%% Copyright (c) 2023, Loïc Hoguin <essen@ninenines.eu>
%%
%% 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 appear in all copies.
%%
%% THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
%% WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
%% MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
%% ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
%% WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
%% ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
%% OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

%% A key difference between cowboy_http2 and cowboy_http3
%% is that HTTP/3 streams are QUIC streams and therefore
%% much of the connection state is handled outside of
%% Cowboy.

-module(cowboy_http3).

-export([init/3]).

%% Temporary callback to do sendfile over QUIC.
-export([send/2]).

-record(stream, {
	id :: non_neg_integer(), %% @todo specs

	%% Whether the stream is currently in a special state.
	status :: header | normal | {data, non_neg_integer()} | stopping,

	%% Stream buffer.
	buffer = <<>> :: binary(),

	%% Stream state.
	state = undefined :: undefined | {module, any()}
}).

-record(state, {
	parent :: pid(),
	conn :: any(), %% @todo specs
	opts = #{} :: any(), %% @todo opts(),

	%% Remote address and port for the connection.
	peer = undefined :: {inet:ip_address(), inet:port_number()},

	%% Local address and port for the connection.
	sock = undefined :: {inet:ip_address(), inet:port_number()},

	%% HTTP/3 state machine.
	http3_machine :: cow_http3_machine:http3_machine(),

	%% Quick pointers for commonly used streams.
	local_control_id :: any(), %% @todo specs Control stream must not be closed.
	local_encoder_id :: any(), %% @todo specs
	local_decoder_id :: any(), %% @todo specs

	%% Bidirectional streams used for requests and responses,
	%% as well as unidirectional streams initiated by the client.
	streams = #{} :: map(), %% @todo specs
	%% @todo a ref/id map because stream_closed we don't have the id

	%% Lingering streams that were recently reset. We may receive
	%% pending data or messages for these streams a short while
	%% after they have been reset.
	lingering_streams = [] :: [non_neg_integer()],

	%% Streams can spawn zero or more children which are then managed
	%% by this module if operating as a supervisor.
	children = cowboy_children:init() :: cowboy_children:children()
}).

-spec init(_, _, _) -> no_return().

init(Parent, Conn, Opts) ->
%ct:pal("init"),
	{ok, SettingsBin, HTTP3Machine0} = cow_http3_machine:init(server, Opts),
	%% Immediately open a control, encoder and decoder stream.
	{ok, ControlID} = cowboy_quicer:start_unidi_stream(Conn, [<<0>>, SettingsBin]),
	{ok, EncoderID} = cowboy_quicer:start_unidi_stream(Conn, <<2>>),
	{ok, DecoderID} = cowboy_quicer:start_unidi_stream(Conn, <<3>>),
%ct:pal("control ~p encoder ~p decoder ~p", [ControlID, EncoderID, DecoderID]),
	%% Set the control, encoder and decoder streams in the machine.
	HTTP3Machine = cow_http3_machine:init_unidi_local_streams(
		ControlID, EncoderID, DecoderID, HTTP3Machine0),
	%% Get the peername/sockname.
	Peer0 = cowboy_quicer:peername(Conn),
	Sock0 = cowboy_quicer:sockname(Conn),
	%% @todo Get the peer certificate here if it makes sense.
	case {Peer0, Sock0} of
		{{ok, Peer}, {ok, Sock}} ->
			%% Quick! Let's go!
			loop(#state{parent=Parent, conn=Conn, opts=Opts,
				peer=Peer, sock=Sock, http3_machine=HTTP3Machine,
				local_control_id=ControlID,
				local_encoder_id=EncoderID,
				local_decoder_id=DecoderID});
		{{error, Reason}, _} ->
			terminate(undefined, {socket_error, Reason,
				'A socket error occurred when retrieving the peer name.'});
		{_, {error, Reason}} ->
			terminate(undefined, {socket_error, Reason,
				'A socket error occurred when retrieving the sock name.'})
	end.

loop(State0=#state{children=Children}) ->
%ct:pal("~p", [process_info(self(), messages)]),
	receive
		Msg when element(1, Msg) =:= quic ->
			handle_quic_msg(State0, Msg);
		%% Timeouts.
		{timeout, Ref, {shutdown, Pid}} ->
			cowboy_children:shutdown_timeout(Children, Ref, Pid),
			loop(State0);
		%% Messages pertaining to a stream.
		{{Pid, StreamID}, Msg} when Pid =:= self() ->
			loop(info(State0, StreamID, Msg));
		%% Exit signal from children.
		Msg = {'EXIT', Pid, _} ->
			loop(down(State0, Pid, Msg));
		Msg ->
			ct:pal("cowboy msg ~p", [Msg]),
			loop(State0)
	end.

handle_quic_msg(State0, Msg) ->
	case cowboy_quicer:handle(Msg) of
		{data, StreamID, IsFin, Data} ->
%			ct:pal("{data, ~p, ~p, ~p}", [StreamID, IsFin, Data]),
			parse(State0, Data, StreamID, IsFin);
		{stream_started, StreamID, StreamType} ->
%			ct:pal("~p stream_started ~p ~p", [self(), StreamID, StreamType]),
			State = stream_new_remote(State0, StreamID, StreamType),
			loop(State);
		{stream_closed, StreamID, ErrorCode} ->
%			ct:pal("stream_closed ~p state ~p code ~p", [StreamID, State0, ErrorCode]),
			State = stream_closed(State0, StreamID, ErrorCode),
			loop(State);
		closed ->
			%% @todo terminate here?
			ok;
		ok ->
			loop(State0)
	end.

