#!/usr/bin/env python3
# -*- mode: python-mode; py-indent-tabs-mode: nil -*-
"""
/*
 * Copyright (C) 2016-2018 sysmocom s.f.m.c. GmbH
 *
 * All Rights Reserved
 *
 * 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.
 */
"""

import struct, random, sys

class IPA(object):
    """
    Stateless IPA protocol multiplexer: add/remove/parse (extended) header
    """
    version = "0.0.7"
    TCP_PORT_OML = 3002
    TCP_PORT_RSL = 3003
    # OpenBSC extensions: OSMO, MGCP_OLD
    PROTO = dict(RSL=0x00, CCM=0xFE, SCCP=0xFD, OML=0xFF, OSMO=0xEE, MGCP_OLD=0xFC)
    # ...OML Router Control, GSUP GPRS extension, Osmocom Authn Protocol
    EXT = dict(CTRL=0, MGCP=1, LAC=2, SMSC=3, ORC=4, GSUP=5, OAP=6, RSPRO=7)
    # OpenBSC extension: SCCP_OLD
    MSGT = dict(PING=0x00, PONG=0x01, ID_GET=0x04, ID_RESP=0x05, ID_ACK=0x06, SCCP_OLD=0xFF)
    _IDTAG = dict(SERNR=0, UNITNAME=1, LOCATION=2, TYPE=3, EQUIPVERS=4, SWVERSION=5, IPADDR=6, MACADDR=7, UNIT=8)
    CTRL_GET = 'GET'
    CTRL_SET = 'SET'
    CTRL_REP = 'REPLY'
    CTRL_ERR = 'ERROR'
    CTRL_TRAP = 'TRAP'
    CTRL_TRAP_ID = 0

    def _l(self, d, p):
        """
        Reverse dictionary lookup: return key for a given value
        """
        if p is None:
            return 'UNKNOWN'
        return list(d.keys())[list(d.values()).index(p)]

    def _tag(self, t, v):
        """
        Create TAG as TLV data
        """
        return struct.pack(">HB", len(v) + 1, t) + v

    def proto(self, p):
        """
        Lookup protocol name
        """
        return self._l(self.PROTO, p)

    def ext(self, p):
        """
        Lookup protocol extension name
        """
        return self._l(self.EXT, p)

    def msgt(self, p):
        """
        Lookup message type name
        """
        return self._l(self.MSGT, p)

    def idtag(self, p):
        """
        Lookup ID tag name
        """
        return self._l(self._IDTAG, p)

    def ext_name(self, proto, exten):
        """
        Return proper extension byte name depending on the protocol used
        """
        if self.PROTO['CCM'] == proto:
            return self.msgt(exten)
        if self.PROTO['OSMO'] == proto:
            return self.ext(exten)
        return None

    def add_header(self, data, proto, ext=None):
        """
        Add IPA header (with extension if necessary), data must be represented as bytes
        """
        if ext is None:
            return struct.pack(">HB", len(data) + 1, proto) + data
        return struct.pack(">HBB", len(data) + 1, proto, ext) + data

    def del_header(self, data):
        """
        Strip IPA protocol header correctly removing extension if present
        Returns data length, IPA protocol, extension (or None if not defined for a give protocol) and the data without header
        """
        if data == None or len(data) == 0:
            return None, None, None, None

        (dlen, proto) = struct.unpack('>HB', data[:3])
        if self.PROTO['OSMO'] == proto or self.PROTO['CCM'] == proto: # there's extension which we have to unpack
            return struct.unpack('>HBB', data[:4]) + (data[4:], ) # length, protocol, extension, data
        return dlen, proto, None, data[3:] # length, protocol, _, data

    def skip_traps(self, data):
        """
        Take one or more ctrl messages and data and return first non-TRAP message or None
        """
        if data == None or len(data) == 0:
            return None

        (head, tail) = self.split_combined(data)
        (length, _, _, payload) = self.del_header(head)
        # skip over broken messages as well as TRAPs
        if length == 0 or payload[:(length + 3)].decode('utf-8').startswith(self.CTRL_TRAP):
                return self.skip_traps(tail)

        return head

    def split_combined(self, data):
        """
        Split the data which contains multiple concatenated IPA messages into tuple (first, rest) where 'rest' contains
        remaining messages and 'first' is the single IPA message. No headers are stripped in 'first' or 'rest'.
        """
        if data == None or len(data) == 0:
            return None, None

