// Copyright Epic Games, Inc. All Rights Reserved.

#include "httpsys.h"

#include "httpshared.h"

#include <zencore/compactbinary.h>
#include <zencore/compactbinarybuilder.h>
#include <zencore/compactbinarypackage.h>
#include <zencore/except.h>
#include <zencore/logging.h>
#include <zencore/scopeguard.h>
#include <zencore/string.h>

#if ZEN_WITH_HTTPSYS

#	include <conio.h>
#	include <mstcpip.h>
#	pragma comment(lib, "httpapi.lib")

std::wstring
UTF8_to_wstring(const char* in)
{
	std::wstring out;
	unsigned int codepoint;

	while (*in != 0)
	{
		unsigned char ch = static_cast<unsigned char>(*in);

		if (ch <= 0x7f)
			codepoint = ch;
		else if (ch <= 0xbf)
			codepoint = (codepoint << 6) | (ch & 0x3f);
		else if (ch <= 0xdf)
			codepoint = ch & 0x1f;
		else if (ch <= 0xef)
			codepoint = ch & 0x0f;
		else
			codepoint = ch & 0x07;

		++in;

		if (((*in & 0xc0) != 0x80) && (codepoint <= 0x10ffff))
		{
			if (sizeof(wchar_t) > 2)
			{
				out.append(1, static_cast<wchar_t>(codepoint));
			}
			else if (codepoint > 0xffff)
			{
				out.append(1, static_cast<wchar_t>(0xd800 + (codepoint >> 10)));
				out.append(1, static_cast<wchar_t>(0xdc00 + (codepoint & 0x03ff)));
			}
			else if (codepoint < 0xd800 || codepoint >= 0xe000)
			{
				out.append(1, static_cast<wchar_t>(codepoint));
			}
		}
	}

	return out;
}

namespace zen {

using namespace std::literals;

class HttpSysServer;
class HttpSysTransaction;
class HttpMessageResponseRequest;

//////////////////////////////////////////////////////////////////////////

HttpVerb
TranslateHttpVerb(HTTP_VERB ReqVerb)
{
	switch (ReqVerb)
	{
		case HttpVerbOPTIONS:
			return HttpVerb::kOptions;

		case HttpVerbGET:
			return HttpVerb::kGet;

		case HttpVerbHEAD:
			return HttpVerb::kHead;

		case HttpVerbPOST:
			return HttpVerb::kPost;

		case HttpVerbPUT:
			return HttpVerb::kPut;

		case HttpVerbDELETE:
			return HttpVerb::kDelete;

		case HttpVerbCOPY:
			return HttpVerb::kCopy;

		default:
			// TODO: invalid request?
			return (HttpVerb)0;
	}
}

uint64_t
GetContentLength(const HTTP_REQUEST* HttpRequest)
{
	const HTTP_KNOWN_HEADER& clh = HttpRequest->Headers.KnownHeaders[HttpHeaderContentLength];
	std::string_view		 cl(clh.pRawValue, clh.RawValueLength);
	uint64_t				 ContentLength = 0;
	std::from_chars(cl.data(), cl.data() + cl.size(), ContentLength);
	return ContentLength;
};

HttpContentType
GetContentType(const HTTP_REQUEST* HttpRequest)
{
	const HTTP_KNOWN_HEADER& CtHdr = HttpRequest->Headers.KnownHeaders[HttpHeaderContentType];
	return ParseContentType({CtHdr.pRawValue, CtHdr.RawValueLength});
};

HttpContentType
GetAcceptType(const HTTP_REQUEST* HttpRequest)
{
	const HTTP_KNOWN_HEADER& CtHdr = HttpRequest->Headers.KnownHeaders[HttpHeaderAccept];
	return ParseContentType({CtHdr.pRawValue, CtHdr.RawValueLength});
};

/**
 * @brief Base class for any pending or active HTTP transactions
 */
class HttpSysRequestHandler
{
public:
	explicit HttpSysRequestHandler(HttpSysTransaction& InRequest) : m_Request(InRequest) {}
	virtual ~HttpSysRequestHandler() = default;

	virtual void				   IssueRequest(std::error_code& ErrorCode)								= 0;
	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) = 0;

	HttpSysTransaction& Transaction() { return m_Request; }

private:
	HttpSysTransaction& m_Request;	// Related HTTP transaction object
};

/**
 * This is the handler for the initial HTTP I/O request which will receive the headers
 * and however much of the remaining payload might fit in the embedded request buffer.
 *
 * It is also used to receive any entity body data relating to the request
 *
 */
struct InitialRequestHandler : public HttpSysRequestHandler
{
	inline HTTP_REQUEST* HttpRequest() { return (HTTP_REQUEST*)m_RequestBuffer; }
	inline uint32_t		 RequestBufferSize() const { return sizeof m_RequestBuffer; }
	inline bool			 IsInitialRequest() const { return m_IsInitialRequest; }

	InitialRequestHandler(HttpSysTransaction& InRequest);
	~InitialRequestHandler();

	virtual void				   IssueRequest(std::error_code& ErrorCode) override final;
	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) override;

	bool	 m_IsInitialRequest		= true;
	uint64_t m_CurrentPayloadOffset = 0;
	uint64_t m_ContentLength		= ~uint64_t(0);
	IoBuffer m_PayloadBuffer;
	UCHAR	 m_RequestBuffer[4096 + sizeof(HTTP_REQUEST)];
};

