% ITU-T Q.71x SCCP Message coding / decoding

% (C) 2010 by Harald Welte <laforge@gnumonks.org>
%
% All Rights Reserved
%
% This program is free software; you can redistribute it and/or modify
% it under the terms of the GNU Affero General Public License as
% published by the Free Software Foundation; either version 3 of the
% License, or (at your option) any later version.
%
% 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 Affero General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

-module(sccp_codec).
-author('Harald Welte <laforge@gnumonks.org>').
-include("sccp.hrl").

-export([parse_sccp_msg/1, encode_sccp_msg/1, encode_sccp_msgt/2]).

-compile(export_all).


% parse SCCP Optional Part
parse_sccp_opt(OptType, OptLen, Content) ->
	{OptType, {OptLen, Content}}.

parse_sccp_opts(<<>>, OptList) ->
	% empty list
	OptList;
parse_sccp_opts(<<0>>, OptList) ->
	% end of options
	OptList;
parse_sccp_opts(OptBin, OptList) ->
	<<OptType, OptLen, Content:OptLen/binary, Remain/binary>> = OptBin,
	NewOpt = parse_sccp_opt(OptType, OptLen, Content),
	parse_sccp_opts(Remain, [NewOpt|OptList]).

% Parse incoming SCCP message, one function for every message type
parse_sccp_msgt(?SCCP_MSGT_CR, DataBin) ->
	% first get the fixed part
	<<_:8, SrcLocalRef:24, ProtoClass:8, RemainVar/binary >> = DataBin,
	% variable length fixed part
	<<PtrVar:8, PtrOpt:8, _/binary>> = RemainVar,
	CalledPartyLen = binary:at(RemainVar, PtrVar),
	CalledParty = binary:part(RemainVar, PtrVar+1, CalledPartyLen),
	% optional part
	OptBin = binary:part(RemainVar, 1 + PtrOpt, byte_size(RemainVar)-(1+PtrOpt)),
	OptList = parse_sccp_opts(OptBin, []),
	%OptList = [],
	% build parsed list of message
	[{src_local_ref, SrcLocalRef},{protocol_class, ProtoClass},{called_party_addr, CalledParty}|OptList];
parse_sccp_msgt(?SCCP_MSGT_CC, DataBin) ->
	% first get the fixed part
	<<_:8, DstLocalRef:24, SrcLocalRef:24, ProtoClass:8, Remain/binary >> = DataBin,
	% optional part
	OptList = parse_sccp_opts(Remain, []),
	% build parsed list of message
	[{dst_local_ref, DstLocalRef},{src_local_ref, SrcLocalRef},{protocol_class, ProtoClass}|OptList];
parse_sccp_msgt(?SCCP_MSGT_CREF, DataBin) ->
	% first get the fixed part
	<<_:8, DstLocalRef:24, RefusalCause:8, Remain/binary >> = DataBin,
	% optional part
	OptList = parse_sccp_opts(Remain, []),
	% build parsed list of message
	[{dst_local_ref, DstLocalRef},{refusal_cause, RefusalCause}|OptList];
parse_sccp_msgt(?SCCP_MSGT_RLSD, DataBin) ->
	<<_:8, DstLocalRef:24, SrcLocalRef:24, ReleaseCause:8, Remain/binary >> = DataBin,
	% optional part
	OptList = parse_sccp_opts(Remain, []),
	% build parsed list of message
	[{dst_local_ref, DstLocalRef},{src_local_ref, SrcLocalRef},{release_cause, ReleaseCause}|OptList];
parse_sccp_msgt(?SCCP_MSGT_RLC, DataBin) ->
	<<_:8, DstLocalRef:24, SrcLocalRef:24>> = DataBin,
