/*
* 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
*/

#ifndef NO_TORRENTS

#include <string.h>
#include "TorrentsTunnel.h"
#include "TorrentsDHT.h"

namespace i2p
{
namespace torrents
{
	std::shared_ptr<Node> Bucket::FindNode (const NodeID& id) const
	{
		auto it = std::find_if (nodes.begin (), nodes.end (),
			[&id](std::shared_ptr<const Node> node)
			{
				return node->id == id;
			});
		return (it != nodes.end ()) ? *it : nullptr;
	}

	std::optional<NodeID> Bucket::GetMiddleID () const
	{
		uint8_t bit = std::max (start.FindLowestBit (), next ? next->start.FindLowestBit () : -1) + 1;
		if (bit >= NodeID::len * 8) return {};
		NodeID middleID = start;
		middleID[bit >> 3] |= (0x80 >> (bit & 0x07));
		return { middleID };
	}

	bool Bucket::Split ()
	{
		auto middleID = GetMiddleID ();
		if (!middleID) return false;
		auto newBucket = new Bucket (*middleID);
		newBucket->next = next;
		next = newBucket;
		// move some nodes
		auto it = nodes.begin ();
		while (it != nodes.end ())
		{
			if ((*it)->id < *middleID)
				it++; // stay in old bucket
			else
			{
				// move to new bucket
				auto node = *it;
				it = nodes.erase (it);
				newBucket->nodes.push_back (node);
			}
		}
		return true;
	}

	RoutingTable::RoutingTable (const NodeID& ourNode):
		m_OurNode (ourNode)
	{
		m_Buckets = new Bucket;
	}

	RoutingTable::~RoutingTable ()
	{
		while (m_Buckets)
		{
			auto bucket = m_Buckets;
			m_Buckets = m_Buckets->next;
			delete bucket;
		}
	}

	Bucket * RoutingTable::FindBucket (const Torrent::InfoHash& id) const
	{
		if (!m_Buckets) return nullptr;
		auto bucket = m_Buckets;
		while (bucket->next)
		{
			if (id < bucket->next->start)
				return bucket;
			bucket = bucket->next;
		}
		return bucket;
	}

	void RoutingTable::RemoveEmptyBuckers ()
	{
		if (m_Buckets)
		{
			auto prev = m_Buckets, bucket = m_Buckets->next;
			while (bucket)
			{
				if (bucket->nodes.empty ())
				{
					prev->next = bucket->next;
					auto tmp = bucket;
					bucket = bucket->next;
					delete tmp;
				}
				else
				{
					prev = bucket;
					bucket = bucket->next;
				}
			}
		}
	}

	std::shared_ptr<Node> RoutingTable::AddNode (const NodeID& id, i2p::data::IdentHash& peer, uint16_t port)
	{
		if (id == m_OurNode) return nullptr;
		auto bucket = FindBucket (id);
		if (!bucket) return nullptr;
		std::shared_ptr<Node> node = bucket->FindNode (id);
		if (node) return node;
		if (bucket->IsFull ())
		{
			if (!bucket->IsInBucket (m_OurNode)) return nullptr;
			do
			{
				if (!bucket->Split ()) return nullptr;
				bucket = FindBucket (id);
			}
			while (bucket->IsFull ());
		}
		if (bucket)
		{
			node = std::make_shared<Node>(id, peer, port);
			bucket->nodes.emplace_back (node);
		}
		RemoveEmptyBuckers ();
		return node;
	}

	std::list<std::pair<std::shared_ptr<Node>, Distance> > RoutingTable::FindClosestNodes (const Torrent::InfoHash& infoHash, size_t num) const
	{
		std::list<std::pair<std::shared_ptr<Node>, Distance> > ret;
		if (num > 0)
		{
			auto bucket = FindBucket (infoHash);
			if (bucket)
			{
				for (auto it: bucket->nodes)
				{
					auto nodeDistance = it->id ^ infoHash;
					auto it1 = std::find_if (ret.begin (), ret.end (),
						[&nodeDistance](const std::pair<std::shared_ptr<Node>, Distance>& alreadyFound)
						{
							return nodeDistance < alreadyFound.second;
						});
					ret.insert (it1, { it, nodeDistance } );
				}
				if (ret.size () > num) ret.resize (num);
			}
		}
		return ret;
	}

