kokkoja-rel/client/js/main.js

// @ts-check
/**
 * The Kokkoja client: the start screen, and the session screen that
 * connects the pen, the page and the other participants.
 */

import {
  deriveSession, formatInvitation, formatInvitationLink, loadIdentity, newIdentity, newSecret,
  parseInvitation, saveIdentity,
} from './crypto.js';
import {
  NotebookWriter, keepCurrentPage, keepIdentity, listKeptPages, listNotebooks, notebooksInBrowser,
  readCurrentPage, readIdentity, readPage, rememberToken, useBrowserStorage,
} from './notebook.js';
import { download, pickImageFile } from './browser_files.js';
import { pageFromSvg, pageToSvg } from './page_file.js';
import { hashOf } from './crypto.js';
import { imageResolution } from './image_info.js';
import {
  LEAST_TEXT_POINTS, MAX_IMAGE_BYTES, MOST_TEXT_POINTS, TEXT_FONTS, TEXT_SIZE,
  UNITS_PER_POINT, strokesTouched, textAt, textsTouched,
} from './page_model.js';
import { attachPenInput } from './pen_input.js';
import { Renderer, ZOOM_STEP } from './renderer.js';
import { Session } from './session.js';
import { NotebookChooser } from './chooser.js';
import { FileChooser } from './file_chooser.js';
import { writePicture } from './files.js';
import { pageToPng } from './page_picture.js';
import { TextEditor } from './text_editor.js';
import { enableTooltips } from './tooltip.js';

const COLORS = ['#1c1c1e', '#1f4fd8', '#d42a2a', '#1c8a3c'];
/** Everyone begins in black (Andy, 2026-10-03; the host began in red before). */
const DEFAULT_COLOR = COLORS[0];

/** Nominal line widths in page units (0.1 mm). */
const WIDTHS = [4, 7, 12];

/** Radius of the eraser on the screen, in CSS pixels. */
const ERASER_RADIUS = 10;

/** With the text tool or the eraser, a press that moves less than this (3 mm) is a tap. */
const TAP_DISTANCE = 30;

/**
 * An image file is shared as it is if it is no larger than this, in bytes
 * and in pixels along its longer side.  Otherwise it is made smaller and
 * stored as JPEG, so that it travels quickly and the page file stays small.
 */
const IMAGE_AS_IS_BYTES = 1500000;
const IMAGE_LONGEST_SIDE = 2400;

const NAME_KEY = 'kokkoja_name';
/** Colours the user added from the palette, remembered in this browser. */
const COLORS_KEY = 'kokkoja_colors';

/**
 * The palette behind "+": eight hues in three shades, and greys.  Our own,
 * not the browser's colour dialog, which crashes Firefox on Linux.
 */
const PALETTE = [
  '#e53935', '#fb8c00', '#fdd835', '#43a047', '#00acc1', '#1e88e5', '#8e24aa', '#d81b60',
  '#b71c1c', '#e65100', '#f9a825', '#1b5e20', '#006064', '#0d47a1', '#4a148c', '#880e4f',
  '#ffcdd2', '#ffe0b2', '#fff9c4', '#c8e6c9', '#b2ebf2', '#bbdefb', '#e1bee7', '#f8bbd0',
  '#ffffff', '#bdbdbd', '#757575', '#424242', '#8d6e63', '#5d4037', '#3e2723', '#000000',
];
const NOTEBOOK_KEY = 'kokkoja_notebook';
const DEFAULT_NOTEBOOK = 'Notebook';

/**
 * Where the installed Kokkoja program serves the client, for a guest who
 * opened an invitation link on a web site but has the program too.
 */
const INSTALLED_ADDRESS = 'http://localhost:8760/';

/**
 * How this client was served (`config.json`): by the local program, which
 * keeps the notebooks as files ("files"), or by a web site, where the
 * notebooks are kept in the browser ("browser").  The relay is the one for
 * sessions started here; the site, if any, is a Kokkoja web site that an
 * invitation can be a link to.
 * @typedef {object} Config
 * @property {string} relay
 * @property {'files' | 'browser'} storage
 * @property {string} site
 */
/** @type {Config} */
let config = { relay: '', storage: 'files', site: '' };

/**
 * @param {string} id
 * @returns {HTMLElement}
 */
function element(id) {
  return /** @type {HTMLElement} */ (document.getElementById(id));
}

