improvise/web/app.js

// The browser half of improvise-cr3, talking to either of two peers: five
// string calls, no protocol knowledge. See context/code/clients.md.

import init, { Client } from "./pkg/improvise_wasm_client.js";

const params = new URLSearchParams(location.search);
// present => socket, absent => in-page worker. The value is a host:port, and
// the scheme is NOT the caller's to get wrong: see `socketUrl`.
const WS_PEER = params.get("ws");

/** The websocket URL for `?ws=`, defaulting to TLS. Why, and when an explicit
 *  `ws://` is upgraded rather than honoured: context/code/clients.md. */
function socketUrl(peer) {
  const secure = location.protocol === "https:";
  if (/^wss:\/\//i.test(peer)) return peer;
  if (/^ws:\/\//i.test(peer)) return secure ? peer.replace(/^ws:/i, "wss:") : peer;
  return `${secure ? "wss" : "ws"}://${peer}`;
}

const WS_URL = WS_PEER ? socketUrl(WS_PEER) : null;
const DOC = params.get("doc") ?? "demo.improv";
const SEED = params.get("seed") ?? "demo.improv";

// Rough character metrics, used only to turn the window size into an extent.
// Being wrong here costs a row of over- or under-fetch, nothing more.
const ROW_PX = 26;
const COL_PX = 110;

const el = {
  grid: document.getElementById("grid"),
  categories: document.getElementById("categories"),
  mode: document.getElementById("mode"),
  hint: document.getElementById("hint"),
  status: document.getElementById("status"),
  viewName: document.getElementById("view-name"),
};

await init();
const client = new Client();

// `#status` carries two independent facts, composed rather than overwritten:
// a repaint must not quietly erase a connection error.
let shellStatus = "";
let modelStatus = "";
function paintStatus() {
  el.status.textContent = [shellStatus, modelStatus].filter(Boolean).join(" · ");
}
function setShellStatus(text) {
  shellStatus = text;
  paintStatus();
}

// What the grid's own frame costs, in whole cells, as of the last repaint —
// measured off the painted model, never predicted. context/code/clients.md.
let frameCost = { rows: 1, cols: 1 };

/** The extent this window can show, in whole DATA cells. */
function extent() {
  const box = el.grid.getBoundingClientRect();
  return {
    rows: Math.max(1, Math.floor(box.height / ROW_PX) - frameCost.rows),
    cols: Math.max(1, Math.floor(box.width / COL_PX) - frameCost.cols),
  };
}

function sendViewport() {
  const { rows, cols } = extent();
  // `client.set_viewport`, NOT the associated `Client.viewport`: the same
  // frame, but it also RECORDS the window. Why that matters: clients.md.
  transport.send(client.set_viewport(rows, cols));
}

// A peer that never answers the handshake. Deliberately about the *first
// frame*, not either peer's own failure modes — context/code/clients.md.
const HANDSHAKE_TIMEOUT_MS = 8000;
let watchdog = null;
function armWatchdog(message) {
  clearTimeout(watchdog);
  watchdog = setTimeout(() => setShellStatus(message), HANDSHAKE_TIMEOUT_MS);
}

// A peer that failed *loudly* has already said something more precise, so the
// watchdog must be DISARMED and not merely pre-empted (PR #13 review).
function setShellFailure(text) {
  clearTimeout(watchdog);
  watchdog = null;
  setShellStatus(text);
}

/** One frame, one fold, in arrival order. Never batch or reorder these. */
function onFrame(text) {
  clearTimeout(watchdog);
  try {
    client.on_frame(text);
  } catch (err) {
    // `on_frame` returns a Result, which wasm-bindgen throws; thrown in a bare
    // listener it reached the console alone and the grid just stopped.
    setShellStatus("bad frame — the grid has stopped updating (see console)");
    console.error("improvise: frame rejected", text, err);
    return;
  }
  repaint();
}

// Transports.

/** The in-page worker: the standalone deployment, no server process. */
function workerTransport() {
  const query = new URLSearchParams({ doc: DOC, seed: SEED });
  // `type: "module"` is not optional: worker.js is an ES module (it `import`s
  // the worker bundle), and a classic worker would fail to parse it.
  const worker = new Worker(`./worker.js?${query}`, { type: "module" });
  worker.addEventListener("message", (event) => onFrame(event.data));
  worker.addEventListener("messageerror", () =>
    setShellFailure("the worker sent a frame this page could not read"),
  );
  worker.addEventListener("error", (event) => {
    setShellFailure(`worker failed to start: ${event.message ?? "see console"}`);
    console.error("improvise: worker error", event);
  });
  setShellStatus(`in-page worker · ${DOC}`);
  // Frames posted before the worker has finished `start()` are held by
  // worker.js in arrival order, so the handshake can go out immediately.
  return { send: (text) => worker.postMessage(text), ready: Promise.resolve() };
}

