// SPDX-License-Identifier: BSD-2-Clause
// Copyright CM4all GmbH
// author: Max Kellermann <mk@cm4all.com>

#pragma once

#include "Chrono.hxx"
#include "util/BindMethod.hxx"
#include "util/IntrusiveList.hxx"

class EventLoop;

/**
 * This class invokes a callback function after a certain amount of
 * time.  Use Schedule() to start the timer or Cancel() to cancel it.
 *
 * Unlike #FineTimerEvent, this class has a granularity of about 1
 * second, and is optimized for timeouts between 1 and 60 seconds
 * which are often canceled before they expire (i.e. optimized for
 * fast insertion and deletion, at the cost of granularity).
 *
 * This class is not thread-safe, all methods must be called from the
 * thread that runs the #EventLoop, except where explicitly documented
 * as thread-safe.
 */
class CoarseTimerEvent final : AutoUnlinkIntrusiveListHook
{
	friend class TimerWheel;
	friend struct IntrusiveListBaseHookTraits<CoarseTimerEvent>;

	EventLoop &loop;

	using Callback = BoundMethod<void() noexcept>;
	const Callback callback;

	/**
	 * When is this timer due?  This is only valid if IsPending()
	 * returns true.
	 */
	Event::TimePoint due;

public:
	CoarseTimerEvent(EventLoop &_loop, Callback _callback) noexcept
		:loop(_loop), callback(_callback) {}

	auto &GetEventLoop() const noexcept {
		return loop;
	}

	constexpr auto GetDue() const noexcept {
		return due;
	}

	/**
	 * Was this timer scheduled?
	 */
	bool IsPending() const noexcept {
		return is_linked();
	}

	void Schedule(Event::Duration d) noexcept;

	/**
	 * Like Schedule(), but is a no-op if there is a due time
	 * earlier than the given one.
	 */
	void ScheduleEarlier(Event::Duration d) noexcept;

	void Cancel() noexcept {
		if (IsPending())
			unlink();
	}

private:
	void Run() noexcept {
		callback();
	}
};