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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
 * Copyright (C) 2019, Google Inc.
 *
 * event_notifier.cpp - File descriptor event notifier
 */

#include <libcamera/event_notifier.h>

#include <libcamera/camera_manager.h>
#include <libcamera/event_dispatcher.h>

/**
 * \file event_notifier.h
 * \brief File descriptor event notifier
 */

namespace libcamera {

/**
 * \class EventNotifier
 * \brief Notify of activity on a file descriptor
 *
 * The EventNotifier models a file descriptor event source that can be
 * monitored. It is created with the file descriptor to be monitored and the
 * type of event, and is enabled by default. It will emit the \ref activated
 * signal whenever an event of the monitored type occurs on the file descriptor.
 *
 * Supported type of events are EventNotifier::Read, EventNotifier::Write and
 * EventNotifier::Exception. The type is specified when constructing the
 * notifier, and can be retrieved using the type() function. To listen to
 * multiple event types on the same file descriptor multiple notifiers must be
 * created.
 *
 * The notifier can be disabled with the setEnable() function. When the notifier
 * is disabled it ignores events and does not emit the \ref activated signal.
 * The notifier can then be re-enabled with the setEnable() function.
 *
 * Creating multiple notifiers of the same type for the same file descriptor is
 * not allowed and results in undefined behaviour.
 *
 * Notifier events are detected and dispatched from the
 * EventDispatcher::processEvents() function.
 */

/**
 * \enum EventNotifier::Type
 * Type of file descriptor event to listen for.
 * \var EventNotifier::Read
 * Data is available to be read from the file descriptor
 * \var EventNotifier::Write
 * Data can be written to the file descriptor
 * \var EventNotifier::Exception
 * An exception has occurred on the file descriptor
 */

/**
 * \brief Construct an event notifier with a file descriptor and event type
 * \param[in] fd The file descriptor to monitor
 * \param[in] type The event type to monitor
 */
EventNotifier::EventNotifier(int fd, Type type)
	: fd_(fd), type_(type), enabled_(false)
{
	setEnabled(true);
}

EventNotifier::~EventNotifier()
{
	setEnabled(false);
}

/**
 * \fn EventNotifier::type()
 * \brief Retrieve the type of the event being monitored
 * \return The type of the event
 */

/**
 * \fn EventNotifier::fd()
 * \brief Retrieve the file descriptor being monitored
 * \return The file descriptor
 */

/**
 * \fn EventNotifier::enabled()
 * \brief Retrieve the notifier state
 * \return True if the notifier is enabled, or false otherwise
 * \sa setEnable()
 */

/**
 * \brief Enable or disable the notifier
 * \param[in] enable True to enable the notifier, false to disable it
 *
 * This function enables or disables the notifier. A disabled notifier ignores
 * events and does not emit the \ref activated signal.
 */
void EventNotifier::setEnabled(bool enable)
{
	if (enabled_ == enable)
		return;

	enabled_ = enable;

	EventDispatcher *dispatcher = CameraManager::instance()->eventDispatcher();
	if (enable)
		dispatcher->registerEventNotifier(this);
	else
		dispatcher->unregisterEventNotifier(this);
}

/**
 * \var EventNotifier::activated
 * \brief Signal emitted when the event occurs
 *
 * This signal is emitted when the event \ref type() occurs on the file
 * descriptor monitored by the notifier. The notifier pointer is passed as a
 * parameter.
 */

} /* namespace libcamera */