parse(State=#state{opts=Opts}, Data, StreamID, IsFin) ->
	case stream_get(State, StreamID) of
		Stream=#stream{buffer= <<>>} ->
			parse1(State, Data, Stream, IsFin);
		Stream=#stream{buffer=Buffer} ->
			Stream1 = Stream#stream{buffer= <<>>},
			parse1(stream_store(State, Stream1),
				<<Buffer/binary, Data/binary>>, Stream1, IsFin);
		%% Pending data for a stream that has been reset. Ignore.
		error ->
			case is_lingering_stream(State, StreamID) of
				true ->
					ok;
				false ->
					%% We avoid logging the data as it could be quite large.
					cowboy:log(warning, "Received data for unknown stream ~p.",
						[StreamID], Opts)
			end,
			loop(State)
	end.

%% @todo Swap Data and Stream/StreamID?
parse1(State, Data, Stream=#stream{status=header}, IsFin) ->
	parse_unidirectional_stream_header(State, Data, Stream, IsFin);
parse1(State, Data, Stream=#stream{status={data, Len}, id=StreamID}, IsFin) ->
	DataLen = byte_size(Data),
	if
		DataLen < Len ->
			%% We don't have the full frame but this is the end of the
			%% data we have. So FrameIsFin is equivalent to IsFin here.
			loop(frame(State, Stream#stream{status={data, Len - DataLen}}, {data, Data}, IsFin));
		true ->
			<<Data1:Len/binary, Rest/bits>> = Data,
			FrameIsFin = is_fin(IsFin, Rest),
			parse(frame(State, Stream#stream{status=normal}, {data, Data1}, FrameIsFin),
				Rest, StreamID, IsFin)
	end;
%% @todo Clause that discards receiving data for stopping streams.
%%       We may receive a few more frames after we abort receiving.
parse1(State, Data, Stream=#stream{id=StreamID}, IsFin) ->
	case cow_http3:parse(Data) of
		{ok, Frame, Rest} ->
			FrameIsFin = is_fin(IsFin, Rest),
%			ct:pal("parse1 Frame= ~p Rest= ~p", [Frame, Rest]),
			parse(frame(State, Stream, Frame, FrameIsFin), Rest, StreamID, IsFin);
		{more, Frame, Len} ->
			%% We're at the end of the data so FrameIsFin is equivalent to IsFin.
			case IsFin of
				nofin ->
					loop(frame(State, Stream#stream{status={data, Len}}, Frame, nofin));
				fin ->
					terminate(State, {connection_error, h3_frame_error,
						'Last frame on stream was truncated. (RFC9114 7.1)'})
			end;
		{ignore, Rest} ->
			parse(ignored_frame(State, Stream), Rest, StreamID, IsFin);
		Error = {connection_error, _, _} ->
			terminate(State, Error);
		more when Data =:= <<>> ->
			loop(stream_store(State, Stream#stream{buffer=Data}));
		more ->
			%% We're at the end of the data so FrameIsFin is equivalent to IsFin.
			case IsFin of
				nofin ->
					loop(stream_store(State, Stream#stream{buffer=Data}));
				fin ->
					terminate(State, {connection_error, h3_frame_error,
						'Last frame on stream was truncated. (RFC9114 7.1)'})
			end
	end.

%% We may receive multiple frames in a single QUIC packet.
%% The FIN flag applies to the QUIC packet, not to the frame.
%% We must therefore only consider the frame to have a FIN
%% flag if there's no data remaining to be read.
is_fin(fin, <<>>) -> fin;
is_fin(_, _) -> nofin.

parse_unidirectional_stream_header(State0=#state{http3_machine=HTTP3Machine0},
		Data, Stream0=#stream{id=StreamID}, IsFin) ->
	case cow_http3:parse_unidi_stream_header(Data) of
		{ok, Type, Rest} when Type =:= control; Type =:= encoder; Type =:= decoder ->
			case cow_http3_machine:set_unidi_remote_stream_type(
					StreamID, Type, HTTP3Machine0) of
				{ok, HTTP3Machine} ->
					State = State0#state{http3_machine=HTTP3Machine},
					Stream = Stream0#stream{status=normal},
					parse(stream_store(State, Stream), Rest, StreamID, IsFin);
				{error, Error={connection_error, _, _}, HTTP3Machine} ->
					terminate(State0#state{http3_machine=HTTP3Machine}, Error)
			end;
		{ok, push, _} ->
			terminate(State0, {connection_error, h3_stream_creation_error,
				'Only servers can push. (RFC9114 6.2.2)'});
		%% Unknown stream types must be ignored. We choose to abort the
		%% stream instead of reading and discarding the incoming data.
		{undefined, _} ->
			loop(stream_abort_receive(State0, Stream0, h3_stream_creation_error))
	end.

