#!/usr/bin/env python3
#
# Copyright (C) 2021 VyOS maintainers and contributors
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 or later as
# published by the Free Software Foundation.
#
# 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/>.

# - T3037, BGP address-family ipv6-unicast capability dynamic does not exist in
#   FRR, there is only a base, per neighbor dynamic capability, migrate config

import sys
from vyos.configtree import ConfigTree

if (len(sys.argv) < 2):
    print("Must specify file name!")
    sys.exit(1)

file_name = sys.argv[1]

with open(file_name, 'r') as f:
    config_file = f.read()

base = ['protocols', 'bgp']
config = ConfigTree(config_file)

if not config.exists(base):
    # Nothing to do
    sys.exit(0)

# Check if BGP is actually configured and obtain the ASN
asn_list = config.list_nodes(base)
if asn_list:
    # There's always just one BGP node, if any
    bgp_base = base + [asn_list[0]]

    for neighbor_type in ['neighbor', 'peer-group']:
        if not config.exists(bgp_base + [neighbor_type]):
            continue
        for neighbor in config.list_nodes(bgp_base + [neighbor_type]):
            cap_dynamic = False
            for afi in ['ipv4-unicast', 'ipv6-unicast']:
                afi_path = bgp_base + [neighbor_type, neighbor, 'address-family', afi, 'capability', 'dynamic']
                if config.exists(afi_path):
                    cap_dynamic = True
                    config.delete(afi_path)

                    # We have now successfully migrated the address-family specific
                    # dynamic capability to the neighbor/peer-group level. If this
                    # has been the only option under the address-family nodes, we
                    # can clean them up by checking if no other nodes are left under
                    # that tree and if so, delete the parent.
                    #
                    # We walk from the most inner node to the most outer one.
                    cleanup = -1
                    while len(config.list_nodes(afi_path[:cleanup])) == 0:
                        config.delete(afi_path[:cleanup])
                        cleanup -= 1

            if cap_dynamic:
                config.set(bgp_base + [neighbor_type, neighbor, 'capability', 'dynamic'])

try:
    with open(file_name, 'w') as f:
        f.write(config.to_string())
except OSError as e:
    print("Failed to save the modified config: {}".format(e))
    sys.exit(1)