/**
 * This is the class which request handlers use to interact with the server instance
 */

class HttpSysServerRequest : public HttpServerRequest
{
public:
	HttpSysServerRequest(HttpSysTransaction& Tx, HttpService& Service, IoBuffer PayloadBuffer);
	~HttpSysServerRequest() = default;

	virtual Oid		 ParseSessionId() const override;
	virtual uint32_t ParseRequestId() const override;

	virtual IoBuffer ReadPayload() override;
	virtual void	 WriteResponse(HttpResponseCode ResponseCode) override;
	virtual void	 WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::span<IoBuffer> Blobs) override;
	virtual void	 WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::u8string_view ResponseString) override;

	using HttpServerRequest::WriteResponse;

	HttpSysTransaction&			m_HttpTx;
	HttpMessageResponseRequest* m_Response = nullptr;  // TODO: make this more general
	IoBuffer					m_PayloadBuffer;
};

/** HTTP transaction

	There will be an instance of this per pending and in-flight HTTP transaction

  */
class HttpSysTransaction final
{
public:
	HttpSysTransaction(HttpSysServer& Server);
	virtual ~HttpSysTransaction();

	enum class Status
	{
		kDone,
		kRequestPending
	};

	Status HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred);

	static void __stdcall IoCompletionCallback(PTP_CALLBACK_INSTANCE Instance,
											   PVOID				 pContext /* HttpSysServer */,
											   PVOID				 pOverlapped,
											   ULONG				 IoResult,
											   ULONG_PTR			 NumberOfBytesTransferred,
											   PTP_IO				 Io);

	void				  IssueInitialRequest(std::error_code& ErrorCode);
	PTP_IO				  Iocp();
	HANDLE				  RequestQueueHandle();
	inline OVERLAPPED*	  Overlapped() { return &m_HttpOverlapped; }
	inline HttpSysServer& Server() { return m_HttpServer; }
	inline HTTP_REQUEST*  HttpRequest() { return m_InitialHttpHandler.HttpRequest(); }

	HttpSysServerRequest& InvokeRequestHandler(HttpService& Service, IoBuffer Payload);

private:
	OVERLAPPED	   m_HttpOverlapped{};
	HttpSysServer& m_HttpServer;

	// Tracks which handler is due to handle the next I/O completion event
	HttpSysRequestHandler*				m_CompletionHandler = nullptr;
	RwLock								m_CompletionMutex;
	InitialRequestHandler				m_InitialHttpHandler{*this};
	std::optional<HttpSysServerRequest> m_HandlerRequest;
	Ref<IHttpPackageHandler>			m_PackageHandler;
};

//////////////////////////////////////////////////////////////////////////

/**
 * @brief HTTP request response I/O request handler
 *
 * Asynchronously streams out a response to an HTTP request via compound
 * responses from memory or directly from file
 */

class HttpMessageResponseRequest : public HttpSysRequestHandler
{
public:
	HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode);
	HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode, std::string_view Message);
	HttpMessageResponseRequest(HttpSysTransaction& InRequest,
							   uint16_t			   ResponseCode,
							   HttpContentType	   ContentType,
							   const void*		   Payload,
							   size_t			   PayloadSize);
	HttpMessageResponseRequest(HttpSysTransaction& InRequest,
							   uint16_t			   ResponseCode,
							   HttpContentType	   ContentType,
							   std::span<IoBuffer> Blobs);
	~HttpMessageResponseRequest();

	virtual void				   IssueRequest(std::error_code& ErrorCode) override final;
	virtual HttpSysRequestHandler* HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred) override;
	void						   SuppressResponseBody();	// typically used for HEAD requests

private:
	std::vector<HTTP_DATA_CHUNK> m_HttpDataChunks;
	uint64_t					 m_TotalDataSize	   = 0;	 // Sum of all chunk sizes
	uint16_t					 m_ResponseCode		   = 0;
	uint32_t					 m_NextDataChunkOffset = 0;	 // Cursor used for very large chunk lists
	uint32_t					 m_RemainingChunkCount = 0;	 // Backlog for multi-call sends
	bool						 m_IsInitialResponse   = true;
	HttpContentType				 m_ContentType		   = HttpContentType::kBinary;
	std::vector<IoBuffer>		 m_DataBuffers;

	void InitializeForPayload(uint16_t ResponseCode, std::span<IoBuffer> Blobs);
};

HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode)
: HttpSysRequestHandler(InRequest)
{
	std::array<IoBuffer, 0> EmptyBufferList;

	InitializeForPayload(ResponseCode, EmptyBufferList);
}

HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest, uint16_t ResponseCode, std::string_view Message)
: HttpSysRequestHandler(InRequest)
, m_ContentType(HttpContentType::kText)
{
	IoBuffer				MessageBuffer(IoBuffer::Wrap, Message.data(), Message.size());
	std::array<IoBuffer, 1> SingleBufferList({MessageBuffer});

	InitializeForPayload(ResponseCode, SingleBufferList);
}

HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest,
													   uint16_t			   ResponseCode,
													   HttpContentType	   ContentType,
													   const void*		   Payload,
													   size_t			   PayloadSize)
: HttpSysRequestHandler(InRequest)
, m_ContentType(ContentType)
{
	IoBuffer				MessageBuffer(IoBuffer::Wrap, Payload, PayloadSize);
	std::array<IoBuffer, 1> SingleBufferList({MessageBuffer});

	InitializeForPayload(ResponseCode, SingleBufferList);
}

HttpMessageResponseRequest::HttpMessageResponseRequest(HttpSysTransaction& InRequest,
													   uint16_t			   ResponseCode,
													   HttpContentType	   ContentType,
													   std::span<IoBuffer> BlobList)
: HttpSysRequestHandler(InRequest)
, m_ContentType(ContentType)
{
	InitializeForPayload(ResponseCode, BlobList);
}

