#pragma once

#include "Utilities.hpp"
#include <sys/epoll.h>
#include <sys/timerfd.h>
#include <sys/eventfd.h>
#include <poll.h>
#include <unistd.h>
#include <vector>
#include <unordered_map>
#include <unordered_set>
#include <functional>
#include <memory>
#include <queue>
#include <chrono>
#include <thread>
#include <atomic>
#include <cassert>
#include <cstring>
#include <mutex>

namespace reactor
{

using TimePoint = std::chrono::steady_clock::time_point;
using Duration = std::chrono::milliseconds;
using TimerCallback = std::function<void()>;
using EventCallback = std::function<void()>;

class EventLoop;

class Channel : public NonCopyable
{
private:
	EventLoop* loop_;
	int fd_;
	int events_;
	int revents_;
	int index_;
	bool tied_;
	std::weak_ptr<void> tie_;
	EventCallback readCallback_;
	EventCallback writeCallback_;
	EventCallback closeCallback_;
	EventCallback errorCallback_;

	/*
	*	Safely handle the event, checking if the tied object is still alive.
	*/
	void handleEventSafely()
	{
		LOG_TRACE << "Channel fd=" << fd_ << " handling events: " << revents_;

		if ((revents_ & POLLHUP) && !(revents_ & POLLIN)) {
			LOG_DEBUG << "Channel fd=" << fd_ << " hangup";
			if (closeCallback_) {
				closeCallback_();
			}
		}
		if (revents_ & POLLERR) {
			LOG_WARN << "Channel fd=" << fd_ << " error event";
			if (errorCallback_) {
				errorCallback_();
			}
		}
		if (revents_ & (POLLIN | POLLPRI | POLLRDHUP)) {
			LOG_TRACE << "Channel fd=" << fd_ << " readable";
			if (readCallback_) {
				readCallback_();
			}
		}
		if (revents_ & POLLOUT) {
			LOG_TRACE << "Channel fd=" << fd_ << " writable";
			if (writeCallback_) {
				writeCallback_();
			}
		}
	}

public:
	static constexpr int kNoneEvent = 0;
	static constexpr int kReadEvent = POLLIN | POLLPRI;
	static constexpr int kWriteEvent = POLLOUT;

	Channel(EventLoop* loop, int fd)
		: loop_(loop), fd_(fd), events_(0), revents_(0), index_(-1), tied_(false)
	{
		LOG_TRACE << "Channel created for fd=" << fd;
	}

	~Channel()
	{
		LOG_TRACE << "Channel destroyed for fd=" << fd_;
	}

	int fd() const { return fd_; }
	int events() const { return events_; }
	int revents() const { return revents_; }
	int index() const { return index_; }
	EventLoop* ownerLoop() const { return loop_; }

	void setRevents(int revents) { revents_ = revents; }
	void setIndex(int index) { index_ = index; }

	void enableReading()
	{
		events_ |= kReadEvent;
		update();
		LOG_TRACE << "Channel fd=" << fd_ << " enabled reading";
	}

	void disableReading()
	{
		events_ &= ~kReadEvent;
		update();
		LOG_TRACE << "Channel fd=" << fd_ << " disabled reading";
	}

	void enableWriting()
	{
		events_ |= kWriteEvent;
		update();
		LOG_TRACE << "Channel fd=" << fd_ << " enabled writing";
	}

	void disableWriting()
	{
		events_ &= ~kWriteEvent;
		update();
		LOG_TRACE << "Channel fd=" << fd_ << " disabled writing";
	}

	void disableAll()
	{
		events_ = kNoneEvent;
		update();
		LOG_TRACE << "Channel fd=" << fd_ << " disabled all events";
	}

	bool isNoneEvent() const { return events_ == kNoneEvent; }
	bool isWriting() const { return events_ & kWriteEvent; }
	bool isReading() const { return events_ & kReadEvent; }

	void tie(const std::shared_ptr<void>& obj)
	{
		tie_ = obj;
		tied_ = true;
	}

	void setReadCallback(EventCallback cb) { readCallback_ = std::move(cb); }
	void setWriteCallback(EventCallback cb) { writeCallback_ = std::move(cb); }
	void setCloseCallback(EventCallback cb) { closeCallback_ = std::move(cb); }
	void setErrorCallback(EventCallback cb) { errorCallback_ = std::move(cb); }

