/*
 * InspIRCd -- Internet Relay Chat Daemon
 *
 *   Copyright (C) 2021 iwalkalone <iwalkalone69@gmail.com>
 *   Copyright (C) 2021 David Schultz <me@zpld.me>
 *   Copyright (C) 2019 Robby <robby@chatbelgie.be>
 *   Copyright (C) 2018-2019 linuxdaemon <linuxdaemon.irc@gmail.com>
 *   Copyright (C) 2018 Matt Schatz <genius3000@g3k.solutions>
 *   Copyright (C) 2017-2019, 2021-2022 Sadie Powell <sadie@witchery.services>
 *   Copyright (C) 2015 James Lu <GLolol@overdrivenetworks.com>
 *   Copyright (C) 2013-2015 Attila Molnar <attilamolnar@hush.com>
 *   Copyright (C) 2013 Daniel Vassdal <shutter@canternet.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/>.
 */


#include "inspircd.h"
#include "modules/exemption.h"

class ChannelSettings
{
 public:
	enum RepeatAction
	{
		ACT_KICK,
		ACT_BLOCK,
		ACT_BAN
	};

	RepeatAction Action;
	unsigned int Backlog;
	unsigned int Lines;
	unsigned int Diff;
	unsigned long Seconds;

	void serialize(std::string& out) const
	{
		if (Action == ACT_BAN)
			out.push_back('*');
		else if (Action == ACT_BLOCK)
			out.push_back('~');

		out.append(ConvToStr(Lines)).push_back(':');
		out.append(ConvToStr(Seconds));
		if (Diff)
		{
			out.push_back(':');
			out.append(ConvToStr(Diff));
			if (Backlog)
			{
				out.push_back(':');
				out.append(ConvToStr(Backlog));
			}
		}
	}
};

class RepeatMode : public ParamMode<RepeatMode, SimpleExtItem<ChannelSettings> >
{
 private:
	struct RepeatItem
	{
		time_t ts;
		std::string line;
		RepeatItem(time_t TS, const std::string& Line) : ts(TS), line(Line) { }
	};

	typedef std::deque<RepeatItem> RepeatItemList;

	struct MemberInfo
	{
		RepeatItemList ItemList;
		unsigned int Counter;
		MemberInfo() : Counter(0) {}
	};

	struct ModuleSettings
	{
		unsigned int MaxLines;
		unsigned int MaxSecs;
		unsigned int MaxBacklog;
		unsigned int MaxDiff;
		unsigned int MaxMessageSize;
		std::string KickMessage;
		ModuleSettings() : MaxLines(0), MaxSecs(0), MaxBacklog(0), MaxDiff() { }
	};

	std::vector<unsigned int> mx[2];
	ModuleSettings ms;

	bool CompareLines(const std::string& message, const std::string& historyline, unsigned int trigger)
	{
		if (message == historyline)
			return true;
		else if (trigger)
			return (Levenshtein(message, historyline) <= trigger);

		return false;
	}

	unsigned int Levenshtein(const std::string& s1, const std::string& s2)
	{
		unsigned int l1 = s1.size();
		unsigned int l2 = s2.size();

		for (unsigned int i = 0; i < l2; i++)
			mx[0][i] = i;
		for (unsigned int i = 0; i < l1; i++)
		{
			mx[1][0] = i + 1;
			for (unsigned int j = 0; j < l2; j++)
				mx[1][j + 1] = std::min(std::min(mx[1][j] + 1, mx[0][j + 1] + 1), mx[0][j] + ((s1[i] == s2[j]) ? 0 : 1));

			mx[0].swap(mx[1]);
		}
		return mx[0][l2];
	}

 public:
	SimpleExtItem<MemberInfo> MemberInfoExt;

	RepeatMode(Module* Creator)
		: ParamMode<RepeatMode, SimpleExtItem<ChannelSettings> >(Creator, "repeat", 'E')
		, MemberInfoExt("repeat_memb", ExtensionItem::EXT_MEMBERSHIP, Creator)
	{
		syntax = "[~|*]<lines>:<duration>[:<difference>][:<backlog>]";
	}

	void OnUnset(User* source, Channel* chan) CXX11_OVERRIDE
	{
		// Unset the per-membership extension when the mode is removed
		const Channel::MemberMap& users = chan->GetUsers();
		for (Channel::MemberMap::const_iterator i = users.begin(); i != users.end(); ++i)
			MemberInfoExt.unset(i->second);
	}

