event loop context and this this#isWorkerContext() will return false. 
Returns:
true if the current context is a worker context, false otherwise/**
   * Is the current context a worker context?
   * <p>
   * NOTE! when running blocking code using {@link io.vertx.core.Vertx#executeBlocking(Handler, Handler)} from a
   * standard (not worker) verticle, the context will still an event loop context and this {@link this#isWorkerContext()}
   * will return false.
   *
   * @return true if the current context is a worker context, false otherwise
   */
  boolean isWorkerContext();

  
Get some data from the context.
Params:
key –  the key of the data
Type parameters:
<T> –  the type of the data
Returns:
the data/**
   * Get some data from the context.
   *
   * @param key  the key of the data
   * @param <T>  the type of the data
   * @return the data
   */
  <T> T get(String key);

  
Put some data in the context.

This can be used to share data between different handlers that share a context
Params:
key –  the key of the data
value –  the data/**
   * Put some data in the context.
   * <p>
   * This can be used to share data between different handlers that share a context
   *
   * @param key  the key of the data
   * @param value  the data
   */
  void put(String key, Object value);

  
Remove some data from the context.
Params:
key –  the key to remove
Returns:
true if removed successfully, false otherwise/**
   * Remove some data from the context.
   *
   * @param key  the key to remove
   * @return true if removed successfully, false otherwise
   */
  boolean remove(String key);

  
Get some local data from the context.
Params:
key –  the key of the data
Type parameters:
<T> –  the type of the data
Returns:
the data/**
   * Get some local data from the context.
   *
   * @param key  the key of the data
   * @param <T>  the type of the data
   * @return the data
   */
  <T> T getLocal(String key);

  
Put some local data in the context.

This can be used to share data between different handlers that share a context
Params:
key –  the key of the data
value –  the data/**
   * Put some local data in the context.
   * <p>
   * This can be used to share data between different handlers that share a context
   *
   * @param key  the key of the data
   * @param value  the data
   */
  void putLocal(String key, Object value);

  
Remove some local data from the context.
Params:
key –  the key to remove
Returns:
true if removed successfully, false otherwise/**
   * Remove some local data from the context.
   *
   * @param key  the key to remove
   * @return true if removed successfully, false otherwise
   */
  boolean removeLocal(String key);

  
Returns:
The Vertx instance that created the context/**
   * @return The Vertx instance that created the context
   */
  Vertx owner();

  
Returns:
 the number of instances of the verticle that were deployed in the deployment (if any) related
to this context/**
   * @return  the number of instances of the verticle that were deployed in the deployment (if any) related
   * to this context
   */
  int getInstanceCount();

  
Set an exception handler called when the context runs an action throwing an uncaught throwable.
 When this handler is called, Vertx.currentContext() will return this context. 
Params:
handler – the exception handler
Returns:
a reference to this, so the API can be used fluently/**
   * Set an exception handler called when the context runs an action throwing an uncaught throwable.<p/>
   *
   * When this handler is called, {@link Vertx#currentContext()} will return this context.
   *
   * @param handler the exception handler
   * @return a reference to this, so the API can be used fluently
   */
  @Fluent
  Context exceptionHandler(@Nullable Handler<Throwable> handler);

  
Returns:
the current exception handler of this context/**
   * @return the current exception handler of this context
   */
  @GenIgnore
  @Nullable
  Handler<Throwable> exceptionHandler();

}