// Inter Instance Service
// Purpose: Publishes this server's public instance profile and polls public profiles from peer servers.
// Scope: Owns only the inter-instance directory/API contract; local control, auth, and rover state stay in their existing services.
const EventEmitter = require('events');
const { v4: uuidv4 } = require('uuid');
const { app } = require('../../globals/http');
const io = require('../../globals/io');
const logger = require('../../globals/logger').child('interInstanceService');
const { loadConfig } = require('../../helpers/configLoader');
const { getFeatureFlags, getConfiguredSocials } = require('../../helpers/features');
const { getMode, MODES } = require('../modeManager');
const roverManager = require('../roverManager');
const { getTurnQueues } = require('../turnService');
const { getRoomCameras, getRoomCameraState } = require('../roomCameraService');
const { getRoverSnapshotState } = require('../roverSnapshotService');
const { getRole } = require('../roleService');
const { getNickname } = require('../nicknameService');

const DEFAULT_POLL_INTERVAL_MS = 30000;
const DEFAULT_REQUEST_TIMEOUT_MS = 5000;
const INFO_PATH = '/api/inter-instance/info';
const INSTANCE_ID = uuidv4();
const config = loadConfig();
const interInstanceConfig = config.interInstance || {};
const profileConfig = interInstanceConfig.profile || {};
const interInstanceEvents = new EventEmitter();
const remoteInstances = new Map();

let polling = false;
function asTrimmedString(value) {
  return typeof value === 'string' ? value.trim() : '';
}

function normalizeBaseUrl(value) {
  const raw = asTrimmedString(value);
  if (!raw) return '';
  try {
    const parsed = new URL(raw);
    parsed.hash = '';
    parsed.search = '';
    return parsed.toString().replace(/\/$/, '');
  } catch {
    return '';
  }
}

function isEnabled() {
  return Boolean(interInstanceConfig.enabled);
}

function requestTimeoutMs() {
  const value = Number(interInstanceConfig.requestTimeoutMs);
  return Number.isFinite(value) && value > 0 ? value : DEFAULT_REQUEST_TIMEOUT_MS;
}

function pollIntervalMs() {
  const value = Number(interInstanceConfig.pollIntervalMs);
  return Number.isFinite(value) && value > 0 ? value : DEFAULT_POLL_INTERVAL_MS;
}

function ownPublicUrl() {
  return normalizeBaseUrl(profileConfig.publicUrl);
}

function ownInstanceId() {
  /*
    This id exists only for this Node process. That is enough to detect self
    aliases during a poll cycle because every public URL that reaches this same
    running server returns the same generated value.
  */
  return INSTANCE_ID;
}

function buildPublicUrl(pathname) {
  const base = ownPublicUrl();
  if (!base || !pathname) return null;
  return `${base}${pathname.startsWith('/') ? pathname : `/${pathname}`}`;
}

function publicProfile() {
  const publicUrl = ownPublicUrl();
  return {
    id: ownInstanceId(),
    name: asTrimmedString(profileConfig.name) || publicUrl || 'Rover server',
    description: asTrimmedString(profileConfig.description),
    color: asTrimmedString(profileConfig.color),
    publicUrl,
  };
}

function isLockdownMode() {
  return getMode() === MODES.LOCKDOWN;
}

function buildUserEntry(socket) {
  const primaryRover = roverManager.getPrimaryRoverForSocket(socket.id);
  return {
    socketId: socket.id,
    userId: socket?.data?.userId || null,
    nickname: getNickname(socket) || null,
    role: getRole(socket),
    roverId: primaryRover || null,
  };
}

function addRoverSnapshotLinks(rover) {
  const id = String(rover?.id || '').trim();
  if (!id) return rover;
  const state = getRoverSnapshotState(id);
  const latestUrl = buildPublicUrl(`/api/inter-instance/rover-snapshots/${encodeURIComponent(id)}/latest`);
  if (!latestUrl) return rover;
  return {
    ...rover,
    snapshots: {
      latestUrl,
      updatedAt: state?.ts || null,
      error: state?.error || null,
    },
  };
}