	/*
	*	Handle an event. If the channel is tied to an object,
	*	ensure the object is still alive before proceeding.
	*/
	void handleEvent()
	{
		if (tied_) {
			std::shared_ptr<void> guard = tie_.lock();
			if (guard) {
				handleEventSafely();
			} else {
				LOG_WARN << "Channel fd=" << fd_ << " tied object expired";
			}
		} else {
			handleEventSafely();
		}
	}

	void remove();
	void update();
};

class Timer : public NonCopyable
{
private:
	TimerCallback callback_;
	TimePoint when_;
	Duration interval_;
	bool repeat_;
	uint64_t id_;
	static inline std::atomic<uint64_t> s_numCreated_{0};

public:
	Timer(TimerCallback cb, TimePoint when, Duration interval = Duration(0))
		: callback_(std::move(cb)), when_(when), interval_(interval),
		  repeat_(interval.count() > 0), id_(++s_numCreated_)
	{
		LOG_TRACE << "Timer created id=" << id_ << " repeat=" << repeat_;
	}

	void run() const
	{
		LOG_TRACE << "Timer id=" << id_ << " executing";
		callback_();
	}

	TimePoint when() const { return when_; }
	bool repeat() const { return repeat_; }
	uint64_t id() const { return id_; }

	void restart(TimePoint now)
	{
		if (repeat_) {
			when_ = now + interval_;
			LOG_TRACE << "Timer id=" << id_ << " restarted";
		}
	}

	bool operator<(const Timer& other) const { return when_ > other.when_; }
};

class TimerQueue : public NonCopyable
{
private:
	EventLoop* loop_;
	int timerfd_;
	std::unique_ptr<Channel> timerChannel_;
	std::priority_queue<std::shared_ptr<Timer>> timers_;
	std::unordered_set<uint64_t> activeTimers_;

	static int createTimerfd()
	{
		int fd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
		if (fd < 0) {
			LOG_FATAL << "Failed to create timerfd: " << strerror(errno);
			abort();
		}
		LOG_DEBUG << "Created timerfd=" << fd;
		return fd;
	}

	void resetTimerfd(TimePoint expiration)
	{
		auto duration = expiration - std::chrono::steady_clock::now();
		auto ns = std::chrono::duration_cast<std::chrono::nanoseconds>(duration).count();
		if (ns < 100000) {
			ns = 100000;
		}

		itimerspec newValue{};
		newValue.it_value.tv_sec = ns / 1000000000;
		newValue.it_value.tv_nsec = ns % 1000000000;

		if (timerfd_settime(timerfd_, 0, &newValue, nullptr) < 0) {
			LOG_ERROR << "timerfd_settime failed: " << strerror(errno);
		}
	}

	void handleRead()
	{
		uint64_t data;
		ssize_t n = read(timerfd_, &data, sizeof(data));
		if (n != sizeof(data)) {
			LOG_ERROR << "TimerQueue read " << n << " bytes instead of 8";
		}

		auto now = std::chrono::steady_clock::now();
		std::vector<std::shared_ptr<Timer>> expired;

		while (!timers_.empty() && timers_.top()->when() <= now) {
			expired.push_back(timers_.top());
			timers_.pop();
		}

		LOG_TRACE << "TimerQueue processed " << expired.size() << " expired timers";

		for (auto& timer : expired) {
			if (activeTimers_.count(timer->id())) {
				timer->run();
				if (timer->repeat()) {
					timer->restart(now);
					timers_.push(timer);
				} else {
					activeTimers_.erase(timer->id());
				}
			}
		}

		if (!timers_.empty()) {
			resetTimerfd(timers_.top()->when());
		}
	}

public:
	TimerQueue(EventLoop* loop)
		: loop_(loop), timerfd_(createTimerfd()),
		  timerChannel_(std::make_unique<Channel>(loop, timerfd_))
	{
		timerChannel_->setReadCallback([this]() { handleRead(); });
		timerChannel_->enableReading();
		LOG_DEBUG << "TimerQueue initialized";
	}

