deskflow/src/lib/base/IEventQueue.h

/*
 * Deskflow -- mouse and keyboard sharing utility
 * SPDX-FileCopyrightText: (C) 2025 Deskflow Developers
 * SPDX-FileCopyrightText: (C) 2012 - 2016 Symless Ltd.
 * SPDX-FileCopyrightText: (C) 2004 Chris Schoeneman
 * SPDX-License-Identifier: GPL-2.0-only WITH LicenseRef-OpenSSL-Exception
 */

#pragma once

#include "base/Event.h"

#include <functional>

class IEventQueueBuffer;

// Opaque type for timer info.  This is defined by subclasses of
// IEventQueueBuffer.
class EventQueueTimer;

//! Event queue interface
/*!
An event queue provides a queue of Events.  Clients can block waiting
on any event becoming available at the head of the queue and can place
new events at the end of the queue.  Clients can also add and remove
timers which generate events periodically.
*/
class IEventQueue
{
public:
  using EventHandler = std::function<void(const Event &)>;

  virtual ~IEventQueue() = default;
  class TimerEvent
  {
  public:
    EventQueueTimer *m_timer; //!< The timer
    uint32_t m_count;         //!< Number of repeats
  };

  //! @name manipulators
  //@{

  //! Loop the event queue until quit
  /*!
  Dequeues and dispatches events until the kQuit event is found.
  */
  virtual void loop() = 0;

  //! Set the buffer
  /*!
  Replace the current event queue buffer.  Any queued events are
  discarded.  The queue takes ownership of the buffer.
  */
  virtual void adoptBuffer(IEventQueueBuffer *) = 0;

  //! Remove event from queue
  /*!
  Returns the next event on the queue into \p event.  If no event is
  available then blocks for up to \p timeout seconds, or forever if
  \p timeout is negative.  Returns true iff an event was available.
  */
  virtual bool getEvent(Event &event, double timeout = -1.0) = 0;

  //! Dispatch an event
  /*!
  Looks up the dispatcher for the event's target and invokes it.
  Returns true iff a dispatcher exists for the target.

  The caller must ensure that the target of the event is not removed by removeHandler() or
  removeHandlers().
  */
  virtual bool dispatchEvent(const Event &event) = 0;

  //! Add event to queue
  /*!
  Adds \p event to the end of the queue.
  */
  virtual void addEvent(Event &&event) = 0;

  //! Create a recurring timer
  /*!
  Creates and returns a timer.  An event is returned after \p duration
  seconds and the timer is reset to countdown again.  When a timer event
  is returned the data points to a \c TimerEvent.  The client must pass
  the returned timer to \c deleteTimer() (whether or not the timer has
  expired) to release the timer.  The returned timer event uses the
  given \p target.  If \p target is nullptr it uses the returned timer as
  the target.

  Events for a single timer don't accumulate in the queue, even if the
  client reading events can't keep up.  Instead, the \c m_count member
  of the \c TimerEvent indicates how many events for the timer would
  have been put on the queue since the last event for the timer was
  removed (or since the timer was added).
  */
  virtual EventQueueTimer *newTimer(double duration, void *target) = 0;

  //! Create a one-shot timer
  /*!
  Creates and returns a one-shot timer.  An event is returned when
  the timer expires and the timer is removed from further handling.
  When a timer event is returned the data points to a \c TimerEvent.
  The c_count member of the \c TimerEvent is always 1.  The client
  must pass the returned timer to \c deleteTimer() (whether or not the
  timer has expired) to release the timer.  The returned timer event
  uses the given \p target.  If \p target is nullptr it uses the returned
  timer as the target.
  */
  virtual EventQueueTimer *newOneShotTimer(double duration, void *target) = 0;

  //! Destroy a timer
  /*!
  Destroys a previously created timer.  The timer is removed from the
  queue and will not generate event, even if the timer has expired.
  */
  virtual void deleteTimer(EventQueueTimer *) = 0;

  //! Register an event handler for an event type
  /*!
  Registers an event handler for \p type and \p target.  The \p handler
  is adopted.  Any existing handler for the type,target pair is deleted.
  \c dispatchEvent() will invoke \p handler for any event for \p target
  of type \p type.  If no such handler exists it will use the handler
  for \p target and type \p kUnknown if it exists.
  */
  virtual void addHandler(EventTypes type, void *target, const EventHandler &handler) = 0;

  //! Unregister an event handler for an event type
  /*!
  Unregisters an event handler for the \p type, \p target pair and
  deletes it.
  */
  virtual void removeHandler(EventTypes type, void *target) = 0;

  //! Unregister all event handlers for an event target
  /*!
  Unregisters all event handlers for the \p target and deletes them.
  */
  virtual void removeHandlers(void *target) = 0;

  //! Wait for event queue to become ready
  /*!
  Blocks on the current thread until the event queue is ready for events to
  be added.
  */
  virtual void waitForReady() const = 0;

  //@}
  //! @name accessors
  //@{

  //! Get the system event type target
  /*!
  Returns the target to use for dispatching \c EventTypes::System events.
  */
  virtual void *getSystemTarget() = 0;

  //@}
};