/**
 * MeshBay desktop client — the Electron main process.
 *
 * The reason this exists, stated once so nobody has to rediscover it: **the
 * interface ships inside this package and loads from disk.** A shell that
 * points a WebView at the hub's /app/ is a browser with a different icon and
 * fixes nothing — the hub could still send whatever code it liked, which is
 * finding T3. The hub is used for its API and for nothing else.
 *
 * What that does and does not buy is worth being honest about: it does not make
 * the hub untrusted. A build downloaded from meshbay.org and signed with a key
 * its operator holds relocates the trust rather than removing it. What changes
 * is **detectability** — an attack has to ship as an artifact that can be
 * hashed and compared, instead of being one HTTP response aimed at one person.
 * That value is realised by reproducible builds and published hashes (18.7),
 * not by the packaging format.
 *
 * See docs/desktop-client-v1.md §2 and §3.
 */

'use strict';

const { app, BrowserWindow, dialog, ipcMain, protocol, safeStorage, shell } =
  require('electron');
const crypto = require('node:crypto');
const fs = require('node:fs');
const fsp = require('node:fs/promises');
const os = require('node:os');
const path = require('node:path');
const { pathToFileURL } = require('node:url');

const UI_DIR = path.join(__dirname, '..', 'ui');
const SCHEME = 'app';

// The policy, sent as a header on every response.
//
// Not a <meta> tag: `frame-ancestors` is ignored there — Chromium says so in
// the console — and a policy with a directive that silently does nothing is
// worse than one without it. A header is authoritative for every directive,
// and this handler is the only thing that serves the interface, so there is one
// source rather than two that can drift.
//
// `'wasm-unsafe-eval'` is required and must stay: the bundle key is Argon2id in
// WebAssembly, and a policy without it does not degrade anything — it locks
// every user out of their keys.
//
// The hub is reachable under connect-src, for its API and its signaling socket.
// It is deliberately absent from script-src: nothing it returns is executed,
// which is the whole reason this application exists (T3).
const CSP = [
  "default-src 'none'",
  "script-src 'self' 'wasm-unsafe-eval'",
  "style-src 'self' 'unsafe-inline'",
  "img-src 'self' data: blob:",
  "media-src 'self' blob:",
  "font-src 'self'",
  "connect-src 'self' https: wss:",
  "worker-src 'self'",
  "frame-ancestors 'none'",
  "base-uri 'none'",
  "form-action 'none'",
].join('; ');

// ── The scheme the interface is served from ─────────────────────────────────
//
// Not file://. Service workers, ES modules and IndexedDB all misbehave there,
// and the streamed-download path needs a *controlled* page — a worker that is
// merely active is not enough, which this codebase has already learned once.
//
// `secure` is what makes it a secure context, and without it the whole of
// `crypto.subtle` is undefined — measured on Electron 42 / Chromium 148, where
// a page on a non-secure scheme failed every algorithm including AES-GCM.
// `standard` gives it a real origin, so IndexedDB survives an update instead of
// being keyed to something that moves.
//
// What it does NOT buy: service workers. Chromium refuses to register one on a
// custom scheme whatever its privileges ("The URL protocol of the current
// origin is not supported"). So `sw.js` never runs here, and the streamed
// download it exists for is replaced by the native save dialog below — which is
// the better path anyway. It stays in the package because the same files serve
// the browser, where it is one of only three ways to write a large file.
protocol.registerSchemesAsPrivileged([{
  scheme: SCHEME,
  privileges: {
    standard: true,
    secure: true,
    supportFetchAPI: true,
    stream: true,          // Range requests, for playing a film
    corsEnabled: true,
  },
}]);