/**
 * @param {string} id
 * @returns {HTMLInputElement}
 */
function input(id) {
  return /** @type {HTMLInputElement} */ (document.getElementById(id));
}

/**
 * Our identity: the signing keys that make us the same participant in
 * every session.  The local program keeps them, so that they survive the
 * browser and are the same from any browser on this computer; the first
 * time, they are made here and given to it.
 * @returns {Promise<import('./crypto.js').Identity>}
 */
async function ownIdentity() {
  const kept = await readIdentity();
  if (kept !== null) return loadIdentity(kept);
  const identity = await newIdentity();
  if (await keepIdentity(await saveIdentity(identity))) return identity;
  // Another tab got there first: use what it kept.
  const other = await readIdentity();
  return other !== null ? loadIdentity(other) : identity;
}

// Start screen.

/** @param {string} [message] */
function showStart(message = '') {
  element('session').hidden = true;
  element('start').hidden = false;
  element('start_message').textContent = message;
  input('name').value = localStorage.getItem(NAME_KEY) ?? '';
  input('notebook').value = localStorage.getItem(NOTEBOOK_KEY) ?? DEFAULT_NOTEBOOK;
  const pending = invitationInAddress();
  if (pending) input('invitation_entry').value = pending;
  // From a web site, a guest who has the Kokkoja program installed may
  // prefer it, for a notebook of real files.
  const installed = /** @type {HTMLAnchorElement} */ (element('open_installed'));
  installed.hidden = !(pending && notebooksInBrowser());
  installed.href = `${INSTALLED_ADDRESS}#join=${encodeURIComponent(pending)}`;
  showNotebooks().catch((error) => {
    element('notebook_note').textContent = String(error.message ?? error);
    element('notebook_note').classList.add('problem');
  });
}

/** Offer the existing notebooks and say where notebooks are kept. */
async function showNotebooks() {
  const { directory, notebooks } = await listNotebooks();
  const choices = element('notebook_choices');
  choices.replaceChildren();
  for (const notebook of notebooks) {
    const option = document.createElement('option');
    option.value = notebook;
    choices.append(option);
  }
  for (const note of document.querySelectorAll('.notebook_directory')) {
    note.textContent = directory ? `Notebooks are kept in ${directory}`
      : 'Notebooks are kept in this browser, on this computer. “Keep page” also downloads the page.';
    note.classList.remove('problem');
  }
}

/**
 * The part of the page address after '#', as named values.  The local
 * program puts the token there; a join link puts the invitation there.
 * Browsers do not send this part of an address to any server.
 */
function addressValues() {
  return new URLSearchParams(location.hash.slice(1));
}

/** @returns {string}  The invitation in the page address, or ''. */
function invitationInAddress() {
  return addressValues().get('join') ?? '';
}

/**
 * Set the page address for a session, or for none.
 * @param {string} [invitation]
 */
function setAddress(invitation) {
  history.replaceState(null, '', invitation
    ? `#join=${encodeURIComponent(invitation)}` : location.pathname);
}

/** @returns {string | null}  The name entered, or null after complaining. */
function enteredName() {
  const name = input('name').value.trim();
  if (!name) {
    element('start_message').textContent = 'Please enter your name.';
    input('name').focus();
    return null;
  }
  localStorage.setItem(NAME_KEY, name);
  return name;
}

/** @returns {string}  The notebook entered. */
function enteredNotebook() {
  const notebook = input('notebook').value.trim() || DEFAULT_NOTEBOOK;
  localStorage.setItem(NOTEBOOK_KEY, notebook);
  return notebook;
}

async function startSession() {
  const name = enteredName();
  if (!name) return;
  const identity = await ownIdentity();
  const secret = newSecret();
  const invitation = formatInvitation({ relay: config.relay, secret, hostId: identity.id });
  await enterSession(invitation, name, enteredNotebook());
}

async function joinSession() {
  const name = enteredName();
  if (!name) return;
  const invitation = input('invitation_entry').value.trim();
  if (!parseInvitation(invitation)) {
    element('start_message').textContent = 'That is not a Kokkoja invitation.';
    return;
  }
  await enterSession(invitation, name, enteredNotebook());
}

// Session screen.