frame(State=#state{http3_machine=HTTP3Machine0, conn=Conn, local_decoder_id=DecoderID},
		Stream=#stream{id=StreamID}, Frame, IsFin) ->
%	ct:pal("cowboy frame ~p ~p", [Frame, IsFin]),
	case cow_http3_machine:frame(Frame, IsFin, StreamID, HTTP3Machine0) of
		{ok, HTTP3Machine} ->
			State#state{http3_machine=HTTP3Machine};
		{ok, {data, Data}, HTTP3Machine} ->
			data_frame(State#state{http3_machine=HTTP3Machine}, Stream, IsFin, Data);
		%% @todo I don't think we need the IsFin in the {headers tuple.
		{ok, {headers, IsFin, Headers, PseudoHeaders, BodyLen}, HTTP3Machine} ->
			headers_frame(State#state{http3_machine=HTTP3Machine},
				Stream, IsFin, Headers, PseudoHeaders, BodyLen);
		{ok, {headers, IsFin, Headers, PseudoHeaders, BodyLen}, DecData, HTTP3Machine} ->
			%% Send the decoder data.
			ok = cowboy_quicer:send(Conn, DecoderID, DecData),
			headers_frame(State#state{http3_machine=HTTP3Machine},
				Stream, IsFin, Headers, PseudoHeaders, BodyLen);
		{ok, {trailers, _Trailers}, HTTP3Machine} ->
			%% @todo Propagate trailers.
			State#state{http3_machine=HTTP3Machine};
		{ok, GoAway={goaway, _}, HTTP3Machine} ->
			goaway(State#state{http3_machine=HTTP3Machine}, GoAway);
		{error, Error={stream_error, _Reason, _Human}, HTTP3Machine} ->
			reset_stream(State#state{http3_machine=HTTP3Machine}, Stream, Error);
		{error, Error={connection_error, _, _}, HTTP3Machine} ->
			terminate(State#state{http3_machine=HTTP3Machine}, Error)
	end.

data_frame(State=#state{opts=Opts},
		Stream=#stream{id=StreamID, state=StreamState0}, IsFin, Data) ->
	try cowboy_stream:data(StreamID, IsFin, Data, StreamState0) of
		{Commands, StreamState} ->
			commands(State, Stream#stream{state=StreamState}, Commands)
	catch Class:Exception:Stacktrace ->
		cowboy:log(cowboy_stream:make_error_log(data,
			[StreamID, IsFin, Data, StreamState0],
			Class, Exception, Stacktrace), Opts),
		reset_stream(State, Stream, {internal_error, {Class, Exception},
			'Unhandled exception in cowboy_stream:data/4.'})
	end.

headers_frame(State, Stream, IsFin, Headers,
		PseudoHeaders=#{method := <<"CONNECT">>}, _)
		when map_size(PseudoHeaders) =:= 2 ->
	early_error(State, Stream, IsFin, Headers, PseudoHeaders, 501,
		'The CONNECT method is currently not implemented. (RFC7231 4.3.6)');
headers_frame(State, Stream, IsFin, Headers,
		PseudoHeaders=#{method := <<"TRACE">>}, _) ->
	early_error(State, Stream, IsFin, Headers, PseudoHeaders, 501,
		'The TRACE method is currently not implemented. (RFC9114 4.4, RFC7231 4.3.8)');
headers_frame(State, Stream, IsFin, Headers, PseudoHeaders=#{authority := Authority}, BodyLen) ->
	headers_frame_parse_host(State, Stream, IsFin, Headers, PseudoHeaders, BodyLen, Authority);
headers_frame(State, Stream, IsFin, Headers, PseudoHeaders, BodyLen) ->
	case lists:keyfind(<<"host">>, 1, Headers) of
		{_, Authority} ->
			headers_frame_parse_host(State, Stream, IsFin, Headers, PseudoHeaders, BodyLen, Authority);
		_ ->
			reset_stream(State, Stream, {stream_error, h3_message_error,
				'Requests translated from HTTP/1.1 must include a host header. (RFC7540 8.1.2.3, RFC7230 5.4)'})
	end.

headers_frame_parse_host(State=#state{peer=Peer, sock=Sock},
		Stream=#stream{id=StreamID}, IsFin, Headers,
		PseudoHeaders=#{method := Method, scheme := Scheme, path := PathWithQs},
		BodyLen, Authority) ->
	try cow_http_hd:parse_host(Authority) of
		{Host, Port0} ->
			Port = ensure_port(Scheme, Port0),
			try cow_http:parse_fullpath(PathWithQs) of
				{<<>>, _} ->
					reset_stream(State, Stream, {stream_error, h3_message_error,
						'The path component must not be empty. (RFC7540 8.1.2.3)'});
				{Path, Qs} ->
					Req0 = #{
						ref => quic, %% @todo Ref,
						pid => self(),
						streamid => StreamID,
						peer => Peer,
						sock => Sock,
						cert => undefined, %Cert, %% @todo
						method => Method,
						scheme => Scheme,
						host => Host,
						port => Port,
						path => Path,
						qs => Qs,
						version => 'HTTP/3',
						headers => headers_to_map(Headers, #{}),
						has_body => IsFin =:= nofin,
						body_length => BodyLen
					},
					%% We add the protocol information for extended CONNECTs.
					Req = case PseudoHeaders of
						#{protocol := Protocol} -> Req0#{protocol => Protocol};
						_ -> Req0
					end,
					headers_frame(State, Stream, Req)
			catch _:_ ->
				reset_stream(State, Stream, {stream_error, h3_message_error,
					'The :path pseudo-header is invalid. (RFC7540 8.1.2.3)'})
			end
	catch _:_ ->
		reset_stream(State, Stream, {stream_error, h3_message_error,
			'The :authority pseudo-header is invalid. (RFC7540 8.1.2.3)'})
	end.

