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

#pragma once

// Shared helpers for curl-based HTTP client implementations (sync and async).
// This is an internal header, not part of the public API.

#include <zencore/string.h>

#include <zenhttp/httpclient.h>

ZEN_THIRD_PARTY_INCLUDES_START
#include <curl/curl.h>
ZEN_THIRD_PARTY_INCLUDES_END

#include <optional>
#include <string>
#include <utility>
#include <vector>

namespace zen {

//////////////////////////////////////////////////////////////////////////
//
// Error mapping

inline HttpClientErrorCode
MapCurlError(CURLcode Code)
{
	switch (Code)
	{
		case CURLE_OK:
			return HttpClientErrorCode::kOK;
		case CURLE_COULDNT_CONNECT:
			return HttpClientErrorCode::kConnectionFailure;
		case CURLE_COULDNT_RESOLVE_HOST:
			return HttpClientErrorCode::kHostResolutionFailure;
		case CURLE_COULDNT_RESOLVE_PROXY:
			return HttpClientErrorCode::kProxyResolutionFailure;
		case CURLE_RECV_ERROR:
			return HttpClientErrorCode::kNetworkReceiveError;
		case CURLE_SEND_ERROR:
			return HttpClientErrorCode::kNetworkSendFailure;
		case CURLE_OPERATION_TIMEDOUT:
			return HttpClientErrorCode::kOperationTimedOut;
		case CURLE_SSL_CONNECT_ERROR:
			return HttpClientErrorCode::kSSLConnectError;
		case CURLE_SSL_CERTPROBLEM:
			return HttpClientErrorCode::kSSLCertificateError;
		case CURLE_PEER_FAILED_VERIFICATION:
			return HttpClientErrorCode::kSSLCACertError;
		case CURLE_SSL_CIPHER:
		case CURLE_SSL_ENGINE_NOTFOUND:
		case CURLE_SSL_ENGINE_SETFAILED:
			return HttpClientErrorCode::kGenericSSLError;
		case CURLE_ABORTED_BY_CALLBACK:
			return HttpClientErrorCode::kRequestCancelled;
		default:
			return HttpClientErrorCode::kOtherError;
	}
}

//////////////////////////////////////////////////////////////////////////
//
// Curl callback data structures and callbacks

struct CurlWriteCallbackData
{
	std::string*		   Body					= nullptr;
	std::function<bool()>* CheckIfAbortFunction = nullptr;
};

inline size_t
CurlWriteCallback(char* Ptr, size_t Size, size_t Nmemb, void* UserData)
{
	auto*  Data		  = static_cast<CurlWriteCallbackData*>(UserData);
	size_t TotalBytes = Size * Nmemb;

	if (Data->CheckIfAbortFunction && *Data->CheckIfAbortFunction && (*Data->CheckIfAbortFunction)())
	{
		return 0;  // Signal abort to curl
	}

	Data->Body->append(Ptr, TotalBytes);
	return TotalBytes;
}

struct CurlHeaderCallbackData
{
	std::vector<std::pair<std::string, std::string>>* Headers = nullptr;
};

// Trims trailing CRLF, splits on the first colon, and trims whitespace from key and value.
// Returns nullopt for blank lines or lines without a colon (e.g. HTTP status lines).
inline std::optional<std::pair<std::string_view, std::string_view>>
ParseHeaderLine(std::string_view Line)
{
	while (!Line.empty() && (Line.back() == '\r' || Line.back() == '\n'))
	{
		Line.remove_suffix(1);
	}

	if (Line.empty())
	{
		return std::nullopt;
	}

	size_t ColonPos = Line.find(':');
	if (ColonPos == std::string_view::npos)
	{
		return std::nullopt;
	}

	std::string_view Key   = Line.substr(0, ColonPos);
	std::string_view Value = Line.substr(ColonPos + 1);

	while (!Key.empty() && Key.back() == ' ')
	{
		Key.remove_suffix(1);
	}
	while (!Value.empty() && Value.front() == ' ')
	{
		Value.remove_prefix(1);
	}

	return std::pair{Key, Value};
}

inline size_t
CurlHeaderCallback(char* Buffer, size_t Size, size_t Nmemb, void* UserData)
{
	auto*  Data		  = static_cast<CurlHeaderCallbackData*>(UserData);
	size_t TotalBytes = Size * Nmemb;

	if (auto Header = ParseHeaderLine(std::string_view(Buffer, TotalBytes)))
	{
		auto& [Key, Value] = *Header;
		Data->Headers->emplace_back(std::string(Key), std::string(Value));
	}

