#include <boostAsioLinkageFix.h>
#include <cstring>
#include <stdexcept>
#include <functional>
#include <sys/socket.h>
#include <sys/eventfd.h>
#include <sys/uio.h>
#include <sys/poll.h>
#include <unistd.h>
#include <errno.h>
#include <boost/system/error_code.hpp>
#include <livoxProto1/device.h>
#include <livoxProto1/livoxProto1.h>
#include "ioUringAssemblyEngine.h"
#include "pcloudStimulusBuffer.h"
#include "livoxGen1.h"

namespace smo {
namespace stim_buff {

inline LivoxProto1DllState& getLivoxProto1State() { return livoxProto1; }

struct DummyLivoxEthHeader
{
	enum : uint32_t {
		INVALID_ERR_CODE = 0xFFFFFFFFu
	};
	enum : uint8_t {
		INVALID_TIMESTAMP_TYPE = 0xFFu,
		INVALID_DATA_TYPE = 0xFFu
	};

	uint8_t version, slot, id, rsvd;
	uint32_t err_code;
	uint8_t timestamp_type, data_type;
	uint8_t timestamp[8];
};

IoUringAssemblyEngine::IoUringAssemblyEngine(PcloudStimulusBuffer& parent_)
: parent(parent_),
frameAssemblyDesc(nullptr), ring{},
isSetup(false),
eventfdFd(-1), eventfdDesc(nullptr), eventfd_value(0),
stallTimer(parent_.device->componentThread->getIoService())
{}

bool IoUringAssemblyEngine::setup()
{
	if (isSetup)
		{ return false; }

	// Get FrameAssemblyDesc from staging buffer
	frameAssemblyDesc = static_cast<std::shared_ptr<FrameAssemblyDesc>>(
		parent.stagingBuffer);

	if (!frameAssemblyDesc || frameAssemblyDesc->slots.empty())
		{ return false; }

	// Get point cloud data socket descriptor from UdpCommandDemuxer
	auto& livoxState = getLivoxProto1State();
	if (!livoxState.livoxProto1_getPcloudDataFdDesc)
		{ return false; }
	pcloudDataFdDesc = (*livoxState.livoxProto1_getPcloudDataFdDesc)();
	if (!pcloudDataFdDesc)
		{ return false; }

	// Get UDP socket file descriptor
	int udpFd = pcloudDataFdDesc->native_handle();
	if (udpFd < 0)
		{ return false; }

	// Declare iovec early to avoid goto crossing initialization
	struct iovec iov;
	int ret;

	/**	EXPLANATION:
	 * Initialize io_uring ring - allocate SQEs and CQEs for one frame assembly
	 * One SQE per slot (one datagram per slot), plus one extra for cancel
	 * operations, since io_uring_prep_cancel() requires a valid SQE. So we
	 * alloc 1 extra SQE to guarantee that we will always have an available SQE
	 * for cancel operations.
	 */
	ret = io_uring_queue_init(
		static_cast<unsigned int>(frameAssemblyDesc->numSlots + 1), &ring, 0);
	if (ret < 0)
		{ goto cleanup; }

	// Register staging buffer with io_uring for DMA-apt I/O
	iov = parent.stagingBuffer.getIoUringRegisterIoVec();
	ret = io_uring_register_buffers(&ring, &iov, 1);
	if (ret < 0)
		{ goto cleanup_ring; }

	// Create eventfd for CQE notifications (used with boost's unified loop)
	eventfdFd = eventfd(0, EFD_NONBLOCK);
	if (eventfdFd < 0)
		{ goto cleanup_buffers; }

	// Register eventfd with io_uring
	ret = io_uring_register_eventfd(&ring, eventfdFd);
	if (ret < 0)
		{ goto cleanup_eventfd; }

	isSetup = true;
	return true;

cleanup_eventfd:
	close(eventfdFd);
	eventfdFd = -1;
cleanup_buffers:
	io_uring_unregister_buffers(&ring);
cleanup_ring:
	io_uring_queue_exit(&ring);
cleanup:
	return false;
}

void IoUringAssemblyEngine::finalize()
{
	// Call stop() to cancel in-flight operations (stop() already cancels the timer)
	stop();

	if (eventfdFd >= 0)
	{
		io_uring_unregister_eventfd(&ring);
		close(eventfdFd);
		eventfdFd = -1;
	}

	if (isSetup)
	{
		io_uring_unregister_buffers(&ring);
		io_uring_queue_exit(&ring);
		isSetup = false;
	}

