#include <boostAsioLinkageFix.h>
#include <config.h>
#include <opts.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 <asynchronousContinuation.h>
#include <asynchronousLoop.h>
#include <asynchronousBridge.h>
#include <callback.h>
#include <callableTracer.h>
#include <spinLock.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()),
isAssembling(false)
{}

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

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

	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.assemblyBuffer.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(
	resetAndAssembleFrameCbFn 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) + ")");
	}

	// Set assembly flag
	isAssembling = true;
	// 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(bool doAcquireLock)
{
	// Clear assembly flag first to signal onEventfdRead to stop re-arming
	// Acquire and release lock tightly around setting the flag
	if (doAcquireLock)
	{
		SpinLock::Guard lock(isAssemblingLock);
		isAssembling = false;
	} else {
		isAssembling = false;
	}

	/**	FIXME:
	 * There's a problem with this bridge here.
	 *
	 * We can't delay during every call to stop because under normal operating
	 * conditions, this whole assembly process should be able to move as fast
	 * as possible and to receive as much data as possible without maximum
	 * throughput.
	 *
	 * Yet we need to delay briefly here to ensure that the onEventfdRead loop
	 * has a chance to see the flag and halt.
	 *
	 * We need to analyze this carefully and figure out what the correct
	 * conditions are for being certain that we aren't destroying state while
	 * the eventfdRead loop is still running; and we need to figure out how to
	 * ensure that we only delay when absolutely necessary.
	 */

	// Cancel in-flight stall timeout timer
	stallTimer.cancel();
	onCqeReadyCallback = std::move([](void *, int){});

	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 && OptionParser::getOptions().verbose) {
			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.
		 *
		 * However, we need to close the descriptor's association with the
		 * io_service before releasing it, otherwise Boost.Asio will complain
		 * when we try to create a new descriptor with the same fd.
		 */
		eventfdDesc->cancel();
		eventfdDesc->release();
		/* Destroy the descriptor object (now that it's unregistered, destroying
		 * it won't close the fd since release() transferred ownership back)
		 */
		eventfdDesc.reset();
	}
}

// Continuation class for assembleFrameReq
class IoUringAssemblyEngine::AssembleFrameReq
:	public PostedAsynchronousContinuation<
		IoUringAssemblyEngine::assembleFrameReqCbFn>
{
public:
	AssembleFrameReq(
		IoUringAssemblyEngine& engine_,
		const std::shared_ptr<ComponentThread>& caller,
		Callback<IoUringAssemblyEngine::assembleFrameReqCbFn> cb)
	:	PostedAsynchronousContinuation<
			IoUringAssemblyEngine::assembleFrameReqCbFn>(caller, cb),
	engine(engine_),
	loop(engine_.frameAssemblyDesc->numSlots),
	timerFired(false), handlerExecuted(false)
	{}

public:
	void assembleFrameReq1_posted(
		std::shared_ptr<AssembleFrameReq> context)
	{
		if (!engine.frameAssemblyDesc)
		{
			throw std::runtime_error(std::string(__func__)
				+ ": frameAssemblyDesc is null");
		}

		// Initialize loop with number of slots
		context->loop = AsynchronousLoop(engine.frameAssemblyDesc->numSlots);

		/**	FIXME:
		 * I'm suspicious of this std::bind return object here. What if us
		 * setting it to null inside of stop() doesn't actually cause the
		 * object to be destroyed? This would cause this contin's sh_ptr's
		 * reference count to never reach 0, causing a memory leak.
		 */
		engine.resetAndAssembleFrame(
			std::bind(&AssembleFrameReq::assembleFrameReq2_2,
				context.get(), context,
				std::placeholders::_1, std::placeholders::_2));

		// Set up timeout timer for CONFIG_STIMBUFF_FRAME_PERIOD_MS/2 ms
		engine.stallTimer.expires_from_now(
			boost::posix_time::milliseconds(
				CONFIG_STIMBUFF_FRAME_PERIOD_MS / 2));
		engine.stallTimer.async_wait(
			std::bind(&AssembleFrameReq::assembleFrameReq2_1,
				context.get(), context,
				std::placeholders::_1));
	}

	void assembleFrameReq2_1(
		std::shared_ptr<AssembleFrameReq> context,
		const boost::system::error_code& error)
	{
		// Check if timer was cancelled (ignore if operation_aborted)
		if (error == boost::asio::error::operation_aborted) { return; }

