#!/usr/bin/env python3
#
# Copyright (C) 2024 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/>.

import ipaddress
import jmespath
import os

from sys import exit

from vyos.config import Config
from vyos.template import render
from vyos.utils.process import cmd
from vyos.utils.process import run
from vyos import ConfigError
from vyos import airbag

airbag.enable()


nftables_cgnat_config = '/run/nftables-cgnat.nft'


class IPOperations:
    def __init__(self, ip_prefix: str):
        self.ip_prefix = ip_prefix
        self.ip_network = ipaddress.ip_network(ip_prefix) if '/' in ip_prefix else None

    def get_ips_count(self) -> int:
        """Returns the number of IPs in a prefix or range.

        Example:
        % ip = IPOperations('192.0.2.0/30')
        % ip.get_ips_count()
        4
        % ip = IPOperations('192.0.2.0-192.0.2.2')
        % ip.get_ips_count()
        3
        """
        if '-' in self.ip_prefix:
            start_ip, end_ip = self.ip_prefix.split('-')
            start_ip = ipaddress.ip_address(start_ip)
            end_ip = ipaddress.ip_address(end_ip)
            return int(end_ip) - int(start_ip) + 1
        elif '/31' in self.ip_prefix:
            return 2
        elif '/32' in self.ip_prefix:
            return 1
        else:
            return sum(
                1
                for _ in [self.ip_network.network_address]
                + list(self.ip_network.hosts())
                + [self.ip_network.broadcast_address]
            )

    def convert_prefix_to_list_ips(self) -> list:
        """Converts a prefix or IP range to a list of IPs including the network and broadcast addresses.

        Example:
        % ip = IPOperations('192.0.2.0/30')
        % ip.convert_prefix_to_list_ips()
        ['192.0.2.0', '192.0.2.1', '192.0.2.2', '192.0.2.3']
        %
        % ip = IPOperations('192.0.0.1-192.0.2.5')
        % ip.convert_prefix_to_list_ips()
        ['192.0.2.1', '192.0.2.2', '192.0.2.3', '192.0.2.4', '192.0.2.5']
        """
        if '-' in self.ip_prefix:
            start_ip, end_ip = self.ip_prefix.split('-')
            start_ip = ipaddress.ip_address(start_ip)
            end_ip = ipaddress.ip_address(end_ip)
            return [
                str(ipaddress.ip_address(ip))
                for ip in range(int(start_ip), int(end_ip) + 1)
            ]
        elif '/31' in self.ip_prefix:
            return [
                str(ip)
                for ip in [
                    self.ip_network.network_address,
                    self.ip_network.broadcast_address,
                ]
            ]
        elif '/32' in self.ip_prefix:
            return [str(self.ip_network.network_address)]
        else:
            return [
                str(ip)
                for ip in [self.ip_network.network_address]
                + list(self.ip_network.hosts())
                + [self.ip_network.broadcast_address]
            ]


def generate_port_rules(
    external_hosts: list,
    internal_hosts: list,
    port_count: int,
    global_port_range: str = '1024-65535',
) -> list:
    """Generates list of nftables rules for the batch file."""
    rules = []
    proto_map_elements = []
    other_map_elements = []
    start_port, end_port = map(int, global_port_range.split('-'))
    total_possible_ports = (end_port - start_port) + 1

    # Calculate the required number of ports per host
    required_ports_per_host = port_count

    # Check if there are enough external addresses for all internal hosts
    if required_ports_per_host * len(internal_hosts) > total_possible_ports * len(
        external_hosts
    ):
        raise ConfigError("Not enough ports available for the specified parameters!")

    current_port = start_port
    current_external_index = 0

    for internal_host in internal_hosts:
        external_host = external_hosts[current_external_index]
        next_end_port = current_port + required_ports_per_host - 1

        # If the port range exceeds the end_port, move to the next external host
        while next_end_port > end_port:
            current_external_index = (current_external_index + 1) % len(external_hosts)
            external_host = external_hosts[current_external_index]
            current_port = start_port
            next_end_port = current_port + required_ports_per_host - 1

        # Ensure the same port is not assigned to the same external host
        if any(
            rule.endswith(f'{external_host}:{current_port}-{next_end_port}')
            for rule in rules
        ):
            raise ConfigError("Not enough ports available for the specified parameters")

        proto_map_elements.append(
            f'{internal_host} : {external_host} . {current_port}-{next_end_port}'
        )
        other_map_elements.append(f'{internal_host} : {external_host}')

        current_port = next_end_port + 1
        if current_port > end_port:
            current_port = start_port
            current_external_index += 1  # Move to the next external host

    return [proto_map_elements, other_map_elements]


def get_config(config=None):
    if config:
        conf = config
    else:
        conf = Config()

    base = ['nat', 'cgnat']
    config = conf.get_config_dict(
        base,
        get_first_key=True,
        key_mangling=('-', '_'),
        no_tag_node_value_mangle=True,
        with_recursive_defaults=True,
    )

    return config


def verify(config):
    # bail out early - looks like removal from running config
    if not config:
        return None

    if 'pool' not in config:
        raise ConfigError(f'Pool must be defined!')
    if 'rule' not in config:
        raise ConfigError(f'Rule must be defined!')