/**
 * Serve the packaged interface, and refuse to leave it.
 *
 * Every path is resolved and checked against the UI directory before anything
 * is read: the renderer is the least trusted part of this process, and a
 * traversal here would hand it the user's filesystem.
 */
function registerUiProtocol() {
  protocol.handle(SCHEME, async (request) => {
    const url = new URL(request.url);
    const rel = decodeURIComponent(url.pathname).replace(/^\/+/, '') || 'index.html';
    const target = path.resolve(UI_DIR, rel);
    const root = path.resolve(UI_DIR);
    if (target !== root && !target.startsWith(root + path.sep)) {
      return new Response('Not found', { status: 404 });
    }
    try {
      const body = await fsp.readFile(target);
      return new Response(body, {
        headers: {
          'Content-Type': contentType(target),
          'Content-Security-Policy': CSP,
          'X-Content-Type-Options': 'nosniff',
        },
      });
    } catch {
      return new Response('Not found', { status: 404 });
    }
  });
}

function contentType(file) {
  const ext = path.extname(file).toLowerCase();
  return {
    '.html': 'text/html; charset=utf-8',
    '.js': 'text/javascript; charset=utf-8',
    '.mjs': 'text/javascript; charset=utf-8',
    '.css': 'text/css; charset=utf-8',
    '.json': 'application/json; charset=utf-8',
    '.wasm': 'application/wasm',
    '.svg': 'image/svg+xml',
    '.png': 'image/png',
    '.woff2': 'font/woff2',
  }[ext] || 'application/octet-stream';
}

// ── Configuration ───────────────────────────────────────────────────────────

function configPath() {
  return path.join(app.getPath('userData'), 'config.json');
}

function readConfig() {
  try {
    return JSON.parse(fs.readFileSync(configPath(), 'utf8'));
  } catch {
    // No default hub. A client that picks its own is a client that can be
    // pointed at one, so the first run asks and the answer is remembered.
    return { hubBase: '', window: null };
  }
}

function writeConfig(next) {
  const dir = path.dirname(configPath());
  fs.mkdirSync(dir, { recursive: true });
  fs.writeFileSync(configPath(), JSON.stringify(next, null, 2), { mode: 0o600 });
}

let config = readConfig();

// ── Secrets ─────────────────────────────────────────────────────────────────
//
// The OS keychain, through safeStorage. What it protects and what it does not
// is reported rather than assumed: on Linux, safeStorage falls back to a fixed
// key when no keyring is running — a headless session, a minimal desktop — and
// it does so silently. Someone who believes the OS is holding their keys should
// be told when it is not.

function secretsFile() {
  return path.join(app.getPath('userData'), 'secrets.bin');
}

function readSecrets() {
  try {
    const raw = fs.readFileSync(secretsFile());
    if (!safeStorage.isEncryptionAvailable()) return {};
    return JSON.parse(safeStorage.decryptString(raw));
  } catch {
    return {};
  }
}

function writeSecrets(all) {
  if (!safeStorage.isEncryptionAvailable()) {
    throw new Error('No OS key storage is available on this system');
  }
  fs.mkdirSync(path.dirname(secretsFile()), { recursive: true });
  fs.writeFileSync(secretsFile(), safeStorage.encryptString(JSON.stringify(all)),
                   { mode: 0o600 });
}

function secretsBackend() {
  if (!safeStorage.isEncryptionAvailable()) return 'unavailable';
  if (process.platform !== 'linux') return process.platform === 'darwin'
    ? 'keychain' : 'dpapi';
  const backend = safeStorage.getSelectedStorageBackend
    ? safeStorage.getSelectedStorageBackend() : 'unknown';
  // "basic_text" is Electron's fixed-key fallback: encrypted on disk, but by a
  // key that is not a secret. Named plainly so the interface can say so.
  return backend === 'basic_text' ? 'unprotected_fallback' : backend;
}