/**
 * Prepare an image file to be put on the page.  The image's natural size
 * comes from the resolution the file records, if any, and otherwise from
 * taking a pixel as 0.1 mm (Andy's decision, 2026-10-03); where it goes on
 * the page is decided when it is added.  An image of more pixels or bytes
 * than is useful is made smaller here, which does not change its natural
 * size.
 * @param {Blob} file
 * @returns {Promise<Parameters<Session['addImage']>[0]>}
 */
async function prepareImage(file) {
  const original = new Uint8Array(await file.arrayBuffer());
  const bitmap = await createImageBitmap(file);
  const dpi = imageResolution(original);
  const unitsPerPixel = dpi === null ? 1 : 254 / dpi;
  let blob = file;
  const longest = Math.max(bitmap.width, bitmap.height);
  const asIs = (file.type === 'image/png' || file.type === 'image/jpeg') &&
    file.size <= IMAGE_AS_IS_BYTES && longest <= IMAGE_LONGEST_SIDE;
  if (!asIs) {
    const scale = Math.min(1, IMAGE_LONGEST_SIDE / longest);
    const canvas = document.createElement('canvas');
    canvas.width = Math.round(bitmap.width * scale);
    canvas.height = Math.round(bitmap.height * scale);
    const context = /** @type {CanvasRenderingContext2D} */ (canvas.getContext('2d'));
    context.fillStyle = '#ffffff';
    context.fillRect(0, 0, canvas.width, canvas.height);
    context.drawImage(bitmap, 0, 0, canvas.width, canvas.height);
    for (const quality of [0.9, 0.75, 0.5]) {
      blob = await new Promise((resolve, reject) => canvas.toBlob(
        (result) => (result ? resolve(result) : reject(new Error('The image could not be prepared.'))),
        'image/jpeg', quality));
      if (blob.size <= MAX_IMAGE_BYTES) break;
    }
  }
  if (blob.size > MAX_IMAGE_BYTES) throw new Error('The image is too large.');
  const data = blob === file ? original : new Uint8Array(await blob.arrayBuffer());
  const type = blob.type === 'image/png' ? 'image/png' : 'image/jpeg';
  return {
    type, data, hash: await hashOf(data),
    naturalWidth: bitmap.width * unitsPerPixel, naturalHeight: bitmap.height * unitsPerPixel,
  };
}

/**
 * The page to begin a session with, from the notebook's current page file.
 * If that file holds a page of this very session (the browser page was
 * reloaded, or we left and came back), the session continues from it.  If
 * it holds a page of another session, that page is kept first, because the
 * file is about to be given over to this session.
 * @param {string} notebook
 * @param {string} roomId
 * @returns {Promise<import('./page_model.js').Page | undefined>}
 */
async function pageToContinue(notebook, roomId) {
  const text = await readCurrentPage(notebook);
  if (text === null) return undefined;
  const saved = pageFromSvg(text);
  if (saved && saved.session === roomId) return saved.page;
  await keepCurrentPage(notebook);
  return undefined;
}

/** True once this browser page has entered a session. */
let entered = false;

/**
 * Where a browser tab remembers the notebook it chose for a session.
 * @param {string} roomId
 */
function notebookKeyFor(roomId) {
  return `kokkoja_notebook_${roomId}`;
}

/**
 * @param {string} invitationText
 * @param {string} name
 * @param {string} notebook
 */
async function enterSession(invitationText, name, notebook) {
  const invitation = parseInvitation(invitationText);
  if (!invitation) {
    showStart('That is not a Kokkoja invitation.');
    return;
  }
  if (entered) return;
  entered = true;
  const { roomId, key } = await deriveSession(invitation.secret);
  const identity = await ownIdentity();
  // A browser tab stays with the notebook it chose for a session.
  const notebookKey = notebookKeyFor(roomId);
  notebook = sessionStorage.getItem(notebookKey) ?? notebook;
  sessionStorage.setItem(notebookKey, notebook);
  const savedPage = await pageToContinue(notebook, roomId);
  setAddress(invitationText);

  element('start').hidden = true;
  element('session').hidden = false;
  // The invitation is shown as a link to the web site when there is one,
  // so that a guest can open it and be in the session with nothing
  // installed.  The link carries the invitation itself.
  const plainInvitation = formatInvitation(invitation);
  input('invitation').value = config.site ? formatInvitationLink(config.site, plainInvitation) : plainInvitation;

  const isHost = identity.id === invitation.hostId;
  let tool = /** @type {'pen' | 'eraser' | 'text'} */ ('pen');
  let color = DEFAULT_COLOR;
  let width = WIDTHS[1];
  let textSize = TEXT_SIZE;
  let textFont = /** @type {import('./page_model.js').TextFont} */ ('sans-serif');