		// Set timer fired flag
		context->timerFired.store(true);
		context->assembleFrameReq3(context);
	}

	void assembleFrameReq2_2(
		std::shared_ptr<AssembleFrameReq> context,
		void *user_data, int cqe_result)
	{
		(void)user_data;  // Not used - we just track success/failure counts

		// Caller decides success: result >= 0 means success
		bool success = (cqe_result >= 0);
		if (context->loop.incrementSuccessOrFailureAndTestForCompletionDueTo(
			success))
		{
			// Loop is complete, call oracle function
			context->assembleFrameReq3(context);
		}
	}

	void assembleFrameReq3(std::shared_ptr<AssembleFrameReq> context)
	{
		// Ensure we only execute once using atomic exchange
		if (context->handlerExecuted.exchange(true)) { return; }
		// Cancel the timer, stop the engine and process frame, if any.
		context->engine.stop(false);

		/**	EXPLANATION:
		 * Timeout doesn't necessarily mean error.
		 *
		 * If we received zero dgrams from the device, that is indeed an error.
		 * But if we received some dgrams, but not all, that is not an error:
		 * it just means we didn't receive as much data as we would have liked.
		 */

		// Error: no slots succeeded - no data received successfully.
		if (context->loop.nSucceeded.load() == 0)
		{
			context->callOriginalCb(false, context->loop);
			return;
		}

		if (context->loop.nSucceeded.load() >= context->loop.nTotal)
		{
			// Success: all or more slots succeeded
			if (context->loop.nSucceeded.load() > context->loop.nTotal)
			{
				std::cerr << __func__ << ": nSucceeded > nTotal: succ ("
					<< context->loop.nSucceeded.load()
					<< ") > nTotal (" << context->loop.nTotal << ")\n";
			}

			context->callOriginalCb(true, context->loop);
			return;
		}

		if (context->loop.nSucceeded.load() < context->loop.nTotal)
		{
			// Success: some slots succeeded (less than total)
			// Note: dummy fill for un-assembled slots will be implemented later
			context->callOriginalCb(true, context->loop);
			return;
		}

		if (OptionParser::getOptions().verbose)
		{
			std::cerr << __func__ << ": Invalid state: nSucceeded ("
				<< context->loop.nSucceeded.load()
				<< ") < nTotal (" << context->loop.nTotal << ")" << std::endl;
		}

		context->callOriginalCb(false, context->loop);
		return;
	}

public:
	IoUringAssemblyEngine& engine;
	AsynchronousLoop loop;
	std::atomic<bool> timerFired;
	std::atomic<bool> handlerExecuted;
};

void IoUringAssemblyEngine::assembleFrameReq(
	Callback<assembleFrameReqCbFn> cb)
{
	if (!frameAssemblyDesc)
	{
		throw std::runtime_error(std::string(__func__)
			+ ": frameAssemblyDesc is null");
	}

	const auto& caller = smoHooksPtr->ComponentThread_getSelf();
	auto request = std::make_shared<AssembleFrameReq>(
		*this, caller, std::move(cb));

	parent.device->componentThread->getIoService().post(
		STC(std::bind(
			&AssembleFrameReq::assembleFrameReq1_posted,
			request.get(), request)));
}

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; }

	/**	EXPLANATION:
	 * This lock should be held throughout this method to ensure that the
	 * IoUringAssemblyEngine's per-assembly state isn't destroyed while this
	 * handler is running.
	 */
	SpinLock::Guard lock(isAssemblingLock);
	if (!isAssembling) { 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);
		// Get result from the CQE
		int cqe_result = cqe->res;
		// Mark the CQE as seen
		io_uring_cqe_seen(&ring, cqe);

		/**	EXPLANATION:
		 * Call the user-provided callback for this CQE with its user_data and
		 * result.
		 *
		 * 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, cqe_result);
		}
	}

	// Re-arm the eventfd read for next CQE notification
	// Only re-arm if assembly is still active (stop() hasn't been called)
	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