HttpMessageResponseRequest::~HttpMessageResponseRequest()
{
}

void
HttpMessageResponseRequest::InitializeForPayload(uint16_t ResponseCode, std::span<IoBuffer> BlobList)
{
	m_ResponseCode = ResponseCode;

	const uint32_t ChunkCount = gsl::narrow<uint32_t>(BlobList.size());

	m_HttpDataChunks.reserve(ChunkCount);
	m_DataBuffers.reserve(ChunkCount);

	for (IoBuffer& Buffer : BlobList)
	{
		m_DataBuffers.emplace_back(std::move(Buffer)).MakeOwned();
	}

	// Initialize the full array up front

	uint64_t LocalDataSize = 0;

	for (IoBuffer& Buffer : m_DataBuffers)
	{
		uint64_t BufferDataSize = Buffer.Size();

		ZEN_ASSERT(BufferDataSize);

		LocalDataSize += BufferDataSize;

		IoBufferFileReference FileRef;
		if (Buffer.GetFileReference(/* out */ FileRef))
		{
			// Use direct file transfer

			m_HttpDataChunks.push_back({});
			auto& Chunk = m_HttpDataChunks.back();

			Chunk.DataChunkType									   = HttpDataChunkFromFileHandle;
			Chunk.FromFileHandle.FileHandle						   = FileRef.FileHandle;
			Chunk.FromFileHandle.ByteRange.StartingOffset.QuadPart = FileRef.FileChunkOffset;
			Chunk.FromFileHandle.ByteRange.Length.QuadPart		   = BufferDataSize;
		}
		else
		{
			// Send from memory, need to make sure we chunk the buffer up since
			// the underlying data structure only accepts 32-bit chunk sizes for
			// memory chunks. When this happens the vector will be reallocated,
			// which is fine since this will be a pretty rare case and sending
			// the data is going to take a lot longer than a memory allocation :)

			const uint8_t* WriteCursor = reinterpret_cast<const uint8_t*>(Buffer.Data());

			while (BufferDataSize)
			{
				const ULONG ThisChunkSize = gsl::narrow<ULONG>(zen::Min(1 * 1024 * 1024 * 1024, BufferDataSize));

				m_HttpDataChunks.push_back({});
				auto& Chunk = m_HttpDataChunks.back();

				Chunk.DataChunkType			  = HttpDataChunkFromMemory;
				Chunk.FromMemory.pBuffer	  = (void*)WriteCursor;
				Chunk.FromMemory.BufferLength = ThisChunkSize;

				BufferDataSize -= ThisChunkSize;
				WriteCursor += ThisChunkSize;
			}
		}
	}

	m_RemainingChunkCount = gsl::narrow<uint32_t>(m_HttpDataChunks.size());
	m_TotalDataSize		  = LocalDataSize;
}

void
HttpMessageResponseRequest::SuppressResponseBody()
{
	m_RemainingChunkCount = 0;
	m_HttpDataChunks.clear();
	m_DataBuffers.clear();
}

HttpSysRequestHandler*
HttpMessageResponseRequest::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
{
	ZEN_UNUSED(NumberOfBytesTransferred);

	if (IoResult)
	{
		ZEN_WARN("response aborted due to error: '{}'", GetErrorAsString(IoResult));

		// if one transmit failed there's really no need to go on
		return nullptr;
	}

	if (m_RemainingChunkCount == 0)
	{
		return nullptr;	 // All done
	}

	return this;
}

void
HttpMessageResponseRequest::IssueRequest(std::error_code& ErrorCode)
{
	HttpSysTransaction& Tx		= Transaction();
	HTTP_REQUEST* const HttpReq = Tx.HttpRequest();
	PTP_IO const		Iocp	= Tx.Iocp();

	StartThreadpoolIo(Iocp);

	// Split payload into batches to play well with the underlying API

	const int MaxChunksPerCall = 9999;

	const int ThisRequestChunkCount	 = std::min<int>(m_RemainingChunkCount, MaxChunksPerCall);
	const int ThisRequestChunkOffset = m_NextDataChunkOffset;

	m_RemainingChunkCount -= ThisRequestChunkCount;
	m_NextDataChunkOffset += ThisRequestChunkCount;

	/* Should this code also use HTTP_SEND_RESPONSE_FLAG_BUFFER_DATA?

		From the docs:

		This flag enables buffering of data in the kernel on a per-response basis. It should
		be used by an application doing synchronous I/O, or by a an application doing
		asynchronous I/O with no more than one send outstanding at a time.

		Applications using asynchronous I/O which may have more than one send outstanding at
		a time should not use this flag.

		When this flag is set, it should be used consistently in calls to the
		HttpSendHttpResponse function as well.
	 */

	ULONG SendFlags = 0;

	if (m_RemainingChunkCount)
	{
		// We need to make more calls to send the full amount of data
		SendFlags |= HTTP_SEND_RESPONSE_FLAG_MORE_DATA;
	}

	ULONG SendResult = 0;

	if (m_IsInitialResponse)
	{
		// Populate response structure

		HTTP_RESPONSE HttpResponse = {};

		HttpResponse.EntityChunkCount = USHORT(ThisRequestChunkCount);
		HttpResponse.pEntityChunks	  = m_HttpDataChunks.data() + ThisRequestChunkOffset;

		// Content-length header

		char ContentLengthString[32];
		_ui64toa_s(m_TotalDataSize, ContentLengthString, sizeof ContentLengthString, 10);

		PHTTP_KNOWN_HEADER ContentLengthHeader = &HttpResponse.Headers.KnownHeaders[HttpHeaderContentLength];
		ContentLengthHeader->pRawValue		   = ContentLengthString;
		ContentLengthHeader->RawValueLength	   = (USHORT)strlen(ContentLengthString);

