import crypto from 'node:crypto';
import net from 'node:net';
import { spawnSync } from 'node:child_process';
import { isDeviceInterface } from '../adapters/neighbors.js';

const COMMAND_OPTIONS = { encoding: 'utf8', timeout: 2_000, killSignal: 'SIGKILL' };
const DEVICE_ID_PATTERN = /^dev_[a-f0-9]{16}$/;
const MAC_PATTERN = /^[0-9a-f]{2}(?::[0-9a-f]{2}){5}$/;
const CHAIN_PATTERN = /^[a-z0-9_-]{1,26}$/i;
const MARK_PATTERN = /^(?:0x)?[0-9a-f]+$/i;
const MAX_DEVICES = 512;

const childChain = (chain, slot) => `${chain}_${slot}`;
const fingerprint = (devices) => crypto.createHash('sha256')
  .update(JSON.stringify(devices))
  .digest('hex');

function commandError(command, result) {
  return new Error(String(
    result.stderr || result.stdout || result.error?.message || `${command} завершился с ошибкой`,
  ).trim());
}

export function normalizeDirectDevices(value) {
  if (!Array.isArray(value) || value.length > MAX_DEVICES) {
    throw new Error('Некорректный набор device policy');
  }
  const ids = new Set();
  const tuples = new Set();
  const devices = value.map((device) => {
    const normalized = {
      id: String(device?.id || ''),
      ip: String(device?.ip || ''),
      mac: String(device?.mac || '').toLowerCase(),
      interface: String(device?.interface || ''),
    };
    const tuple = `${normalized.ip}|${normalized.mac}|${normalized.interface}`;
    if (!DEVICE_ID_PATTERN.test(normalized.id) || !net.isIPv4(normalized.ip)
      || !MAC_PATTERN.test(normalized.mac) || !isDeviceInterface(normalized.interface)
      || ids.has(normalized.id) || tuples.has(tuple)) {
      throw new Error('Некорректная или повторяющаяся device policy identity');
    }
    ids.add(normalized.id);
    tuples.add(tuple);
    return normalized;
  });
  return devices.sort((left, right) => left.id.localeCompare(right.id));
}

export const fingerprintDirectDevices = (value) => fingerprint(normalizeDirectDevices(value));

export function buildDevicePolicyRestore({ devices, chain, slot, tproxyPort, tproxyMark }) {
  const child = childChain(chain, slot);
  const rules = ['*mangle', `-F ${child}`];
  for (const device of devices) {
    rules.push(`-A ${child} -i ${device.interface} -s ${device.ip} -m mac --mac-source ${device.mac} -m comment --comment harbor-policy:${device.id}:direct -j RETURN`);
  }
  rules.push(
    `-A ${child} -p tcp -j TPROXY --on-port ${tproxyPort} --tproxy-mark ${tproxyMark}/${tproxyMark}`,
    `-A ${child} -p udp -j TPROXY --on-port ${tproxyPort} --tproxy-mark ${tproxyMark}/${tproxyMark}`,
    'COMMIT',
    '',
  );
  return rules.join('\n');
}

export function createDevicePolicyService({
  chain,
  tproxyPort,
  tproxyMark,
  run = spawnSync,
  now = () => new Date(),
  nextGeneration = () => crypto.randomUUID(),
}) {
  if (!CHAIN_PATTERN.test(String(chain || ''))
    || !Number.isInteger(tproxyPort) || tproxyPort < 1 || tproxyPort > 65_535
    || !MARK_PATTERN.test(String(tproxyMark || ''))) {
    throw new Error('Некорректная конфигурация device policy');
  }
  const epoch = nextGeneration();
  let activeSlot = 'A';
  let activeSignature = JSON.stringify([]);
  let generation = epoch;
  let appliedDevices = [];
  let observedAt = now().toISOString();
  let queue = Promise.resolve();

  function execute(command, args, input) {
    const result = run(command, args, input == null ? COMMAND_OPTIONS : { ...COMMAND_OPTIONS, input });
    if (result.error || result.status !== 0) throw commandError(command, result);
  }

  function snapshot(changed = false) {
    return {
      epoch,
      generation,
      fingerprint: fingerprint(appliedDevices),
      observedAt,
      appliedIds: appliedDevices.map(({ id }) => id),
      changed,
    };
  }

  function performApply(value) {
    const devices = normalizeDirectDevices(value);
    const signature = JSON.stringify(devices);
    if (signature === activeSignature) return snapshot(false);
    const nextSlot = activeSlot === 'A' ? 'B' : 'A';
    execute('iptables-restore', ['-w', '1', '--noflush'], buildDevicePolicyRestore({
      devices,
      chain,
      slot: nextSlot,
      tproxyPort,
      tproxyMark,
    }));
    execute('iptables', [
      '-w', '1', '-t', 'mangle', '-R', chain, '1', '-j', childChain(chain, nextSlot),
    ]);
    activeSlot = nextSlot;
    activeSignature = signature;
    appliedDevices = devices;
    generation = nextGeneration();
    observedAt = now().toISOString();
    return snapshot(true);
  }

  function apply(devices) {
    const result = queue.then(() => performApply(devices));
    queue = result.catch(() => {});
    return result;
  }

  return { apply, snapshot: () => snapshot(false) };
}