	return TotalBytes;
}

struct CurlReadCallbackData
{
	const uint8_t*		   DataPtr				= nullptr;
	size_t				   DataSize				= 0;
	size_t				   Offset				= 0;
	std::function<bool()>* CheckIfAbortFunction = nullptr;
};

inline size_t
CurlReadCallback(char* Buffer, size_t Size, size_t Nmemb, void* UserData)
{
	auto*  Data	   = static_cast<CurlReadCallbackData*>(UserData);
	size_t MaxRead = Size * Nmemb;

	if (Data->CheckIfAbortFunction && *Data->CheckIfAbortFunction && (*Data->CheckIfAbortFunction)())
	{
		return CURL_READFUNC_ABORT;
	}

	size_t Remaining = Data->DataSize - Data->Offset;
	size_t ToRead	 = std::min(MaxRead, Remaining);

	if (ToRead > 0)
	{
		memcpy(Buffer, Data->DataPtr + Data->Offset, ToRead);
		Data->Offset += ToRead;
	}

	return ToRead;
}

//////////////////////////////////////////////////////////////////////////
//
// URL and header construction

inline void
AppendUrlEncoded(StringBuilderBase& Out, std::string_view Input)
{
	static constexpr char	  HexDigits[] = "0123456789ABCDEF";
	static constexpr AsciiSet Unreserved("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.~");

	for (char C : Input)
	{
		if (Unreserved.Contains(C))
		{
			Out.Append(C);
		}
		else
		{
			uint8_t Byte	   = static_cast<uint8_t>(C);
			char	Encoded[3] = {'%', HexDigits[Byte >> 4], HexDigits[Byte & 0x0F]};
			Out.Append(std::string_view(Encoded, 3));
		}
	}
}

inline void
BuildUrlWithParameters(StringBuilderBase&			  Url,
					   std::string_view				  BaseUrl,
					   std::string_view				  ResourcePath,
					   const HttpClient::KeyValueMap& Parameters)
{
	Url.Append(BaseUrl);
	Url.Append(ResourcePath);

	if (!Parameters->empty())
	{
		char Separator = '?';
		for (const auto& [Key, Value] : *Parameters)
		{
			Url.Append(Separator);
			AppendUrlEncoded(Url, Key);
			Url.Append('=');
			AppendUrlEncoded(Url, Value);
			Separator = '&';
		}
	}
}

inline std::pair<std::string, std::string>
HeaderContentType(ZenContentType ContentType)
{
	return std::make_pair("Content-Type", std::string(MapContentTypeToString(ContentType)));
}

inline curl_slist*
BuildHeaderList(const HttpClient::KeyValueMap&							AdditionalHeader,
				std::string_view										SessionId,
				const std::optional<std::string>&						AccessToken,
				const std::vector<std::pair<std::string, std::string>>& ExtraHeaders = {})
{
	curl_slist* Headers = nullptr;

	for (const auto& [Key, Value] : *AdditionalHeader)
	{
		ExtendableStringBuilder<64> HeaderLine;
		HeaderLine << Key << ": " << Value;
		Headers = curl_slist_append(Headers, HeaderLine.c_str());
	}

	if (!SessionId.empty())
	{
		ExtendableStringBuilder<64> SessionHeader;
		SessionHeader << "UE-Session: " << SessionId;
		Headers = curl_slist_append(Headers, SessionHeader.c_str());
	}

	if (AccessToken.has_value())
	{
		ExtendableStringBuilder<128> AuthHeader;
		AuthHeader << "Authorization: " << AccessToken.value();
		Headers = curl_slist_append(Headers, AuthHeader.c_str());
	}

	for (const auto& [Key, Value] : ExtraHeaders)
	{
		ExtendableStringBuilder<128> HeaderLine;
		HeaderLine << Key << ": " << Value;
		Headers = curl_slist_append(Headers, HeaderLine.c_str());
	}

	return Headers;
}

inline HttpClient::KeyValueMap
BuildHeaderMap(const std::vector<std::pair<std::string, std::string>>& Headers)
{
	HttpClient::KeyValueMap HeaderMap;
	for (const auto& [Key, Value] : Headers)
	{
		HeaderMap->insert_or_assign(Key, Value);
	}
	return HeaderMap;
}

// Scans response headers for Content-Type and applies it to the buffer.
inline void
ApplyContentTypeFromHeaders(IoBuffer& Buffer, const std::vector<std::pair<std::string, std::string>>& Headers)
{
	for (const auto& [Key, Value] : Headers)
	{
		if (StrCaseCompare(Key, "Content-Type") == 0)
		{
			Buffer.SetContentType(ParseContentType(Value));
			break;
		}
	}
}

}  // namespace zen