		// Content-type header

		PHTTP_KNOWN_HEADER ContentTypeHeader = &HttpResponse.Headers.KnownHeaders[HttpHeaderContentType];

		std::string_view ContentTypeString = MapContentTypeToString(m_ContentType);

		ContentTypeHeader->pRawValue	  = ContentTypeString.data();
		ContentTypeHeader->RawValueLength = (USHORT)ContentTypeString.size();

		HttpResponse.StatusCode	  = m_ResponseCode;
		HttpResponse.pReason	  = ReasonStringForHttpResultCode(m_ResponseCode);
		HttpResponse.ReasonLength = (USHORT)strlen(HttpResponse.pReason);

		// Cache policy

		HTTP_CACHE_POLICY CachePolicy;

		CachePolicy.Policy		  = HttpCachePolicyNocache;	 //  HttpCachePolicyUserInvalidates;
		CachePolicy.SecondsToLive = 0;

		// Initial response API call

		SendResult = HttpSendHttpResponse(Tx.RequestQueueHandle(),
										  HttpReq->RequestId,
										  SendFlags,
										  &HttpResponse,
										  &CachePolicy,
										  NULL,
										  NULL,
										  0,
										  Tx.Overlapped(),
										  NULL);

		m_IsInitialResponse = false;
	}
	else
	{
		// Subsequent response API calls

		SendResult = HttpSendResponseEntityBody(Tx.RequestQueueHandle(),
												HttpReq->RequestId,
												SendFlags,
												(USHORT)ThisRequestChunkCount,				// EntityChunkCount
												&m_HttpDataChunks[ThisRequestChunkOffset],	// EntityChunks
												NULL,										// BytesSent
												NULL,										// Reserved1
												0,											// Reserved2
												Tx.Overlapped(),							// Overlapped
												NULL										// LogData
		);
	}

	if ((SendResult != NO_ERROR)			 // Synchronous completion, but the completion event will still be posted to IOCP
		&& (SendResult != ERROR_IO_PENDING)	 // Asynchronous completion
	)
	{
		// Some error occurred, no completion will be posted

		CancelThreadpoolIo(Iocp);

		ZEN_ERROR("failed to send HTTP response (error: '{}'), request URL: {}"sv, SendResult, HttpReq->pRawUrl);

		ErrorCode = MakeWin32ErrorCode(SendResult);
	}
	else
	{
		ErrorCode = {};
	}
}

/**
			  _________
			 /   _____/ ______________  __ ___________
			 \_____  \_/ __ \_  __ \  \/ // __ \_  __ \
			 /        \  ___/|  | \/\   /\  ___/|  | \/
			/_______  /\___  >__|    \_/  \___  >__|
					\/     \/                 \/
*/

HttpSysServer::HttpSysServer(unsigned int ThreadCount) : m_ThreadPool(ThreadCount)
{
	ULONG Result = HttpInitialize(HTTPAPI_VERSION_2, HTTP_INITIALIZE_SERVER, nullptr);

	if (Result != NO_ERROR)
	{
		return;
	}

	m_IsHttpInitialized = true;
	m_IsOk				= true;
}

HttpSysServer::~HttpSysServer()
{
	if (m_IsHttpInitialized)
	{
		Cleanup();

		HttpTerminate(HTTP_INITIALIZE_SERVER, nullptr);
	}
}

void
HttpSysServer::Initialize(const wchar_t* UrlPath)
{
	m_IsOk = false;

	ULONG Result = HttpCreateServerSession(HTTPAPI_VERSION_2, &m_HttpSessionId, 0);

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("Failed to create server session for '{}': {x}"sv, WideToUtf8(UrlPath), Result);

		return;
	}

	Result = HttpCreateUrlGroup(m_HttpSessionId, &m_HttpUrlGroupId, 0);

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("Failed to create URL group for '{}': {x}"sv, WideToUtf8(UrlPath), Result);

		return;
	}

	m_BaseUri = UrlPath;

	Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, UrlPath, HTTP_URL_CONTEXT(0), 0);

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("Failed to add base URL to URL group for '{}': {x}"sv, WideToUtf8(UrlPath), Result);

		return;
	}

	HTTP_BINDING_INFO HttpBindingInfo = {{0}, 0};

	Result = HttpCreateRequestQueue(HTTPAPI_VERSION_2,
									/* Name */ nullptr,
									/* SecurityAttributes */ nullptr,
									/* Flags */ 0,
									&m_RequestQueueHandle);

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("Failed to create request queue for '{}': {x}"sv, WideToUtf8(UrlPath), Result);

		return;
	}

	HttpBindingInfo.Flags.Present	   = 1;
	HttpBindingInfo.RequestQueueHandle = m_RequestQueueHandle;

	Result = HttpSetUrlGroupProperty(m_HttpUrlGroupId, HttpServerBindingProperty, &HttpBindingInfo, sizeof(HttpBindingInfo));

