"""LAN access control and local network address discovery."""
import ipaddress
import json
import os
from pathlib import Path
import secrets
import subprocess


class LanAccess:
    def __init__(self, config, enabled, port):
        self.enabled, self.port = enabled, port
        self.key = ''
        self.urls = []
        if enabled:
            path = Path(config).with_name('lan-key')
            path.parent.mkdir(parents=True, exist_ok=True)
            try:
                fd = os.open(path, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
            except FileExistsError:
                self.key = path.read_text().strip()
                if len(self.key) < 20:
                    raise ValueError('Ungültiger LAN-Zugangscode in ' + str(path))
            else:
                self.key = secrets.token_urlsafe(24)
                with os.fdopen(fd, 'w') as file:
                    file.write(self.key)
            try:
                result = subprocess.run(['ip', '-j', '-4', 'route', 'get', '1.1.1.1'], capture_output=True, text=True, timeout=3)
                addresses = {entry['prefsrc'] for entry in json.loads(result.stdout) if entry.get('prefsrc')}
                self.urls = [f'http://{address}:{port}' for address in sorted(addresses)]
            except (OSError, ValueError, subprocess.TimeoutExpired):
                pass

    @staticmethod
    def local(address):
        try:
            return ipaddress.ip_address(address).is_loopback
        except ValueError:
            return False

    def allowed(self, address, supplied):
        return self.local(address) or (self.enabled and bool(supplied) and secrets.compare_digest(self.key.encode(), supplied.encode()))

    def info(self, address):
        return {'enabled': self.enabled, 'urls': self.urls,
                'key': self.key if self.local(address) else None}