	ModeAction OnSet(User* source, Channel* channel, std::string& parameter) CXX11_OVERRIDE
	{
		ChannelSettings settings;
		if (!ParseSettings(source, parameter, settings))
		{
			source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter));
			return MODEACTION_DENY;
		}

		if ((settings.Backlog > 0) && (settings.Lines > settings.Backlog))
		{
			source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter,
				"You can't set lines higher than backlog."));
			return MODEACTION_DENY;
		}

		LocalUser* localsource = IS_LOCAL(source);
		if ((localsource) && (!ValidateSettings(localsource, channel, parameter, settings)))
			return MODEACTION_DENY;

		ext.set(channel, settings);

		return MODEACTION_ALLOW;
	}

	bool MatchLine(Membership* memb, ChannelSettings* rs, std::string message)
	{
		// If the message is larger than whatever size it's set to,
		// let's pretend it isn't. If the first 512 (def. setting) match, it's probably spam.
		if (message.size() > ms.MaxMessageSize)
			message.erase(ms.MaxMessageSize);

		MemberInfo* rp = MemberInfoExt.get(memb);
		if (!rp)
		{
			rp = new MemberInfo;
			MemberInfoExt.set(memb, rp);
		}

		unsigned int matches = 0;
		if (!rs->Backlog)
			matches = rp->Counter;

		RepeatItemList& items = rp->ItemList;
		const unsigned int trigger = (message.size() * rs->Diff / 100);
		const time_t now = ServerInstance->Time();

		std::transform(message.begin(), message.end(), message.begin(), ::tolower);

		for (std::deque<RepeatItem>::iterator it = items.begin(); it != items.end(); ++it)
		{
			if (it->ts < now)
			{
				items.erase(it, items.end());
				matches = 0;
				break;
			}

			if (CompareLines(message, it->line, trigger))
			{
				if (++matches >= rs->Lines)
				{
					if (rs->Action != ChannelSettings::ACT_BLOCK)
						rp->Counter = 0;
					return true;
				}
			}
			else if ((ms.MaxBacklog == 0) || (rs->Backlog == 0))
			{
				matches = 0;
				items.clear();
				break;
			}
		}

		unsigned int max_items = (rs->Backlog ? rs->Backlog : 1);
		if (items.size() >= max_items)
			items.pop_back();

		items.push_front(RepeatItem(now + rs->Seconds, message));
		rp->Counter = matches;
		return false;
	}

	void Resize(size_t size)
	{
		size_t newsize = size+1;
		if (newsize <= mx[0].size())
			return;
		ms.MaxMessageSize = size;
		mx[0].resize(newsize);
		mx[1].resize(newsize);
	}

	void ReadConfig()
	{
		ConfigTag* conf = ServerInstance->Config->ConfValue("repeat");
		ms.MaxLines = conf->getUInt("maxlines", 20);
		ms.MaxBacklog = conf->getUInt("maxbacklog", 20);
		ms.MaxSecs = conf->getDuration("maxtime", conf->getDuration("maxsecs", 0));

		ms.MaxDiff = conf->getUInt("maxdistance", 50);
		if (ms.MaxDiff > 100)
			ms.MaxDiff = 100;

		unsigned int newsize = conf->getUInt("size", 512);
		if (newsize > ServerInstance->Config->Limits.MaxLine)
			newsize = ServerInstance->Config->Limits.MaxLine;
		Resize(newsize);

		ms.KickMessage = conf->getString("kickmessage", "Repeat flood");
	}

	std::string GetModuleSettings() const
	{
		return ConvToStr(ms.MaxLines) + ":" + ConvToStr(ms.MaxSecs) + ":" + ConvToStr(ms.MaxDiff) + ":" + ConvToStr(ms.MaxBacklog);
	}

	std::string GetKickMessage() const
	{
		return ms.KickMessage;
	}

	void SerializeParam(Channel* chan, const ChannelSettings* chset, std::string& out)
	{
		chset->serialize(out);
	}

 private:
	bool ParseSettings(User* source, std::string& parameter, ChannelSettings& settings)
	{
		irc::sepstream stream(parameter, ':');
		std::string	item;
		if (!stream.GetToken(item))
			// Required parameter missing
			return false;

		if ((item[0] == '*') || (item[0] == '~'))
		{
			settings.Action = ((item[0] == '*') ? ChannelSettings::ACT_BAN : ChannelSettings::ACT_BLOCK);
			item.erase(item.begin());
		}
		else
			settings.Action = ChannelSettings::ACT_KICK;

		if ((settings.Lines = ConvToNum<unsigned int>(item)) == 0)
			return false;

		if ((!stream.GetToken(item)) || !InspIRCd::Duration(item, settings.Seconds) || (settings.Seconds == 0))
			// Required parameter missing
			return false;