  /** @type {Renderer} */
  let renderer;
  let layerOrder = '';

  function syncLayers() {
    const order = session.layerOrder();
    if (order.join(' ') === layerOrder) return;
    layerOrder = order.join(' ');
    renderer.setLayerOrder(order);
  }

  /**
   * @param {import('./page_model.js').Page} page
   * @returns {string}  The page file.
   */
  const fileOf = (page) => pageToSvg(page, { session: roomId, hostId: invitation.hostId });

  function showPageNumber() {
    element('page_number').textContent = session.page.number > 0
      ? `Page ${session.page.number}` : 'Waiting for the host’s page';
  }

  const session = new Session(
    {
      relay: invitation.relay, roomId, key, identity, hostId: invitation.hostId, name,
      page: savedPage,
    },
    {
      onLayerReplaced: (layerId) => {
        syncLayers();
        renderer.redrawLayer(layerId);
        writer.changed();
      },
      onStrokeProgress: (layerId, stroke) => {
        syncLayers();
        renderer.strokeProgress(layerId, stroke);
        if (stroke.done) writer.changed();
      },
      onTextChanged: (layerId) => {
        syncLayers();
        renderer.redrawLayer(layerId);
        writer.changed();
      },
      onPageReplaced: (oldPage, newPage) => {
        textEditor?.stop();
        // Nothing is lost: the page being left is kept in the notebook.
        writer.pageReplaced(oldPage.number > 0 ? fileOf(oldPage) : null);
        renderer.setPage(newPage);
        layerOrder = '';
        syncLayers();
        showParticipants(session, renderer);
        showPageNumber();
      },
      onImagesChanged: () => {
        renderer.showImages();
        writer.writeNow();
      },
      onPageResized: (byImages) => {
        // An image added or taken back does not rescale what is in view.
        if (byImages) renderer.holdScale();
        renderer.resize();
        textEditor?.layout();
        writer.changed();
      },
      onPermissionsChanged: () => {
        showHostTools();
        showParticipants(session, renderer);
      },
      onParticipantsChanged: () => {
        syncLayers();
        showParticipants(session, renderer);
      },
      onStatus: (status, detail) => {
        const text = { connecting: 'Connecting…', connected: 'Connected', failed: detail ?? 'Disconnected' };
        element('status').textContent = text[status];
        element('status').classList.toggle('problem', status !== 'connected');
      },
    });

  const writer = new NotebookWriter(
    notebook,
    () => (session.page.number > 0 ? fileOf(session.page) : null),
    (message, problem) => {
      element('save_status').textContent = message;
      element('save_status').classList.toggle('problem', problem);
    });
  element('save_status').textContent = savedPage ? 'Continued from the notebook' : '';

  const pageElement = element('page');
  renderer = new Renderer(pageElement, session.page);
  /** @type {TextEditor | null} */
  let textEditor = null;
  syncLayers();
  for (const layerId of session.page.layers.keys()) renderer.redrawLayer(layerId);
  showParticipants(session, renderer);
  showPageNumber();
  new ResizeObserver(() => {
    renderer.resize();
    textEditor?.layout();
  }).observe(/** @type {Element} */ (pageElement.parentElement));

  textEditor = new TextEditor(pageElement, renderer, {
    setText: (block) => session.setText(block),
    removeText: (id) => session.removeTexts([id]),
  });

