// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

namespace ircd::m::sync
{
	static bool room_state_append(data &, json::stack::array &, const m::event &, const m::event::idx &, const bool &query_prev);

	static bool room_state_phased_member_events(data &, json::stack::array &);
	static bool room_state_phased_events(data &);
	static bool room_state_phased_prefetch(data &);
	static bool room_state_polylog_events(data &);
	static bool room_state_polylog_prefetch(data &);
	static bool _room_state_polylog(data &);
	static bool room_state_polylog(data &);
	static bool room_invite_state_polylog(data &);

	static bool room_state_linear_events(data &);
	static bool room_invite_state_linear(data &);
	static bool room_state_linear(data &);

	static const size_t MEMBER_SCAN_MAX {32};
	extern conf::item<size_t> member_scan_max;
	extern conf::item<bool> lazyload_members_enable;
	extern conf::item<bool> crazyload_historical_members;

	extern item room_invite_state;
	extern item room_state;
}

ircd::mapi::header
IRCD_MODULE
{
	"Client Sync :Room State"
};

decltype(ircd::m::sync::room_state)
ircd::m::sync::room_state
{
	"rooms.state",
	room_state_polylog,
	room_state_linear,
	{
		{ "phased",   true },
		{ "prefetch", true },
	}
};

decltype(ircd::m::sync::room_invite_state)
ircd::m::sync::room_invite_state
{
	"rooms.invite_state",
	room_invite_state_polylog,
	room_invite_state_linear,
	{
		{ "phased", true },
	}
};

bool
ircd::m::sync::room_state_linear(data &data)
{
	if(data.membership == "invite")
		return false;

	return room_state_linear_events(data);
}

bool
ircd::m::sync::room_invite_state_linear(data &data)
{
	if(data.membership != "invite")
		return false;

	return room_state_linear_events(data);
}

bool
ircd::m::sync::room_state_linear_events(data &data)
{
	if(!data.event_idx)
		return false;

	if(!data.room)
		return false;

	if(!data.membership)
		return false;

	assert(data.event);
	if(!json::get<"state_key"_>(*data.event))
		return false;

	const bool is_own_membership
	{
		json::get<"type"_>(*data.event) == "m.room.member"
		&& json::get<"state_key"_>(*data.event) == data.user.user_id
	};

	const bool is_own_join
	{
		is_own_membership
		&& data.membership == "join"
	};

	if(is_own_join)
	{
		// Special case gimmick; this effectively stops the linear-sync at this
		// event and has /sync respond with a token containing a flag. When the
		// client makes the next request with this flag we treat it as if they
		// were using the ?full_state=true query parameter. This will enter the
		// polylog handler instead of the linear handler (here) so as to
		// efficiently sync the entire room's state to the client; as we cannot
		// perform that feat from this handler.
		data.reflow_full_state = true;
		return false;
	}

	const ssize_t &viewport_size
	{
		room::events::viewport_size
	};

	const auto sounding
	{
		data.room_depth - json::get<"depth"_>(*data.event)
	};

	// Figure out whether the event was included in the timeline
	const bool viewport_visible
	{
		viewport_size <= 0
		|| data.membership == "invite"
		|| sounding < viewport_size
	};

	// Query whether this state cell has been overwritten. Unlike the timeline,
	// the state field will not be processed sequentially by our client.
	const bool stale
	{
		m::room::state::next(data.event_idx) != 0
	};

	if(!viewport_visible && stale)
		return false;

	json::stack::object rooms
	{
		*data.out, "rooms"
	};

	json::stack::object membership_
	{
		*data.out, data.membership
	};

	json::stack::object room_
	{
		*data.out, data.room->room_id
	};

	const auto &state_member_name
	{
		data.membership == "invite"?
			"invite_state": // "invite_state"_sv:
			"state"
	};

	json::stack::object state
	{
		*data.out, state_member_name
	};

	json::stack::array array
	{
		*data.out, "events"
	};

	bool ret{false};
	const auto append
	{
		[&data, &array, &ret](const event::idx &event_idx)
		{
			const event::fetch event
			{
				std::nothrow, event_idx
			};

			if(event.valid)
				ret |= room_state_append(data, array, event, event_idx, true);

			return true;
		}
	};

	if(is_own_membership && data.membership == "invite")
	{
		const m::room::state state{*data.room};
		state.get(std::nothrow, "m.room.create", "", append);
		state.get(std::nothrow, "m.room.join_rules", "", append);
		state.get(std::nothrow, "m.room.power_levels", "", append);
		state.get(std::nothrow, "m.room.history_visibility", "", append);
		state.get(std::nothrow, "m.room.avatar", "", append);
		state.get(std::nothrow, "m.room.name", "", append);
		state.get(std::nothrow, "m.room.canonical_alias", "", append);
		state.get(std::nothrow, "m.room.aliases", my_host(), append);
	}