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("Failed to set server binding property for '{}': {x}"sv, WideToUtf8(UrlPath), Result);

		return;
	}

	// Create I/O completion port

	std::error_code ErrorCode;
	m_ThreadPool.CreateIocp(m_RequestQueueHandle, HttpSysTransaction::IoCompletionCallback, /* Context */ this, /* out */ ErrorCode);

	if (ErrorCode)
	{
		ZEN_ERROR("Failed to create IOCP for '{}': {}"sv, WideToUtf8(UrlPath), ErrorCode.message());
	}
	else
	{
		m_IsOk = true;
	}
}

void
HttpSysServer::Cleanup()
{
	++m_IsShuttingDown;

	if (m_RequestQueueHandle)
	{
		HttpCloseRequestQueue(m_RequestQueueHandle);
		m_RequestQueueHandle = nullptr;
	}

	if (m_HttpUrlGroupId)
	{
		HttpCloseUrlGroup(m_HttpUrlGroupId);
		m_HttpUrlGroupId = 0;
	}

	if (m_HttpSessionId)
	{
		HttpCloseServerSession(m_HttpSessionId);
		m_HttpSessionId = 0;
	}
}

void
HttpSysServer::StartServer()
{
	const int InitialRequestCount = 32;

	for (int i = 0; i < InitialRequestCount; ++i)
	{
		IssueNewRequestMaybe();
	}
}

void
HttpSysServer::Run(bool TestMode)
{
	if (TestMode == false)
	{
		zen::logging::ConsoleLog().info("Zen Server running. Press ESC or Q to quit");
	}

	do
	{
		int WaitTimeout = -1;

		if (!TestMode)
		{
			WaitTimeout = 1000;
		}

		if (!TestMode && _kbhit() != 0)
		{
			char c = (char)_getch();

			if (c == 27 || c == 'Q' || c == 'q')
			{
				RequestApplicationExit(0);
			}
		}

		m_ShutdownEvent.Wait(WaitTimeout);
	} while (!IsApplicationExitRequested());
}

void
HttpSysServer::OnHandlingRequest()
{
	if (--m_PendingRequests > m_MinPendingRequests)
	{
		// We have more than the minimum number of requests pending, just let someone else
		// enqueue new requests
		return;
	}

	IssueNewRequestMaybe();
}

void
HttpSysServer::IssueNewRequestMaybe()
{
	if (m_IsShuttingDown.load(std::memory_order::acquire))
	{
		return;
	}

	if (m_PendingRequests.load(std::memory_order::relaxed) >= m_MaxPendingRequests)
	{
		return;
	}

	std::unique_ptr<HttpSysTransaction> Request = std::make_unique<HttpSysTransaction>(*this);

	std::error_code ErrorCode;
	Request->IssueInitialRequest(ErrorCode);

	if (ErrorCode)
	{
		// No request was actually issued. What is the appropriate response?

		return;
	}

	// This may end up exceeding the MaxPendingRequests limit, but it's not
	// really a problem. I'm doing it this way mostly to avoid dealing with
	// exceptions here
	++m_PendingRequests;

	Request.release();
}

void
HttpSysServer::RegisterService(const char* UrlPath, HttpService& Service)
{
	if (UrlPath[0] == '/')
	{
		++UrlPath;
	}

	const std::wstring Path16 = UTF8_to_wstring(UrlPath);
	Service.SetUriPrefixLength(Path16.size() + 1 /* leading slash */);

	// Convert to wide string

	std::wstring Url16 = m_BaseUri + Path16;

	ULONG Result = HttpAddUrlToUrlGroup(m_HttpUrlGroupId, Url16.c_str(), HTTP_URL_CONTEXT(&Service), 0 /* Reserved */);

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("HttpAddUrlToUrlGroup failed with result {}"sv, Result);

		return;
	}
}

void
HttpSysServer::UnregisterService(const char* UrlPath, HttpService& Service)
{
	ZEN_UNUSED(Service);

	if (UrlPath[0] == '/')
	{
		++UrlPath;
	}

	const std::wstring Path16 = UTF8_to_wstring(UrlPath);

	// Convert to wide string

	std::wstring Url16 = m_BaseUri + Path16;

	ULONG Result = HttpRemoveUrlFromUrlGroup(m_HttpUrlGroupId, Url16.c_str(), 0);

	if (Result != NO_ERROR)
	{
		ZEN_ERROR("HttpRemoveUrlFromUrlGroup failed with result {}"sv, Result);
	}
}

//////////////////////////////////////////////////////////////////////////

HttpSysTransaction::HttpSysTransaction(HttpSysServer& Server) : m_HttpServer(Server), m_CompletionHandler(&m_InitialHttpHandler)
{
}

HttpSysTransaction::~HttpSysTransaction()
{
}

PTP_IO
HttpSysTransaction::Iocp()
{
	return m_HttpServer.m_ThreadPool.Iocp();
}

HANDLE
HttpSysTransaction::RequestQueueHandle()
{
	return m_HttpServer.m_RequestQueueHandle;
}

void
HttpSysTransaction::IssueInitialRequest(std::error_code& ErrorCode)
{
	m_InitialHttpHandler.IssueRequest(ErrorCode);
}

void
HttpSysTransaction::IoCompletionCallback(PTP_CALLBACK_INSTANCE Instance,
										 PVOID				   pContext /* HttpSysServer */,
										 PVOID				   pOverlapped,
										 ULONG				   IoResult,
										 ULONG_PTR			   NumberOfBytesTransferred,
										 PTP_IO				   Io)
{
	UNREFERENCED_PARAMETER(Io);
	UNREFERENCED_PARAMETER(Instance);
	UNREFERENCED_PARAMETER(pContext);

	// Note that for a given transaction we may be in this completion function on more
	// than one thread at any given moment. This means we need to be careful about what
	// happens in here

	HttpSysTransaction* Transaction = CONTAINING_RECORD(pOverlapped, HttpSysTransaction, m_HttpOverlapped);

	if (Transaction->HandleCompletion(IoResult, NumberOfBytesTransferred) == HttpSysTransaction::Status::kDone)
	{
		delete Transaction;
	}
}

HttpSysTransaction::Status
HttpSysTransaction::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
{
	// We use this to ensure sequential execution of completion handlers
	// for any given transaction. It also ensures all member variables are
	// in a consistent state for the current thread

