// 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.

#include "rooms.h"

using namespace ircd;

struct pagination_tokens
{
	uint8_t limit;
	char dir;
	m::event::id::buf from;
	m::event::id::buf to;

	pagination_tokens(const m::resource::request &);
};

conf::item<size_t>
max_filter_miss
{
	{ "name",      "ircd.client.rooms.messages.max_filter_miss" },
	{ "default",   2048L                                        },
};

conf::item<float>
postfetch_multiplier
{
	{ "name",      "ircd.client.rooms.messages.postfetch.multiplier" },
	{ "default",   2.0                                               },
};

log::log
messages_log
{
	"m.messages"
};

m::resource::response
get__messages(client &client,
              const m::resource::request &request,
              const m::room::id &room_id)
{
	const pagination_tokens page
	{
		request
	};

	const auto &filter_query
	{
		request.query["filter"]
	};

	const unique_buffer<mutable_buffer> filter_buf
	{
		size(filter_query)
	};

	const json::object &filter_json
	{
		url::decode(filter_buf, filter_query)
	};

	const m::room_event_filter filter
	{
		filter_json.has("filter_json")?
			json::object{filter_json.get("filter_json")}:
			filter_json
	};

	const m::room room
	{
		room_id, page.from
	};

	if(!visible(room, request.user_id))
		throw m::ACCESS_DENIED
		{
			"You are not permitted to view the room at this event"
		};

	const m::user::room user_room
	{
		request.user_id
	};

	const auto room_depth
	{
		m::depth(std::nothrow, room)
	};

	m::resource::response::chunked response
	{
		client, http::OK
	};

	json::stack out
	{
		response.buf, response.flusher()
	};

	json::stack::object top
	{
		out
	};

	m::event::id::buf start
	{
		page.from
	};

	m::event::id::buf end
	{
		page.to
	};

	json::stack::array chunk
	{
		top, "chunk"
	};

	size_t hit{0}, miss{0};
	m::room::events it
	{
		room
	};

	m::event::fetch event;
	for(; it; page.dir == 'b'? --it : ++it)
	{
		const auto &event_idx(it.event_idx());
		if(!seek(std::nothrow, event, event_idx))
			continue;

		end = event.event_id;
		if(hit >= page.limit || miss >= size_t(max_filter_miss))
			break;

		const bool ok
		{
			(empty(filter_json) || match(filter, event))

			&& visible(event, request.user_id)

			&& m::event::append
			{
				chunk, event,
				{
					.event_idx = &event_idx,
					.user_id = &user_room.user.user_id,
					.user_room = &user_room,
					.room_depth = &room_depth,
				}
			}
		};

		hit += ok;
		miss += !ok;
	}
	chunk.~array();

	if(it || page.dir == 'b')
		json::stack::member
		{
			top, "start", json::value{start}
		};

	if(it || page.dir != 'b')
		json::stack::member
		{
			top, "end", json::value{end}
		};

	// Manually close out and flush here so the client isn't impacted by
	// anything related to the postprefetching loop below.
	top.~object();
	out.flush(true);
	response.finish();

	// Continue the room::events iteration to prefetch the next results for a
	// client hitting /messages to paginate. This endpoint does not conduct any
	// other prefetching because: 1. The first /messages is predicted by other
	// requests which initiate prefetches. 2. Subsequent /messages are
	// prefetched by the following loop after each request from here. Note that
	// this loop does not yet account for visibility and filters etc.
	size_t postfetched(0);
	const size_t postfetch_max(page.limit * float(postfetch_multiplier));
	for(size_t i(0); i <= postfetch_max && it; ++i, page.dir == 'b'? --it : ++it)
	{
		const auto &event_idx(it.event_idx());
		postfetched += m::prefetch(event_idx);
	}

	log::debug
	{
		messages_log, "%s in %s from:%s to:%s dir:%c limit:%zu start:%s end:%s hit:%zu miss:%zu post:%zu",
		loghead(client),
		string_view{room_id},
		string_view{page.from},
		string_view{page.to},
		page.dir,
		page.limit,
		string_view{start},
		string_view{end},
		hit,
		miss,
		postfetched,
	};

	return {};
}

// Client-Server 6.3.6 query parameters
pagination_tokens::pagination_tokens(const m::resource::request &request)
try
:limit
{
	// The maximum number of events to return. Default: 10.
	// > we limit this to 255 via narrowing cast
	request.query["limit"]?
		uint8_t(lex_cast<ulong>(request.query.at("limit"))):
		uint8_t(10)
}
,dir
{
	// Required. The direction to return events from. One of: ["b", "f"]
	request.query.at("dir").at(0)
}
{
	// Required. The token to start returning events from. This token can be
	// obtained from a prev_batch token returned for each room by the sync
	// API, or from a start or end token returned by a previous request to
	// this endpoint.
	//
	// NOTE: Synapse doesn't require this and many clients have forgotten to
	// NOTE: use it so we have to relax the requirement here.
	if(!empty(request.query["from"]))
		from = url::decode(from, request.query.at("from"));

	// The token to stop returning events at. This token can be obtained from
	// a prev_batch token returned for each room by the sync endpoint, or from
	// a start or end token returned by a previous request to this endpoint.
	if(!empty(request.query["to"]))
		to = url::decode(to, request.query.at("to"));

	if(dir != 'b' && dir != 'f')
		throw m::BAD_PAGINATION
		{
			"query parameter 'dir' must be 'b' or 'f'"
		};
}
catch(const bad_lex_cast &)
{
	throw m::BAD_PAGINATION
	{
		"query parameter 'limit' is invalid"
	};
}
catch(const m::INVALID_MXID &)
{
	throw m::BAD_PAGINATION
	{
		"query parameter 'from' or 'to' is not a valid token"
	};
}