function buildRoomCameraInfo(camera) {
  const state = getRoomCameraState(camera.id);
  const snapshotUrl = buildPublicUrl(`/api/inter-instance/room-cameras/${encodeURIComponent(camera.id)}/snapshot`);
  /*
    Room camera config can point at private LAN URLs. The inter-instance payload
    advertises this server's public snapshot endpoint instead, so remote clients
    do not learn or depend on the local camera's internal address.
  */
  return {
    id: camera.id,
    name: camera.name,
    description: camera.description || null,
    snapshotUrl,
    updatedAt: state?.ts || null,
    error: state?.error || null,
  };
}

function isClosedPrivateRover(rover) {
  return Boolean(rover?.private?.enabled && !rover?.private?.open);
}

function getPublicRoster() {
  return roverManager
    .getRoster()
    /*
      Closed private rovers are intentionally absent from the public
      inter-instance contract. If a rover is private and closed, other servers
      should not see its row or receive any derived snapshot URL for it.
    */
    .filter((rover) => !isClosedPrivateRover(rover));
}

function publicRoverIdSet(roster = []) {
  return new Set(roster.map((rover) => String(rover?.id || '')).filter(Boolean));
}

function filterPublicTurnQueues(turnQueues = {}, publicIds) {
  const visible = publicIds instanceof Set ? publicIds : new Set();
  const next = {};
  /*
    RoverQueuesPanel creates fallback rows for queue ids that are not present in
    the roster, so the public payload must filter queues with the exact same
    privacy boundary as the roster. Otherwise a closed-private rover can leak as
    an orphan queue row after a private access grant assigns someone to it.
  */
  Object.entries(turnQueues || {}).forEach(([roverId, info]) => {
    if (!visible.has(String(roverId))) return;
    next[roverId] = info;
  });
  return next;
}

function filterPublicUsers(users = [], publicIds) {
  const visible = publicIds instanceof Set ? publicIds : new Set();
  /*
    A user's current rover id is also part of the public inter-instance surface.
    If that rover is not in the public roster, scrub only that association while
    leaving the rest of the public user entry intact for normal queue display.
  */
  return users.map((user) => {
    const roverId = user?.roverId ? String(user.roverId) : '';
    if (!roverId || visible.has(roverId)) return user;
    return { ...user, roverId: null };
  });
}

function buildLocalInfo() {
  const mode = getMode();
  const lockdown = isLockdownMode();
  const features = getFeatureFlags();
  const publicRoster = getPublicRoster();
  const publicIds = publicRoverIdSet(publicRoster);
  const roster = publicRoster.map((rover) => (lockdown ? rover : addRoverSnapshotLinks(rover)));
  const users = filterPublicUsers(Array.from(io.sockets.sockets.values()).map(buildUserEntry), publicIds);
  const roomCameras = lockdown || !features.roomCameras ? [] : getRoomCameras().map(buildRoomCameraInfo);
  return {
    instance: {
      ...publicProfile(),
      mode,
      open: mode !== MODES.ADMIN && mode !== MODES.LOCKDOWN,
      features,
      updatedAt: Date.now(),
    },
    roster,
    turnQueues: filterPublicTurnQueues(getTurnQueues(), publicIds),
    users,
    roomCameras,
    socials: features.socials ? getConfiguredSocials(config) : [],
  };
}

function sendJpegState(res, state, missingMessage) {
  if (!state?.frame) {
    res.status(404).json({ error: missingMessage });
    return;
  }
  res.set('Cache-Control', 'no-store');
  res.set('X-Rover-Snapshot-Ts', String(state.ts || ''));
  res.type('jpeg').send(state.frame);
}

app.get(INFO_PATH, (req, res) => {
  if (!isEnabled()) {
    res.status(404).json({ error: 'Inter-instance sharing disabled' });
    return;
  }
  res.set('Cache-Control', 'no-store');
  res.json(buildLocalInfo());
});