	TorrentsDHT::TorrentsDHT (TorrentsTunnel& tunnel, uint16_t port):
		m_Tunnel (tunnel), m_Port (port)
	{
		auto dest = tunnel.GetLocalDestination ();
		if (dest)
		{
			memcpy (m_NodeID.data (), dest->GetIdentHash (), m_NodeID.size ());
			m_NodeID[4] ^= (port >> 8);
			m_NodeID[5] ^= (port & 0xFF);
			memcpy (m_NodeInfo.data (), m_NodeID.data (), m_NodeID.size ());
			memcpy (m_NodeInfo.data () + m_NodeID.size (), dest->GetIdentHash (), i2p::data::IdentHash::len);
			htobe16buf (m_NodeInfo.data () + m_NodeInfo.size () - 2, port);
			m_RoutingTable = std::make_unique<RoutingTable> (m_NodeID);
		}
		else
		{
			m_NodeID.fill (0);
			m_NodeInfo.fill (0);
		}
	}

	void TorrentsDHT::Start ()
	{
		auto dest = m_Tunnel.GetLocalDestination ();
		if (dest)
		{
			auto dgramDest = dest->GetDatagramDestination ();
			if (dgramDest)
				dgramDest->SetReceiver (std::bind_front (&TorrentsDHT::HandleDatagram, this));
		}
	}

	void TorrentsDHT::Stop ()
	{
		auto dest = m_Tunnel.GetLocalDestination ();
		if (dest)
		{
			auto dgramDest = dest->GetDatagramDestination ();
			if (dgramDest)
				dgramDest->ResetReceiver ();
		}
	}

	void TorrentsDHT::HandleRawDatagram (const uint8_t * buf, size_t len)
	{
		// response or error
		char type = 0;
		std::string transactionID, id;
		ParseDictionary (std::string_view ((const char *)buf, len),
			[&type, &transactionID, &id](std::string_view key, std::string_view buf)->size_t
			{
				if (key == "y")
				{
					auto [value, l] = ExtractByteString (buf);
					if (l && !value.empty ()) type = value[0];
					return l;
				}
				else if (key == "t")
				{
					auto [value, l] = ExtractByteString (buf);
					if (l) transactionID = value;
					return l;
				}
				else if (key == "r")
				{
					return ParseDictionary (buf,
						[&id](std::string_view key, std::string_view buf)->size_t
						{
							if (key == "id")
							{
								auto [value, l] = ExtractByteString (buf);
								if (l) id = value;
								return l;
							}
							return 0;
						});
				}
				return 0;
			});
		if (type)
		{
			switch (type)
			{
				 case 'r':
					HandleResponse (transactionID, id);
				 break;
				 case 'e':
					LogPrint (eLogDebug, "TorrentsDHT: Error msg received");
				 break;
				 case 'q':
					LogPrint (eLogError, "TorrentsDHT: Query can't come as raw datagram");
				break;
				 default:
					LogPrint (eLogInfo, "TorrentsDHT: Unxpected msg type ", (int)type);
			}
		}
	}

	void TorrentsDHT::HandleDatagram (const i2p::data::IdentityEx& from, uint16_t fromPort, uint16_t toPort,
			const uint8_t * buf, size_t len, const i2p::util::Mapping * options)
	{
		// query
		char type = 0;
		std::string transactionID, query, id;
		ParseDictionary (std::string_view ((const char *)buf, len),
			[&type, &transactionID, &query, &id](std::string_view key, std::string_view buf)->size_t
			{
				if (key == "y")
				{
					auto [value, l] = ExtractByteString (buf);
					if (l && !value.empty ()) type = value[0];
					return l;
				}
				else if (key == "t")
				{
					auto [value, l] = ExtractByteString (buf);
					if (l) transactionID = value;
					return l;
				}
				else if (key == "q")
				{
					auto [value, l] = ExtractByteString (buf);
					if (l) query = value;
					return l;
				}
				else if (key == "a")
				{
					return ParseDictionary (buf,
						[&id](std::string_view key, std::string_view buf)->size_t
						{
							if (key == "id")
							{
								auto [value, l] = ExtractByteString (buf);
								if (l) id = value;
								return l;
							}
							return 0;
						});
				}
				return 0;
			});
		if (type == 'q')
			HandleQuery (from.GetIdentHash (), fromPort, transactionID, query, id);
		else if (type)
			LogPrint (eLogInfo, "TorrentsDHT: Unxpected msg type ", (int)type);
	}