	RwLock::ExclusiveLockScope _(m_CompletionMutex);

	bool IsRequestPending = false;

	if (HttpSysRequestHandler* CurrentHandler = m_CompletionHandler)
	{
		const bool IsInitialRequest = (CurrentHandler == &m_InitialHttpHandler) && m_InitialHttpHandler.IsInitialRequest();

		if (IsInitialRequest)
		{
			// Ensure we have a sufficient number of pending requests outstanding
			m_HttpServer.OnHandlingRequest();
		}

		m_CompletionHandler = CurrentHandler->HandleCompletion(IoResult, NumberOfBytesTransferred);

		if (m_CompletionHandler)
		{
			try
			{
				std::error_code ErrorCode;
				m_CompletionHandler->IssueRequest(ErrorCode);

				if (ErrorCode)
				{
					ZEN_ERROR("IssueRequest() failed {}"sv, ErrorCode.message());
				}
				else
				{
					IsRequestPending = true;
				}
			}
			catch (std::exception& Ex)
			{
				ZEN_ERROR("exception caught from IssueRequest(): {}"sv, Ex.what());

				// something went wrong, no request is pending
			}
		}
		else
		{
			if (IsInitialRequest == false)
			{
				delete CurrentHandler;
			}
		}
	}

	// Ensure new requests are enqueued as necessary
	m_HttpServer.IssueNewRequestMaybe();

	if (IsRequestPending)
	{
		// There is another request pending on this transaction, so it needs to remain valid
		return Status::kRequestPending;
	}

	// Transaction done, caller should clean up (delete) this instance
	return Status::kDone;
}

HttpSysServerRequest&
HttpSysTransaction::InvokeRequestHandler(HttpService& Service, IoBuffer Payload)
{
	HttpSysServerRequest& ThisRequest = m_HandlerRequest.emplace(*this, Service, Payload);

	if (ThisRequest.RequestVerb() == HttpVerb::kPost)
	{
		if (ThisRequest.RequestContentType() == HttpContentType::kCbPackageOffer)
		{
			// The client is presenting us with a package attachments offer, we need
			// to filter it down to the list of attachments we need them to send in
			// the follow-up request

			m_PackageHandler = Service.HandlePackageRequest(ThisRequest);

			if (m_PackageHandler)
			{
				CbObject OfferMessage = LoadCompactBinaryObject(Payload);

				std::vector<IoHash> OfferCids;

				for (auto& CidEntry : OfferMessage["offer"])
				{
					if (!CidEntry.IsHash())
					{
						// Should yield bad request response?

						continue;
					}

					OfferCids.push_back(CidEntry.AsHash(IoHash::Zero));
				}

				m_PackageHandler->FilterOffer(OfferCids);

				CbObjectWriter ResponseWriter;
				ResponseWriter.BeginArray("need");

				for (const IoHash& Cid : OfferCids)
				{
					ResponseWriter.AddHash(Cid);
				}

				ResponseWriter.EndArray();

				// Emit filter response
				ThisRequest.WriteResponse(HttpResponseCode::OK, ResponseWriter.Save());

				return ThisRequest;
			}
		}
		else if (ThisRequest.RequestContentType() == HttpContentType::kCbPackage)
		{
			// Process chunks in package request

			m_PackageHandler = Service.HandlePackageRequest(ThisRequest);

			// TODO: this should really be done in a streaming fashion, currently this emulates
			// the intended flow from an API perspective

			if (m_PackageHandler)
			{
				m_PackageHandler->OnRequestBegin();

				auto CreateBuffer = [&](const IoHash& Cid, uint64_t Size) -> IoBuffer { return m_PackageHandler->CreateTarget(Cid, Size); };

				CbPackage Package = ParsePackageMessage(ThisRequest.ReadPayload(), CreateBuffer);

				m_PackageHandler->OnRequestComplete();
			}
		}
	}

	// Default request handling

	Service.HandleRequest(ThisRequest);

	return ThisRequest;
}

//////////////////////////////////////////////////////////////////////////

HttpSysServerRequest::HttpSysServerRequest(HttpSysTransaction& Tx, HttpService& Service, IoBuffer PayloadBuffer)
: m_HttpTx(Tx)
, m_PayloadBuffer(std::move(PayloadBuffer))
{
	const HTTP_REQUEST* HttpRequestPtr = Tx.HttpRequest();

	const int PrefixLength	= Service.UriPrefixLength();
	const int AbsPathLength = HttpRequestPtr->CookedUrl.AbsPathLength / sizeof(char16_t);

	if (AbsPathLength >= PrefixLength)
	{
		// We convert the URI immediately because most of the code involved prefers to deal
		// with utf8. This has some performance impact which I'd prefer to avoid but for now
		// we just have to live with it

		WideToUtf8({(char16_t*)HttpRequestPtr->CookedUrl.pAbsPath + PrefixLength, gsl::narrow<size_t>(AbsPathLength - PrefixLength)},
				   m_UriUtf8);
	}
	else
	{
		m_UriUtf8.Reset();
	}

	if (auto QueryStringLength = HttpRequestPtr->CookedUrl.QueryStringLength)
	{
		--QueryStringLength;

		WideToUtf8({(char16_t*)(HttpRequestPtr->CookedUrl.pQueryString) + 1, QueryStringLength / sizeof(char16_t)}, m_QueryStringUtf8);
	}
	else
	{
		m_QueryStringUtf8.Reset();
	}

	m_Verb			= TranslateHttpVerb(HttpRequestPtr->Verb);
	m_ContentLength = GetContentLength(HttpRequestPtr);
	m_ContentType	= GetContentType(HttpRequestPtr);
	m_AcceptType	= GetAcceptType(HttpRequestPtr);
}

