/*
 * InspIRCd -- Internet Relay Chat Daemon
 *
 *   Copyright (C) 2021 Dominic Hamon
 *   Copyright (C) 2019-2023 Sadie Powell <sadie@witchery.services>
 *   Copyright (C) 2014-2015 Attila Molnar <attilamolnar@hush.com>
 *   Copyright (C) 2013, 2015-2016 Adam <Adam@anope.org>
 *
 * This file is part of InspIRCd.  InspIRCd is free software: you can
 * redistribute it and/or modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation, version 2.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once

namespace DNS
{
	/** Valid query types
	 */
	enum QueryType
	{
		/* Nothing */
		QUERY_NONE,
		/* A simple A lookup */
		QUERY_A = 1,
		/* A CNAME lookup */
		QUERY_CNAME = 5,
		/* Reverse DNS lookup */
		QUERY_PTR = 12,
		/* TXT */
		QUERY_TXT = 16,
		/* IPv6 AAAA lookup */
		QUERY_AAAA = 28,
		/** SRV */
		QUERY_SRV = 33,
	};

	/** Flags that can be AND'd into DNSPacket::flags to receive certain values
	 */
	enum
	{
		QUERYFLAGS_QR = 0x8000,
		QUERYFLAGS_OPCODE = 0x7800,
		QUERYFLAGS_AA = 0x400,
		QUERYFLAGS_TC = 0x200,
		QUERYFLAGS_RD = 0x100,
		QUERYFLAGS_RA = 0x80,
		QUERYFLAGS_Z = 0x70,
		QUERYFLAGS_RCODE = 0xF
	};

	enum Error
	{
		ERROR_NONE,
		ERROR_DISABLED,
		ERROR_UNKNOWN,
		ERROR_UNLOADED,
		ERROR_TIMEDOUT,
		ERROR_MALFORMED,
		ERROR_NOT_AN_ANSWER,
		ERROR_NONSTANDARD_QUERY,
		ERROR_FORMAT_ERROR,
		ERROR_SERVER_FAILURE,
		ERROR_DOMAIN_NOT_FOUND,
		ERROR_NOT_IMPLEMENTED,
		ERROR_REFUSED,
		ERROR_NO_RECORDS,
		ERROR_INVALIDTYPE
	};

	typedef uint16_t RequestId;

	const int PORT = 53;

	class Exception final
		: public ModuleException
	{
	public:
		Exception(const Module* mod, const std::string& message)
			: ModuleException(mod, message)
		{
		}
	};

	struct Question
	{
		std::string name;
		QueryType type;

		Question() : type(QUERY_NONE) { }
		Question(const std::string& n, QueryType t) : name(n), type(t) { }
		bool operator==(const Question& other) const { return ((name == other.name) && (type == other.type)); }
		bool operator!=(const Question& other) const { return (!(*this == other)); }

		struct hash final
		{
			size_t operator()(const Question& question) const
			{
				return irc::insensitive()(question.name);
			}
		};
	};

	namespace Record
	{
		struct SRV final
		{
			uint16_t priority = UINT16_MAX;
			uint16_t weight = 0;
			uint16_t port = 0;
			std::string host;
		};
	}

	struct ResourceRecord : Question
	{
		unsigned int ttl = 0;
		std::string rdata;
		std::shared_ptr<void> rdataobj;
		time_t created;

		ResourceRecord(const std::string& n, QueryType t)
			: Question(n, t)
			, created(ServerInstance->Time())
		{
		}

		ResourceRecord(const Question& question)
			: Question(question)
			, created(ServerInstance->Time())
		{
		}
	};

	struct Query
	{
		Question question;
		std::vector<ResourceRecord> answers;
		Error error = ERROR_NONE;
		bool cached = false;

		Query() = default;

		Query(const Question& q)
			: question(q)
		{
		}

		const ResourceRecord* FindAnswerOfType(QueryType qtype) const
		{
			for (const auto& rr : answers)
			{
				if (rr.type == qtype)
					return &rr;
			}

			return nullptr;
		}
	};

	class ReplySocket;
	class Request;

	/** DNS manager
	 */
	class Manager : public DataProvider
	{
	public:
		Manager(Module* mod)
			: DataProvider(mod, "DNS")
		{
		}

		virtual void Process(Request* req) = 0;
		virtual void RemoveRequest(Request* req) = 0;
		virtual std::string GetErrorStr(Error) = 0;
		virtual std::string GetTypeStr(QueryType) = 0;
	};

	/** Reference to the DNS manager. */
	class ManagerRef final
		: public dynamic_reference<DNS::Manager>
	{
	public:
		ManagerRef(Module* mod)
			: dynamic_reference<DNS::Manager>(mod, "DNS")
		{
		}
	};

	/** A DNS query.
	 */
	class Request : public Timer
	{
	protected:
		Manager* const manager;
	public:
		Question question;
		/* Use result cache if available */
		bool use_cache;
		/* Request id */
		RequestId id = 0;
		/* Creator of this request */
		Module* const creator;

		Request(Manager* mgr, Module* mod, const std::string& addr, QueryType qt, bool usecache = true, unsigned long timeout = 0)
			: Timer(timeout ? timeout : ServerInstance->Config->ConfValue("dns")->getDuration("timeout", 5, 1), false)
			, manager(mgr)
			, question(addr, qt)
			, use_cache(usecache)
			, creator(mod)
		{
		}

		~Request() override
		{
			manager->RemoveRequest(this);
		}

		/** Called when this request succeeds
		 * @param req The query sent back from the nameserver
		 */
		virtual void OnLookupComplete(const Query* req) = 0;

		/** Called when this request fails or times out.
		 * @param req The query sent back from the nameserver, check the error code.
		 */
		virtual void OnError(const Query* req) { }

		/** Used to time out the query, calls OnError and asks the TimerManager
		 * to delete this request
		 */
		bool Tick() override
		{
			Query rr(this->question);
			rr.error = ERROR_TIMEDOUT;
			this->OnError(&rr);
			delete this;
			return false;
		}
	};

} // namespace DNS