# This file is a part of sedbgmux, an open source DebugMux client.
# Copyright (c) 2022  Vadim Yanitskiy <axilirator@gmail.com>
#
# SPDX-License-Identifier: GPL-3.0-or-later
#
# This program 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, 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 General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.

from construct import *

import crcmod

# DebugMux frame definition
class DbgMuxFrame:
	# Kudos to Stefan @Sec Zehl for finding the CRC function parameters
	fcs_func = crcmod.mkCrcFun(0x11021, rev=True, initCrc=0x0, xorOut=0xffff)

	MsgType = Enum(subcon=Int8ul,
		Enquiry		= 0x65, # 'e'
		Ident		= 0x66, # 'f'
		Ping		= 0x67, # 'g'
		Pong		= 0x68, # 'h'

		DPAnnounce	= 0x69, # 'i'
		# TODO:		= 0x6a, # 'j'
		ConnEstablish	= 0x6b, # 'k'
		ConnEstablished	= 0x6c, # 'l'
		ConnTerminate	= 0x6d, # 'm'
		ConnTerminated	= 0x6e, # 'n'
		ConnData	= 0x6f, # 'o'

		# TODO:		= 0x70, # 'p'
		Ack		= 0x71, # 'q'
	)

	Frame = Struct(
		'Magic' / Const(b'\x42\x42'),
		'Length' / Rebuild(Int16ul, lambda ctx: len(ctx.MsgData) + 5),
		'TxCount' / Int8ul,
		'RxCount' / Int8ul,
		'MsgType' / MsgType,
		'MsgData' / Bytes(lambda ctx: ctx.Length - 5),
		'FCS' / Int16ul, # fcs_func() on all preceeding fields
	)

	# MsgType.Ident structure
	MsgIdent = Struct(
		'Magic' / Bytes(4), # TODO
		'Ident' / PascalString(Int8ul, 'ascii'),
	)

	# MsgType.{Ping,Pong} structure
	MsgPingPong = PascalString(Int8ul, 'ascii')

	# MsgType.DPAnnounce structure
	MsgDPAnnounce = Struct(
		'DPRef' / Int16ul,
		'Name' / PascalString(Int8ul, 'ascii'),
	)

	# MsgType.ConnEstablish[ed] structure
	MsgConnEstablish = Struct('DPRef' / Int16ul)
	MsgConnEstablished = Struct(
		'DPRef' / Int16ul,
		'ConnRef' / Int16ul,
		'DataBlockLimit' / Int16ul,
	)

	# MsgType.ConnTerminate[ed] structure
	MsgConnTerminate = Struct('ConnRef' / Int16ul)
	MsgConnTerminated = Struct(
		'DPRef' / Int16ul,
		'ConnRef' / Int16ul,
	)

	# MsgType.ConnData structure
	MsgConnData = Struct(
		'ConnRef' / Int16ul,
		'Data' / GreedyBytes,
	)

	# Complete message definition
	Msg = Switch(this.MsgType, default=GreedyBytes, cases={
		MsgType.Enquiry		: Const(b''),
		MsgType.Ident		: MsgIdent,
		MsgType.Ping		: MsgPingPong,
		MsgType.Pong		: MsgPingPong,
		MsgType.DPAnnounce	: MsgDPAnnounce,
		MsgType.ConnEstablish	: MsgConnEstablish,
		MsgType.ConnEstablished	: MsgConnEstablished,
		MsgType.ConnTerminate	: MsgConnTerminate,
		MsgType.ConnTerminated	: MsgConnTerminated,
		MsgType.ConnData	: MsgConnData,
		MsgType.Ack		: Const(b''),
	})