Oid
HttpSysServerRequest::ParseSessionId() const
{
	const HTTP_REQUEST* HttpRequestPtr = m_HttpTx.HttpRequest();

	for (int i = 0; i < HttpRequestPtr->Headers.UnknownHeaderCount; ++i)
	{
		HTTP_UNKNOWN_HEADER& Header = HttpRequestPtr->Headers.pUnknownHeaders[i];
		std::string_view	 HeaderName{Header.pName, Header.NameLength};

		if (HeaderName == "UE-Session"sv)
		{
			if (Header.RawValueLength == Oid::StringLength)
			{
				return Oid::FromHexString({Header.pRawValue, Header.RawValueLength});
			}
		}
	}

	return {};
}

uint32_t
HttpSysServerRequest::ParseRequestId() const
{
	const HTTP_REQUEST* HttpRequestPtr = m_HttpTx.HttpRequest();

	for (int i = 0; i < HttpRequestPtr->Headers.UnknownHeaderCount; ++i)
	{
		HTTP_UNKNOWN_HEADER& Header = HttpRequestPtr->Headers.pUnknownHeaders[i];
		std::string_view	 HeaderName{Header.pName, Header.NameLength};

		if (HeaderName == "UE-Request"sv)
		{
			std::string_view RequestValue{Header.pRawValue, Header.RawValueLength};
			uint32_t		 RequestId = 0;
			std::from_chars(RequestValue.data(), RequestValue.data() + RequestValue.size(), RequestId);
			return RequestId;
		}
	}

	return 0;
}

IoBuffer
HttpSysServerRequest::ReadPayload()
{
	return m_PayloadBuffer;
}

void
HttpSysServerRequest::WriteResponse(HttpResponseCode ResponseCode)
{
	ZEN_ASSERT(IsHandled() == false);

	m_Response = new HttpMessageResponseRequest(m_HttpTx, (uint16_t)ResponseCode);

	if (SuppressBody())
	{
		m_Response->SuppressResponseBody();
	}

	SetIsHandled();
}

void
HttpSysServerRequest::WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::span<IoBuffer> Blobs)
{
	ZEN_ASSERT(IsHandled() == false);

	m_Response = new HttpMessageResponseRequest(m_HttpTx, (uint16_t)ResponseCode, ContentType, Blobs);

	if (SuppressBody())
	{
		m_Response->SuppressResponseBody();
	}

	SetIsHandled();
}

void
HttpSysServerRequest::WriteResponse(HttpResponseCode ResponseCode, HttpContentType ContentType, std::u8string_view ResponseString)
{
	ZEN_ASSERT(IsHandled() == false);

	m_Response =
		new HttpMessageResponseRequest(m_HttpTx, (uint16_t)ResponseCode, ContentType, ResponseString.data(), ResponseString.size());

	if (SuppressBody())
	{
		m_Response->SuppressResponseBody();
	}

	SetIsHandled();
}

//////////////////////////////////////////////////////////////////////////

InitialRequestHandler::InitialRequestHandler(HttpSysTransaction& InRequest) : HttpSysRequestHandler(InRequest)
{
}

InitialRequestHandler::~InitialRequestHandler()
{
}

void
InitialRequestHandler::IssueRequest(std::error_code& ErrorCode)
{
	HttpSysTransaction& Tx		= Transaction();
	PTP_IO				Iocp	= Tx.Iocp();
	HTTP_REQUEST*		HttpReq = Tx.HttpRequest();

	StartThreadpoolIo(Iocp);

	ULONG HttpApiResult;

	if (IsInitialRequest())
	{
		HttpApiResult = HttpReceiveHttpRequest(Tx.RequestQueueHandle(),
											   HTTP_NULL_ID,
											   HTTP_RECEIVE_REQUEST_FLAG_COPY_BODY,
											   HttpReq,
											   RequestBufferSize(),
											   NULL,
											   Tx.Overlapped());
	}
	else
	{
		// The http.sys team recommends limiting the size to 128KB
		static const uint64_t kMaxBytesPerApiCall = 128 * 1024;

		uint64_t	   BytesToRead		   = m_ContentLength - m_CurrentPayloadOffset;
		const uint64_t BytesToReadThisCall = zen::Min(BytesToRead, kMaxBytesPerApiCall);
		void*		   BufferWriteCursor   = reinterpret_cast<uint8_t*>(m_PayloadBuffer.MutableData()) + m_CurrentPayloadOffset;

		HttpApiResult = HttpReceiveRequestEntityBody(Tx.RequestQueueHandle(),
													 HttpReq->RequestId,
													 0, /* Flags */
													 BufferWriteCursor,
													 gsl::narrow<ULONG>(BytesToReadThisCall),
													 nullptr,  // BytesReturned
													 Tx.Overlapped());
	}

	if (HttpApiResult != ERROR_IO_PENDING && HttpApiResult != NO_ERROR)
	{
		CancelThreadpoolIo(Iocp);

		if (HttpApiResult == ERROR_MORE_DATA)
		{
			// ProcessReceiveAndPostResponse(pIoRequest, pServerContext->Io, ERROR_MORE_DATA);
		}

		// CleanupHttpIoRequest(pIoRequest);

		ErrorCode = MakeWin32ErrorCode(HttpApiResult);