app.get('/api/inter-instance/rover-snapshots/:roverId/latest', (req, res) => {
  if (!isEnabled() || isLockdownMode()) {
    res.status(404).json({ error: 'Snapshot unavailable' });
    return;
  }
  const roverId = String(req.params.roverId || '');
  const publicRover = getPublicRoster().find((rover) => String(rover.id) === roverId);
  if (!publicRover) {
    /*
      Do not rely on "not advertising the URL" as the privacy boundary. Public
      snapshot hosting must also reject direct requests for closed-private or
      unknown rovers because old URLs, logs, or guesses can outlive roster state.
    */
    res.status(404).json({ error: 'Rover snapshot unavailable' });
    return;
  }
  sendJpegState(res, getRoverSnapshotState(roverId), 'Rover snapshot unavailable');
});

app.get('/api/inter-instance/room-cameras/:cameraId/snapshot', (req, res) => {
  if (!isEnabled() || isLockdownMode()) {
    res.status(404).json({ error: 'Snapshot unavailable' });
    return;
  }
  const cameraId = String(req.params.cameraId || '');
  sendJpegState(res, getRoomCameraState(cameraId), 'Room camera snapshot unavailable');
});

function normalizeDirectoryEntry(entry) {
  if (typeof entry === 'string') {
    const url = normalizeBaseUrl(entry);
    return url ? { url, name: '' } : null;
  }
  if (!entry || typeof entry !== 'object') return null;
  const url = normalizeBaseUrl(entry.url || entry.baseUrl || entry.publicUrl);
  if (!url) return null;
  return {
    url,
    name: asTrimmedString(entry.name),
  };
}

function uniqueDirectoryEntries(entries) {
  const seen = new Set();
  return entries.filter((entry) => {
    if (!entry?.url || seen.has(entry.url)) return false;
    seen.add(entry.url);
    return true;
  });
}

async function fetchJson(url) {
  const controller = new AbortController();
  const timer = setTimeout(() => controller.abort(), requestTimeoutMs());
  try {
    const res = await fetch(url, { signal: controller.signal, headers: { Accept: 'application/json' } });
    if (!res.ok) throw new Error(`HTTP ${res.status}`);
    return await res.json();
  } finally {
    clearTimeout(timer);
  }
}

async function fetchDirectoryEntries() {
  const urls = Array.isArray(interInstanceConfig.directoryUrls)
    ? interInstanceConfig.directoryUrls.map((url) => asTrimmedString(url)).filter(Boolean)
    : [];
  const lists = await Promise.allSettled(urls.map((url) => fetchJson(url)));
  const entries = [];
  lists.forEach((result, idx) => {
    if (result.status !== 'fulfilled') {
      logger.warn('Directory fetch failed', { url: urls[idx], error: result.reason?.message || String(result.reason) });
      return;
    }
    if (!Array.isArray(result.value)) {
      logger.warn('Directory response was not an array', { url: urls[idx] });
      return;
    }
    result.value.forEach((entry) => {
      const normalized = normalizeDirectoryEntry(entry);
      if (normalized) entries.push(normalized);
    });
  });
  const self = ownPublicUrl();
  return uniqueDirectoryEntries(entries).filter((entry) => entry.url !== self);
}

function normalizeRemotePayload(entry, payload) {
  const instance = payload?.instance && typeof payload.instance === 'object' ? payload.instance : {};
  /*
    Remote payloads are intentionally additive. Every read below has a passive
    fallback so older or partially configured servers still produce a useful
    listing instead of breaking the whole directory view.
  */
  return {
    url: entry.url,
    online: true,
    lastSuccessAt: Date.now(),
    lastError: null,
    latencyMs: null,
    instance: {
      ...instance,
      id: asTrimmedString(instance.id),
      name: asTrimmedString(instance.name) || entry.name || entry.url,
      publicUrl: normalizeBaseUrl(instance.publicUrl) || entry.url,
      description: asTrimmedString(instance.description),
      color: asTrimmedString(instance.color),
      features: instance.features && typeof instance.features === 'object' ? instance.features : {},
    },
    roster: Array.isArray(payload?.roster) ? payload.roster : [],
    turnQueues: payload?.turnQueues && typeof payload.turnQueues === 'object' ? payload.turnQueues : {},
    users: Array.isArray(payload?.users) ? payload.users : [],
    roomCameras: Array.isArray(payload?.roomCameras) ? payload.roomCameras : [],
    socials: Array.isArray(payload?.socials) ? payload.socials : [],
  };
}

