import { lookup } from 'node:dns/promises';

import { request as httpsRequest } from 'node:https';

import { isIP } from 'node:net';

const RESPONSE_LIMIT = 64 * 1024;

function isPrivateIpv4(address: string) {

  const values = address.split('.').map(Number);

  const [a, b] = values;

  if (values.length !== 4 || values.some((value) => !Number.isInteger(value))) return true;

  return (

    a === 0 ||

    a === 10 ||

    a === 127 ||

    (a === 100 && b! >= 64 && b! <= 127) ||

    (a === 169 && b === 254) ||

    (a === 172 && b! >= 16 && b! <= 31) ||

    (a === 192 && b === 168) ||

    (a === 192 && b === 0) ||

    (a === 192 && b === 2) ||

    (a === 198 && (b === 18 || b === 19 || b === 51)) ||

    (a === 203 && b === 0) ||

    a! >= 224

  );

}

function isPrivateIp(address: string) {

  if (isIP(address) === 4) return isPrivateIpv4(address);

  const normalized = address.toLowerCase();

  if (normalized.startsWith('::ffff:')) return isPrivateIpv4(normalized.slice(7));

  return (

    normalized === '::' ||

    normalized === '::1' ||

    normalized.startsWith('fc') ||

    normalized.startsWith('fd') ||

    /^fe[89ab]/.test(normalized) ||

    normalized.startsWith('2001:db8:')

  );

}

export async function resolvePublicRuntimeEndpoint(value: string) {

  const url = new URL(value);

  if (url.protocol !== 'https:') throw new Error('Runtime endpoint must use HTTPS');

  if (url.username || url.password) throw new Error('Runtime endpoint cannot contain credentials');

  if (url.port && url.port !== '443') throw new Error('Runtime endpoint must use port 443');

  if (isIP(url.hostname) || url.hostname === 'localhost' || url.hostname.endsWith('.local'))

    throw new Error('Runtime endpoint must use a public DNS hostname');

  const addresses = await lookup(url.hostname, { all: true, verbatim: true });

  if (!addresses.length || addresses.some(({ address }) => isPrivateIp(address)))

    throw new Error('Runtime endpoint resolves to a private or reserved network');

  return { url, address: addresses[0]!.address };

}

export async function postRuntimeJson(

  endpoint: string,

  body: unknown,

  headers: Record<string, string> = {},

) {

  const target = await resolvePublicRuntimeEndpoint(endpoint);

  const encoded = JSON.stringify(body);

  return new Promise<{ status: number; body: unknown }>((resolve, reject) => {

    const request = httpsRequest(

      {

        protocol: 'https:',

        hostname: target.address,

        port: 443,

        path: `${target.url.pathname}${target.url.search}`,

        method: 'POST',

        servername: target.url.hostname,

        headers: {

          host: target.url.host,

          'content-type': 'application/json',

          'content-length': Buffer.byteLength(encoded),

          ...headers,

        },

        timeout: 10_000,

      },

      (response) => {

        const chunks: Buffer[] = [];

        let size = 0;

        response.on('data', (chunk: Buffer) => {

          size += chunk.length;

          if (size > RESPONSE_LIMIT) request.destroy(new Error('Runtime response is too large'));

          else chunks.push(chunk);

        });

        response.on('end', () => {

          const text = Buffer.concat(chunks).toString('utf8');

          let parsed: unknown = undefined;

          if (text) {

            try {

              parsed = JSON.parse(text);

            } catch {

              parsed = text;

            }

          }

          resolve({ status: response.statusCode ?? 500, body: parsed });

        });

      },

    );

    request.on('timeout', () => request.destroy(new Error('Runtime endpoint timed out')));

    request.on('error', reject);

    request.end(encoded);

  });

}