const KIOSK_QUERY_VALUE = '1';
const REVISION_KEY = 'analyzer_kiosk_backup_revision_v1';
const SYNC_INTERVAL_MS = 2000;

function isKioskBrowser() {
  try {
    return new URLSearchParams(globalThis.location?.search || '').get('kiosk') === KIOSK_QUERY_VALUE;
  } catch (_) {
    return false;
  }
}

function isPhoenixStorageKey(key) {
  return key !== REVISION_KEY && (
    key.startsWith('analyzer_') ||
    key.startsWith('MIGRATE_') ||
    [
      'ppm_din_mode',
      'calibration_notice_seen_v1',
      'recorder_warning_ack_v1',
      'ppm_din_loudness_warn_ack_v1',
      'migrate_rta_peak_fall_default_v1',
      'migrate_vu_offset_default_zero_v2',
      'migrate_lr_delay_zero_to_0_05_v1',
    ].includes(key)
  );
}

function collectStorage() {
  const storage = {};
  try {
    for (let index = 0; index < localStorage.length; index += 1) {
      const key = localStorage.key(index);
      if (!key || !isPhoenixStorageKey(key)) continue;
      const value = localStorage.getItem(key);
      if (value !== null) storage[key] = value;
    }
  } catch (_) {}
  return storage;
}

function storageFingerprint(storage) {
  return JSON.stringify(Object.entries(storage).sort(([left], [right]) => left.localeCompare(right)));
}

function localRevision() {
  try {
    const value = Number(localStorage.getItem(REVISION_KEY));
    return Number.isSafeInteger(value) && value >= 0 ? value : 0;
  } catch (_) {
    return 0;
  }
}

function setLocalRevision(revision) {
  try { localStorage.setItem(REVISION_KEY, String(revision)); } catch (_) {}
}

function applyStorage(storage, revision) {
  try {
    const remove = [];
    for (let index = 0; index < localStorage.length; index += 1) {
      const key = localStorage.key(index);
      if (key && isPhoenixStorageKey(key)) remove.push(key);
    }
    remove.forEach((key) => localStorage.removeItem(key));
    Object.entries(storage || {}).forEach(([key, value]) => {
      if (isPhoenixStorageKey(key) && typeof value === 'string') localStorage.setItem(key, value);
    });
    setLocalRevision(revision);
    return true;
  } catch (error) {
    console.warn('Kiosk browser restore failed:', error);
    return false;
  }
}

function apiUrl() {
  const hostname = String(globalThis.location?.hostname || '127.0.0.1');
  return `http://${hostname}:8789/api/v1/kiosk-browser-config`;
}

async function readRemote() {
  const response = await fetch(`${apiUrl()}?_=${Date.now()}`, { cache: 'no-store' });
  if (!response.ok) throw new Error(`HTTP ${response.status}`);
  return response.json();
}

async function writeRemote(baseRevision, storage) {
  const response = await fetch(apiUrl(), {
    method: 'POST',
    headers: { 'content-type': 'application/json' },
    cache: 'no-store',
    body: JSON.stringify({ baseRevision, storage }),
  });
  const payload = await response.json().catch(() => null);
  if (!response.ok) {
    const error = new Error(payload?.error || `HTTP ${response.status}`);
    error.status = response.status;
    throw error;
  }
  return payload;
}

export async function setupKioskBrowserBackup() {
  if (!isKioskBrowser()) return true;

  let remote;
  try {
    remote = await readRemote();
  } catch (error) {
    console.warn('Kiosk browser backup unavailable:', error);
    return true;
  }

  let revision = Number(remote?.revision) || 0;
  const storedRevision = localRevision();
  if (revision > storedRevision) {
    if (applyStorage(remote?.storage || {}, revision)) {
      globalThis.location?.reload?.();
      return false;
    }
  } else if (revision === 0 && Object.keys(remote?.storage || {}).length === 0) {
    try {
      const result = await writeRemote(0, collectStorage());
      revision = Number(result?.revision) || 1;
      setLocalRevision(revision);
    } catch (error) {
      console.warn('Initial kiosk browser backup failed:', error);
    }
  } else {
    setLocalRevision(revision);
  }

  let fingerprint = storageFingerprint(collectStorage());
  let running = false;
  globalThis.setInterval(async () => {
    if (running) return;
    running = true;
    try {
      const latest = await readRemote();
      const latestRevision = Number(latest?.revision) || 0;
      if (latestRevision > revision) {
        if (applyStorage(latest?.storage || {}, latestRevision)) globalThis.location?.reload?.();
        return;
      }
      const storage = collectStorage();
      const nextFingerprint = storageFingerprint(storage);
      if (nextFingerprint !== fingerprint) {
        const result = await writeRemote(revision, storage);
        revision = Number(result?.revision) || (revision + 1);
        setLocalRevision(revision);
        fingerprint = nextFingerprint;
      }
    } catch (error) {
      if (error?.status !== 409) console.warn('Kiosk browser backup sync failed:', error);
    } finally {
      running = false;
    }
  }, SYNC_INTERVAL_MS);
  return true;
}