  attachPenInput(pageElement, {
    toPage: (clientX, clientY) => renderer.pageFromClient(clientX, clientY),
    tool: () => tool,
    canWrite: () => session.page.number > 0,
    beginStroke: () => {
      textEditor?.stop();
      renderer.holdFit = true;
      session.beginStroke(color, width);
    },
    addPoints: (points) => session.addPoints(points),
    endStroke: () => {
      session.endStroke();
      renderer.holdFit = false;
      if (renderer.zoom === 'fit') renderer.resize();
    },
    eraseAlong: (x0, y0, x1, y1) => {
      textEditor?.stop();
      const radius = renderer.pageLength(ERASER_RADIUS);
      session.erase(strokesTouched(session.ownLayer, x0, y0, x1, y1, radius));
      session.removeTexts(textsTouched(session.ownLayer, x0, y0, x1, y1, radius));
    },
    eraseEnded: (x, y, reach) => {
      // A tap of the eraser on the image we have just added takes it back.
      const image = session.removableImage;
      if (image && reach < TAP_DISTANCE && x >= image.x && x <= image.x + image.width &&
          y >= image.y && y <= image.y + image.height) {
        session.removeAddedImage();
      }
    },
    previewText: (x0, y0, x1) => {
      if (Math.abs(x1 - x0) >= TAP_DISTANCE) textEditor?.showPreview(x0, y0, x1);
      else textEditor?.hidePreview();
    },
    placeText: (x0, y0, x1, y1) => {
      if (!textEditor) return;
      textEditor.hidePreview();
      const editing = textEditor.block;
      textEditor.stop();
      const own = textAt(session.ownLayer, x0, y0);
      if (Math.hypot(x1 - x0, y1 - y0) < TAP_DISTANCE) {
        // A tap: into our own text to change it, or a new block here.
        if (own && own !== editing) textEditor.edit(own);
        else if (!own) textEditor.begin(x0, y0, null, { color, size: textSize, font: textFont });
      } else {
        // A drag along the top edge: a new block that wraps at its width.
        textEditor.begin(Math.min(x0, x1), y0, Math.max(100, Math.round(Math.abs(x1 - x0))),
                         { color, size: textSize, font: textFont });
      }
    },
    onReport: (report) => {
      element('pen_report').textContent =
        `Input: ${report.pointerType}, pressure ${report.pressure.toFixed(2)}, ` +
        `${report.pointsPerSecond} points per second`;
    },
  });

  buildToolbar({
    color, width, textSize, textFont,
    setTool: (value) => {
      if (value !== 'text') textEditor?.stop();
      tool = value;
      // Only the chosen tool's settings show: the pen's colours and line
      // widths, the text's colours, size and font, nothing for the eraser.
      element('colors').hidden = value === 'eraser';
      element('widths').hidden = value !== 'pen';
      element('text_style').hidden = value !== 'text';
    },
    setColor: (value) => {
      color = value;
      textEditor?.restyle({ color });
    },
    setWidth: (value) => { width = value; },
    setTextSize: (value) => {
      textSize = value;
      textEditor?.restyle({ size: value });
    },
    setTextFont: (value) => {
      textFont = value;
      textEditor?.restyle({ font: value });
    },
  });

  // Zoom is each person's own; it changes nothing on the page.
  const showZoom = () => {
    element('zoom_fit').setAttribute('aria-pressed', String(renderer.zoom === 'fit'));
  };
  // A reloaded tab shows the page as it was last seen in it (Andy,
  // 2026-10-05: the least surprise): the zoom and the place scrolled to
  // are remembered in the tab, for the page they belong to.
  const viewKey = `kokkoja_view_${roomId}`;
  const saveView = () => {
    if (session.page.number === 0) return;
    sessionStorage.setItem(viewKey, JSON.stringify({ page: session.page.id, ...renderer.view() }));
  };
  let viewTimer = 0;
  const viewChanged = () => {
    clearTimeout(viewTimer);
    viewTimer = setTimeout(saveView, 300);
  };
  renderer.onZoomChanged = () => {
    showZoom();
    textEditor?.layout();
    viewChanged();
  };
  element('zoom_fit').addEventListener('click', () => renderer.setZoom('fit'));
  element('zoom_in').addEventListener('click', () => renderer.zoomBy(ZOOM_STEP));
  element('zoom_out').addEventListener('click', () => renderer.zoomBy(1 / ZOOM_STEP));
  showZoom();
  try {
    const seen = JSON.parse(sessionStorage.getItem(viewKey) ?? 'null');
    if (seen && seen.page === session.page.id && (seen.zoom === 'fit' || seen.zoom > 0) &&
        Number.isFinite(seen.x) && Number.isFinite(seen.y)) {
      renderer.showView(seen);
    }
  } catch {
    // Nothing usable was remembered: the page is shown as a new one is.
  }
  element('desk').addEventListener('scroll', viewChanged, { passive: true });
  window.addEventListener('pagehide', saveView);

  // The host drives: the host starts new pages, and may let a guest do so.
  function showHostTools() {
    element('host_tools').hidden = !session.mayMakePages();
  }
  showHostTools();
  element('new_page').addEventListener('click', () => session.newPage());