    # As PoC allow only one rule for CGNAT translations
    # one internal pool and one external pool
    if len(config['rule']) > 1:
        raise ConfigError(f'Only one rule is allowed for translations!')

    for pool in ('external', 'internal'):
        if pool not in config['pool']:
            raise ConfigError(f'{pool} pool must be defined!')
        for pool_name, pool_config in config['pool'][pool].items():
            if 'range' not in pool_config:
                raise ConfigError(
                    f'Range for "{pool} pool {pool_name}" must be defined!'
                )

    external_pools_query = "keys(pool.external)"
    external_pools: list = jmespath.search(external_pools_query, config)
    internal_pools_query = "keys(pool.internal)"
    internal_pools: list = jmespath.search(internal_pools_query, config)

    for rule, rule_config in config['rule'].items():
        if 'source' not in rule_config:
            raise ConfigError(f'Rule "{rule}" source pool must be defined!')
        if 'pool' not in rule_config['source']:
            raise ConfigError(f'Rule "{rule}" source pool must be defined!')

        if 'translation' not in rule_config:
            raise ConfigError(f'Rule "{rule}" translation pool must be defined!')

        internal_pool = rule_config['source']['pool']
        if internal_pool not in internal_pools:
            raise ConfigError(f'Internal pool "{internal_pool}" does not exist!')

        external_pool = rule_config['translation']['pool']
        if external_pool not in external_pools:
            raise ConfigError(f'External pool "{external_pool}" does not exist!')


def generate(config):
    if not config:
        return None
    # first external pool as we allow only one as PoC
    ext_pool_name = jmespath.search("rule.*.translation | [0]", config).get('pool')
    int_pool_name = jmespath.search("rule.*.source | [0]", config).get('pool')
    ext_query = f'pool.external."{ext_pool_name}".range | keys(@)'
    int_query = f'pool.internal."{int_pool_name}".range'
    external_ranges = jmespath.search(ext_query, config)
    internal_ranges = [jmespath.search(int_query, config)]

    external_list_count = []
    external_list_hosts = []
    internal_list_count = []
    internal_list_hosts = []
    for ext_range in external_ranges:
        # External hosts count
        e_count = IPOperations(ext_range).get_ips_count()
        external_list_count.append(e_count)
        # External hosts list
        e_hosts = IPOperations(ext_range).convert_prefix_to_list_ips()
        external_list_hosts.extend(e_hosts)
    for int_range in internal_ranges:
        # Internal hosts count
        i_count = IPOperations(int_range).get_ips_count()
        internal_list_count.append(i_count)
        # Internal hosts list
        i_hosts = IPOperations(int_range).convert_prefix_to_list_ips()
        internal_list_hosts.extend(i_hosts)

    external_host_count = sum(external_list_count)
    internal_host_count = sum(internal_list_count)
    ports_per_user = int(
        jmespath.search(f'pool.external."{ext_pool_name}".per_user_limit.port', config)
    )
    external_port_range: str = jmespath.search(
        f'pool.external."{ext_pool_name}".external_port_range', config
    )

    proto_maps, other_maps = generate_port_rules(
        external_list_hosts, internal_list_hosts, ports_per_user, external_port_range
    )

    config['proto_map_elements'] = ', '.join(proto_maps)
    config['other_map_elements'] = ', '.join(other_maps)

    render(nftables_cgnat_config, 'firewall/nftables-cgnat.j2', config)

    # dry-run newly generated configuration
    tmp = run(f'nft --check --file {nftables_cgnat_config}')
    if tmp > 0:
        raise ConfigError('Configuration file errors encountered!')


def apply(config):
    if not config:
        # Cleanup cgnat
        cmd('nft delete table ip cgnat')
        if os.path.isfile(nftables_cgnat_config):
            os.unlink(nftables_cgnat_config)
        return None
    cmd(f'nft --file {nftables_cgnat_config}')


if __name__ == '__main__':
    try:
        c = get_config()
        verify(c)
        generate(c)
        apply(c)
    except ConfigError as e:
        print(e)
        exit(1)