	% build parsed list of message
	[{dst_local_ref, DstLocalRef},{src_local_ref, SrcLocalRef}];
parse_sccp_msgt(?SCCP_MSGT_DT1, DataBin) ->
	<<_:8, DstLocalRef:24, SegmReass:8, DataPtr:8, Remain/binary >> = DataBin,
	DataLen = binary:at(Remain, DataPtr-1),
	UserData = binary:part(Remain, DataPtr-1+1, DataLen),
	% build parsed list of message
	[{dst_local_ref, DstLocalRef},{segm_reass, SegmReass},{user_data, UserData}];
parse_sccp_msgt(?SCCP_MSGT_DT2, DataBin) ->
	<<_:8, DstLocalRef:24, SeqSegm:16, DataPtr:8, Remain/binary >> = DataBin,
	DataLen = binary:at(Remain, DataPtr-1),
	UserData = binary:part(Remain, DataPtr-1+1, DataLen),
	% build parsed list of message
	[{dst_local_ref, DstLocalRef},{seq_segm, SeqSegm},{user_data, UserData}];
parse_sccp_msgt(?SCCP_MSGT_AK, DataBin) ->
	<<_:8, DstLocalRef:24, RxSeqnr:8, Credit:8>> = DataBin,
	[{dst_local_ref, DstLocalRef},{rx_seq_nr, RxSeqnr},{credit, Credit}];
parse_sccp_msgt(?SCCP_MSGT_UDT, DataBin) ->
	<<_:8, ProtoClass:8, CalledPartyPtr:8, CallingPartyPtr:8, DataPtr:8, Remain/binary >> = DataBin,
	% variable part
	CalledPartyLen = binary:at(Remain, CalledPartyPtr-3),
	CalledParty = binary:part(Remain, CalledPartyPtr-3+1, CalledPartyLen),
	CallingPartyLen = binary:at(Remain, CallingPartyPtr-2),
	CallingParty = binary:part(Remain, CallingPartyPtr-2+1, CallingPartyLen),
	DataLen = binary:at(Remain, DataPtr-1),
	UserData = binary:part(Remain, DataPtr-1+1, DataLen),
	[{protocol_class, ProtoClass},{called_party_addr, CalledParty},
	 {calling_party_addr, CallingParty},{user_data, UserData}];
parse_sccp_msgt(?SCCP_MSGT_UDTS, DataBin) ->
	parse_sccp_msgt(?SCCP_MSGT_UDT, DataBin);
parse_sccp_msgt(?SCCP_MSGT_ED, DataBin) ->
	<<_:8, DstLocalRef:24, DataPtr:8, Remain/binary>> = DataBin,
	DataLen = binary:at(Remain, DataPtr-1),
	UserData = binary:part(Remain, DataPtr-1+1, DataLen),
	[{dst_local_ref, DstLocalRef}, {user_data, UserData}];
parse_sccp_msgt(?SCCP_MSGT_EA, DataBin) ->
	<<_:8, DstLocalRef:24>> = DataBin,
	[{dst_local_ref, DstLocalRef}];
parse_sccp_msgt(?SCCP_MSGT_RSR, DataBin) ->
	<<_:8, DstLocalRef:24, SrcLocalRef:24, ResetCause:8>> = DataBin,
	[{dst_local_ref, DstLocalRef},{src_local_ref, SrcLocalRef},{reset_cause, ResetCause}];
parse_sccp_msgt(?SCCP_MSGT_RSC, DataBin) ->
	<<_:8, DstLocalRef:24, SrcLocalRef:24>> = DataBin,
	[{dst_local_ref, DstLocalRef},{src_local_ref, SrcLocalRef}];
parse_sccp_msgt(?SCCP_MSGT_ERR, DataBin) ->
	<<_:8, DstLocalRef:24, ErrCause:8>> = DataBin,
	[{dst_local_ref, DstLocalRef},{error_cause, ErrCause}];
parse_sccp_msgt(?SCCP_MSGT_IT, DataBin) ->
	<<_:8, DstLocalRef:24, SrcLocalRef:24, ProtoClass:8, SegmSeq:16, Credit:8>> = DataBin,
	[{dst_local_ref, DstLocalRef},{src_local_ref, SrcLocalRef},
         {protocol_class, ProtoClass},{seq_segm, SegmSeq},{credit, Credit}].
% FIXME: XUDT/XUDTS, LUDT/LUDTS

