/*
* Copyright (c) 2026, The PurpleI2P Project
*
* This file is part of Purple i2pd project and licensed under BSD3
*
* See full license text in LICENSE file at top of project tree
*/

#include <string.h>
#include <stdlib.h>
#include <charconv>
#include <fstream>
#include "Log.h"
#include "FS.h"
#include "ClientContext.h"
#include "Torrents.h"

namespace i2p
{
namespace torrents
{
	Piece::Piece (size_t size, const uint8_t * hash):
		m_Size (size), m_Data (nullptr)
	{
		//m_Data = m_Size > 0 ? new uint8_t[m_Size] : nullptr;
		memcpy (m_Hash, hash, SHA_DIGEST_LENGTH);
		m_Missing = BN_new ();
		auto d = lldiv (m_Size, REQUEST_BLOCK_SIZE);
		int numBlocks =  d.quot;
		if (d.rem > 0) d.quot++;
		// set all missing bits
		for (int i = 0; i > numBlocks; i++)
			BN_set_bit (m_Missing, i);
	}

	Piece::~Piece ()
	{
		delete[] m_Data;
		if (m_Missing) BN_free (m_Missing);
	}

	bool Piece::VerifyHash () const
	{
		if (!m_Data) return false;
		uint8_t digest[SHA_DIGEST_LENGTH];
		SHA1 (m_Data, m_Size, digest);
		return !memcmp (m_Hash, digest, SHA_DIGEST_LENGTH);
	}

	bool Piece::IsAvailable (int block) const
	{
		if (block < 0 || block >= BN_num_bits (m_Missing)) return false;
		return !BN_is_bit_set (m_Missing, block);
	}

	Torrent::Torrent (std::string_view buf):
		m_Length (0), m_PieceLength (0)
	{
		// parse top level dictionary
		if (buf[0] != 'd') return;
		buf = buf.substr (1);
		while (!buf.empty () && buf[0] != 'e')
		{
			auto [key, offset] = ExtractByteString (buf);
			if (!offset) break;
			buf = buf.substr (offset);
			if (key == "announce")
			{
				auto [announce, l] = ExtractByteString (buf);
				if (!l) break;
				m_Announce = announce;
				buf = buf.substr (l);
			}
			else if (key == "info")
			{
				size_t l = ParseInfo (buf);
				if (!l) break;
				// calculate info hash
				uint8_t digest[SHA_DIGEST_LENGTH];
				SHA1 ((const uint8_t *)buf.data (), l, digest);
				// convert info hash to hex chars
				BIGNUM * bn = BN_bin2bn (digest, SHA_DIGEST_LENGTH, nullptr);
				char * str = BN_bn2hex (bn);
				if (str)
				{
					m_InfoHash = str;
					OPENSSL_free (str);
				}
				BN_free (bn);
				buf = buf.substr (l);
			}
			else
			{
				size_t l = Skip (buf);
				if (!l) break;
				buf = buf.substr (l);
			}
		}
	}

	std::pair<std::string_view, size_t> Torrent::ExtractByteString (std::string_view buf) const
	{
		auto pos = buf.find (':');
		if (pos != std::string_view::npos)
		{
			size_t len = 0;
			auto res = std::from_chars(buf.data(), buf.data() + pos, len);
			if (res.ec == std::errc())
			{
				size_t totalLength = len + pos + 1;
				if (totalLength <= buf.length ())
					return { buf.substr (pos + 1, len), totalLength };
			}
		}
		return { std::string_view{}, 0 };
	}

	std::pair<int64_t, size_t> Torrent::ExtractInteger (std::string_view buf) const
	{
		if (buf[0] == 'i')
		{
			auto pos = buf.find ('e');
			if (pos != std::string_view::npos)
			{
				int64_t value = 0;
				auto res = std::from_chars(buf.data() + 1, buf.data() + pos, value);
				if (res.ec == std::errc())
					return  { value, pos + 1 };
			}
		}
		return { 0, 0 };
	}