// ── The device's hub key ────────────────────────────────────────────────────
//
// Ed25519, generated here on first sign-in, registered with the hub, and used
// from then on instead of deriving a key from the passphrase every time. The
// passphrase remains the account's credential and its only recovery path.
//
// **The renderer never holds it.** It parses decrypted content from nodes —
// video, images, filenames — which is attacker-controlled input, so it asks for
// a signature rather than being handed a key it could leak. This is the same
// rule as the save dialog: the renderer asks, this process acts.
//
// Note what this key is *not*: it is not a per-node identity key. Those are
// generated per node, pinned there, and never leave that relationship
// (docs/per-node-identity-v1.md). Nothing here correlates a person across
// operators, and nothing wraps a group key for it.

const DEVICE_KEY = 'device_auth_ed25519';

function deviceKey() {
  const stored = readSecrets()[DEVICE_KEY];
  if (!stored) return null;
  return crypto.createPrivateKey({
    key: Buffer.from(stored, 'base64'), format: 'der', type: 'pkcs8',
  });
}

function ensureDeviceKey() {
  const existing = deviceKey();
  if (existing) return publicKeyB64(existing);
  const { privateKey } = crypto.generateKeyPairSync('ed25519');
  const all = readSecrets();
  all[DEVICE_KEY] = privateKey.export({ format: 'der', type: 'pkcs8' })
    .toString('base64');
  writeSecrets(all);
  return publicKeyB64(crypto.createPrivateKey({
    key: Buffer.from(all[DEVICE_KEY], 'base64'), format: 'der', type: 'pkcs8' }));
}

function publicKeyB64(privateKey) {
  // Raw 32 bytes, as the hub stores and as `pk_to_b64` produces: the DER
  // SubjectPublicKeyInfo for Ed25519 is a fixed 12-byte prefix and the key.
  const der = crypto.createPublicKey(privateKey)
    .export({ format: 'der', type: 'spki' });
  return der.subarray(der.length - 32).toString('base64');
}

// Everything the interface is allowed to ask Chromium for. Watching a film
// full-screen is the whole list.
const GRANTED_PERMISSIONS = new Set(['fullscreen']);

// No hub call is still going to be answered after this. The hub's longest is
// signaling a WebRTC offer, which gives up at fifteen seconds of its own.
const HUB_FETCH_TIMEOUT_MS = 30000;

// ── Window ──────────────────────────────────────────────────────────────────

let mainWindow = null;

function createWindow() {
  const bounds = (config.window && config.window.width) ? config.window : {
    width: 1200, height: 800,
  };

  const win = new BrowserWindow({
    ...bounds,
    minWidth: 320,
    show: false,
    webPreferences: {
      // The three that matter. `sandbox` keeps the Chromium renderer sandbox —
      // the strongest one available, and the reason Electron is not the
      // trade-off the earlier design recorded against "native". Without
      // `contextIsolation` the preload's objects are reachable and mutable from
      // page script, which would make the bridge below decorative.
      sandbox: true,
      contextIsolation: true,
      nodeIntegration: false,
      preload: path.join(__dirname, 'preload.js'),
      // The hub address, handed over as a process argument rather than fetched.
      // `platform.hubBase()` runs while the module graph is loading — before
      // anything can await — so it has to be synchronous, and synchronous IPC
      // would block the renderer on every call for a value that never changes
      // within a run. Changing it restarts the window.
      additionalArguments: [`--meshbay-hub=${config.hubBase || ''}`],
      // The page is loaded over app:// and talks to the hub over https. Neither
      // needs to reach the local filesystem.
      webSecurity: true,
    },
  });

  win.once('ready-to-show', () => win.show());