        (length, _, _, _) = self.del_header(data)
        return data[:(length + 3)], data[(length + 3):]

    def tag_serial(self, data):
        """
        Make TAG for serial number
        """
        return self._tag(self._IDTAG['SERNR'], data)

    def tag_name(self, data):
        """
        Make TAG for unit name
        """
        return self._tag(self._IDTAG['UNITNAME'], data)

    def tag_loc(self, data):
        """
        Make TAG for location
        """
        return self._tag(self._IDTAG['LOCATION'], data)

    def tag_type(self, data):
        """
        Make TAG for unit type
        """
        return self._tag(self._IDTAG['TYPE'], data)

    def tag_equip(self, data):
        """
        Make TAG for equipment version
        """
        return self._tag(self._IDTAG['EQUIPVERS'], data)

    def tag_sw(self, data):
        """
        Make TAG for software version
        """
        return self._tag(self._IDTAG['SWVERSION'], data)

    def tag_ip(self, data):
        """
        Make TAG for IP address
        """
        return self._tag(self._IDTAG['IPADDR'], data)

    def tag_mac(self, data):
        """
        Make TAG for MAC address
        """
        return self._tag(self._IDTAG['MACADDR'], data)

    def tag_unit(self, data):
        """
        Make TAG for unit ID
        """
        return self._tag(self._IDTAG['UNIT'], data)

    def identity(self, unit=b'', mac=b'', location=b'', utype=b'', equip=b'', sw=b'', name=b'', serial=b''):
        """
        Make IPA IDENTITY tag list, by default returns empty concatenated bytes of tag list
        """
        return self.tag_unit(unit) + self.tag_mac(mac) + self.tag_loc(location) + self.tag_type(utype) + self.tag_equip(equip) + self.tag_sw(sw) + self.tag_name(name) + self.tag_serial(serial)

    def ping(self):
        """
        Make PING message
        """
        return self.add_header(b'', self.PROTO['CCM'], self.MSGT['PING'])

    def pong(self):
        """
        Make PONG message
        """
        return self.add_header(b'', self.PROTO['CCM'], self.MSGT['PONG'])

    def id_ack(self):
        """
        Make ID_ACK CCM message
        """
        return self.add_header(b'', self.PROTO['CCM'], self.MSGT['ID_ACK'])

    def id_get(self):
        """
        Make ID_GET CCM message
        """
        return self.add_header(self.identity(), self.PROTO['CCM'], self.MSGT['ID_GET'])

    def id_resp(self, data):
        """
        Make ID_RESP CCM message
        """
        return self.add_header(data, self.PROTO['CCM'], self.MSGT['ID_RESP'])

class Ctrl(IPA):
    """
    Osmocom CTRL protocol implemented on top of IPA multiplexer
    """
    def __init__(self):
        random.seed()

    def add_header(self, data):
        """
        Add CTRL header
        """
        return super(Ctrl, self).add_header(data.encode('utf-8'), IPA.PROTO['OSMO'], IPA.EXT['CTRL'])

    def rem_header(self, data):
        """
        Remove CTRL header, check for appropriate protocol and extension
        """
        (_, proto, ext, d) = super(Ctrl, self).del_header(data)
        if self.PROTO['OSMO'] != proto or self.EXT['CTRL'] != ext:
            return None
        return d

    def parse(self, raw_data):
        """
        Parse Ctrl string returning (id, var, value) tuple
        var could be None in case of ERROR message
        value could be None in case of GET message
        both could be None in case of TRAP with non-zero id
        """
        data = self.rem_header(raw_data)
        if data == None:
            return None, None, None
        data = data.decode('utf-8')
        (s, i, v) = data.split(' ', 2)
        if s == self.CTRL_ERR:
            return i, None, v
        if s == self.CTRL_GET:
            return i, v, None
        if s == self.CTRL_GET + '_' + self.CTRL_REP:
            return i, v, None
        (s, i, var, val) = data.split(' ', 3)
        if s == self.CTRL_TRAP and int(i) != self.CTRL_TRAP_ID:
            return i, None, None
        return i, var, val

    def parse_kv(self, raw_data):
        """
        Parse Ctrl string returning (var, value) pair
        var could be None in case of ERROR message
        value could be None in case of GET message
        """
        (i, var, val) = self.parse(raw_data)
        return var, val

    def trap(self, var, val):
        """
        Make TRAP message with given (vak, val) pair
        """
        return self.add_header("%s %d %s %s" % (self.CTRL_TRAP, self.CTRL_TRAP_ID, var, val))

    def cmd(self, var, val=None):
        """
        Make SET/GET command message: returns (r, m) tuple where r is random operation id and m is assembled message
        """
        r = random.randint(1, sys.maxsize)
        if val is not None:
            return r, self.add_header("%s %s %s %s" % (self.CTRL_SET, r, var, val))
        return r, self.add_header("%s %s %s" % (self.CTRL_GET, r, var))

    def reply(self, op_id, var, val=None):
        """
        Make SET/GET command reply: returns assembled message
        """
        if val is not None:
            return self.add_header("%s_%s %s %s %s" % (self.CTRL_SET, self.CTRL_REP, op_id, var, val))
        return self.add_header("%s_%s %s %s" % (self.CTRL_GET, self.CTRL_REP, op_id, var))

    def verify(self, reply, r, var, val=None):
        """
        Verify reply to SET/GET command: returns (b, v) tuple where v is True/False verification result and v is the variable value
        """
        (k, v) = self.parse_kv(reply)
        if k != var or (val is not None and v != val):
            return False, v
        return True, v

if __name__ == '__main__':
    print("IPA multiplexer v%s loaded." % IPA.version)
