Store Handler in common::CallbackList, and execute callbacks on proper handlers

#pragma once

#include <utility>

#include "base/callback_list.h"

#include "os/handler.h"

/* This file contains CallbackList implementation that will execute callback on provided Handler thread

Example usage inside your class:

private:

  common::CallbackList<void(int)> callbacks_list_;

public:

  std::unique_ptr<common::CallbackList<void(int)>::Subscription> RegisterCallback(

      const base::RepeatingCallback<void(int)>& cb, os::Handler* handler) {

    return callbacks_list_.Add({cb, handler});

  }

  void NotifyAllCallbacks(int value) {

    callbacks_list_.Notify(value);

  }

*/

namespace bluetooth {

namespace common {

using base::CallbackList;

namespace {

template <typename CallbackType>

struct CallbackWithHandler {

  CallbackWithHandler(base::RepeatingCallback<CallbackType> callback, os::Handler* handler)

      : callback(callback), handler(handler) {}

  bool is_null() const {

    return callback.is_null();

  }

  void Reset() {

    callback.Reset();

  }

  base::RepeatingCallback<CallbackType> callback;

  os::Handler* handler;

};

}  // namespace

template <typename Sig>

class CallbackList;

template <typename... Args>

class CallbackList<void(Args...)> : public base::internal::CallbackListBase<CallbackWithHandler<void(Args...)>> {

 public:

  using CallbackType = CallbackWithHandler<void(Args...)>;

  CallbackList() = default;

  template <typename... RunArgs>

  void Notify(RunArgs&&... args) {

    auto it = this->GetIterator();

    CallbackType* cb;

    while ((cb = it.GetNext()) != nullptr) {

      cb->handler->Post(base::Bind(cb->callback, args...));

    }

  }

 private:

  DISALLOW_COPY_AND_ASSIGN(CallbackList);

};

}  // namespace common

}  // namespace bluetooth