#!/usr/bin/python3
# -*- mode: python-mode; py-indent-tabs-mode: nil -*-
"""
/*
 * Copyright (C) 2016 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 = "0.0.5"
    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)
    # 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 = 'ERR'
    CTRL_TRAP = 'TRAP'

    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 not len(data):
            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 split_combined(self, data):
        """
        Split the data which contains multiple concatenated IPA messages into tuple (first, rest) where rest contains remaining messages, first is the single IPA message
        """
        (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, data, op=None):
        """
        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
        """
        (s, i, v) = data.split(' ', 2)
        if s == self.CTRL_ERR:
            return None, v
        if s == self.CTRL_GET:
            return v, None
        (s, i, var, val) = data.split(' ', 3)
        if s == self.CTRL_TRAP and i != '0':
            return None, '%s with non-zero id %s' % (s, i)
        if op is not None and i != op:
            if s == self.CTRL_GET + '_' + self.CTRL_REP or s == self.CTRL_SET + '_' + self.CTRL_REP:
                return None, '%s with unexpected id %s' % (s, i)
        return var, val

    def trap(self, var, val):
        """
        Make TRAP message with given (vak, val) pair
        """
        return self.add_header("%s 0 %s %s" % (self.CTRL_TRAP, 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 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(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)