		// The diff and backlog parameters are optional
		settings.Diff = settings.Backlog = 0;
		if (stream.GetToken(item))
		{
			// There is a diff parameter, see if it's valid (> 0)
			if ((settings.Diff = ConvToNum<unsigned int>(item)) == 0)
				return false;

			if (stream.GetToken(item))
			{
				// There is a backlog parameter, see if it's valid
				if ((settings.Backlog = ConvToNum<unsigned int>(item)) == 0)
					return false;

				// If there are still tokens, then it's invalid because we allow only 4
				if (stream.GetToken(item))
					return false;
			}
		}

		return true;
	}

	bool ValidateSettings(LocalUser* source, Channel* channel, const std::string& parameter, const ChannelSettings& settings)
	{
		if (ms.MaxLines && settings.Lines > ms.MaxLines)
		{
			source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter, InspIRCd::Format(
				"The line number you specified is too big. Maximum allowed is %u.", ms.MaxLines)));
			return false;
		}

		if (ms.MaxSecs && settings.Seconds > ms.MaxSecs)
		{
			source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter, InspIRCd::Format(
				"The seconds you specified are too big. Maximum allowed is %u.", ms.MaxSecs)));
			return false;
		}

		if (settings.Diff && settings.Diff > ms.MaxDiff)
		{
			if (ms.MaxDiff == 0)
				source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter,
					"The server administrator has disabled matching on edit distance."));
			else
				source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter, InspIRCd::Format(
					"The distance you specified is too big. Maximum allowed is %u.", ms.MaxDiff)));
			return false;
		}

		if (settings.Backlog && settings.Backlog > ms.MaxBacklog)
		{
			if (ms.MaxBacklog == 0)
				source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter,
					"The server administrator has disabled backlog matching."));
			else
				source->WriteNumeric(Numerics::InvalidModeParameter(channel, this, parameter, InspIRCd::Format(
					"The backlog you specified is too big. Maximum allowed is %u.", ms.MaxBacklog)));
			return false;
		}

		return true;
	}
};

class RepeatModule : public Module
{
 private:
	ChanModeReference banmode;
	CheckExemption::EventProvider exemptionprov;
	RepeatMode rm;

 public:
	RepeatModule()
		: banmode(this, "ban")
		, exemptionprov(this)
		, rm(this)
	{
	}

	void ReadConfig(ConfigStatus& status) CXX11_OVERRIDE
	{
		rm.ReadConfig();
	}

	ModResult OnUserPreMessage(User* user, const MessageTarget& target, MessageDetails& details) CXX11_OVERRIDE
	{
		if (target.type != MessageTarget::TYPE_CHANNEL || !IS_LOCAL(user))
			return MOD_RES_PASSTHRU;

		Channel* chan = target.Get<Channel>();
		ChannelSettings* settings = rm.ext.get(chan);
		if (!settings)
			return MOD_RES_PASSTHRU;

		Membership* memb = chan->GetUser(user);
		if (!memb)
			return MOD_RES_PASSTHRU;

		ModResult res = CheckExemption::Call(exemptionprov, user, chan, "repeat");
		if (res == MOD_RES_ALLOW)
			return MOD_RES_PASSTHRU;

		if (user->HasPrivPermission("channels/ignore-repeat"))
			return MOD_RES_PASSTHRU;

		if (rm.MatchLine(memb, settings, details.text))
		{
			if (settings->Action == ChannelSettings::ACT_BLOCK)
			{
				user->WriteNotice("*** This line is too similar to one of your last lines.");
				return MOD_RES_DENY;
			}

			if (settings->Action == ChannelSettings::ACT_BAN)
			{
				Modes::ChangeList changelist;
				changelist.push_add(*banmode, "*!" + user->GetBanIdent() + "@" + user->GetDisplayedHost());
				ServerInstance->Modes->Process(ServerInstance->FakeClient, chan, NULL, changelist);
			}

			memb->chan->KickUser(ServerInstance->FakeClient, user, rm.GetKickMessage());
			return MOD_RES_DENY;
		}
		return MOD_RES_PASSTHRU;
	}

	void Prioritize() CXX11_OVERRIDE
	{
		ServerInstance->Modules->SetPriority(this, I_OnUserPreMessage, PRIORITY_LAST);
	}

	Version GetVersion() CXX11_OVERRIDE
	{
		return Version("Adds channel mode E (repeat) which helps protect against spammers which spam the same message repeatedly.", VF_COMMON|VF_VENDOR, rm.GetModuleSettings());
	}
};

MODULE_INIT(RepeatModule)
