/**
 * 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 fs = require('node:fs');
const fsp = require('node:fs/promises');
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;
}

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

let mainWindow = null;

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

  mainWindow = 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,
    },
  });

  mainWindow.once('ready-to-show', () => mainWindow.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 === `${SCHEME}:`; } catch { return false; }
  };
  mainWindow.webContents.on('will-navigate', (event, target) => {
    if (!isOurs(target)) event.preventDefault();
  });
  mainWindow.webContents.setWindowOpenHandler(({ url }) => {
    if (/^https?:$/.test(new URL(url).protocol)) shell.openExternal(url);
    return { action: 'deny' };
  });
  // Nothing in this application needs a camera, a microphone or a location.
  mainWindow.webContents.session.setPermissionRequestHandler(
    (_wc, _permission, callback) => callback(false));

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

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

// ── 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', (_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');
    }
    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.
    if (mainWindow) {
      mainWindow.close();
      createWindow();
    }
    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');
    }
    const response = await fetch(target, {
      method: (init && init.method) || 'GET',
      headers: (init && init.headers) || {},
      body: (init && init.body) || undefined,
    });
    return {
      status: response.status,
      ok: response.ok,
      headers: Object.fromEntries(response.headers),
      body: await response.text(),
    };
  });

  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;
  });

  // The renderer never names a path. It asks for a dialog; the user chooses;
  // the main process holds the handle and the renderer only ever refers to it
  // by an opaque id.
  const sinks = new Map();
  let sinkId = 0;

  ipcMain.handle('save:begin', async (_e, suggestedName) => {
    const result = await dialog.showSaveDialog(mainWindow, {
      defaultPath: path.basename(String(suggestedName || 'download')),
    });
    if (result.canceled || !result.filePath) return null;
    const id = String(++sinkId);
    sinks.set(id, fs.createWriteStream(result.filePath));
    return { id, name: path.basename(result.filePath) };
  });

  ipcMain.handle('save:write', async (_e, id, chunk) => {
    const sink = sinks.get(String(id));
    if (!sink) throw new Error('No such download');
    await new Promise((resolve, reject) =>
      sink.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));
    await new Promise((resolve) => sink.end(resolve));
    return true;
  });
}

// ── 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 };