	// Reset state to allow setup() to be called again
	frameAssemblyDesc = nullptr;
}

void IoUringAssemblyEngine::resetAndAssembleFrame(
	std::function<void(void*)> onCqeReady)
{
	if (!onCqeReady)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": onCqeReady callback is invalid");
	}

	if (!frameAssemblyDesc || !pcloudDataFdDesc || eventfdFd < 0)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": invalid state: "
			+ ( !frameAssemblyDesc ? "frameAssemblyDesc is null; " : "" )
			+ ( !pcloudDataFdDesc ? "pcloudDataFdDesc is null; " : "" )
			+ ( eventfdFd < 0 ? "eventfdFd is invalid." : "" ));
	}

	// eventfdDesc should not be valid when resetAndAssembleFrame is called
	if (eventfdDesc)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": eventfdDesc is already set");
	}

	// Store the callback for re-arming
	onCqeReadyCallback = std::move(onCqeReady);

	/**	EXPLANATION:
	 * Flush eventfd state: poll and read any pending events before creating
	 * descriptor.
	 * Use poll() to check if data is available (non-blocking check).
	 * If data is available, read it to flush.
	 */
	struct pollfd pfd;
	pfd.fd = eventfdFd;
	pfd.events = POLLIN;
	pfd.revents = 0;
	int poll_ret = poll(&pfd, 1, 0);  // Timeout 0 = non-blocking
	if (poll_ret > 0 && (pfd.revents & POLLIN))
	{
		uint64_t discard;
		ssize_t ret = read(eventfdFd, &discard, sizeof(discard));
		(void)ret;  // Ignore errors - just trying to flush
	}

	eventfdDesc = std::make_unique<boost::asio::posix::stream_descriptor>(
		parent.device->componentThread->getIoService(), eventfdFd);

	if (!eventfdDesc)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": failed to create eventfd stream descriptor");
	}

	// Get UDP socket file descriptor
	int udpFd = pcloudDataFdDesc->native_handle();
	if (udpFd < 0)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": invalid UDP socket file descriptor");
	}

	// Prepare SQEs for each slot in the frame
	struct io_uring_sqe *sqe;
	for (size_t i = 0; i < frameAssemblyDesc->numSlots; ++i)
	{
		sqe = io_uring_get_sqe(&ring);
		if (!sqe)
		{
			throw std::runtime_error(std::string(__func__)
				+ ": failed to get SQE for slot " + std::to_string(i));
		}

		const auto& slot = frameAssemblyDesc->slots[i];

		// Prepare recvmsg SQE for this slot
		struct msghdr msg = {};
		struct iovec iov;
		iov.iov_base = slot.vaddr;
		iov.iov_len = slot.nBytes;
		msg.msg_iov = &iov;
		msg.msg_iovlen = 1;

		io_uring_prep_recvmsg(sqe, udpFd, &msg, 0);
		// Set user_data to slot index for tracking
		io_uring_sqe_set_data(sqe, reinterpret_cast<void*>(i));
	}

	// Submit all SQEs
	int ret = io_uring_submit(&ring);
	if (ret < 0)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": io_uring_submit failed: " + std::strerror(errno)
			+ " (errno=" + std::to_string(errno) + ")");
	}

	// Start listening for CQE notifications on eventfd
	eventfdDesc->async_read_some(
		boost::asio::buffer(&eventfd_value, sizeof(eventfd_value)),
		std::bind(
			&IoUringAssemblyEngine::onEventfdRead, this,
			std::placeholders::_1,
			std::placeholders::_2));
}

void IoUringAssemblyEngine::stop()
{
	// Cancel in-flight stall timeout timer
	stallTimer.cancel();

	if (isSetup)
	{
		struct io_uring_sqe *sqe = io_uring_get_sqe(&ring);
		if (!sqe)
		{
			std::cerr << __func__ << ": failed to get SQE for cancel op. "
				<< "Continuing cleanup without cancelling.\n";

			goto cleanup_eventfd;
		}

		/* Cancel all in-flight operations on our ring
		 * using IORING_ASYNC_CANCEL_ANY. Identify the CQE for the cancel
		 * op as numSlots since numSlots is an invalid slot index for a
		 * real slot.
		 */
		io_uring_prep_cancel(
			sqe, reinterpret_cast<void*>(frameAssemblyDesc->numSlots),
			IORING_ASYNC_CANCEL_ANY);

		io_uring_submit(&ring);