% process one incoming SCCP message
parse_sccp_msg(DataBin) ->
	MsgType = binary:first(DataBin),
	Parsed = parse_sccp_msgt(MsgType, DataBin),
	{ok, #sccp_msg{msg_type = MsgType, parameters = Parsed}}.

% Encoding Part

encode_sccp_opt({OptNum, {DataBinLen, DataBin}}) when is_integer(OptNum) ->
	DataBinLen8 = DataBinLen*8,
	<<OptNum:8, DataBinLen:8, DataBin:DataBinLen8>>;
encode_sccp_opt({OptAtom,_}) when is_atom(OptAtom) ->
	<<>>.

encode_sccp_opts([], OptEnc) ->
	% end of options + convert to binary
	list_to_binary([OptEnc, ?SCCP_PNC_END_OF_OPTIONAL]);
encode_sccp_opts([CurOpt|OptPropList], OptEnc) ->
	CurOptEnc = encode_sccp_opt(CurOpt),
	encode_sccp_opts(OptPropList, list_to_binary([OptEnc,CurOptEnc])).

	
encode_sccp_msgt(?SCCP_MSGT_CR, Params) ->
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	ProtoClass = proplists:get_value(protocol_class, Params),
	OptBin = encode_sccp_opts(Params, []),
	<<?SCCP_MSGT_CR:8, SrcLocalRef:24, ProtoClass:8, OptBin/binary>>;
encode_sccp_msgt(?SCCP_MSGT_CC, Params) ->
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	ProtoClass = proplists:get_value(protocol_class, Params),
	OptBin = encode_sccp_opts(Params, []),
	<<?SCCP_MSGT_CC:8, DstLocalRef:24, SrcLocalRef:24, ProtoClass:8, OptBin/binary>>;
encode_sccp_msgt(?SCCP_MSGT_CREF, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	RefusalCause = proplists:get_value(refusal_cause, Params),
	OptBin = encode_sccp_opts(Params, []),
	<<?SCCP_MSGT_CREF:8, DstLocalRef:24, RefusalCause:8, OptBin/binary>>;
encode_sccp_msgt(?SCCP_MSGT_RLSD, Params) ->
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	ReleaseCause = proplists:get_value(release_cause, Params),
	OptBin = encode_sccp_opts(Params, []),
	<<?SCCP_MSGT_RLSD:8, DstLocalRef:24, SrcLocalRef:24, ReleaseCause:8, OptBin/binary>>;
encode_sccp_msgt(?SCCP_MSGT_RLC, Params) ->
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	<<?SCCP_MSGT_RLC:8, DstLocalRef:24, SrcLocalRef:24>>;
encode_sccp_msgt(?SCCP_MSGT_DT1, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	SegmReass = proplists:get_value(segm_reass, Params),
	UserData = proplists:get_value(user_data, Params),
	UserDataLen = byte_size(UserData),
	<<?SCCP_MSGT_DT1:8, DstLocalRef:24, SegmReass:8, 1:8, UserDataLen:8, UserData/binary>>;
encode_sccp_msgt(?SCCP_MSGT_DT2, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	SeqSegm = proplists:get_value(seq_segm, Params),
	UserData = proplists:get_value(user_data, Params),
	UserDataLen = byte_size(UserData),
	<<?SCCP_MSGT_DT2:8, DstLocalRef:24, SeqSegm:16, 1:8, UserDataLen:8, UserData/binary>>;
encode_sccp_msgt(?SCCP_MSGT_AK, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	RxSeqnr = proplists:get_value(rx_seqnr, Params),
	Credit = proplists:get_value(credit, Params),
	<<?SCCP_MSGT_AK:8, DstLocalRef:24, RxSeqnr:8, Credit:8>>;
encode_sccp_msgt(?SCCP_MSGT_UDT, Params) ->
	ProtoClass = proplists:get_value(protocol_class, Params),
	CalledParty = proplists:get_value(called_party_addr, Params),
	CalledPartyLen = byte_size(CalledParty),
	CallingParty = proplists:get_value(calling_party_addr, Params),
	CallingPartyLen = byte_size(CallingParty),
	UserData = proplists:get_value(user_data, Params),
	UserDataLen = byte_size(UserData),
	% variable part
	CalledPartyPtr = 3,
	CallingPartyPtr = 2 + (1 + CalledPartyLen),
	DataPtr = 1 + (1 + CalledPartyLen) + (1 + CallingPartyLen),
	Remain = <<CalledPartyLen:8, CalledParty/binary,
		   CallingPartyLen:8, CallingParty/binary,
		   UserDataLen:8, UserData/binary>>,
	<<?SCCP_MSGT_UDT:8, ProtoClass:8, CalledPartyPtr:8, CallingPartyPtr:8, DataPtr:8, Remain/binary>>;
%encode_sccp_msgt(?SCCP_MSGT_UDTS, Params) ->
	% FIXME !!!
encode_sccp_msgt(?SCCP_MSGT_ED, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	UserData = proplists:get_value(user_data, Params),
	UserDataLen = byte_size(UserData),
	DataPtr = 1,
	<<?SCCP_MSGT_ED:8, DstLocalRef:24, DataPtr:8, UserDataLen:8, UserData/binary>>;
encode_sccp_msgt(?SCCP_MSGT_EA, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	<<?SCCP_MSGT_EA:8, DstLocalRef:24>>;
encode_sccp_msgt(?SCCP_MSGT_RSR, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	ResetCause = proplists:get_value(reset_cause, Params),
	<<?SCCP_MSGT_RSR:8, DstLocalRef:24, SrcLocalRef:24, ResetCause:8>>;
encode_sccp_msgt(?SCCP_MSGT_RSC, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	<<?SCCP_MSGT_RSC:8, DstLocalRef:24, SrcLocalRef:24>>;
encode_sccp_msgt(?SCCP_MSGT_ERR, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	ErrCause = proplists:get_value(error_cause, Params),
	<<?SCCP_MSGT_ERR:8, DstLocalRef:24, ErrCause:8>>;
encode_sccp_msgt(?SCCP_MSGT_IT, Params) ->
	DstLocalRef = proplists:get_value(dst_local_ref, Params),
	SrcLocalRef = proplists:get_value(src_local_ref, Params),
	ProtoClass = proplists:get_value(protocol_class, Params),
	SegmSeq = proplists:get_value(seq_segm, Params),
	Credit = proplists:get_value(credit, Params),
	<<?SCCP_MSGT_IT:8, DstLocalRef:24, SrcLocalRef:24, ProtoClass:8, SegmSeq:16, Credit:8>>.
% FIXME: XUDT/XUDTS, LUDT/LUDTS


% encode one sccp message data structure into the on-wire format
encode_sccp_msg(#sccp_msg{msg_type = MsgType, parameters = Params}) ->
	encode_sccp_msgt(MsgType, Params).