// Copyright (c) 2010 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Illustrates how to use worker threads that issue completion callbacks

#include "base/logging.h"
#include "base/message_loop.h"
#include "base/task.h"
#include "base/threading/worker_pool.h"
#include "net/base/completion_callback.h"
#include "net/base/test_completion_callback.h"
#include "testing/gtest/include/gtest/gtest.h"
#include "testing/platform_test.h"

typedef PlatformTest TestCompletionCallbackTest;

using net::CompletionCallback;

const int kMagicResult = 8888;

// ExampleEmployer is a toy version of HostResolver
// TODO: restore damage done in extracting example from real code
// (e.g. bring back real destructor, bring back comments)
class ExampleEmployer {
 public:
  ExampleEmployer();
  ~ExampleEmployer();

  // Do some imaginary work on a worker thread;
  // when done, worker posts callback on the original thread.
  // Returns true on success
  bool DoSomething(CompletionCallback* callback);

 private:
  class ExampleWorker;
  friend class ExampleWorker;
  scoped_refptr<ExampleWorker> request_;
  DISALLOW_COPY_AND_ASSIGN(ExampleEmployer);
};

// Helper class; this is how ExampleEmployer puts work on a different thread
class ExampleEmployer::ExampleWorker
    : public base::RefCountedThreadSafe<ExampleWorker> {
 public:
  ExampleWorker(ExampleEmployer* employer, CompletionCallback* callback)
      : employer_(employer), callback_(callback),
        origin_loop_(MessageLoop::current()) {
  }
  void DoWork();
  void DoCallback();
 private:
  friend class base::RefCountedThreadSafe<ExampleWorker>;

  ~ExampleWorker() {}

  // Only used on the origin thread (where DoSomething was called).
  ExampleEmployer* employer_;
  CompletionCallback* callback_;
  // Used to post ourselves onto the origin thread.
  base::Lock origin_loop_lock_;
  MessageLoop* origin_loop_;
};

void ExampleEmployer::ExampleWorker::DoWork() {
  // Running on the worker thread
  // In a real worker thread, some work would be done here.
  // Pretend it is, and send the completion callback.
  Task* reply = NewRunnableMethod(this, &ExampleWorker::DoCallback);

  // The origin loop could go away while we are trying to post to it, so we
  // need to call its PostTask method inside a lock.  See ~ExampleEmployer.
  {
    base::AutoLock locked(origin_loop_lock_);
    if (origin_loop_) {
      origin_loop_->PostTask(FROM_HERE, reply);
      reply = NULL;
    }
  }

  // Does nothing if it got posted.
  delete reply;
}

void ExampleEmployer::ExampleWorker::DoCallback() {
  // Running on the origin thread.

  // Drop the employer_'s reference to us.  Do this before running the
  // callback since the callback might result in the employer being
  // destroyed.
  employer_->request_ = NULL;

  callback_->Run(kMagicResult);
}

ExampleEmployer::ExampleEmployer() {
}

ExampleEmployer::~ExampleEmployer() {
}

bool ExampleEmployer::DoSomething(CompletionCallback* callback) {
  DCHECK(!request_) << "already in use";

  request_ = new ExampleWorker(this, callback);

  // Dispatch to worker thread...
  if (!base::WorkerPool::PostTask(FROM_HERE,
          NewRunnableMethod(request_.get(), &ExampleWorker::DoWork), true)) {
    NOTREACHED();
    request_ = NULL;
    return false;
  }

  return true;
}

TEST_F(TestCompletionCallbackTest, Simple) {
  ExampleEmployer boss;
  TestCompletionCallback callback;
  bool queued = boss.DoSomething(&callback);
  EXPECT_EQ(queued, true);
  int result = callback.WaitForResult();
  EXPECT_EQ(result, kMagicResult);
}

// TODO: test deleting ExampleEmployer while work outstanding