		/* Wait for cancellation to complete. According to the man page,
		 * cancellation is synchronous and a CQE is guaranteed to be
		 * generated by the time submission returns.
		 */
		struct io_uring_cqe *cqe;
		bool sawCancelCqe = false;
		while (io_uring_peek_cqe(&ring, &cqe) == 0)
		{
			// Call seen() on all CQEs for completeness/correctness.
			io_uring_cqe_seen(&ring, cqe);
			void *user_data = io_uring_cqe_get_data(cqe);
			if (user_data == reinterpret_cast<void*>(
				frameAssemblyDesc->numSlots))
			{
				sawCancelCqe = true;
			}
		}

		if (!sawCancelCqe) {
			std::cerr << __func__ << ": no CQE seen for cancel operation\n";
		}
	}

cleanup_eventfd:
	if (eventfdDesc)
	{
		/**	EXPLANATION:
		 * The goal here is to ensure that our io_service's event loop will not
		 * get any events from the eventfd after we've called stop(). So we
		 * completely deinitialize the eventfd descriptor.
		 *
		 * But we still want to reuse the underlying eventfd file descriptor,
		 * itself in the next resetAndAssembleFrame() cycle, so we call
		 * release() instead of reset() to ensure that the underlying fd
		 * is not closed.
		 */
		eventfdDesc->cancel();
		eventfdDesc.release();
	}

	onCqeReadyCallback = nullptr;
}

void IoUringAssemblyEngine::onEventfdRead(
	const boost::system::error_code& error,
	std::size_t bytes_transferred)
{
	(void)bytes_transferred;

	// Ignore cancellation errors
	if (error == boost::asio::error::operation_aborted)
		{ return; }

	/**	FIXME:
	 * It may be necessary to specifically check for and handle the cancel op
	 * CQE here. I'm not sure as yet though, but I'll highlight it here for now.
	 */

	// Process all available CQEs and call callback for each one
	struct io_uring_cqe *cqe;
	while (io_uring_peek_cqe(&ring, &cqe) == 0)
	{
		// Get user_data from the CQE
		void* user_data = io_uring_cqe_get_data(cqe);
		// Mark the CQE as seen
		io_uring_cqe_seen(&ring, cqe);

		/**	EXPLANATION:
		 * Call the user-provided callback for this CQE with its user_data.
		 *
		 * 1. Notice that we call the caller's cb *after* marking the CQE as
		 * seen. We may later need to change this if the caller needs
		 * information from the CQE before it is marked as seen.
		 *
		 * 2. Notice that we do not check for or filter out the cancel op CQE
		 * here. The caller's handler will be able to see the cancel op CQE
		 * because of this.
		 */
		if (onCqeReadyCallback) {
			onCqeReadyCallback(user_data);
		}
	}

	// Re-arm the eventfd read for next CQE notification
	if (eventfdDesc && eventfdFd >= 0)
	{
		eventfdDesc->async_read_some(
			boost::asio::buffer(&eventfd_value, sizeof(eventfd_value)),
			std::bind(&IoUringAssemblyEngine::onEventfdRead, this,
				std::placeholders::_1,
				std::placeholders::_2));
	}
}

void IoUringAssemblyEngine::cancelIncompleteAndFillDummies()
{
	if (!frameAssemblyDesc)
		{ return; }

	for (size_t i = 0; i < frameAssemblyDesc->numSlots; ++i)
	{
		// In the real path, decide from CQE accounting whether slot i completed.
		// Here, demonstrate dummy header insertion API.
		auto* hdr = reinterpret_cast<DummyLivoxEthHeader*>(frameAssemblyDesc->slots[i].vaddr);
		hdr->err_code = DummyLivoxEthHeader::INVALID_ERR_CODE;
		hdr->timestamp_type = DummyLivoxEthHeader::INVALID_TIMESTAMP_TYPE;
		hdr->data_type = DummyLivoxEthHeader::INVALID_DATA_TYPE;
	}
}

size_t IoUringAssemblyEngine::computePointsPerDgram(int returnMode)
{
	/*
	 * Map modes to points per datagram based on Livox docs
	 * 1: first, 2: strongest -> 96 samples => 96 points
	 * 3: dual -> 48 samples * 2 points = 96
	 * 4: triple -> 30 samples * 3 points = 90
	 */
	switch (returnMode)
	{
	case static_cast<int>(livoxProto1::Device::ReturnMode::SingleFirst):
	case static_cast<int>(livoxProto1::Device::ReturnMode::SingleStrongest):
	case static_cast<int>(livoxProto1::Device::ReturnMode::Dual):
		return 96u;
	case static_cast<int>(livoxProto1::Device::ReturnMode::Triple):
		return 90u;
	default:
		throw std::runtime_error(
			std::string(__func__) + ": Unknown returnMode "
			+ std::to_string(returnMode));
	}
}

} // namespace stim_buff
} // namespace smo