	// Branch for supplying state to the client after its user's invite
	// is processed. At this point the client has not received prior room
	// state in /sync.
	if(is_own_membership && data.membership == "invite")
	{
		const m::room::state state{*data.room};
		const auto &sender
		{
			json::get<"sender"_>(*data.event)
		};

		state.get(std::nothrow, "m.room.member", sender, append);
	}

	ret |= room_state_append(data, array, *data.event, data.event_idx, true);
	return ret;
}

bool
ircd::m::sync::room_state_polylog(data &data)
{
	if(data.membership == "invite")
		return false;

	return _room_state_polylog(data);
}

bool
ircd::m::sync::room_invite_state_polylog(data &data)
{
	if(data.membership != "invite")
		return false;

	return _room_state_polylog(data);
}

bool
ircd::m::sync::_room_state_polylog(data &data)
{
	assert(data.args);

	const bool full_state_all
	{
		data.args->full_state &&
		!has(std::get<2>(data.args->since), 'P')
	};

	if(likely(!full_state_all))
		if(!data.phased && int64_t(data.range.first) > 0)
			if(!apropos(data, data.room_head))
				return false;

	if(data.phased && data.range.first == 0)
	{
		if(data.prefetch)
			return room_state_phased_prefetch(data);
		else
			return room_state_phased_events(data);
	}

	if(data.prefetch)
		return room_state_polylog_prefetch(data);
	else
		return room_state_polylog_events(data);
}

decltype(ircd::m::sync::member_scan_max)
ircd::m::sync::member_scan_max
{
	{ "name",         "ircd.client.sync.rooms.state.members.scan.max" },
	{ "default",      12L                                             },
};

decltype(ircd::m::sync::lazyload_members_enable)
ircd::m::sync::lazyload_members_enable
{
	{ "name",         "ircd.client.sync.rooms.state.members.lazyload" },
	{ "default",      true                                            },
	{ "persist",      false                                           },
};

decltype(ircd::m::sync::crazyload_historical_members)
ircd::m::sync::crazyload_historical_members
{
	{ "name",         "ircd.client.sync.rooms.state.members.historical" },
	{ "default",      false                                             },
};

bool
ircd::m::sync::room_state_polylog_prefetch(data &data)
{
	return false;
}

bool
ircd::m::sync::room_state_polylog_events(data &data)
{
	bool ret{false};
	ctx::mutex mutex;
	json::stack::array array
	{
		*data.out, "events"
	};

	static const auto num(64); //TODO: XXX
	sync::pool.min(num);

	unsigned long long a_mask[2] {0};
	allocator::state a(num, a_mask);
	std::vector<m::event::fetch> events(num);
	ctx::concurrent<event::idx> concurrent
	{
		sync::pool, [&data, &ret, &mutex, &array, &events, &a](const auto &event_idx)
		{
			const auto i(a.allocate(1)); const unwind i_{[&a, &i]
			{
				a.deallocate(i, 1);
			}};

			assert(i < events.size());
			auto &event(events.at(i));
			if(!m::seek(std::nothrow, event, event_idx))
			{
				log::error
				{
					log, "Failed to fetch event idx:%lu in room %s state.",
					event_idx,
					string_view{data.room->room_id},
				};

				assert(!event.valid);
				return;
			}

			assert(event.valid);
			const std::lock_guard lock{mutex};
			ret |= room_state_append(data, array, event, event_idx, false);
		}
	};

	const auto &room_filter
	{
		json::get<"room"_>(data.filter)
	};

	const auto &state_filter
	{
		json::get<"state"_>(room_filter)
	};

	const room::state state
	{
		*data.room
	};

	const auto &lazyload_members
	{
		lazyload_members_enable
		&& json::get<"lazy_load_members"_>(state_filter)
	};

	const bool full_state_reflow
	{
		data.args->full_state
		&& has(std::get<2>(data.args->since), 'P')
	};

	const bool full_state_all
	{
		data.args->full_state
		&& !full_state_reflow
	};

	state.for_each([&data, &concurrent, &lazyload_members]
	(const string_view &type, const string_view &state_key, const event::idx &event_idx)
	{
		// Conditions to skip state when not forcing full_state
		if(likely(!data.args->full_state))
		{
			// If this event is not in the sync range
			if(likely(!apropos(data, event_idx)))
				return true;

			// Branch for crazy/lazyloading conditions to skip.
			if(type == "m.room.member")
			{
				if(lazyload_members)
					return true;

				if(!crazyload_historical_members)
					if(data.membership == "leave" || data.membership == "ban")
						return true;
			}
		}

		this_ctx::interruption_point();
		concurrent(event_idx);
		return true;
	});

	const ctx::uninterruptible::nothrow ui;
	concurrent.wait();
	return ret;
}

bool
ircd::m::sync::room_state_phased_prefetch(data &data)
{
	const size_t configured_count
	{
		std::min(size_t(room::events::viewport_size), size_t(member_scan_max))
	};

	const size_t member_count
	{
		std::min(configured_count, MEMBER_SCAN_MAX)
	};

	const std::pair<string_view, string_view> state_keys[]
	{
		{ "m.room.create",           ""                        },
		{ "m.room.canonical_alias",  ""                        },
		{ "m.room.name",             ""                        },
		{ "m.room.avatar",           ""                        },
		{ "m.room.aliases",          data.user.user_id.host()  },
		{ "m.room.member",           data.user.user_id         },
	};