	void TorrentsDHT::HandleQuery (const i2p::data::IdentHash& fromIdent, uint16_t fromPort,
		std::string_view transactionID, std::string_view query, std::string_view id)
	{
		LogPrint (eLogDebug, "TorrentsDHT: Query msg received");
		if (query == "ping")
			SendPingResponse (transactionID, fromIdent, fromPort + 1); // to rport
		else
			LogPrint (eLogDebug, "TorrentsDHT: Unexpected query ", query);
	}

	void TorrentsDHT::HandleResponse (std::string_view transactionID, std::string_view id)
	{
		LogPrint (eLogDebug, "TorrentsDHT: Response msg received");
		auto it = m_Queries.find (transactionID);
		if (it != m_Queries.end ())
		{
			// assume ping for now
			if (id.size () < NodeID::len)
			{
				LogPrint (eLogInfo, "TorrentsDHT: received id is too short ", id.size ());
				return;
			}
			if (m_RoutingTable)
			{
				NodeID nodeID;
				memcpy (nodeID.data (), id.data (), NodeID::len);
				if (m_RoutingTable->AddNode (nodeID, it->second.first, it->second.second))
					LogPrint (eLogDebug, "TorrentsDHT: Node ", it->second.first.ToBase64 (), ":", it->second.second, " added");
				else
					LogPrint (eLogError, "TorrentsDHT: Failed to add node ", it->second.first.ToBase64 ());
			}
		}
		else
			LogPrint (eLogInfo, "TorrentsDHT: Query now found");
	}

	void TorrentsDHT::SendDatagram (std::string_view msg, const i2p::data::IdentHash& toIdent, uint16_t toPort)
	{
		auto dest = m_Tunnel.GetLocalDestination ();
		if (dest)
		{
			auto dgramDest = dest->GetDatagramDestination ();
			if (dgramDest)
				dgramDest->SendDatagramTo ((const uint8_t *)msg.data (), msg.size (), toIdent, m_Port, toPort);
		}
	}

	void TorrentsDHT::SendRawDatagram (std::string_view msg, const i2p::data::IdentHash& toIdent, uint16_t toPort)
	{
		auto dest = m_Tunnel.GetLocalDestination ();
		if (dest)
		{
			auto dgramDest = dest->GetDatagramDestination ();
			if (dgramDest)
				dgramDest->SendRawDatagramTo ((const uint8_t *)msg.data (), msg.size (), toIdent, m_Port, toPort);
		}
	}

	void TorrentsDHT::SendQueryMsg (std::string_view query, std::string_view arguments,
		const i2p::data::IdentHash& toIdent, uint16_t toPort)
	{
		std::string transactionID;
		if (m_Tunnel.GetLocalDestination ())
		{
			transactionID.push_back (m_Tunnel.GetLocalDestination ()->GetRng ()() % ('z' -'a' + 1) + 'a');
			transactionID.push_back (m_Tunnel.GetLocalDestination ()->GetRng ()() % ('z' -'a' + 1) + 'a');
		}
		else
			transactionID = "xx";
		auto msg = CreateDictionary ({
				{ "a", arguments },
				{ "q", CreateByteString (query) },
				{ "t", CreateByteString (transactionID) },
				{ "y", CreateByteString ("q") }
									});
		m_Queries.insert_or_assign (transactionID, std::make_pair (toIdent, toPort));
		SendDatagram (msg, toIdent, toPort);
	}

	void TorrentsDHT::SendResponseMsg (std::string_view response, std::string_view transactionID,
		const i2p::data::IdentHash& toIdent, uint16_t toPort)
	{
		auto msg = CreateDictionary ({
				{ "r", response },
				{ "t", CreateByteString (transactionID) },
				{ "y", CreateByteString ("r") }
									});
		SendRawDatagram (msg, toIdent, toPort);
	}

	void TorrentsDHT::SendPingQuery (const i2p::data::IdentHash& toIdent, uint16_t toPort)
	{
		SendQueryMsg ("ping", CreateDictionary ({
			{ "id", CreateByteString (std::string_view ((const char *)m_NodeID.data (), m_NodeID.size ())) }
												}),
			toIdent, toPort);
	}

	void TorrentsDHT::SendPingResponse (std::string_view transactionID, const i2p::data::IdentHash& toIdent, uint16_t toPort)
	{
		SendResponseMsg (CreateDictionary ({
			{ "id", CreateByteString (std::string_view ((const char *)m_NodeID.data (), m_NodeID.size ())) }
											}),
			transactionID, toIdent, toPort);
	}
}
}

#endif