		ZEN_ERROR("HttpReceiveHttpRequest failed, error {}", ErrorCode.message());

		return;
	}

	ErrorCode = std::error_code();
}

HttpSysRequestHandler*
InitialRequestHandler::HandleCompletion(ULONG IoResult, ULONG_PTR NumberOfBytesTransferred)
{
	auto _ = MakeGuard([&] { m_IsInitialRequest = false; });

	switch (IoResult)
	{
		case ERROR_OPERATION_ABORTED:
			return nullptr;

		case ERROR_MORE_DATA:
			// Insufficient buffer space
			break;
	}

	// Route requests

	try
	{
		HTTP_REQUEST* HttpReq = HttpRequest();

#	if 0
		for (int i = 0; i < HttpReq->RequestInfoCount; ++i)
		{
			auto& ReqInfo = HttpReq->pRequestInfo[i];

			switch (ReqInfo.InfoType)
			{
				case HttpRequestInfoTypeRequestTiming:
					{
						const HTTP_REQUEST_TIMING_INFO* TimingInfo = reinterpret_cast<HTTP_REQUEST_TIMING_INFO*>(ReqInfo.pInfo);

						ZEN_INFO("");
					}
					break;
				case HttpRequestInfoTypeAuth:
					ZEN_INFO("");
					break;
				case HttpRequestInfoTypeChannelBind:
					ZEN_INFO("");
					break;
				case HttpRequestInfoTypeSslProtocol:
					ZEN_INFO("");
					break;
				case HttpRequestInfoTypeSslTokenBindingDraft:
					ZEN_INFO("");
					break;
				case HttpRequestInfoTypeSslTokenBinding:
					ZEN_INFO("");
					break;
				case HttpRequestInfoTypeTcpInfoV0:
					{
						const TCP_INFO_v0* TcpInfo = reinterpret_cast<const TCP_INFO_v0*>(ReqInfo.pInfo);

						ZEN_INFO("");
					}
					break;
				case HttpRequestInfoTypeRequestSizing:
					{
						const HTTP_REQUEST_SIZING_INFO* SizingInfo = reinterpret_cast<const HTTP_REQUEST_SIZING_INFO*>(ReqInfo.pInfo);
						ZEN_INFO("");
					}
					break;
				case HttpRequestInfoTypeQuicStats:
					ZEN_INFO("");
					break;
				case HttpRequestInfoTypeTcpInfoV1:
					{
						const TCP_INFO_v1* TcpInfo = reinterpret_cast<const TCP_INFO_v1*>(ReqInfo.pInfo);

						ZEN_INFO("");
					}
					break;
			}
		}
#	endif

		if (HttpService* Service = reinterpret_cast<HttpService*>(HttpReq->UrlContext))
		{
			if (m_IsInitialRequest)
			{
				m_ContentLength					  = GetContentLength(HttpReq);
				const HttpContentType ContentType = GetContentType(HttpReq);

				if (m_ContentLength)
				{
					// Handle initial chunk read by copying any payload which has already been copied
					// into our embedded request buffer

					m_PayloadBuffer = IoBuffer(m_ContentLength);
					m_PayloadBuffer.SetContentType(ContentType);

					uint64_t	   BytesToRead		 = m_ContentLength;
					uint8_t* const BufferBase		 = reinterpret_cast<uint8_t*>(m_PayloadBuffer.MutableData());
					uint8_t*	   BufferWriteCursor = BufferBase;

					const int EntityChunkCount = HttpReq->EntityChunkCount;

					for (int i = 0; i < EntityChunkCount; ++i)
					{
						HTTP_DATA_CHUNK& EntityChunk = HttpReq->pEntityChunks[i];

						ZEN_ASSERT(EntityChunk.DataChunkType == HttpDataChunkFromMemory);

						const uint64_t BufferLength = EntityChunk.FromMemory.BufferLength;

						ZEN_ASSERT(BufferLength <= BytesToRead);

						memcpy(BufferWriteCursor, EntityChunk.FromMemory.pBuffer, BufferLength);

						BufferWriteCursor += BufferLength;
						BytesToRead -= BufferLength;
					}

					m_CurrentPayloadOffset = BufferWriteCursor - BufferBase;
				}
			}
			else
			{
				m_CurrentPayloadOffset += NumberOfBytesTransferred;
			}

			if (m_CurrentPayloadOffset == m_ContentLength)
			{
				m_PayloadBuffer.MakeImmutable();

				// Body received completely - call request handler

				HttpSysServerRequest& ThisRequest = Transaction().InvokeRequestHandler(*Service, m_PayloadBuffer);

				if (!ThisRequest.IsHandled())
				{
					return new HttpMessageResponseRequest(Transaction(), 404, "Not found"sv);
				}

				if (HttpMessageResponseRequest* Response = ThisRequest.m_Response)
				{
					return Response;
				}
			}
			else
			{
				// Issue a read request for more body data
				return this;
			}
		}

		// Unable to route
		return new HttpMessageResponseRequest(Transaction(), 404, "No suitable route found"sv);
	}
	catch (std::exception& ex)
	{
		// TODO provide more meaningful error output

		return new HttpMessageResponseRequest(Transaction(), 500, ex.what());
	}
}

//////////////////////////////////////////////////////////////////////////
//
// HttpServer interface implementation
//

void
HttpSysServer::Initialize(int BasePort)
{
	using namespace std::literals;

	WideStringBuilder<64> BaseUri;
	BaseUri << u8"http://*:"sv << int64_t(BasePort) << u8"/"sv;

	Initialize(BaseUri.c_str());
	StartServer();
}

void
HttpSysServer::RequestExit()
{
	m_ShutdownEvent.Set();
}
void
HttpSysServer::RegisterService(HttpService& Service)
{
	RegisterService(Service.BaseUri(), Service);
}

}  // namespace zen
#endif