#!/usr/bin/env python3

"""A caching layer around the kernel's network mapping between IPs and MACs"""


import datetime
import logging
import os
from typing import Any, Optional
import warnings

from overrides import overrides

import argparse_utils
from collect.bidict import BiDict
import config
import exec_utils
import file_utils
import persistent
import string_utils
import site_config

logger = logging.getLogger(__name__)

cfg = config.add_commandline_args(
    f'MAC <--> IP Address mapping table cache ({__file__})',
    'Commandline args related to MAC <--> IP Address mapping',
)
cfg.add_argument(
    '--arper_cache_location',
    default=f'{os.environ["HOME"]}/cache/.arp_table_cache',
    metavar='FILENAME',
    help='Where to cache the kernel ARP table',
)
cfg.add_argument(
    '--arper_cache_max_staleness',
    type=argparse_utils.valid_duration,
    default=datetime.timedelta(seconds=60 * 15),
    metavar='DURATION',
    help='Max acceptable age of the kernel arp table cache',
)
cfg.add_argument(
    '--arper_min_entries_to_be_valid',
    type=int,
    default=site_config.get_config().arper_minimum_device_count,
    help='Min number of arp entries to bother persisting.',
)


@persistent.persistent_autoloaded_singleton()
class Arper(persistent.Persistent):
    def __init__(self, cached_state: Optional[BiDict] = None) -> None:
        self.state = BiDict()
        if cached_state is not None:
            logger.debug('Loading Arper map from cached state.')
            self.state = cached_state
        else:
            logger.debug('No usable cached state; calling /usr/sbin/arp')
            self.update_from_arp_scan()
            self.update_from_arp()
        if len(self.state) < config.config['arper_min_entries_to_be_valid']:
            raise Exception(
                f'Arper didn\'t find enough entries; only got {len(self.state)}.'
            )

    def update_from_arp_scan(self):
        network_spec = site_config.get_config().network
        try:
            output = exec_utils.cmd(
                f'/usr/local/bin/arp-scan --retry=6 --timeout 350 --backoff=1.4 --random --numeric --plain --ignoredups {network_spec}',
                timeout_seconds=10.0,
            )
        except Exception as e:
            logger.exception(e)
            return
        for line in output.split('\n'):
            ip = string_utils.extract_ip_v4(line)
            mac = string_utils.extract_mac_address(line)
            if (
                ip is not None
                and mac is not None
                and mac != 'UNKNOWN'
                and ip != 'UNKNOWN'
            ):
                mac = mac.lower()
                logger.debug(f'ARPER: {mac} => {ip}')
                self.state[mac] = ip

    def update_from_arp(self):
        try:
            output = exec_utils.cmd('/usr/sbin/arp -a', timeout_seconds=10.0)
        except Exception as e:
            logger.exception(e)
            return
        for line in output.split('\n'):
            ip = string_utils.extract_ip_v4(line)
            mac = string_utils.extract_mac_address(line)
            if (
                ip is not None
                and mac is not None
                and mac != 'UNKNOWN'
                and ip != 'UNKNOWN'
            ):
                mac = mac.lower()
                logger.debug(f'ARPER: {mac} => {ip}')
                self.state[mac] = ip

    def get_ip_by_mac(self, mac: str) -> Optional[str]:
        mac = mac.lower()
        return self.state.get(mac, None)

    def get_mac_by_ip(self, ip: str) -> Optional[str]:
        return self.state.inverse.get(ip, None)

    @classmethod
    @overrides
    def load(cls) -> Any:
        cache_file = config.config['arper_cache_location']
        if persistent.was_file_written_within_n_seconds(
            cache_file,
            config.config['arper_cache_max_staleness'].total_seconds(),
        ):
            logger.debug(f'Loading state from {cache_file}')
            cached_state = BiDict()
            with open(cache_file, 'r') as rf:
                contents = rf.readlines()
                for line in contents:
                    line = line[:-1]
                    logger.debug(f'ARPER:{cache_file}> {line}')
                    (mac, ip) = line.split(',')
                    mac = mac.strip()
                    mac = mac.lower()
                    ip = ip.strip()
                    cached_state[mac] = ip
            if len(cached_state) > config.config['arper_min_entries_to_be_valid']:
                return cls(cached_state)
            else:
                msg = f'{cache_file} is invalid: only {len(cached_state)} entries.  Deleting it.'
                logger.warning(msg)
                warnings.warn(msg, stacklevel=2)
                os.remove(cache_file)
        logger.debug('No usable saved state found')
        return None

    @overrides
    def save(self) -> bool:
        if len(self.state) > config.config['arper_min_entries_to_be_valid']:
            logger.debug(f'Persisting state to {config.config["arper_cache_location"]}')
            with file_utils.FileWriter(config.config['arper_cache_location']) as wf:
                for (mac, ip) in self.state.items():
                    mac = mac.lower()
                    print(f'{mac}, {ip}', file=wf)
            return True
        else:
            logger.warning(
                f'Only saw {len(self.state)} entries; needed at least {config.config["arper_min_entries_to_be_valid"]} to bother persisting.'
            )
            return False