	~TimerQueue()
	{
		timerChannel_->disableAll();
		timerChannel_->remove();
		close(timerfd_);
		LOG_DEBUG << "TimerQueue destroyed";
	}

	uint64_t addTimer(TimerCallback cb, TimePoint when, Duration interval = Duration(0))
	{
		auto timer = std::make_shared<Timer>(std::move(cb), when, interval);
		bool earliestChanged = timers_.empty() || when < timers_.top()->when();

		timers_.push(timer);
		activeTimers_.insert(timer->id());

		if (earliestChanged) {
			resetTimerfd(when);
		}

		LOG_DEBUG << "Added timer id=" << timer->id() << " earliest_changed=" << earliestChanged;
		return timer->id();
	}

	void cancel(uint64_t timerId)
	{
		auto erased = activeTimers_.erase(timerId);
		LOG_DEBUG << "Cancelled timer id=" << timerId << " found=" << (erased > 0);
	}
};

class EpollPoller : public NonCopyable
{
private:
	static constexpr int kNew = -1;
	static constexpr int kAdded = 1;
	static constexpr int kDeleted = 2;
	static constexpr int kInitEventListSize = 16;

	int epollfd_;
	std::vector<epoll_event> events_;
	std::unordered_map<int, Channel*> channels_;

	void update(int operation, Channel* channel)
	{
		epoll_event event{};
		event.events = channel->events();
		event.data.ptr = channel;

		if (epoll_ctl(epollfd_, operation, channel->fd(), &event) < 0) {
			LOG_ERROR << "epoll_ctl op=" << operation << " fd=" << channel->fd()
					  << " failed: " << strerror(errno);
		} else {
			LOG_TRACE << "epoll_ctl op=" << operation << " fd=" << channel->fd() << " success";
		}
	}

public:
	EpollPoller() : epollfd_(epoll_create1(EPOLL_CLOEXEC)), events_(kInitEventListSize)
	{
		if (epollfd_ < 0) {
			LOG_FATAL << "epoll_create1 failed: " << strerror(errno);
			abort();
		}
		LOG_DEBUG << "EpollPoller created with epollfd=" << epollfd_;
	}

	~EpollPoller()
	{
		close(epollfd_);
		LOG_DEBUG << "EpollPoller destroyed";
	}

	std::vector<Channel*> poll(int timeoutMs = -1)
	{
		int numEvents = epoll_wait(epollfd_, events_.data(),
								   static_cast<int>(events_.size()), timeoutMs);

		std::vector<Channel*> activeChannels;

		if (numEvents > 0) {
			LOG_TRACE << "EpollPoller got " << numEvents << " events";

			for (int i = 0; i < numEvents; ++i) {
				auto channel = static_cast<Channel*>(events_[i].data.ptr);
				channel->setRevents(events_[i].events);
				activeChannels.push_back(channel);
			}

			if (static_cast<size_t>(numEvents) == events_.size()) {
				events_.resize(events_.size() * 2);
				LOG_DEBUG << "EpollPoller events buffer grown to " << events_.size();
			}
		} else if (numEvents < 0 && errno != EINTR) {
			LOG_ERROR << "EpollPoller::poll failed: " << strerror(errno);
		}

		return activeChannels;
	}

	void updateChannel(Channel* channel)
	{
		int index = channel->index();
		int fd = channel->fd();

		if (index == kNew || index == kDeleted) {
			if (index == kNew) {
				channels_[fd] = channel;
			}
			channel->setIndex(kAdded);
			update(EPOLL_CTL_ADD, channel);
		} else {
			if (channel->isNoneEvent()) {
				update(EPOLL_CTL_DEL, channel);
				channel->setIndex(kDeleted);
			} else {
				update(EPOLL_CTL_MOD, channel);
			}
		}
	}

	void removeChannel(Channel* channel)
	{
		int fd = channel->fd();
		int index = channel->index();

		auto n = channels_.erase(fd);
		assert(n == 1);

		if (index == kAdded) {
			update(EPOLL_CTL_DEL, channel);
		}

		channel->setIndex(kNew);
		LOG_TRACE << "Channel fd=" << fd << " removed from poller";
	}
};

class EventLoop : public NonCopyable
{
private:
	std::unique_ptr<EpollPoller> poller_;
	std::unique_ptr<TimerQueue> timerQueue_;
	int wakeupFd_;
	std::unique_ptr<Channel> wakeupChannel_;
	std::atomic<bool> looping_;
	std::atomic<bool> quit_;
	std::thread::id threadId_;
	std::mutex mutex_;
	std::vector<std::function<void()>> pendingFunctors_;
	bool callingPendingFunctors_;

	static int createEventfd()
	{
		int fd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
		if (fd < 0) {
			LOG_FATAL << "Failed to create eventfd: " << strerror(errno);
			abort();
		}
		LOG_DEBUG << "Created eventfd=" << fd;
		return fd;
	}

