quill/val Public Public: anyone can read this; nobody can change it.

/**

 * val, in a browser. It draws what the server sends and sends what the

 * person does — nothing else. There is no position here the server did not

 * hand over, and no enemy in a snapshot the server decided you cannot see,

 * so a patched client learns nothing a plain one does not.

 *

 * This file is the wiring: the socket, the keys and the pointer, the HUD.

 * The drawing lives beside it — `scene.js` for the first-person view,

 * `topdown.js` for the map, `gun.js` for the crosshair, `prompt.js` for the

 * line of advice and `raycast.js` for the maths all of it stands on.

 */

"use strict";

import { makeBeeper } from "./beep.js";

import { BODY_R, moveSpeed } from "../src/glide.ts";

import { drawGun, gunSnapshot, gunTick, makeGun } from "./gun.js";

import { advance, anchor, holdBack, insideWall, makeLocal, project, reconcile } from "./predict.js";

import { choosePrompt, REACH } from "./prompt.js";

import { roster, rosterKey } from "./roster.js";

import { AGENT_COLOUR, drawScene, makeScene } from "./scene.js";

import { moveVector } from "./steer.js";

import { drawTopdown } from "./topdown.js";

import { aim as aimAt, makeYaw, settle, told, turn } from "./yaw.js";

const $ = (id) => document.getElementById(id);

const view = $("view");

const ctx = view.getContext("2d");

const KEY_SLOT = { KeyC: "c", KeyQ: "q", KeyE: "e", KeyX: "x" };

const COARSE = matchMedia("(pointer: coarse)").matches;

const LOOK = 0.0022; // radians per pixel of mouse travel

const HELP_SEEN = "val.help.seen";

let map = null;

let solid = () => true;

let world = null; // what predict.js slides against: the grid, from map.json

let snap = null;

let socket = null;

let agents = null;

const shown = new Map(); // smoothed positions, so 15 frames a second look like 60

const keys = new Set();

// Where this person is looking: the browser's between snapshots, and the

// server's word taken only when it is saying something we did not. See

// yaw.js — a snapshot that stomps this is what made looking around choppy.

const head = makeYaw();

let locked = false;

let firing = false;

let mode = COARSE ? "top" : "fp"; // a raycaster with touch look is miserable

let mapOpen = false;

let pointer = null; // aim target in canvas pixels, top-down only

let stick = null; // { id, ox, oy, mx, my }

let aimTouch = null;

let helpShown = false;

let last = performance.now();

let snapAt = last; // when the last snapshot landed: how stale the answer is

const walk = { x: 0, y: 0 };

// What this person is doing right now, read once a frame for the drawing and

// once every 50ms for the server. The same object either way: no allocation

// in a loop that runs sixty times a second.

const intent = { mx: 0, my: 0, angle: 0, fire: false, use: false, reload: false };

// Your own body, run forward from your own keys between snapshots, and the

// object the drawing is handed for it.

const local = makeLocal();

const drawnMe = { id: "", x: 0, y: 0, angle: 0 };

const scene = makeScene();

const gun = makeGun();

const beeper = makeBeeper();

// ------------------------------------------------------------------ socket

function connect() {

  const url = (location.protocol === "https:" ? "wss://" : "ws://") + location.host + "/ws";

  socket = new WebSocket(url);

  socket.onopen = () => ($("conn").textContent = "live");

  socket.onclose = () => {

    $("conn").textContent = "reconnecting…";

    setTimeout(connect, 1500);

  };

  socket.onmessage = (event) => {

    const data = JSON.parse(event.data);

    if (data.t !== "s") return;

    snap = data;

    snapAt = performance.now();

    // The server's angle is taken only when it is a correction, never as the

    // routine echo of the angle we sent it a moment ago.

    settle(head, data.me, snapAt / 1000);

    gunSnapshot(gun, data);

    paintHud(data);

    maybeHelp(data);

  };

}

const send = (message) => {

  if (socket && socket.readyState === 1) socket.send(JSON.stringify(message));

};

// ------------------------------------------------------------------- input

function setMode(next) {

  mode = next;

  $("stage").dataset.mode = next;

  if (next !== "fp" && document.pointerLockElement === view) document.exitPointerLock();

  // The two views share one facing: whichever you leave, you keep looking

  // the way you were looking. The server has nothing to add to that.

