/*
 * InspIRCd -- Internet Relay Chat Daemon
 *
 *   Copyright (C) 2013-2014, 2016, 2018 Attila Molnar <attilamolnar@hush.com>
 *   Copyright (C) 2013, 2017-2019, 2022 Sadie Powell <sadie@witchery.services>
 *   Copyright (C) 2012, 2019 Robby <robby@chatbelgie.be>
 *   Copyright (C) 2009-2010 Daniel De Graaf <danieldg@inspircd.org>
 *   Copyright (C) 2008 Robin Burchell <robin+git@viroteck.net>
 *   Copyright (C) 2007-2008 Craig Edwards <brain@inspircd.org>
 *   Copyright (C) 2007, 2009 Dennis Friis <peavey@inspircd.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 "clientprotocolevent.h"
#include "modules/exemption.h"
#include "modules/names.h"
#include "modules/who.h"

class AuditoriumMode final
	: public SimpleChannelMode
{
public:
	AuditoriumMode(Module* Creator)
		: SimpleChannelMode(Creator, "auditorium", 'u')
	{
		ranktoset = ranktounset = OP_VALUE;
	}
};

class ModuleAuditorium;

namespace
{

/** Hook handler for join client protocol events.
 * This allows us to block join protocol events completely, including all associated messages (e.g. MODE, away-notify AWAY).
 * This is not the same as OnUserJoin() because that runs only when a real join happens but this runs also when a module
 * such as delayjoin or hostcycle generates a join.
 */
class JoinHook final
	: public ClientProtocol::EventHook
{
	ModuleAuditorium* const parentmod;
	bool active;

public:
	JoinHook(ModuleAuditorium* mod);
	void OnEventInit(const ClientProtocol::Event& ev) override;
	ModResult OnPreEventSend(LocalUser* user, const ClientProtocol::Event& ev, ClientProtocol::MessageList& messagelist) override;
};

}

class ModuleAuditorium final
	: public Module
	, public Names::EventListener
	, public Who::EventListener
	, public Who::VisibleEventListener
{
	CheckExemption::EventProvider exemptionprov;
	AuditoriumMode aum;
	bool OpsVisible;
	bool OpsCanSee;
	bool OperCanSee;
	JoinHook joinhook;

public:
	ModuleAuditorium()
		: Module(VF_VENDOR, "Adds channel mode u (auditorium) which hides unprivileged users in a channel from each other.")
		, Names::EventListener(this)
		, Who::EventListener(this)
		, Who::VisibleEventListener(this)
		, exemptionprov(this)
		, aum(this)
		, joinhook(this)
	{
	}

	void ReadConfig(ConfigStatus& status) override
	{
		const auto& tag = ServerInstance->Config->ConfValue("auditorium");
		OpsVisible = tag->getBool("opvisible");
		OpsCanSee = tag->getBool("opcansee");
		OperCanSee = tag->getBool("opercansee", true);
	}

	/* Can they be seen by everyone? */
	bool IsVisible(Membership* memb)
	{
		if (!memb->chan->IsModeSet(&aum))
			return true;

		ModResult res = exemptionprov.Check(memb->user, memb->chan, "auditorium-vis");
		return res.check(OpsVisible && memb->GetRank() >= OP_VALUE);
	}

	/* Can they see this specific membership? */
	bool CanSee(User* issuer, Membership* memb)
	{
		// If user is oper and operoverride is on, don't touch the list
		if (OperCanSee && issuer->HasPrivPermission("channels/auspex"))
			return true;

		// You can always see yourself
		if (issuer == memb->user)
			return true;

		// Can you see the list by permission?
		ModResult res = exemptionprov.Check(issuer, memb->chan, "auditorium-see");
		return res.check(OpsCanSee && memb->chan->GetPrefixValue(issuer) >= OP_VALUE);
	}

	ModResult OnNamesListItem(LocalUser* issuer, Membership* memb, std::string& prefixes, std::string& nick) override
	{
		if (IsVisible(memb))
			return MOD_RES_PASSTHRU;

		if (CanSee(issuer, memb))
			return MOD_RES_PASSTHRU;

		// Don't display this user in the NAMES list
		return MOD_RES_DENY;
	}

	/** Build CUList for showing this join/part/kick */
	void BuildExcept(Membership* memb, CUList& excepts)
	{
		if (IsVisible(memb))
			return;

		for (const auto& [user, _] : memb->chan->GetUsers())
		{
			if (IS_LOCAL(user) && !CanSee(user, memb))
				excepts.insert(user);
		}
	}

	void OnUserPart(Membership* memb, std::string& partmessage, CUList& excepts) override
	{
		BuildExcept(memb, excepts);
	}

	void OnUserKick(User* source, Membership* memb, const std::string& reason, CUList& excepts) override
	{
		BuildExcept(memb, excepts);
	}

	void OnBuildNeighborList(User* source, User::NeighborList& include, User::NeighborExceptions& exception) override
	{
		for (User::NeighborList::iterator i = include.begin(); i != include.end(); )
		{
			Membership* memb = *i;
			if (IsVisible(memb))
			{
				++i;
				continue;
			}

			// this channel should not be considered when listing my neighbors
			i = include.erase(i);
			// however, that might hide me from ops that can see me...
			for (const auto& [user, _] : memb->chan->GetUsers())
			{
				if (IS_LOCAL(user) && CanSee(user, memb))
					exception[user] = true;
			}
		}
	}

	ModResult OnWhoLine(const Who::Request& request, LocalUser* source, User* user, Membership* memb, Numeric::Numeric& numeric) override
	{
		if (!memb)
			return MOD_RES_PASSTHRU;
		if (IsVisible(memb))
			return MOD_RES_PASSTHRU;
		if (CanSee(source, memb))
			return MOD_RES_PASSTHRU;
		return MOD_RES_DENY;
	}

	ModResult OnWhoVisible(const Who::Request& request, LocalUser* source, Membership* memb) override
	{
		// Never pick a channel as the first visible one if the channel is in auditorium mode.
		return IsVisible(memb) || CanSee(source, memb) ? MOD_RES_PASSTHRU : MOD_RES_DENY;
	}
};

JoinHook::JoinHook(ModuleAuditorium* mod)
	: ClientProtocol::EventHook(mod, "JOIN", 10)
	, parentmod(mod)
{
}

void JoinHook::OnEventInit(const ClientProtocol::Event& ev)
{
	const ClientProtocol::Events::Join& join = static_cast<const ClientProtocol::Events::Join&>(ev);
	active = !parentmod->IsVisible(join.GetMember());
}

ModResult JoinHook::OnPreEventSend(LocalUser* user, const ClientProtocol::Event& ev, ClientProtocol::MessageList& messagelist)
{
	if (!active)
		return MOD_RES_PASSTHRU;

	const ClientProtocol::Events::Join& join = static_cast<const ClientProtocol::Events::Join&>(ev);
	return ((parentmod->CanSee(user, join.GetMember())) ? MOD_RES_PASSTHRU : MOD_RES_DENY);
}

MODULE_INIT(ModuleAuditorium)