  /**
   * Add an image file to the page, below the images already on it.
   * @param {Blob} file
   * @param {boolean} [shrink]  Whether an image wider than the sheet is
   *     scaled down to it.
   */
  async function loadImage(file, shrink = true) {
    if (!session.mayMakePages() || session.page.number === 0) return;
    try {
      if (!session.addImage(await prepareImage(file), shrink)) {
        throw new Error('The page has no room for another image.');
      }
    } catch (error) {
      element('save_status').textContent =
        error instanceof Error && error.message ? error.message : 'That file is not an image.';
      element('save_status').classList.add('problem');
    }
  }
  const chooser = new NotebookChooser((chosenNotebook, pageName, text) => {
    const kept = pageFromSvg(text);
    if (!kept) {
      element('save_status').textContent = `${pageName} is not a Kokkoja page.`;
      element('save_status').classList.add('problem');
      return;
    }
    session.loadPage(kept.page);
  });
  element('load_notebook_page').addEventListener('click', () => { chooser.open(writer.notebook); });

  // Image files are chosen, and pictures of the page exported, through a
  // chooser of our own, which begins where the notebooks are.
  const fileChooser = new FileChooser();
  element('load_image').addEventListener('click', async () => {
    if (notebooksInBrowser()) {
      // No local program to look through the files: the browser's own chooser.
      const file = await pickImageFile();
      if (file) loadImage(file);
      return;
    }
    const file = await fileChooser.chooseImage();
    if (file) loadImage(file, fileChooser.shrinksWideImages());
  });

  /**
   * Save a picture of the page as it is shown here (layers hidden on this
   * screen are left out) where the user chooses.
   */
  async function exportPage() {
    const page = session.page;
    if (page.number === 0) return;
    textEditor?.stop();
    // Anything still waiting to be saved is saved first, so that its
    // "Saved" does not take the place of "Exported" a moment later.
    await writer.writeNow();
    const now = new Date();
    const day = [now.getFullYear(), now.getMonth() + 1, now.getDate()]
      .map((part) => String(part).padStart(2, '0')).join('_');
    if (notebooksInBrowser()) {
      download(`${day}_page_${page.number}.png`,
               await pageToPng(page, { session: roomId, hostId: session.hostId, hidden: renderer.hidden }));
      element('save_status').textContent = 'Exported to your downloads';
      element('save_status').classList.remove('problem');
      return;
    }
    const saved = await fileChooser.chooseWhereToSave(
      'Export', `${day}_page_${page.number}.png`,
      async (directory, name, replace) => writePicture(
        directory, name,
        await pageToPng(page, { session: roomId, hostId: session.hostId, hidden: renderer.hidden }),
        replace));
    if (saved === null) return;
    element('save_status').textContent = `Exported to ${saved}`;
    element('save_status').classList.remove('problem');
  }
  element('export_page').addEventListener('click', () => { exportPage(); });

  // The notebook: its name, and keeping the page.
  const notebookField = input('session_notebook');
  notebookField.value = notebook;
  showNotebooks().catch(() => {});
  notebookField.addEventListener('change', () => {
    const chosen = notebookField.value.trim();
    if (!chosen || chosen === writer.notebook) {
      notebookField.value = writer.notebook;
      return;
    }
    sessionStorage.setItem(notebookKey, chosen);
    localStorage.setItem(NOTEBOOK_KEY, chosen);
    writer.changeNotebook(chosen, (text) => {
      const saved = pageFromSvg(text);
      return saved !== null && saved.session === roomId && saved.page.id === session.page.id;
    }).then(() => showNotebooks()).catch(() => {});
  });
  element('keep_page').addEventListener('click', async () => {
    const kept = await writer.keepPage();
    // In the browser the notebook is out of reach of the user's own
    // programs: a kept page is also downloaded, which is how a page gets out.
    if (kept && notebooksInBrowser()) {
      const text = await readPage(writer.notebook, kept);
      if (text !== null) download(kept, new Blob([text], { type: 'image/svg+xml' }));
    }
  });

  element('copy_invitation').addEventListener('click', async () => {
    const field = input('invitation');
    field.select();
    try {
      await navigator.clipboard.writeText(field.value);
      element('copy_invitation').textContent = 'Copied';
      setTimeout(() => { element('copy_invitation').textContent = 'Copy'; }, 1500);
    } catch {
      // The field is selected; the user can copy it with the keyboard.
    }
  });

  if (notebooksInBrowser()) {
    element('keep_page').setAttribute('data-help',
      'Keep a dated copy of the page as it is now in this browser’s notebook, and download it. ' +
      'The page is also kept by itself whenever it is about to be replaced.');
    element('export_page').setAttribute('data-help',
      'Download a picture of the page, as it is shown here, as a PNG file.');
  }

  session.start();
  // For looking at the session from the browser's console during development.
  Object.assign(window, { kokkoja: {
    session, renderer, writer, loadImage, textEditor,
    notebook: { listNotebooks, listKeptPages, readPage, readCurrentPage, notebooksInBrowser },
  } });
}