/** A websocket to `improvise-ws-server`: how a TUI-hosted document is shared. */
function socketTransport() {
  const socket = new WebSocket(WS_URL);
  const unreachable = `cannot reach ${WS_URL} — is improvise-ws-server running?`;
  // Did this socket ever open? The page must record it itself: nothing on the
  // close event can discriminate. See context/code/clients.md.
  let opened = false;
  const ready = new Promise((resolve) => {
    socket.addEventListener("open", () => {
      opened = true;
      setShellStatus(`connected · ${WS_URL}`);
      resolve();
    });
  });
  socket.addEventListener("message", (event) => onFrame(event.data));
  // Without this, a connection that never opens left #status blank and
  // "server not running" read exactly like "still connecting".
  socket.addEventListener("error", () => setShellFailure(unreachable));
  // A socket that never opened did not "disconnect" (improvise-taxx). BOTH arms
  // route through `setShellFailure`, which disarms the watchdog — clients.md.
  socket.addEventListener("close", () =>
    setShellFailure(opened ? "disconnected" : unreachable),
  );
  setShellStatus(`connecting to ${WS_URL}…`);
  return {
    send: (text) => {
      if (socket.readyState === WebSocket.OPEN) socket.send(text);
    },
    ready,
  };
}

const transport = WS_URL ? socketTransport() : workerTransport();

// Painting.

let painted = -1;
let editing = null; // {row, col} while an input is open, so a repaint cannot steal it

function repaint() {
  if (editing) return;
  let model;
  try {
    model = JSON.parse(client.render_model());
  } catch (err) {
    setShellStatus("cannot render the current state (see console)");
    console.error("improvise: render failed", err);
    return;
  }
  if (model.revision === painted) return;
  painted = model.revision;

  el.mode.textContent = model.mode;
  // The mode's own hint, off `AppMode::hint_text()`. The page spells no
  // keys itself; see `RenderModel::hint`.
  el.hint.textContent = model.hint;
  modelStatus = model.status;
  paintStatus();
  el.viewName.textContent = model.view_name;
  el.grid.replaceChildren(gridTable(model));
  el.categories.replaceChildren(categoryList(model));

  // What the frame costs, so the NEXT viewport announcement is honest.
  // Inline group ROWS are deliberately NOT counted — context/code/clients.md.
  const next = {
    rows: model.col_levels.length + (model.col_groups.length > 0 ? 1 : 0),
    cols: model.row_levels,
  };
  const changed = next.rows !== frameCost.rows || next.cols !== frameCost.cols;
  frameCost = next;
  if (changed) sendViewport();
}

/** The grid, painted from a model in which every frame decision is already
 *  made (improvise-anr9). The page decides nothing here: which labels repeat
 *  and are therefore blank, how many header levels there are, which columns
 *  share a group and whether it is collapsed all arrive answered, by the same
 *  `AxisFrame` the TUI widget reads. */
function gridTable(model) {
  const table = document.createElement("table");
  const head = table.createTHead();
  const corner = () => {
    const th = document.createElement("th");
    th.colSpan = model.row_levels;
    return th;
  };

  // The column-group line, when there is one. An empty `col_groups` means
  // this grid has no column groups at all -- not that every group is blank.
  if (model.col_groups.length > 0) {
    const groups = head.insertRow();
    groups.appendChild(corner());
    for (const group of model.col_groups) {
      const th = document.createElement("th");
      th.colSpan = group.span;
      // `label` is null for a run in no group; an empty STRING is a legal group
      // name, so this is a null check and not a truthiness test.
      th.textContent =
        group.label === null ? "" : indicator(group.collapsed) + " " + group.label;
      th.classList.add("group");
      groups.appendChild(th);
    }
  }