%% @todo Copied from cowboy_http2.
%% @todo Remove "http"? Probably.
ensure_port(<<"http">>, undefined) -> 80;
ensure_port(<<"https">>, undefined) -> 443;
ensure_port(_, Port) -> Port.

%% @todo Copied from cowboy_http2.
%% This function is necessary to properly handle duplicate headers
%% and the special-case cookie header.
headers_to_map([], Acc) ->
	Acc;
headers_to_map([{Name, Value}|Tail], Acc0) ->
	Acc = case Acc0 of
		%% The cookie header does not use proper HTTP header lists.
		#{Name := Value0} when Name =:= <<"cookie">> ->
			Acc0#{Name => << Value0/binary, "; ", Value/binary >>};
		#{Name := Value0} ->
			Acc0#{Name => << Value0/binary, ", ", Value/binary >>};
		_ ->
			Acc0#{Name => Value}
	end,
	headers_to_map(Tail, Acc).

headers_frame(State=#state{opts=Opts}, Stream=#stream{id=StreamID}, Req) ->
%ct:pal("req ~p", [Req]),
	try cowboy_stream:init(StreamID, Req, Opts) of
		{Commands, StreamState} ->
%logger:error("~p", [Commands]),
%logger:error("~p", [StreamState]),
			commands(State, Stream#stream{state=StreamState}, Commands)
	catch Class:Exception:Stacktrace ->
		cowboy:log(cowboy_stream:make_error_log(init,
			[StreamID, Req, Opts],
			Class, Exception, Stacktrace), Opts),
		reset_stream(State, Stream, {internal_error, {Class, Exception},
			'Unhandled exception in cowboy_stream:init/3.'})
	end.






early_error(State0=#state{opts=Opts, peer=Peer},
		Stream=#stream{id=StreamID}, _IsFin, Headers, #{method := Method},
		StatusCode0, HumanReadable) ->
	%% We automatically terminate the stream but it is not an error
	%% per se (at least not in the first implementation).
	Reason = {stream_error, h3_no_error, HumanReadable},
	%% The partial Req is minimal for now. We only have one case
	%% where it can be called (when a method is completely disabled).
	%% @todo Fill in the other elements.
	PartialReq = #{
		ref => quic, %% @todo Ref,
		peer => Peer,
		method => Method,
		headers => headers_to_map(Headers, #{})
	},
	Resp = {response, StatusCode0, RespHeaders0=#{<<"content-length">> => <<"0">>}, <<>>},
	try cowboy_stream:early_error(StreamID, Reason, PartialReq, Resp, Opts) of
		{response, StatusCode, RespHeaders, RespBody} ->
			send_response(State0, Stream, StatusCode, RespHeaders, RespBody)
	catch Class:Exception:Stacktrace ->
		cowboy:log(cowboy_stream:make_error_log(early_error,
			[StreamID, Reason, PartialReq, Resp, Opts],
			Class, Exception, Stacktrace), Opts),
		%% We still need to send an error response, so send what we initially
		%% wanted to send. It's better than nothing.
		send_headers(State0, StreamID, fin, StatusCode0, RespHeaders0)
	end.







%% Erlang messages.

down(State0=#state{opts=Opts, children=Children0}, Pid, Msg) ->
	State = case cowboy_children:down(Children0, Pid) of
		%% The stream was terminated already.
		{ok, undefined, Children} ->
			State0#state{children=Children};
		%% The stream is still running.
		{ok, StreamID, Children} ->
			info(State0#state{children=Children}, StreamID, Msg);
		%% The process was unknown.
		error ->
			cowboy:log(warning, "Received EXIT signal ~p for unknown process ~p.~n",
				[Msg, Pid], Opts),
			State0
	end,
	if
%% @todo
%		State#state.http2_status =:= closing, State#state.streams =:= #{} ->
%			terminate(State, {stop, normal, 'The connection is going away.'});
		true ->
			State
	end.

info(State=#state{opts=Opts, http3_machine=_HTTP3Machine}, StreamID, Msg) ->
%ct:pal("INFO ~p ~p ~p", [State, StreamID, Msg]),
	case stream_get(State, StreamID) of
		Stream=#stream{state=StreamState0} ->
			try cowboy_stream:info(StreamID, Msg, StreamState0) of
				{Commands, StreamState} ->
%ct:pal("~p", [Commands]),
%logger:error("~p ~p", [StreamID, Streams]),
					commands(State, Stream#stream{state=StreamState}, Commands)
			catch Class:Exception:Stacktrace ->
				cowboy:log(cowboy_stream:make_error_log(info,
					[StreamID, Msg, StreamState0],
					Class, Exception, Stacktrace), Opts),
				reset_stream(State, Stream, {internal_error, {Class, Exception},
					'Unhandled exception in cowboy_stream:info/3.'})
			end;
		error ->
			case is_lingering_stream(State, StreamID) of
				true ->
					ok;
				false ->
					cowboy:log(warning, "Received message ~p for unknown stream ~p.",
						[Msg, StreamID], Opts)
			end,
			State
	end.