  // The hub must never become the document origin. Anything that would navigate
  // away from the packaged interface is refused, and an external link opens in
  // the user's own browser rather than inside a window holding their keys.
  const isOurs = (target) => {
    try { return new URL(target).protocol === `${SCHEME}:`; } catch { return false; }
  };
  win.webContents.on('will-navigate', (event, target) => {
    if (!isOurs(target)) event.preventDefault();
  });
  win.webContents.setWindowOpenHandler(({ url }) => {
    if (/^https?:$/.test(new URL(url).protocol)) shell.openExternal(url);
    return { action: 'deny' };
  });
  // Deny by default, with one exception, and the exception is the point of the
  // comment. A blanket `callback(false)` here is what stopped a film going
  // fullscreen: Chromium's own video controls ask for `fullscreen`, and a
  // **denial does not reject** — `requestFullscreen()` returns a promise that
  // never settles, so the button simply does nothing and there is no error
  // anywhere to find. Measured, not deduced: the probe reported `NEVER SETTLED`
  // and the main process logged `PERMISSION ASKED: fullscreen`.
  //
  // So: enumerate what is granted rather than what is refused. A camera, a
  // microphone, a location, notifications and MIDI are all still refused, and
  // anything Chromium adds later arrives refused rather than quietly allowed.
  win.webContents.session.setPermissionRequestHandler(
    (_wc, permission, callback) => callback(GRANTED_PERMISSIONS.has(permission)));
  // `Permissions.query` takes the other handler; same answer, or the two can
  // disagree about what the page is allowed to do.
  win.webContents.session.setPermissionCheckHandler(
    (_wc, permission) => GRANTED_PERMISSIONS.has(permission));

  win.on('close', () => {
    if (!win.isMinimized() && !win.isFullScreen()) {
      config = { ...config, window: win.getBounds() };
      writeConfig(config);
    }
  });

  // `win`, not `mainWindow`. Changing the hub closes one window and opens
  // another, and `closed` arrives *after* the replacement has been assigned —
  // so a handler reading the module variable nulls out the new window, and the
  // new window's `ready-to-show` then crashes on it. Every handler here belongs
  // to the window it was created with, and only the current one may clear the
  // reference.
  win.on('closed', () => { if (mainWindow === win) mainWindow = null; });

  mainWindow = win;
  win.loadURL(`${SCHEME}://meshbay/index.html`);
  return win;
}

// ── Bridge ──────────────────────────────────────────────────────────────────
//
// Everything the interface may ask of this process, enumerated. A handler that
// takes a path from the renderer and acts on it is the shape to avoid: the
// renderer parses decrypted content from nodes, which is attacker-controlled
// input, so it is treated as hostile even though it is our own code.

function registerBridge() {
  ipcMain.handle('hub:set', async (_e, base) => {
    const url = String(base || '').trim().replace(/\/+$/, '');
    if (url && !/^https:\/\//.test(url) && !/^http:\/\/(localhost|127\.)/.test(url)) {
      // http is allowed only to a loopback address, for someone running a hub
      // on their own machine. Anywhere else it would put the session token on
      // the wire in clear.
      throw new Error('The hub address must be https');
    }
    // Ask the hub whether it is one, before writing the address down.
    //
    // Without this the first-run screen accepts anything shaped like a URL and
    // the application is then broken with no way back — there was no way to
    // change the hub once it was set, so a typo meant editing a JSON file by
    // hand. `https` typed at an `http` hub is the obvious case and it fails
    // with a TLS error that says nothing to anyone.
    let version;
    try {
      const probe = await fetch(`${url}/v1/hub/version`,
                                { signal: AbortSignal.timeout(10000) });
      if (!probe.ok) throw new Error(`answered ${probe.status}`);
      version = await probe.json();
      if (!version || !version.hub) throw new Error('did not answer as a hub');
    } catch (e) {
      throw new Error(describeUnreachable(url, e));
    }

    config = { ...config, hubBase: url };
    writeConfig(config);
    // The renderer reads the address from a process argument, so the window has
    // to be rebuilt for a change to take. Reloading in place would leave the
    // interface talking to the old hub with no sign of it.
    // Build the replacement first, then close the old one: the new window is
    // what `mainWindow` points at, so the outgoing window's `closed` handler
    // finds a reference that is no longer its own and leaves it alone.
    const outgoing = mainWindow;
    createWindow();
    if (outgoing && !outgoing.isDestroyed()) outgoing.close();
    return url;
  });