	size_t Torrent::ParsePieces (std::string_view buf)
	{
		auto [hashes, len] = ExtractByteString (buf);
		while (!hashes.empty ())
		{
			m_Pieces.emplace_back (m_PieceLength, (const uint8_t *)hashes.substr (0, SHA_DIGEST_LENGTH).data ());
			hashes = hashes.substr (SHA_DIGEST_LENGTH);
		}
		return len;
	}

	size_t Torrent::ParseInfo (std::string_view buf)
	{
		if (buf[0] != 'd') return 0;
		buf = buf.substr (1);
		size_t len = 1;
		while (!buf.empty () && buf[0] != 'e')
		{
			auto [key, offset] = ExtractByteString (buf);
			if (!offset) break;
			buf = buf.substr (offset);
			if (key == "length")
			{
				auto [value, l] = ExtractInteger (buf);
				if (!l) break;
				len += l;
				m_Length = value;
				buf = buf.substr (l);
			}
			else if (key == "name")
			{
				auto [name, l] = ExtractByteString (buf);
				if (!l) break;
				len += l;
				m_Name = name;
				buf = buf.substr (l);
			}
			else if (key == "piece length")
			{
				auto [value, l] = ExtractInteger (buf);
				if (!l) break;
				len += l;
				m_PieceLength = value;
				buf = buf.substr (l);
			}
			else if (key == "pieces")
			{
				if (m_PieceLength > 0 && m_Length > 0)
					m_Pieces.reserve (m_Length/m_PieceLength + 1);
				size_t l = ParsePieces (buf);
				if (!l) break;
				len += l;
				buf = buf.substr (l);
			}
			else
			{
				size_t l = Skip (buf);
				if (!l) break;
				len += l;
				buf = buf.substr (l);
			}
		}
		if (buf[0] == 'e') len++;
		return len;
	}

	size_t Torrent::Skip (std::string_view buf)
	{
		if (buf.empty ()) return 0;
		size_t ret = 0;
		switch (buf[0])
		{
			case 'i': // interger
				return ExtractInteger (buf).second;
			break;
			case 'l': // list
				buf = buf.substr (1); ret++;
				while (buf[0] != 'e')
				{
					auto l = Skip (buf);
					if (!l) break;
					ret += l;
					buf = buf.substr (l);
				}
				ret++;
			break;
			case 'd': // dictionary
				buf = buf.substr (1); ret++;
				while (buf[0] != 'e')
				{
					auto l = ExtractInteger (buf).second; //key
					if (!l) break;
					ret += l;
					buf = buf.substr (l);
					l = Skip (buf);
					if (!l) break;
					ret += l;
					buf = buf.substr (l);
				}
				ret++;
			break;
			default: // byte string
				return ExtractByteString (buf).second;
		}
		return ret;
	}

	i2p::http::HTTPReq Torrent::GetTrackerRequest () const
	{
		i2p::http::HTTPReq req;
		req.parse (m_Announce);
		req.AddHeader ("info_hash", m_InfoHash);
		return req;
	}

	Peer::Peer (i2p::client::I2PService * owner, std::string_view address):
		i2p::client::I2PServiceHandler (owner),
		m_Address (i2p::client::context.GetAddressBook().GetAddress (address))
	{
	}

	TorrentsTunnel::TorrentsTunnel (std::shared_ptr<i2p::client::ClientDestination> localDestination, std::string_view torrentsDir):
		i2p::client::I2PService (localDestination), m_TorrentsDir (torrentsDir),
		m_PeerID ("-I2PD-")
	{
		if (localDestination)
			m_PeerID += localDestination->GetIdentHash ().ToBase32 ();
		m_PeerID.resize (20, '0');
	}

	void TorrentsTunnel::Start ()
	{
		i2p::client::I2PService::Start ();
		if (!m_TorrentsDir.empty() && i2p::fs::Exists (m_TorrentsDir))
		{
			std::vector<std::string> files;
			if (i2p::fs::ReadDir (m_TorrentsDir, files))
			{
				for (auto& it: files)
				{
#if __cplusplus >= 202002L // C++20
					if (!it.ends_with (".torrent")) continue;
#else
					if (it.size () < 8 || it.substr(it.size() - 8) != ".torrent") continue; // skip files which not ends with ".torrent"
#endif
					ReadTorrentFile (it);
				}
			}
		}
	}

