improvise/web/shell.js

// Everything `web/app.js` decides that is not painting: no DOM, no browser
// API, one `node --test` away. What belongs here: context/code/clients.md.

/** The websocket URL for `?ws=`, defaulting to TLS. Why, and when an explicit
 *  `ws://` is upgraded rather than honoured: context/code/clients.md. */
export function socketUrl(peer, pageProtocol) {
  const secure = pageProtocol === "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}`;
}

/** `#status` carries two independent facts, composed rather than overwritten:
 *  a repaint must not quietly erase a connection error. */
export function composeStatus(shell, model) {
  return [shell, model].filter(Boolean).join(" · ");
}

/** 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). */
export function indicator(collapsed) {
  return collapsed ? "▶" : "▼";
}

// 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.
export const ROW_PX = 26;
export const COL_PX = 110;

/** How long a peer has to answer the handshake. Exported because the harness
 *  must jump *past* it: a spec with its own copy can understate it silently
 *  and every watchdog assertion then passes vacuously (clients.md). */
export const HANDSHAKE_TIMEOUT_MS = 8000;

/** The extent a box of this size can show, in whole DATA cells: the frame is
 *  charged for first, and at least one cell is always asked for. */
export function extentOf(box, frameCost, metrics = { rowPx: ROW_PX, colPx: COL_PX }) {
  return {
    rows: Math.max(1, Math.floor(box.height / metrics.rowPx) - frameCost.rows),
    cols: Math.max(1, Math.floor(box.width / metrics.colPx) - frameCost.cols),
  };
}

/** What the grid's own frame costs, in whole cells — measured off the painted
 *  model, never predicted. Inline group ROWS are deliberately not counted. */
export function frameCostOf(model) {
  return {
    rows: model.col_levels.length + (model.col_groups.length > 0 ? 1 : 0),
    cols: model.row_levels,
  };
}

/** The grid, as a description: every decision made, nothing created. The page
 *  decides nothing here and neither does this — which labels repeat, how many
 *  header levels there are and which columns share a group all arrive
 *  answered, by the same `AxisFrame` the TUI widget reads (improvise-anr9). */
export function gridPlan(model) {
  const cornerSpan = model.row_levels;
  const groups = model.col_groups.map((group) => ({
    span: 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.
    text: group.label === null ? "" : `${indicator(group.collapsed)} ${group.label}`,
  }));

  // 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 the row's position.
  let dataRow = -1;
  const body = model.rows.map((row) => {
    if (row.kind === "group") {
      return {
        kind: "group",
        colSpan: model.row_levels + model.col_levels[0].length,
        text: `${indicator(row.collapsed)} ${row.label}`,
      };
    }
    dataRow += 1;
    return {
      kind: "data",
      row: dataRow,
      labels: row.labels,
      cells: row.cells.map((cell, col) => {
        // A keyboard edit is open when `model.editing` is a string, and it
        // holds what has been typed. Both facts are decided in Rust.
        const typing = cell.selected && typeof model.editing === "string";
        return {
          row: dataRow,
          col,
          text: typing ? `${model.editing}▏` : cell.text,
          editText: cell.edit_text,
          editable: cell.editable,
          classes: {
            numeric: cell.numeric && !typing,
            error: cell.error,
            selected: cell.selected,
            typing,
            // `editable` is the server's answer relayed through Rust: a stored
            // cell. Drill is not on the wire, so an aggregate is not offered.
            editable: cell.editable,
          },
        };
      }),
    };
  });

  return { cornerSpan, groups, levels: model.col_levels, body };
}

/** The page's two status facts and the handshake watchdog, which share a home
 *  because the one rule between them is that a *failure disarms the timer*. */
export function createShell({ onStatus, timeoutMs, setTimer = setTimeout, clearTimer = clearTimeout }) {
  let shell = "";
  let model = "";
  let watchdog = null;
  let arms = 0;
  const paint = () => onStatus(composeStatus(shell, model));

  return {
    setShell(text) {
      shell = text;
      paint();
    },
    setModel(text) {
      model = text;
      paint();
    },
    /** A peer that never answers the handshake. Deliberately about the *first
     *  frame*, not either peer's own failure modes — clients.md. */
    arm(message) {
      arms += 1;
      clearTimer(watchdog);
      watchdog = setTimer(() => {
        watchdog = null;
        this.setShell(message);
      }, timeoutMs);
    },
    /** A frame arrived, so the peer answered: the watchdog has no question
     *  left to ask. */
    sawFrame() {
      clearTimer(watchdog);
      watchdog = null;
    },
    /** A peer that failed *loudly* has already said something more precise, so
     *  the watchdog must be DISARMED and not merely pre-empted (PR #13). */
    fail(text) {
      this.sawFrame();
      this.setShell(text);
    },
    armed: () => watchdog !== null,
    /** How many times the watchdog has been armed. A test denying its message
     *  needs this to be nonzero, or it is denying an unreachable event. */
    timesArmed: () => arms,
  };
}