  // One header line per level. A blank entry is repeat suppression, decided
  // in Rust -- never an absent label.
  for (const level of model.col_levels) {
    const tr = head.insertRow();
    tr.appendChild(corner());
    for (const label of level) {
      const th = document.createElement("th");
      th.textContent = label;
      tr.appendChild(th);
    }
  }

  const body = table.createTBody();
  // The cell coordinates a click sends are DATA row indices and a group header
  // is not a data row, so this counts rather than trusting `model.rows`.
  let r = -1;
  for (const row of model.rows) {
    const tr = body.insertRow();
    if (row.kind === "group") {
      const th = document.createElement("th");
      th.colSpan = model.row_levels + model.col_levels[0].length;
      th.textContent = indicator(row.collapsed) + " " + row.label;
      th.classList.add("group");
      tr.appendChild(th);
      continue;
    }
    r += 1;
    // `r` is one binding shared by every closure below, so a click handler
    // that captured it would fire with the LAST row's index. Snapshot it.
    const dataRow = r;

    for (const label of row.labels) {
      const header = document.createElement("th");
      header.scope = "row";
      header.textContent = label;
      tr.appendChild(header);
    }

    row.cells.forEach((cell, c) => {
      const td = tr.insertCell();
      // A keyboard edit is open when `model.editing` is a string, and it holds
      // what has been typed. Both facts are decided in Rust.
      const typing = cell.selected && typeof model.editing === "string";
      td.textContent = typing ? model.editing + "\u258f" : cell.text;
      td.classList.toggle("numeric", cell.numeric && !typing);
      td.classList.toggle("error", cell.error);
      td.classList.toggle("selected", cell.selected);
      td.classList.toggle("typing", typing);
      // `editable` is the server's answer relayed through Rust: a stored cell.
      // Drill is not on the wire yet, so an aggregate is not offered.
      td.classList.toggle("editable", cell.editable);
      if (cell.editable)
        td.addEventListener("click", () => edit(td, dataRow, c, cell.edit_text));
    });
  }
  return table;
}

/** The collapse glyph. `collapsed` is the fact, decided by the view and
 *  carried on the frame; only this spelling is the page's (gotcha 26). */
function indicator(collapsed) {
  return collapsed ? "\u25b6" : "\u25bc";
}

/** Open an inline editor. Committing sends a frame; the value that comes
 *  back is the server's, never the string typed here. */
function edit(td, row, col, seed) {
  if (editing) return;
  editing = { row, col };
  // `seed` is `RenderCell::edit_text` -- the STORED value, not the drawn one:
  // `td.textContent` has been through the number format.
  const original = seed;
  const input = document.createElement("input");
  input.value = original;
  td.replaceChildren(input);
  input.focus();
  input.select();

  // Enter removes the focused <input>, which fires `blur`, which calls
  // `close` again. Harmless before, but only by accident.
  let closed = false;
  const close = (commit) => {
    if (closed) return;
    closed = true;
    editing = null;
    if (commit) {
      const frame = client.typed_cell(row, col, input.value);
      // null only if the grid moved under the editor; the repaint that
      // follows restores whatever the server now says is there.
      if (frame) transport.send(frame);
    }
    td.replaceChildren(original);
    painted = -1;
    repaint();
  };

  input.addEventListener("keydown", (e) => {
    if (e.key === "Enter") close(true);
    else if (e.key === "Escape") close(false);
    // The editor owns the keyboard while it is open; the page-level handler
    // below must not also see these.
    e.stopPropagation();
  });
  input.addEventListener("blur", () => close(false));
}

function categoryList(model) {
  const list = document.createElement("ul");
  for (const row of model.categories) {
    const li = document.createElement("li");
    li.className = row.is_category ? "category" : "item";
    li.classList.toggle("selected", row.selected);
    li.textContent = row.is_category
      ? `${row.expanded ? "▾" : "▸"} ${row.label} (${row.item_count}) ${row.axis}`
      : row.label;
    list.appendChild(li);
  }
  return list;
}

// The keyboard. `Client::on_key_event` folds locally where it can; what it
// cannot answer is sent and does nothing, by design (context/code/clients.md).

window.addEventListener("keydown", (e) => {
  // The inline editor owns the keyboard while it is open. It stops
  // propagation, so this is belt and braces for a focus we did not predict.
  if (editing) return;
  // BrowserKey drops anything held with the platform meta key precisely so
  // Cmd-R does not arrive as a bare `r`; do not claim it here either.
  if (e.metaKey) return;

  const frame = client.on_key_event(e.key, e.ctrlKey, e.altKey, e.shiftKey, e.metaKey);
  if (frame) {
    // A frame means the page claimed the key, so the browser must not also act
    // on it. Ctrl/Alt combinations are left alone: they are the browser's.
    if (!e.ctrlKey && !e.altKey) e.preventDefault();
    transport.send(frame);
  }
  repaint();
});

// Start.

await transport.ready;
sendViewport(); // the handshake: the snapshot is built at this extent
armWatchdog(
  WS_URL
    ? `${WS_URL} accepted the connection but sent no document`
    : "the in-page worker did not answer — this browser may not allow it (see console)",
);
new ResizeObserver(sendViewport).observe(el.grid);