%% Stream handler commands.

commands(State, Stream, []) ->
	stream_store(State, Stream);
%% Error responses are sent only if a response wasn't sent already.
commands(State=#state{http3_machine=HTTP3Machine}, Stream=#stream{id=StreamID},
		[{error_response, StatusCode, Headers, Body}|Tail]) ->
	case cow_http3_machine:get_stream_local_state(StreamID, HTTP3Machine) of
		{ok, idle} ->
			commands(State, Stream, [{response, StatusCode, Headers, Body}|Tail]);
		_ ->
			commands(State, Stream, Tail)
	end;
%% Send an informational response.
commands(State0, Stream, [{inform, StatusCode, Headers}|Tail]) ->
	State = send_headers(State0, Stream, idle, StatusCode, Headers),
	commands(State, Stream, Tail);
%% Send response headers.
commands(State0, Stream, [{response, StatusCode, Headers, Body}|Tail]) ->
%	ct:pal("~p commands response ~p ~p ~p", [self(), StatusCode, Headers, try iolist_size(Body) catch _:_ -> Body end]),
	State = send_response(State0, Stream, StatusCode, Headers, Body),
	commands(State, Stream, Tail);
%% Send response headers.
commands(State0, Stream, [{headers, StatusCode, Headers}|Tail]) ->
%	ct:pal("commands headers ~p ~p", [StatusCode, Headers]),
	State = send_headers(State0, Stream, nofin, StatusCode, Headers),
	commands(State, Stream, Tail);
%%% Send a response body chunk.
commands(State0=#state{conn=Conn}, Stream=#stream{id=StreamID}, [{data, IsFin, Data}|Tail]) ->
%	ct:pal("commands data ~p ~p", [IsFin, try iolist_size(Data) catch _:_ -> Data end]),
	_ = case Data of
		{sendfile, Offset, Bytes, Path} ->
			%% Temporary solution to do sendfile over QUIC.
			{ok, _} = ranch_transport:sendfile(?MODULE, {Conn, StreamID},
				Path, Offset, Bytes, []),
			ok = cowboy_quicer:send(Conn, StreamID, cow_http3:data(<<>>), IsFin);
		_ ->
			ok = cowboy_quicer:send(Conn, StreamID, cow_http3:data(Data), IsFin)
	end,
	State = maybe_send_is_fin(State0, Stream, IsFin),
	commands(State, Stream, Tail);
%%% Send trailers.
commands(State=#state{conn=Conn, http3_machine=HTTP3Machine0},
		Stream=#stream{id=StreamID}, [{trailers, Trailers}|Tail]) ->
%	ct:pal("commands trailers ~p", [Trailers]),
	HTTP3Machine = case cow_http3_machine:prepare_trailers(
			StreamID, HTTP3Machine0, maps:to_list(Trailers)) of
		{trailers, HeaderBlock, _EncData, HTTP3Machine1} ->
%			ct:pal("trailers"),
			%% @todo EncData!!
			ok = cowboy_quicer:send(Conn, StreamID, cow_http3:headers(HeaderBlock), fin),
			HTTP3Machine1;
		{no_trailers, HTTP3Machine1} ->
%			ct:pal("no_trailers"),
			ok = cowboy_quicer:send(Conn, StreamID, cow_http3:data(<<>>), fin),
			HTTP3Machine1
	end,
	commands(State#state{http3_machine=HTTP3Machine}, Stream, Tail);
%% Send a push promise.
%%
%% @todo Responses sent as a result of a push_promise request
%% must not send push_promise frames themselves.
%%
%% @todo We should not send push_promise frames when we are
%% in the closing http2_status.
%commands(State0=#state{socket=Socket, transport=Transport, http3_machine=HTTP3Machine0},
%		Stream, [{push, Method, Scheme, Host, Port, Path, Qs, Headers0}|Tail]) ->
%	Authority = case {Scheme, Port} of
%		{<<"http">>, 80} -> Host;
%		{<<"https">>, 443} -> Host;
%		_ -> iolist_to_binary([Host, $:, integer_to_binary(Port)])
%	end,
%	PathWithQs = iolist_to_binary(case Qs of
%		<<>> -> Path;
%		_ -> [Path, $?, Qs]
%	end),
%	PseudoHeaders = #{
%		method => Method,
%		scheme => Scheme,
%		authority => Authority,
%		path => PathWithQs
%	},
%	%% We need to make sure the header value is binary before we can
%	%% create the Req object, as it expects them to be flat.
%	Headers = maps:to_list(maps:map(fun(_, V) -> iolist_to_binary(V) end, Headers0)),
%	%% @todo
%	State = case cow_http2_machine:prepare_push_promise(StreamID, HTTP3Machine0,
%			PseudoHeaders, Headers) of
%		{ok, PromisedStreamID, HeaderBlock, HTTP3Machine} ->
%			Transport:send(Socket, cow_http2:push_promise(
%				StreamID, PromisedStreamID, HeaderBlock)),
%			headers_frame(State0#state{http3_machine=HTTP2Machine},
%				PromisedStreamID, fin, Headers, PseudoHeaders, 0);
%		{error, no_push} ->
%			State0
%	end,
%	commands(State, Stream, Tail);
%%% Read the request body.
%commands(State0=#state{flow=Flow, streams=Streams}, Stream, [{flow, Size}|Tail]) ->
commands(State, Stream, [{flow, _Size}|Tail]) ->
	%% @todo We should tell the QUIC stream to increase its window size.
%	#{StreamID := Stream=#stream{flow=StreamFlow}} = Streams,
%	State = update_window(State0#state{flow=Flow + Size,
%		streams=Streams#{StreamID => Stream#stream{flow=StreamFlow + Size}}},
%		StreamID),
	commands(State, Stream, Tail);
%% Supervise a child process.
commands(State=#state{children=Children}, Stream=#stream{id=StreamID},
		[{spawn, Pid, Shutdown}|Tail]) ->
	 commands(State#state{children=cowboy_children:up(Children, Pid, StreamID, Shutdown)},
		Stream, Tail);
%% Error handling.
commands(State, Stream, [Error = {internal_error, _, _}|_Tail]) ->
	%% @todo Do we want to run the commands after an internal_error?
	%% @todo Do we even allow commands after?
	%% @todo Only reset when the stream still exists.
	reset_stream(State, Stream, Error);
%% Use a different protocol within the stream (CONNECT :protocol).
%% @todo Make sure we error out when the feature is disabled.
commands(State0, Stream0=#stream{id=StreamID},
		[{switch_protocol, Headers, _Mod, _ModState}|Tail]) ->
	State = info(stream_store(State0, Stream0), StreamID, {headers, 200, Headers}),
	Stream = stream_get(State, StreamID),
	commands(State, Stream, Tail);
%% Set options dynamically.
commands(State, Stream, [{set_options, _Opts}|Tail]) ->
	commands(State, Stream, Tail);
commands(State, Stream, [stop|_Tail]) ->
%	ct:pal("stop"),
	%% @todo Do we want to run the commands after a stop?
	%% @todo Do we even allow commands after?
	stop_stream(stream_store(State, Stream), Stream);
%% Log event.
commands(State=#state{opts=Opts}, Stream, [Log={log, _, _, _}|Tail]) ->
	cowboy:log(Log, Opts),
	commands(State, Stream, Tail).

