/**
 * Net capability pack — CORS-free HTTPS/HTTP via bare-fetch.
 * Private / loopback / link-local / metadata destinations are blocked.
 */

const b4a = require('b4a');

const MAX_BODY_BYTES = 2 * 1024 * 1024;
const DEFAULT_TIMEOUT_MS = 30000;
const MAX_TIMEOUT_MS = 60000;
const MAX_CHUNK_CHARS = 700000;

function isBlockedHostname(hostname) {
  if (!hostname) return true;
  const h = String(hostname).toLowerCase().replace(/^\[|\]$/g, '');
  if (
    h === 'localhost' ||
    h.endsWith('.localhost') ||
    h === '0.0.0.0' ||
    h === '::' ||
    h === '::1' ||
    h === 'metadata.google.internal' ||
    h.endsWith('.internal')
  ) {
    return true;
  }
  const v4 = h.match(/^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/);
  if (v4) {
    const a = Number(v4[1]);
    const b = Number(v4[2]);
    if (a === 0 || a === 10 || a === 127) return true;
    if (a === 169 && b === 254) return true;
    if (a === 172 && b >= 16 && b <= 31) return true;
    if (a === 192 && b === 168) return true;
    if (a === 100 && b >= 64 && b <= 127) return true;
  }
  if (h.includes(':')) {
    if (h === '::1' || h.startsWith('fe80:') || h.startsWith('fc') || h.startsWith('fd')) return true;
  }
  return false;
}

function assertPublicHttpUrl(raw) {
  let url;
  try {
    url = new URL(String(raw));
  } catch (_) {
    throw new Error('invalid URL');
  }
  if (url.protocol !== 'https:' && url.protocol !== 'http:') {
    throw new Error('only http(s) URLs are allowed');
  }
  if (isBlockedHostname(url.hostname)) {
    throw new Error('private, loopback, and metadata hosts are blocked');
  }
  return url;
}

function headersToObject(headers) {
  const out = {};
  if (!headers) return out;
  if (typeof headers.forEach === 'function') {
    headers.forEach((value, name) => {
      out[name] = value;
    });
    return out;
  }
  if (typeof headers === 'object') {
    for (const [k, v] of Object.entries(headers)) out[k] = String(v);
  }
  return out;
}

function emitBase64Chunks(emit, jobId, buffer) {
  const b64 = b4a.toString(buffer, 'base64');
  let index = 0;
  for (let offset = 0; offset < b64.length; offset += MAX_CHUNK_CHARS) {
    emit('cap-chunk', {
      pack: 'net',
      jobId,
      index,
      data: b64.slice(offset, offset + MAX_CHUNK_CHARS),
    });
    index++;
  }
  return index;
}

function createNetPack() {
  let fetchImpl = null;

  function loadFetch() {
    if (fetchImpl) return fetchImpl;
    const mod = require('bare-fetch');
    fetchImpl = typeof mod === 'function' ? mod : mod.default || mod.fetch;
    return fetchImpl;
  }

  const commands = {
    async fetch(ctx) {
      const { payload, reply, emit } = ctx;
      const parsed = assertPublicHttpUrl(payload.url);
      const method = String(payload.method || 'GET').toUpperCase();
      if (!/^[A-Z]+$/.test(method) || ['CONNECT', 'TRACE', 'TRACK'].includes(method)) {
        reply({ ok: false, error: 'method not allowed' });
        return;
      }
      const timeoutMs = Math.min(
        Math.max(1, payload.timeoutMs || DEFAULT_TIMEOUT_MS),
        MAX_TIMEOUT_MS
      );
      const fetch = loadFetch();
      const init = {
        method,
        headers: payload.headers || {},
      };
      if (payload.bodyBase64) init.body = b4a.from(payload.bodyBase64, 'base64');
      else if (payload.body != null) init.body = typeof payload.body === 'string' ? payload.body : JSON.stringify(payload.body);

      let controller = null;
      if (typeof AbortController === 'function') {
        controller = new AbortController();
        init.signal = controller.signal;
      }
      const timer = setTimeout(() => {
        try {
          if (controller) controller.abort();
        } catch (_) {}
      }, timeoutMs);

      try {
        const res = await fetch(parsed.href, init);
        let finalUrl = parsed;
        try {
          if (res.url) finalUrl = assertPublicHttpUrl(res.url);
        } catch (err) {
          reply({ ok: false, error: 'redirect blocked: ' + err.message });
          return;
        }
        const buf = await res.buffer();
        if (buf.length > MAX_BODY_BYTES) {
          reply({
            ok: false,
            error: `response too large (${buf.length} > ${MAX_BODY_BYTES})`,
            status: res.status,
            url: finalUrl.href,
          });
          return;
        }
        const as = payload.as || 'text';
        const meta = {
          ok: true,
          status: res.status,
          statusText: res.statusText || '',
          url: finalUrl.href,
          redirected: !!res.redirected,
          headers: headersToObject(res.headers),
          size: buf.length,
        };
        if (as === 'json') {
          try {
            meta.json = JSON.parse(b4a.toString(buf, 'utf8'));
          } catch (err) {
            reply({ ok: false, error: 'invalid JSON: ' + err.message, status: res.status });
            return;
          }
          reply(meta);
          return;
        }
        if (as === 'base64') {
          if (buf.length > 400 * 1024) {
            const jobId = payload.jobId || `net_${Date.now()}`;
            reply({ ...meta, jobId, streaming: true });
            const chunks = emitBase64Chunks(emit, jobId, buf);
            emit('cap-end', { pack: 'net', jobId, chunks, size: buf.length, url: finalUrl.href });
            return;
          }
          meta.dataBase64 = b4a.toString(buf, 'base64');
          reply(meta);
          return;
        }
        meta.text = b4a.toString(buf, 'utf8');
        reply(meta);
      } catch (err) {
        const msg = err && err.name === 'AbortError' ? 'request timed out' : err.message;
        reply({ ok: false, error: msg || 'fetch failed' });
      } finally {
        clearTimeout(timer);
      }
    },
  };

  return {
    id: 'net',
    commands,
  };
}

module.exports = { createNetPack, isBlockedHostname, assertPublicHttpUrl };