import {createServer} from 'node:net';

function toListenHosts(host) {
  if (host === '0.0.0.0') {
    return ['0.0.0.0'];
  }

  if (host === '::') {
    return ['::'];
  }

  return [host];
}

export function normalizePort(value, fallback) {
  const port = Number.parseInt(String(value ?? ''), 10);
  if (!Number.isInteger(port) || port < 0 || port > 65535) {
    return fallback;
  }

  return port;
}

export async function isPortAvailable({host, port}) {
  if (port === 0) {
    return true;
  }

  const listenHosts = toListenHosts(host);

  for (const listenHost of listenHosts) {
    const available = await new Promise((resolve) => {
      const server = createServer();
      server.unref();
      server.once('error', () => resolve(false));
      server.listen({host: listenHost, port}, () => {
        server.close(() => resolve(true));
      });
    });

    if (!available) {
      return false;
    }
  }

  return true;
}

export async function findAvailablePort({host, preferredPort, reservedPorts = new Set(), maxAttempts = 200}) {
  const startPort = normalizePort(preferredPort, 0);

  if (startPort === 0) {
    return await reserveEphemeralPort(host, reservedPorts);
  }

  for (let offset = 0; offset <= maxAttempts; offset += 1) {
    const candidate = startPort + offset;
    if (candidate > 65535) {
      break;
    }

    if (reservedPorts.has(candidate)) {
      continue;
    }

    if (await isPortAvailable({host, port: candidate})) {
      return candidate;
    }
  }

  throw new Error(`无法从 ${host}:${startPort} 开始找到可用端口`);
}

async function reserveEphemeralPort(host, reservedPorts) {
  for (let attempt = 0; attempt < 20; attempt += 1) {
    const port = await new Promise((resolve, reject) => {
      const server = createServer();
      server.unref();
      server.once('error', reject);
      server.listen({host, port: 0}, () => {
        const address = server.address();
        const resolvedPort = typeof address === 'object' && address ? address.port : 0;
        server.close(() => resolve(resolvedPort));
      });
    });

    if (typeof port === 'number' && port > 0 && !reservedPorts.has(port)) {
      return port;
    }
  }

  throw new Error(`无法为 ${host} 分配临时可用端口`);
}

export async function resolveDevStackPorts(config) {
  const reservedPorts = new Set();
  const entries = [
    ['spacetime', config.spacetime],
    ['api', config.api],
    ['web', config.web],
    ['adminWeb', config.adminWeb],
  ].filter(([, portConfig]) => Boolean(portConfig));
  const result = {};

  for (const [name, portConfig] of entries) {
    const resolvedPort = await findAvailablePort({
      host: portConfig.host,
      preferredPort: portConfig.preferredPort,
      reservedPorts,
    });
    reservedPorts.add(resolvedPort);
    result[name] = resolvedPort;
  }

  return result;
}

export function formatPortDecision({name, host, preferredPort, resolvedPort}) {
  if (preferredPort === resolvedPort && preferredPort !== 0) {
    return `[dev:ports] ${name}: ${host}:${resolvedPort} 可用`;
  }

  return `[dev:ports] ${name}: ${host}:${preferredPort} 不可用，改用 ${host}:${resolvedPort}`;
}

function parseCliPortConfig(rawArgs) {
  const config = {};

  for (const rawArg of rawArgs) {
    const [name, host, rawPreferredPort] = rawArg.split(':');
    if (!name || !host || rawPreferredPort == null) {
      throw new Error(`端口配置参数格式错误: ${rawArg}`);
    }

    config[name] = {
      host,
      preferredPort: normalizePort(rawPreferredPort, 0),
    };
  }

  return config;
}

function envKeyForPortName(name) {
  return `${name.replace(/[A-Z]/gu, (letter) => `_${letter}`).toUpperCase()}_PORT`;
}

if (process.argv[2] === 'resolve-dev-stack') {
  const config = parseCliPortConfig(process.argv.slice(3));
  const resolvedPorts = await resolveDevStackPorts(config);

  for (const [name, resolvedPort] of Object.entries(resolvedPorts)) {
    const portConfig = config[name];
    console.error(
      formatPortDecision({
        name,
        host: portConfig.host,
        preferredPort: portConfig.preferredPort,
        resolvedPort,
      }),
    );
    console.log(`${envKeyForPortName(name)}=${resolvedPort}`);
  }
}