function remoteIdentityKey(remote) {
  const advertisedId = asTrimmedString(remote?.instance?.id);
  if (advertisedId) return `id:${advertisedId}`;
  const advertisedPublicUrl = normalizeBaseUrl(remote?.instance?.publicUrl);
  if (advertisedPublicUrl) return `url:${advertisedPublicUrl}`;
  return `url:${normalizeBaseUrl(remote?.url) || remote?.url || ''}`;
}

function isSelfRemote(remote) {
  const ownId = ownInstanceId();
  const remoteId = asTrimmedString(remote?.instance?.id);
  if (ownId && remoteId && ownId === remoteId) return true;
  const self = ownPublicUrl();
  const remotePublicUrl = normalizeBaseUrl(remote?.instance?.publicUrl);
  const remoteUrl = normalizeBaseUrl(remote?.url);
  return Boolean(self && (remotePublicUrl === self || remoteUrl === self));
}

function preferRemoteEntry(current, candidate) {
  /*
    When the directory has multiple URLs for one instance, keep the healthier
    entry. Online data beats offline placeholders, and lower latency is a useful
    tiebreaker when two aliases both work.
  */
  if (!current) return candidate;
  if (candidate.online && !current.online) return candidate;
  if (!candidate.online && current.online) return current;
  if (candidate.online && current.online) {
    const currentLatency = Number.isFinite(current.latencyMs) ? current.latencyMs : Infinity;
    const candidateLatency = Number.isFinite(candidate.latencyMs) ? candidate.latencyMs : Infinity;
    return candidateLatency < currentLatency ? candidate : current;
  }
  const currentName = asTrimmedString(current?.instance?.name);
  const candidateName = asTrimmedString(candidate?.instance?.name);
  return !currentName && candidateName ? candidate : current;
}

function replaceRemoteInstances(nextEntries) {
  const deduped = new Map();
  nextEntries.forEach((entry) => {
    if (!entry || isSelfRemote(entry)) return;
    const key = remoteIdentityKey(entry);
    deduped.set(key, preferRemoteEntry(deduped.get(key), entry));
  });
  remoteInstances.clear();
  Array.from(deduped.values()).forEach((entry) => {
    remoteInstances.set(remoteIdentityKey(entry), entry);
  });
}

function markOffline(entry, error) {
  const previous = remoteInstances.get(`url:${entry.url}`) || {};
  return {
    ...previous,
    url: entry.url,
    online: false,
    lastError: error?.message || String(error || 'Unknown error'),
    instance: {
      ...(previous.instance || {}),
      name: previous.instance?.name || entry.name || entry.url,
      publicUrl: previous.instance?.publicUrl || entry.url,
    },
    roster: previous.roster || [],
    turnQueues: previous.turnQueues || {},
    users: previous.users || [],
    roomCameras: previous.roomCameras || [],
    socials: previous.socials || [],
  };
}

async function pollRemoteInstance(entry) {
  const start = Date.now();
  try {
    const payload = await fetchJson(`${entry.url}${INFO_PATH}`);
    const normalized = normalizeRemotePayload(entry, payload);
    normalized.latencyMs = Date.now() - start;
    return normalized;
  } catch (err) {
    return markOffline(entry, err);
  }
}

async function pollNow() {
  if (!isEnabled() || polling) return;
  polling = true;
  try {
    const entries = await fetchDirectoryEntries();
    const nextEntries = await Promise.all(entries.map((entry) => pollRemoteInstance(entry)));
    replaceRemoteInstances(nextEntries);
    interInstanceEvents.emit('change');
  } catch (err) {
    logger.warn('Inter-instance poll failed', { error: err.message });
  } finally {
    polling = false;
  }
}

function startPolling() {
  if (!isEnabled()) return;
  pollNow();
  setInterval(pollNow, pollIntervalMs());
}

function getState() {
  return {
    enabled: isEnabled(),
    profile: publicProfile(),
    instances: Array.from(remoteInstances.values()).sort((a, b) =>
      String(a.instance?.name || a.url).localeCompare(String(b.instance?.name || b.url)),
    ),
  };
}

startPolling();

module.exports = {
  getState,
  interInstanceEvents,
  buildLocalInfo,
  pollNow,
};