  // Every call to the hub leaves from here, not from the renderer.
  //
  // Not a preference. The page's origin is `app://meshbay`, and a browser fetch
  // from it is refused by CORS — the hub has no CORS middleware at all, which is
  // a posture worth keeping: its API is reachable from no web origin whatever.
  // Widening it for `app://meshbay` would be worse than it looks, because that
  // origin is not a credential — any Electron application on any machine can
  // claim the same scheme and host.
  //
  // So the renderer asks and this process goes, exactly as it does for saving a
  // file. Node's fetch has no origin and no CORS, the hub stays closed to the
  // web, and there is one place where network egress happens.
  ipcMain.handle('hub:fetch', async (_e, url, init) => {
    const target = new URL(String(url));
    const base = config.hubBase ? new URL(config.hubBase) : null;
    // The renderer may only reach the hub it is signed in to. A path it
    // controls must not become a request to somewhere else.
    if (!base || target.origin !== base.origin) {
      throw new Error('Refused: not this hub');
    }
    let response;
    try {
      response = await fetch(target, {
        method: (init && init.method) || 'GET',
        headers: (init && init.headers) || {},
        body: (init && init.body) || undefined,
        // Node's fetch waits as long as the OS lets it, which for a host that
        // accepts a connection and then says nothing is minutes. The hub's own
        // longest call is signaling, which gives up at fifteen seconds, so
        // anything past this is not an answer that is still coming.
        signal: AbortSignal.timeout(HUB_FETCH_TIMEOUT_MS),
      });
    } catch (e) {
      if (e && (e.name === 'TimeoutError' || e.name === 'AbortError')) {
        throw new Error(
          `${target.origin} accepted the connection but did not answer within `
          + `${Math.round(HUB_FETCH_TIMEOUT_MS / 1000)}s.`);
      }
      // Node's fetch says "fetch failed" for everything from a refused
      // connection to a TLS mismatch, which tells a person nothing at all.
      throw new Error(describeUnreachable(target.origin, e));
    }
    return {
      status: response.status,
      ok: response.ok,
      headers: Object.fromEntries(response.headers),
      body: await response.text(),
    };
  });

  ipcMain.handle('hub:probe', async (_e, url) => {
    const target = String(url || config.hubBase || '').replace(/\/+$/, '');
    if (!target) return null;
    try {
      const r = await fetch(`${target}/v1/hub/version`,
                            { signal: AbortSignal.timeout(10000) });
      return r.ok ? await r.json() : null;
    } catch { return null; }
  });

  ipcMain.handle('device:ensure', () => ensureDeviceKey());
  ipcMain.handle('device:public', () => {
    const key = deviceKey();
    return key ? publicKeyB64(key) : null;
  });
  ipcMain.handle('device:sign', (_e, username) => {
    const key = deviceKey();
    if (!key) return null;
    const timestamp = Math.floor(Date.now() / 1000);
    // The same bytes `POST /v1/users/auth` verifies. The username is inside the
    // signature, so one collected for a different account is not usable.
    const message = Buffer.from(
      `meshbay:user_auth:${String(username)}:${timestamp}`);
    return {
      timestamp,
      signature: crypto.sign(null, message, key).toString('base64'),
    };
  });
  ipcMain.handle('device:forget', () => {
    const all = readSecrets();
    delete all[DEVICE_KEY];
    writeSecrets(all);
    return true;
  });

  ipcMain.handle('secrets:backend', () => secretsBackend());
  ipcMain.handle('secrets:get', (_e, name) => readSecrets()[String(name)] ?? null);
  ipcMain.handle('secrets:set', (_e, name, value) => {
    const all = readSecrets();
    all[String(name)] = String(value);
    writeSecrets(all);
    return true;
  });
  ipcMain.handle('secrets:clear', (_e, name) => {
    const all = readSecrets();
    delete all[String(name)];
    writeSecrets(all);
    return true;
  });