	void wakeup()
	{
		uint64_t one = 1;
		ssize_t n = write(wakeupFd_, &one, sizeof(one));
		if (n != sizeof(one)) {
			LOG_ERROR << "EventLoop wakeup writes " << n << " bytes instead of 8";
		}
	}

	void handleRead()
	{
		uint64_t one;
		ssize_t n = read(wakeupFd_, &one, sizeof(one));
		if (n != sizeof(one)) {
			LOG_ERROR << "EventLoop handleRead reads " << n << " bytes instead of 8";
		}
	}

	void doPendingFunctors()
	{
		std::vector<std::function<void()>> functors;
		callingPendingFunctors_ = true;
		{
			std::lock_guard<std::mutex> lock(mutex_);
			functors.swap(pendingFunctors_);
		}

		if (!functors.empty()) {
			LOG_TRACE << "EventLoop executed " << functors.size() << " pending functors";
		}

		for (const auto& functor : functors) {
			functor();
		}

		callingPendingFunctors_ = false;
	}

public:
	EventLoop()
		: poller_(std::make_unique<EpollPoller>()),
		  timerQueue_(std::make_unique<TimerQueue>(this)),
		  wakeupFd_(createEventfd()),
		  wakeupChannel_(std::make_unique<Channel>(this, wakeupFd_)),
		  looping_(false), quit_(false),
		  threadId_(),
		  pendingFunctors_(),
		  callingPendingFunctors_(false)
	{
		wakeupChannel_->setReadCallback([this]() { handleRead(); });
		wakeupChannel_->enableReading();
		LOG_INFO << "EventLoop created";
	}

	~EventLoop()
	{
		wakeupChannel_->disableAll();
		wakeupChannel_->remove();
		close(wakeupFd_);
		LOG_INFO << "EventLoop destroyed";
	}

	void loop()
	{
		assert(!looping_);
		threadId_ = std::this_thread::get_id();
		looping_ = true;
		quit_ = false;

		LOG_INFO << "EventLoop started looping in thread " << threadId_;

		while (!quit_) {
			auto activeChannels = poller_->poll(10000);
			for (auto channel : activeChannels) {
				channel->handleEvent();
			}
			doPendingFunctors();
		}

		looping_ = false;
		LOG_INFO << "EventLoop stopped looping";
	}

	void quit()
	{
		quit_ = true;
		if (!isInLoopThread()) {
			wakeup();
		}
		LOG_DEBUG << "EventLoop quit requested";
	}

	template<typename F>
	void runInLoop(F&& cb)
	{
		if (isInLoopThread()) {
			cb();
		} else {
			queueInLoop(std::forward<F>(cb));
		}
	}

	template<typename F>
	void queueInLoop(F&& cb)
	{
		{
			std::lock_guard<std::mutex> lock(mutex_);
			pendingFunctors_.emplace_back(std::forward<F>(cb));
		}

		if (!isInLoopThread() || callingPendingFunctors_) {
			wakeup();
		}
	}

	uint64_t runAt(TimePoint when, TimerCallback cb)
	{
		return timerQueue_->addTimer(std::move(cb), when);
	}

	uint64_t runAfter(Duration delay, TimerCallback cb)
	{
		return runAt(std::chrono::steady_clock::now() + delay, std::move(cb));
	}

	uint64_t runEvery(Duration interval, TimerCallback cb)
	{
		auto when = std::chrono::steady_clock::now() + interval;
		return timerQueue_->addTimer(std::move(cb), when, interval);
	}

	void cancel(uint64_t timerId) { timerQueue_->cancel(timerId); }

	void updateChannel(Channel* channel) { poller_->updateChannel(channel); }
	void removeChannel(Channel* channel) { poller_->removeChannel(channel); }

	bool isInLoopThread() const
	{
		return threadId_ == std::this_thread::get_id();
	}

	void assertInLoopThread() const
	{
		if (!isInLoopThread()) {
			LOG_FATAL << "EventLoop was created in thread " << threadId_
					  << " but accessed from thread " << std::this_thread::get_id();
			abort();
		}
	}
};

inline void Channel::update()
{
	loop_->updateChannel(this);
}

inline void Channel::remove()
{
	assert(isNoneEvent());
	loop_->removeChannel(this);
}

}