	// Prefetch the state cells
	const room::state state
	{
		*data.room
	};

	for(const auto &[type, state_key] : state_keys)
		state.prefetch(type, state_key);

	m::room::events events
	{
		*data.room
	};

	// Prefetch the senders of the recent room events
	for(size_t i(0); events && i < member_count; --events, ++i)
		m::prefetch(events.event_idx(), "sender");

	return true;
}

bool
ircd::m::sync::room_state_phased_events(data &data)
{
	bool ret{false};
	ctx::mutex mutex;
	json::stack::array array
	{
		*data.out, "events"
	};

	const auto append
	{
		[&data, &array, &ret, &mutex]
		(const m::event::idx &event_idx, const m::event &event)
		{
			const std::lock_guard lock{mutex};
			ret |= room_state_append(data, array, event, event_idx, true);
		}
	};

	const std::pair<string_view, string_view> keys[]
	{
		{ "m.room.create",           ""                        },
		{ "m.room.canonical_alias",  ""                        },
		{ "m.room.name",             ""                        },
		{ "m.room.avatar",           ""                        },
		{ "m.room.aliases",          data.user.user_id.host()  },
		{ "m.room.member",           data.user.user_id         },
	};

	const room::state state
	{
		*data.room
	};

	// Fetch the state cells and prefetch the event data
	size_t i(0);
	size_t prev_content_prefetched(0);
	static const auto num_keys(sizeof(keys) / sizeof(*keys));
	std::array<event::idx, num_keys> event_idx;
	for(const auto &[type, state_key] : keys)
	{
		auto &idx(event_idx.at(i++));
		idx = state.get(std::nothrow, type, state_key);

		// Prefetch the content of the previous state for event::append()
		if(likely(type != "m.room.create"))
		{
			const auto &prev_idx
			{
				room::state::prev(idx)
			};

			prev_content_prefetched += m::prefetch(prev_idx, "content");
		}
	}

	// Fetch the event data and stream to client
	m::event::fetch event;
	assert(i <= event_idx.size());
	for(i = 0; i < event_idx.size(); ++i) try
	{
		if(!event_idx.at(i))
			continue;

		seek(event, event_idx.at(i));
		append(event_idx.at(i), event);
	}
	catch(const std::exception &e)
	{
		const auto &[type, state_key]
		{
			keys[i]
		};

		log::error
		{
			log, "Failed to find event_idx:%lu in room %s state (%s,%s)",
			event_idx.at(i),
			string_view{data.room->room_id},
			type,
			state_key,
		};
	}

	if(data.membership == "join")
		ret |= room_state_phased_member_events(data, array);

	return ret;
}

bool
ircd::m::sync::room_state_phased_member_events(data &data,
                                               json::stack::array &array)
{
	// The number of recent room events we'll seek senders for.
	const size_t configured_count
	{
		std::min(size_t(room::events::viewport_size), size_t(member_scan_max))
	};

	const size_t count
	{
		std::min(configured_count, MEMBER_SCAN_MAX)
	};

	m::room::events it
	{
		*data.room
	};

	// Prefetch the senders of the recent room events
	size_t i(0), prefetched(0);
	std::array<event::idx, MEMBER_SCAN_MAX> event_idx;
	assert(count <= MEMBER_SCAN_MAX && count <= event_idx.size());
	for(; it && i < count; --it, ++i)
	{
		event_idx[i] = it.event_idx();
		prefetched += m::prefetch(event_idx[i], "sender");
	}

	// Transform the senders into member event::idx's and prefetch events
	std::transform(begin(event_idx), begin(event_idx) + i, begin(event_idx), [&data]
	(const m::event::idx &event_idx)
	{
		const event::idx &member_idx
		{
			m::query(std::nothrow, event_idx, "sender", [&data]
			(const string_view &sender)
			{
				return data.room->get(std::nothrow, "m.room.member", sender);
			})
		};

		m::prefetch(member_idx);
		return member_idx;
	});

	// Eliminate duplicate member event::idx
	std::sort(begin(event_idx), begin(event_idx) + i);
	const auto end(std::unique(begin(event_idx), begin(event_idx) + i));
	assert(std::distance(begin(event_idx), end) > 0 || i == 0);

	// Fetch and stream those member events to client
	bool ret{false};
	m::event::fetch event;
	std::for_each(begin(event_idx), end, [&data, &array, &ret, &event]
	(const event::idx &sender_idx)
	{
		if(!seek(std::nothrow, event, sender_idx))
			return;

		ret |= room_state_append(data, array, event, sender_idx, false);
	});

	return ret;
}

bool
ircd::m::sync::room_state_append(data &data,
                                 json::stack::array &events,
                                 const m::event &event,
                                 const m::event::idx &event_idx,
                                 const bool &query_prev)
{
	return m::event::append
	{
		events, event,
		{
			.event_idx = &event_idx,
			.user_id = &data.user.user_id,
			.user_room = &data.user_room,
			.room_depth = &data.room_depth,
			.query_txnid = false,
			.query_prev_state = query_prev,
		}
	};
}