send_response(State0=#state{conn=Conn, http3_machine=HTTP3Machine0},
		Stream=#stream{id=StreamID}, StatusCode, Headers, Body) ->
	Size = case Body of
		{sendfile, _, Bytes0, _} -> Bytes0;
		_ -> iolist_size(Body)
	end,
	case Size of
		0 ->
			State = send_headers(State0, Stream, fin, StatusCode, Headers),
			maybe_send_is_fin(State, Stream, fin);
		_ ->
			%% @todo Add a test for HEAD to make sure we don't send the body when
			%% returning {response...} from a stream handler (or {headers...} then {data...}).
			%% @todo We must send EncData!
			{ok, _IsFin, HeaderBlock, _EncData, HTTP3Machine}
				= cow_http3_machine:prepare_headers(StreamID, HTTP3Machine0, nofin,
					#{status => cow_http:status_to_integer(StatusCode)},
					headers_to_list(Headers)),
			%% @todo It might be better to do async sends.
			_ = case Body of
				{sendfile, Offset, Bytes, Path} ->
					ok = cowboy_quicer:send(Conn, StreamID,
						cow_http3:headers(HeaderBlock)),
					%% Temporary solution to do sendfile over QUIC.
					{ok, _} = ranch_transport:sendfile(?MODULE, {Conn, StreamID},
						Path, Offset, Bytes, []),
					ok = cowboy_quicer:send(Conn, StreamID,
						cow_http3:data(<<>>), fin);
				_ ->
					ok = cowboy_quicer:send(Conn, StreamID, [
						cow_http3:headers(HeaderBlock),
						cow_http3:data(Body)
					], fin)
			end,
			maybe_send_is_fin(State0#state{http3_machine=HTTP3Machine}, Stream, fin)
	end.

maybe_send_is_fin(State=#state{http3_machine=HTTP3Machine0},
		Stream=#stream{id=StreamID}, fin) ->
	HTTP3Machine = cow_http3_machine:close_bidi_stream_for_sending(StreamID, HTTP3Machine0),
	maybe_terminate_stream(State#state{http3_machine=HTTP3Machine}, Stream);
maybe_send_is_fin(State, _, _) ->
	State.