  // Downloads are written to disk as they arrive — never collected in memory
  // and handed over at the end.
  //
  // That is what the browser does through the File System Access API or a
  // service worker, and **this application has neither**: `showDirectoryPicker`
  // is absent, and Chromium refuses to register a worker on a custom scheme. So
  // the chain fell through to its floor, which accumulates the whole file in
  // the page and hands Chromium a blob — a gigabyte of RAM for a gigabyte of
  // film, and a Save As dialog at the *end*, which is how it was noticed.
  //
  // The renderer still never names a path. It asks; the user chooses once; the
  // main process holds the handle and the renderer refers to it by an opaque id.
  const sinks = new Map();
  const completedPaths = new Map();
  let sinkId = 0;

  /** `name`, or the first "name (n).ext" that is not taken — never an overwrite. */
  function freeName(dir, filename) {
    if (!fs.existsSync(path.join(dir, filename))) return filename;
    const ext = path.extname(filename);
    const stem = path.basename(filename, ext);
    for (let n = 2; n < 1000; n++) {
      const candidate = `${stem} (${n})${ext}`;
      if (!fs.existsSync(path.join(dir, candidate))) return candidate;
    }
    throw new Error(`No free name for ${filename}`);
  }

  ipcMain.handle('folder:choose', async () => {
    const result = await dialog.showOpenDialog(mainWindow, {
      properties: ['openDirectory', 'createDirectory'],
    });
    if (result.canceled || !result.filePaths.length) return null;
    config = { ...config, downloadDir: result.filePaths[0] };
    writeConfig(config);
    return config.downloadDir;
  });

  // Where downloads land when nobody has chosen anywhere. A browser does not
  // make you pick a folder before it will save a file, and neither should this
  // — "save automatically" that opens a dialog is not automatic.
  function defaultDownloadDir() {
    try { return app.getPath('downloads'); } catch { return os.homedir(); }
  }

  function chosenDownloadDir() {
    const dir = config.downloadDir;
    // A folder that has been removed or unmounted is not a folder any more,
    // and saying so beats failing on the first chunk of a download.
    if (!dir) return null;
    try { return fs.statSync(dir).isDirectory() ? dir : null; } catch { return null; }
  }

  ipcMain.handle('folder:get', () => {
    const chosen = chosenDownloadDir();
    // `name` is what the settings row already renders, for the browser's
    // directory handle as much as for this. `isDefault` is how it knows not to
    // offer "forget" for a folder nobody chose.
    return { name: chosen || defaultDownloadDir(), isDefault: !chosen };
  });

  ipcMain.handle('folder:forget', () => {
    config = { ...config, downloadDir: '' };
    writeConfig(config);
    return true;
  });

  ipcMain.handle('root:choose', async () => {
    const result = await dialog.showOpenDialog(mainWindow, {
      properties: ['openDirectory', 'createDirectory'],
    });
    if (result.canceled || !result.filePaths.length) return null;
    const chosen = result.filePaths[0];
    return { path: chosen, name: path.basename(chosen) };
  });

  ipcMain.handle('save:begin', async (_e, suggestedName, opts) => {
    const wanted = path.basename(String(suggestedName || 'download'));
    const chosen = chosenDownloadDir();
    let target = null;

    // "Save automatically" means exactly that: no dialog. Into the chosen
    // folder if there is one, otherwise the system's Downloads folder — the
    // first version required a folder to have been picked first, so the very
    // first automatic download opened a dialog, which is the one thing the
    // setting says it will not do.
    //
    // The one case that still asks: a folder *was* chosen and has since gone.
    // Redirecting those files somewhere else without saying so is worse than a
    // dialog — someone who picked an external drive wants to know it is not
    // there, not to find the film in their home directory a week later.
    if (opts && opts.auto && !(config.downloadDir && !chosen)) {
      const dir = chosen || defaultDownloadDir();
      try {
        fs.mkdirSync(dir, { recursive: true });
        target = path.join(dir, freeName(dir, wanted));
      } catch { target = null; }
    }