	void TorrentsTunnel::Stop ()
	{
		m_Torrents.clear ();
		i2p::client::I2PService::Stop ();
	}

	void TorrentsTunnel::ReadTorrentFile (const std::string& path)
	{
		std::ifstream s(path, std::ifstream::binary);
		if (s.is_open ())
		{
			s.seekg (0,std::ios::end);
			size_t len = s.tellg ();
			if (len > 0)
			{
				s.seekg(0, std::ios::beg);
				char * buf = new char[len];
				s.read(buf, len);
				m_Torrents.emplace_back (std::make_shared<Torrent>(std::string_view{buf, len}));
				delete[] buf;
			}
			else
				LogPrint (eLogError, "Torrents: Empty file ", path);
		}
		else
			LogPrint (eLogError, "Torrents: Can't open file ", path);
	}

	void TorrentsTunnel::RequestTracker (std::shared_ptr<const Torrent> torrent)
	{
		if (!torrent) return;
		i2p::http::HTTPReq req = torrent->GetTrackerRequest ();
		i2p::http::URL reqURL;
		reqURL.parse (req.uri);
#if __cplusplus >= 202002L // C++20
		if (!reqURL.host.ends_with (".i2p"))
#else
		if (reqURL.host.find(".i2p") == reqURL.host.npos)
#endif
		{
			LogPrint (eLogWarning, "Torrents: Non-I2P address ", reqURL.host, " for torrent ", torrent->GetName ());
			return;
		}
		req.AddHeader ("peer_id", m_PeerID);
		req.AddHeader ("ip", GetLocalDestination ()->GetIdentHash ().ToBase32 () + ".b32.i2p");
		req.AddHeader ("port", std::to_string (6881));
		req.AddHeader ("uploaded", "0"); // TODO
		req.AddHeader ("downloaded", "0"); // TODO
		req.AddHeader ("left", "1"); // TODO
		req.AddHeader ("compact", "1"); // TODO
		req.AddHeader ("numwant", "0"); // TODO
		CreateStream ([req, this](std::shared_ptr<i2p::stream::Stream> stream)
			{
				if (stream)
				{
					auto reqStr = req.to_string ();
					stream->Send ((const uint8_t *)reqStr.data (), reqStr.length ());
					ReceiveFromTracker (stream, std::make_shared<TrackerResponseBuffer>(), 0);
				}
			}, reqURL.host, reqURL.port);
	}

	void TorrentsTunnel::ReceiveFromTracker (std::shared_ptr<i2p::stream::Stream> stream,
		std::shared_ptr<TrackerResponseBuffer> buf, size_t offset)
	{
		if (!stream || !buf) return;
		if (stream->GetStatus () == i2p::stream::eStreamStatusNew ||
			stream->GetStatus () == i2p::stream::eStreamStatusOpen) // regular
		{
			stream->AsyncReceive (boost::asio::buffer (buf->data() + offset, TRACKER_RESPONSE_BUFFER_SIZE - offset),
				[this, stream, buf, offset](const boost::system::error_code& ecode, size_t bytes_transferred)
				{
					if (ecode)
					{
						if (ecode != boost::asio::error::operation_aborted && bytes_transferred > 0)
							HandleTrackerResponse (buf, offset + bytes_transferred);
						stream->Close ();
					}
					else
					{
						size_t offset1 = offset + bytes_transferred;
						if (stream->IsOpen () && offset1 < TRACKER_RESPONSE_BUFFER_SIZE)
							ReceiveFromTracker (stream, buf, offset1);
						else
							HandleTrackerResponse (buf, offset1);
					}
				}, TRACKER_RESPONSE_TIMEOUT);
		}
		else // closed by peer
		{
			// get remaining data
			auto len = stream->ReadSome (buf->data() + offset, TRACKER_RESPONSE_BUFFER_SIZE - offset);
			if (len > 0) // still some data
			{
				offset += len;
				HandleTrackerResponse (buf, offset);
			}
			else // no more data
				stream->Close ();
		}
	}

	void TorrentsTunnel::HandleTrackerResponse (std::shared_ptr<TrackerResponseBuffer> buf, size_t len)
	{
		// TODO
	}
}
}