%% Temporary callback to do sendfile over QUIC.
-spec send(_, _) -> _. %% @todo

send({Conn, StreamID}, IoData) ->
	cowboy_quicer:send(Conn, StreamID, cow_http3:data(IoData)).

send_headers(State=#state{conn=Conn, http3_machine=HTTP3Machine0},
		#stream{id=StreamID}, IsFin0, StatusCode, Headers) ->
	{ok, IsFin, HeaderBlock, _EncData, HTTP3Machine}
		= cow_http3_machine:prepare_headers(StreamID, HTTP3Machine0, IsFin0,
			#{status => cow_http:status_to_integer(StatusCode)},
			headers_to_list(Headers)),
	ok = cowboy_quicer:send(Conn, StreamID, cow_http3:headers(HeaderBlock), IsFin),
	%% @todo Send _EncData.
	State#state{http3_machine=HTTP3Machine}.

%% The set-cookie header is special; we can only send one cookie per header.
headers_to_list(Headers0=#{<<"set-cookie">> := SetCookies}) ->
	Headers = maps:to_list(maps:remove(<<"set-cookie">>, Headers0)),
	Headers ++ [{<<"set-cookie">>, Value} || Value <- SetCookies];
headers_to_list(Headers) ->
	maps:to_list(Headers).

reset_stream(State0=#state{conn=Conn, http3_machine=HTTP3Machine0},
		Stream=#stream{id=StreamID}, Error) ->
%ct:pal("~p reset_stream ~p ~p", [self(), Stream, Error]),
	Reason = case Error of
		{internal_error, _, _} -> h3_internal_error;
		{stream_error, Reason0, _} -> Reason0
	end,
	%% @todo Do we want to close both sides?
	%% @todo Should we close the send side if the receive side was already closed?
	Res = cowboy_quicer:shutdown_stream(Conn, StreamID,
		both, cow_http3:error_to_code(Reason)),
%	ct:pal("~p reset_stream res ~p", [self(), Res]),
	State1 = case cow_http3_machine:reset_stream(StreamID, HTTP3Machine0) of
		{ok, HTTP3Machine} ->
			terminate_stream(State0#state{http3_machine=HTTP3Machine}, Stream, Error);
		{error, not_found} ->
			terminate_stream(State0, Stream, Error)
	end,
%% @todo
%	case reset_rate(State1) of
%		{ok, State} ->
%			State;
%		error ->
%			terminate(State1, {connection_error, enhance_your_calm,
%				'Stream reset rate larger than configuration allows. Flood? (CVE-2019-9514)'})
%	end.
	State1.

stop_stream(State0=#state{http3_machine=HTTP3Machine}, Stream=#stream{id=StreamID}) ->
%ct:pal("stop_stream ~p ~p", [State0, Stream]),
	%% We abort reading when stopping the stream but only
	%% if the client was not finished sending data.
	%% We mark the stream as 'stopping' either way.
	State = case cow_http3_machine:get_stream_remote_state(StreamID, HTTP3Machine) of
		{ok, fin} ->
			stream_store(State0, Stream#stream{status=stopping});
		{error, not_found} ->
			stream_store(State0, Stream#stream{status=stopping});
		_ ->
			stream_abort_receive(State0, Stream, h3_no_error)
	end,
	%% Then we may need to send a response or terminate it
	%% if the stream handler did not do so already.
	case cow_http3_machine:get_stream_local_state(StreamID, HTTP3Machine) of
		%% When the stream terminates normally (without resetting the stream)
		%% and no response was sent, we need to send a proper response back to the client.
		{ok, idle} ->
			info(State, StreamID, {response, 204, #{}, <<>>});
		%% When a response was sent but not terminated, we need to close the stream.
		%% We send a final DATA frame to complete the stream.
		{ok, nofin} ->
%			ct:pal("error nofin"),
			info(State, StreamID, {data, fin, <<>>});
		%% When a response was sent fully we can terminate the stream,
		%% regardless of the stream being in half-closed or closed state.
		_ ->
			terminate_stream(State, Stream, normal)
	end.

maybe_terminate_stream(State, Stream=#stream{status=stopping}) ->
	terminate_stream(State, Stream, normal);
%% The Stream will be stored in the State at the end of commands processing.
maybe_terminate_stream(State, _) ->
	State.

terminate_stream(State=#state{streams=Streams0, children=Children0},
		#stream{id=StreamID, state=StreamState}, Reason) ->
	Streams = maps:remove(StreamID, Streams0),
	terminate_stream_handler(State, StreamID, Reason, StreamState),
	Children = cowboy_children:shutdown(Children0, StreamID),
	stream_linger(State#state{streams=Streams, children=Children}, StreamID).

terminate_stream_handler(#state{opts=Opts}, StreamID, Reason, StreamState) ->
	try
		cowboy_stream:terminate(StreamID, Reason, StreamState)
	catch Class:Exception:Stacktrace ->
		cowboy:log(cowboy_stream:make_error_log(terminate,
			[StreamID, Reason, StreamState],
			Class, Exception, Stacktrace), Opts)
	end.

ignored_frame(State=#state{http3_machine=HTTP3Machine0}, #stream{id=StreamID}) ->
	case cow_http3_machine:ignored_frame(StreamID, HTTP3Machine0) of
		{ok, HTTP3Machine} ->
			State#state{http3_machine=HTTP3Machine};
		{error, Error={connection_error, _, _}, HTTP3Machine} ->
			terminate(State#state{http3_machine=HTTP3Machine}, Error)
	end.

stream_abort_receive(State=#state{conn=Conn}, Stream=#stream{id=StreamID}, Reason) ->
	cowboy_quicer:shutdown_stream(Conn, StreamID,
		receiving, cow_http3:error_to_code(Reason)),
	stream_store(State, Stream#stream{status=stopping}).