    if (!target) {
      const dir = chosen || defaultDownloadDir();
      const result = await dialog.showSaveDialog(mainWindow, {
        defaultPath: path.join(dir, wanted),
      });
      if (result.canceled || !result.filePath) return null;
      target = result.filePath;
    }

    const id = String(++sinkId);
    sinks.set(id, { stream: fs.createWriteStream(target), path: target });
    return { id, name: path.basename(target), path: target };
  });

  ipcMain.handle('save:write', async (_e, id, chunk) => {
    const sink = sinks.get(String(id));
    if (!sink) throw new Error('No such download');
    // Awaiting the callback is what applies backpressure: without it the
    // renderer would outrun the disk and queue the file in memory anyway,
    // which is the thing this exists to avoid.
    await new Promise((resolve, reject) =>
      sink.stream.write(Buffer.from(chunk),
                        (err) => (err ? reject(err) : resolve())));
    return true;
  });

  ipcMain.handle('save:end', async (_e, id) => {
    const sink = sinks.get(String(id));
    if (!sink) return false;
    sinks.delete(String(id));
    completedPaths.set(String(id), sink.path);
    await new Promise((resolve) => sink.stream.end(resolve));
    return true;
  });

  ipcMain.handle('save:open', async (_e, id) => {
    const p = completedPaths.get(String(id));
    if (!p) return false;
    await shell.openPath(p);
    return true;
  });

  ipcMain.handle('save:abort', async (_e, id) => {
    const sink = sinks.get(String(id));
    if (!sink) return false;
    sinks.delete(String(id));
    await new Promise((resolve) => sink.stream.close(resolve));
    // A cancelled download leaves a truncated file, which is worse than none:
    // it looks like a complete one to whoever opens it next.
    try { fs.unlinkSync(sink.path); } catch { /* already gone */ }
    return true;
  });
}

/**
 * Why the hub could not be reached, in words somebody can act on.
 *
 * `TypeError: fetch failed` is what Node says for a refused connection, a DNS
 * failure and a TLS mismatch alike. The most common mistake by far is `https`
 * typed at a hub speaking plain `http`, so that one is named outright.
 */
function describeUnreachable(url, error) {
  const cause = (error && error.cause) || {};
  const code = cause.code || '';
  const detail = cause.message || error.message || String(error);

  if (/^https:/.test(url) &&
      (code === 'ECONNRESET' || /wrong version|SSL|TLS|EPROTO/i.test(detail))) {
    return `${url} does not speak https. If this hub is on your own machine, ` +
           `it is probably http — try http:// instead.`;
  }
  if (code === 'ECONNREFUSED') {
    return `Nothing is listening at ${url}. Is the hub running?`;
  }
  if (code === 'ENOTFOUND' || code === 'EAI_AGAIN') {
    return `${url} could not be found. Check the address.`;
  }
  if (error && error.name === 'TimeoutError') {
    return `${url} did not answer in time.`;
  }
  return `Could not reach ${url}: ${detail}`;
}

// ── Lifecycle ───────────────────────────────────────────────────────────────

// One instance. Two would fight over the config file and the secrets blob, and
// the second would look like the first had lost its state.
if (!app.requestSingleInstanceLock()) {
  app.quit();
} else {
  app.on('second-instance', () => {
    if (mainWindow) {
      if (mainWindow.isMinimized()) mainWindow.restore();
      mainWindow.focus();
    }
  });

  app.whenReady().then(() => {
    registerUiProtocol();
    registerBridge();
    createWindow();
    app.on('activate', () => {
      if (BrowserWindow.getAllWindows().length === 0) createWindow();
    });
  });

  app.on('window-all-closed', () => {
    if (process.platform !== 'darwin') app.quit();
  });
}

module.exports = { contentType, secretsBackend, CSP };