/**
 * Mark one button of a group as chosen.
 * @param {Element} group
 * @param {Element} chosen
 */
function press(group, chosen) {
  for (const button of group.querySelectorAll('button')) {
    button.setAttribute('aria-pressed', String(button === chosen));
  }
}

/**
 * @param {object} options
 * @param {string} options.color  Initial color.
 * @param {number} options.width  Initial width.
 * @param {number} options.textSize
 * @param {import('./page_model.js').TextFont} options.textFont
 * @param {(tool: 'pen' | 'eraser' | 'text') => void} options.setTool
 * @param {(color: string) => void} options.setColor
 * @param {(width: number) => void} options.setWidth
 * @param {(size: number) => void} options.setTextSize
 * @param {(font: import('./page_model.js').TextFont) => void} options.setTextFont
 */
function buildToolbar(options) {
  for (const button of document.querySelectorAll('[data-tool]')) {
    button.addEventListener('click', () => {
      press(/** @type {Element} */ (button.parentElement), button);
      const chosen = button.getAttribute('data-tool');
      options.setTool(chosen === 'eraser' ? 'eraser' : chosen === 'text' ? 'text' : 'pen');
    });
  }

  const colors = element('colors');
  const palette = element('color_palette');
  const more = element('more_colors');

  /** @param {string} color */
  const addSwatch = (color) => {
    const button = document.createElement('button');
    button.type = 'button';
    button.className = 'swatch';
    button.style.setProperty('--swatch', color);
    button.setAttribute('aria-label', `Color ${color}`);
    button.setAttribute('data-help', 'Write in this color.');
    button.setAttribute('aria-pressed', String(color === options.color));
    button.addEventListener('click', () => {
      press(colors, button);
      options.setColor(color);
    });
    colors.insertBefore(button, more);
    return button;
  };
  /** @type {string[]} */
  let added = [];
  try {
    added = JSON.parse(localStorage.getItem(COLORS_KEY) ?? '[]');
  } catch {
    added = [];
  }
  for (const color of COLORS) addSwatch(color);
  for (const color of added) {
    if (/^#[0-9a-f]{6}$/.test(color)) addSwatch(color);
  }

  // "+" opens a palette below it; a chosen colour becomes a swatch before
  // the "+" and is the colour from then on.
  /** @param {string} color */
  const choose = (color) => {
    palette.hidden = true;
    const existing = [...colors.querySelectorAll('.swatch')]
      .find((swatch) => swatch.getAttribute('aria-label') === `Color ${color}`);
    const button = existing ?? addSwatch(color);
    if (!existing) {
      added.push(color);
      localStorage.setItem(COLORS_KEY, JSON.stringify(added));
    }
    press(colors, button);
    options.setColor(color);
  };
  for (const color of PALETTE) {
    const button = document.createElement('button');
    button.type = 'button';
    button.className = 'swatch';
    button.style.setProperty('--swatch', color);
    button.setAttribute('aria-label', `Color ${color}`);
    button.addEventListener('click', () => choose(color));
    palette.append(button);
  }
  more.addEventListener('click', () => {
    if (!palette.hidden) {
      palette.hidden = true;
      return;
    }
    const box = more.getBoundingClientRect();
    palette.style.left = `${box.left}px`;
    palette.style.top = `${box.bottom + 6}px`;
    palette.hidden = false;
  });
  document.addEventListener('pointerdown', (event) => {
    if (!palette.hidden && !palette.contains(/** @type {Node} */ (event.target)) && event.target !== more) {
      palette.hidden = true;
    }
  });
  document.addEventListener('keydown', (event) => {
    if (event.key === 'Escape') palette.hidden = true;
  });

  const widths = element('widths');
  for (const width of WIDTHS) {
    const button = document.createElement('button');
    button.type = 'button';
    button.className = 'width_choice';
    button.setAttribute('aria-label', `Line width ${width / 10} mm`);
    button.setAttribute('data-help', `Write with a ${width / 10} mm line. Pressing harder widens it.`);
    button.setAttribute('aria-pressed', String(width === options.width));
    const line = document.createElement('span');
    line.style.height = `${Math.max(1, Math.round(width / 2.5))}px`;
    button.append(line);
    button.addEventListener('click', () => {
      press(widths, button);
      options.setWidth(width);
    });
    widths.append(button);
  }