%% @todo Graceful connection shutdown.
%% We terminate the connection immediately if it hasn't fully been initialized.
goaway(State, {goaway, _}) ->
	terminate(State, {stop, goaway, 'The connection is going away.'}).

terminate(State=#state{conn=Conn, %http3_status=Status,
		%http3_machine=HTTP3Machine,
		streams=Streams, children=Children}, Reason) ->
%	if
%		Status =:= connected; Status =:= closing_initiated ->
%% @todo
%			ok = cowboy_quicer:send(Conn, ControlID, cow_http3:goaway(
%				cow_http3_machine:get_last_streamid(HTTP3Machine))),
		%% We already sent the GOAWAY frame.
%		Status =:= closing ->
%			ok
%	end,
	terminate_all_streams(State, maps:to_list(Streams), Reason),
	cowboy_children:terminate(Children),
%	terminate_linger(State),
	cowboy_quicer:shutdown(Conn, cow_http3:error_to_code(terminate_reason(Reason))),
	exit({shutdown, Reason}).

terminate_reason({connection_error, Reason, _}) -> Reason;
terminate_reason({stop, _, _}) -> h3_no_error.
%terminate_reason({socket_error, _, _}) -> internal_error;
%terminate_reason({internal_error, _, _}) -> internal_error.


terminate_all_streams(_, [], _) ->
	ok;
terminate_all_streams(State, [{StreamID, #stream{state=StreamState}}|Tail], Reason) ->
	terminate_stream_handler(State, StreamID, Reason, StreamState),
	terminate_all_streams(State, Tail, Reason).




stream_get(#state{streams=Streams}, StreamID) ->
	maps:get(StreamID, Streams, error).

stream_new_remote(State=#state{http3_machine=HTTP3Machine0, streams=Streams},
		StreamID, StreamType) ->
	{HTTP3Machine, Status} = case StreamType of
		unidi ->
			{cow_http3_machine:init_unidi_stream(StreamID, unidi_remote, HTTP3Machine0),
				header};
		bidi ->
			{cow_http3_machine:init_bidi_stream(StreamID, HTTP3Machine0),
				normal}
	end,
	Stream = #stream{id=StreamID, status=Status},
	State#state{http3_machine=HTTP3Machine, streams=Streams#{StreamID => Stream}}.

%% Stream closed message for a local (write-only) unidi stream.
stream_closed(State=#state{local_control_id=StreamID}, StreamID, _) ->
	stream_closed1(State, StreamID);
stream_closed(State=#state{local_encoder_id=StreamID}, StreamID, _) ->
	stream_closed1(State, StreamID);
stream_closed(State=#state{local_decoder_id=StreamID}, StreamID, _) ->
	stream_closed1(State, StreamID);
stream_closed(State=#state{opts=Opts,
		streams=Streams0, children=Children0}, StreamID, ErrorCode) ->
	case maps:take(StreamID, Streams0) of
		{#stream{state=undefined}, Streams} ->
			%% Unidi stream has no handler/children.
			stream_closed1(State#state{streams=Streams}, StreamID);
		%% We only stop bidi streams if the stream was closed with an error
		%% or the stream was already in the process of stopping.
		{#stream{status=Status, state=StreamState}, Streams}
				when Status =:= stopping; ErrorCode =/= 0 ->
			terminate_stream_handler(State, StreamID, closed, StreamState),
			Children = cowboy_children:shutdown(Children0, StreamID),
			stream_closed1(State#state{streams=Streams, children=Children}, StreamID);
		%% Don't remove a stream that terminated properly but
		%% has chosen to remain up (custom stream handlers).
		{_, _} ->
			stream_closed1(State, StreamID);
		%% Stream closed message for a stream that has been reset. Ignore.
		error ->
			case is_lingering_stream(State, StreamID) of
				true ->
					ok;
				false ->
					%% We avoid logging the data as it could be quite large.
					cowboy:log(warning, "Received stream_closed for unknown stream ~p. ~p ~p",
						[StreamID, self(), Streams0], Opts)
			end,
			State
	end.

stream_closed1(State=#state{http3_machine=HTTP3Machine0}, StreamID) ->
	case cow_http3_machine:close_stream(StreamID, HTTP3Machine0) of
		{ok, HTTP3Machine} ->
			State#state{http3_machine=HTTP3Machine};
		{error, Error={connection_error, _, _}, HTTP3Machine} ->
			terminate(State#state{http3_machine=HTTP3Machine}, Error)
	end.

stream_store(State=#state{streams=Streams}, Stream=#stream{id=StreamID}) ->
	State#state{streams=Streams#{StreamID => Stream}}.

stream_linger(State=#state{lingering_streams=Lingering0}, StreamID) ->
	%% We only keep up to 100 streams in this state. @todo Make it configurable?
	Lingering = [StreamID|lists:sublist(Lingering0, 100 - 1)],
	State#state{lingering_streams=Lingering}.

is_lingering_stream(#state{lingering_streams=Lingering}, StreamID) ->
	lists:member(StreamID, Lingering).