import http from 'node:http';
import {
  FAILOVER_PRIMARY_TAG,
  FAILOVER_RESERVE_TAG,
  FAILOVER_SELECTOR_TAG,
} from '../singbox.js';

type Role = 'primary' | 'reserve';
const SELECTOR_READY_ATTEMPTS = 20;
const SELECTOR_READY_DELAY_MS = 100;

const transientStartupError = (error: unknown) => (
  error && typeof error === 'object' && 'code' in error
    ? ['ECONNREFUSED', 'ECONNRESET'].includes(String(error.code))
    : false
);

async function whenReady<T>(operation: () => Promise<T>): Promise<T> {
  for (let attempt = 1; ; attempt += 1) {
    try {
      return await operation();
    } catch (error) {
      if (!transientStartupError(error) || attempt === SELECTOR_READY_ATTEMPTS) throw error;
      await new Promise((resolve) => setTimeout(resolve, SELECTOR_READY_DELAY_MS));
    }
  }
}

function request(port: number, method: string, body?: unknown): Promise<unknown> {
  return new Promise((resolve, reject) => {
    const encoded = body === undefined ? null : JSON.stringify(body);
    const req = http.request({
      host: '127.0.0.1',
      port,
      path: `/proxies/${encodeURIComponent(FAILOVER_SELECTOR_TAG)}`,
      method,
      headers: encoded ? {
        'content-type': 'application/json',
        'content-length': Buffer.byteLength(encoded),
      } : {},
    }, (res) => {
      const chunks: Buffer[] = [];
      res.on('data', (chunk: Buffer) => chunks.push(chunk));
      res.on('end', () => {
        if ((res.statusCode || 500) >= 400) return reject(new Error(`Sing-box selector HTTP ${res.statusCode}`));
        if (!chunks.length) return resolve({});
        try {
          resolve(JSON.parse(Buffer.concat(chunks).toString('utf8')));
        } catch (cause) {
          reject(new Error('Sing-box selector вернул невалидный JSON', { cause }));
        }
      });
    });
    req.setTimeout(2_000, () => req.destroy(new Error('Sing-box selector timeout')));
    req.on('error', reject);
    req.end(encoded);
  });
}

const tagFor = (role: Role) => role === 'primary' ? FAILOVER_PRIMARY_TAG : FAILOVER_RESERVE_TAG;
const roleFor = (tag: unknown): Role | null => (
  tag === FAILOVER_PRIMARY_TAG ? 'primary' : tag === FAILOVER_RESERVE_TAG ? 'reserve' : null
);

export function createSingboxSelectorService({
  port,
  send = (method: string, body?: unknown) => request(port, method, body),
}: {
  port: number;
  send?: (method: string, body?: unknown) => Promise<unknown>;
}) {
  async function read() {
    const value = await whenReady(() => send('GET')) as Record<string, unknown>;
    const role = roleFor(value.now);
    if (!role) throw new Error('Sing-box selector вернул неизвестный outbound');
    return { role };
  }
  async function select(role: Role) {
    await whenReady(() => send('PUT', { name: tagFor(role) }));
    const selected = await read();
    if (selected.role !== role) throw new Error('Sing-box selector не подтвердил переключение');
    return selected;
  }
  return { read, select };
}