  // The text size is a number of points; any size works, since the fonts
  // scale.  The font is one of the three generic families.
  const size = input('text_size');
  size.value = String(Math.round(options.textSize / UNITS_PER_POINT));
  const applySize = () => {
    const points = Math.max(LEAST_TEXT_POINTS, Math.min(MOST_TEXT_POINTS, Number(size.value) || 0));
    size.value = String(points);
    options.setTextSize(Math.round(points * UNITS_PER_POINT * 10) / 10);
  };
  size.addEventListener('change', applySize);
  size.addEventListener('input', () => {
    if (Number(size.value) >= LEAST_TEXT_POINTS) applySize();
  });

  const font = /** @type {HTMLSelectElement} */ (document.getElementById('text_font'));
  font.value = options.textFont;
  font.style.fontFamily = options.textFont;
  font.addEventListener('change', () => {
    const chosen = TEXT_FONTS.find((family) => family === font.value) ?? 'sans-serif';
    font.style.fontFamily = chosen;
    options.setTextFont(chosen);
  });
}

/**
 * @param {Session} session
 * @param {Renderer} renderer
 */
function showParticipants(session, renderer) {
  const list = element('participants');
  list.replaceChildren();
  for (const participant of session.participantList()) {
    const item = document.createElement('li');
    const present = participant.self || participant.peer !== null;
    item.classList.toggle('absent', !present);

    if (session.isHost && !participant.self) {
      const allow = document.createElement('button');
      allow.type = 'button';
      allow.className = 'allow';
      allow.textContent = 'pages';
      allow.setAttribute('data-help', 'Let this participant start new pages and load images.');
      const allowed = session.permitted.has(participant.id);
      allow.setAttribute('aria-pressed', String(allowed));
      allow.addEventListener('click', () => session.setPermitted(participant.id, !allowed));
      item.append(allow);
    }

    const label = document.createElement('label');
    const visible = document.createElement('input');
    visible.type = 'checkbox';
    visible.checked = !renderer.hidden.has(participant.id);
    visible.setAttribute('data-help', 'Show or hide this participant’s writing on your screen only.');
    visible.addEventListener('change', () => renderer.setLayerVisible(participant.id, visible.checked));
    label.append(visible, ` ${participant.name}`);
    item.append(label);

    const roles = [];
    if (participant.self) roles.push('you');
    if (participant.host) roles.push('host');
    if (!present) roles.push('away');
    if (roles.length) {
      const role = document.createElement('span');
      role.className = 'role';
      role.textContent = roles.join(', ');
      item.append(role);
    }
    list.append(item);
  }
}

// Startup.

/** @param {any} error */
function failedToEnter(error) {
  entered = false;
  showStart(String(error?.message ?? error));
}

element('start_session').addEventListener('click', () => {
  startSession().catch(failedToEnter);
});
element('join_session').addEventListener('click', () => {
  joinSession().catch(failedToEnter);
});

/**
 * Begin where this browser tab left off.  A tab that was in a session and
 * is reloaded goes straight back into it.  A tab that arrives with an
 * invitation in its address shows the start screen with the invitation
 * filled in, so that the name and the notebook can be chosen.
 */
async function resume() {
  const invitationText = invitationInAddress();
  const invitation = parseInvitation(invitationText);
  const name = localStorage.getItem(NAME_KEY);
  if (invitation && name) {
    const { roomId } = await deriveSession(invitation.secret);
    const notebook = sessionStorage.getItem(notebookKeyFor(roomId));
    if (notebook) {
      await enterSession(invitationText, name, notebook);
      return;
    }
  }
  showStart();
}

enableTooltips();

const token = addressValues().get('token');
if (token) {
  rememberToken(token);
  setAddress(invitationInAddress());
}

/** Learn how this client was served, then begin. */
async function startUp() {
  const served = await (await fetch('config.json')).json();
  config = {
    relay: String(served.relay ?? ''),
    storage: served.storage === 'browser' ? 'browser' : 'files',
    site: String(served.site ?? ''),
  };
  if (config.storage === 'browser') useBrowserStorage();
  await resume();
}

if (!window.isSecureContext) {
  showStart('Kokkoja must be opened from this computer (http://localhost) or over HTTPS.');
} else {
  startUp().catch(failedToEnter);
}