}

addEventListener("keydown", (event) => {

  if (event.target instanceof HTMLInputElement) return;

  if (event.code === "Tab") {

    mapOpen = true;

    event.preventDefault();

    return;

  }

  if (event.code === "KeyH" || event.key === "?") {

    toggleHelp();

    event.preventDefault();

    return;

  }

  if (event.code === "KeyV") {

    setMode(mode === "fp" ? "top" : "fp");

    event.preventDefault();

    return;

  }

  if (event.code === "KeyB") {

    toggleBuy();

    event.preventDefault();

    return;

  }

  if (KEY_SLOT[event.code]) {

    send({ t: "i", c: KEY_SLOT[event.code] });

    event.preventDefault();

    return;

  }

  keys.add(event.code);

  if (["KeyW", "KeyA", "KeyS", "KeyD", "Space", "KeyF", "KeyR", "ArrowLeft", "ArrowRight"].includes(event.code))

    event.preventDefault();

});

addEventListener("keyup", (event) => {

  if (event.code === "Tab") mapOpen = false;

  keys.delete(event.code);

});

addEventListener("blur", () => {

  keys.clear();

  mapOpen = false;

  firing = false;

});

// Aiming is pointer lock: click the canvas to capture the mouse, move to

// look, Escape gives it back. The angle sent is the same angle as ever.

view.addEventListener("click", () => {

  beeper.wake();

  if (mode !== "fp" || locked) return;

  if (!view.requestPointerLock) return setMode("top"); // no lock, no first person

  // Asked for too soon after the last release, a browser rejects this; that

  // is a shrug, not an error, and the hint stays up until it takes.

  const asked = view.requestPointerLock();

  if (asked && asked.catch) asked.catch(() => {});

});

document.addEventListener("pointerlockchange", () => {

  locked = document.pointerLockElement === view;

  if (!locked) firing = false;

  $("stage").dataset.locked = locked ? "1" : "";

});

addEventListener("mousemove", (event) => {

  if (locked) turn(head, event.movementX * LOOK);

});

addEventListener("mousedown", (event) => {

  if (locked && event.button === 0) firing = true;

});

addEventListener("mouseup", (event) => {

  if (locked && event.button === 0) firing = false;

});

// The top-down view keeps the pointer aim it always had: it is the phone

// control scheme, and the fallback when the first-person view is not wanted.

const canvasPoint = (event) => {

  const box = view.getBoundingClientRect();

  return {

    x: ((event.clientX - box.left) / box.width) * view.width,

    y: ((event.clientY - box.top) / box.height) * view.height,

  };

};

view.addEventListener("pointermove", (event) => {

  if (mode !== "top" || event.pointerType === "touch") return;

  pointer = canvasPoint(event);

});

view.addEventListener("pointerdown", (event) => {

  beeper.wake();

  if (mode !== "top") return;

  view.setPointerCapture(event.pointerId);

  const box = view.getBoundingClientRect();

  if (event.pointerType === "touch") {

    if (event.clientX - box.left < box.width / 2)

      stick = { id: event.pointerId, ox: event.clientX, oy: event.clientY, mx: 0, my: 0 };

    else {

      aimTouch = { id: event.pointerId, ...canvasPoint(event) };

      firing = true;

    }

    event.preventDefault();

    return;

  }

  pointer = canvasPoint(event);

  firing = true;

});

view.addEventListener("pointermove", (event) => {

  if (stick && event.pointerId === stick.id) {

    const dx = event.clientX - stick.ox;

    const dy = event.clientY - stick.oy;

    const len = Math.hypot(dx, dy) || 1;

    const reach = Math.min(len, 48) / 48;

    stick.mx = (dx / len) * reach;

    stick.my = (dy / len) * reach;

  }

  if (aimTouch && event.pointerId === aimTouch.id) Object.assign(aimTouch, canvasPoint(event));

});

const endPointer = (event) => {

  if (stick && event.pointerId === stick.id) stick = null;

  else if (aimTouch && event.pointerId === aimTouch.id) {

    aimTouch = null;

    firing = false;

  } else firing = false;

};

view.addEventListener("pointerup", endPointer);

view.addEventListener("pointercancel", endPointer);

view.addEventListener("contextmenu", (event) => event.preventDefault());

// What this person is doing, in the world's terms. In the first-person view

// the keys are read against the way you are facing; in the top-down view they

// are the compass, the way they always were.

function readIntent() {

  let ax = 0;

  let ay = 0;

  if (keys.has("KeyW")) ay -= 1;

  if (keys.has("KeyS")) ay += 1;

  if (keys.has("KeyA")) ax -= 1;

  if (keys.has("KeyD")) ax += 1;

  if (stick) {

    ax = stick.mx;

    ay = stick.my;

  }

  intent.mx = ax;

  intent.my = ay;

  if (mode === "fp") {

    intent.angle = head.angle;

    moveVector(ax, ay, head.angle, walk);

    intent.mx = walk.x;

    intent.my = walk.y;

  } else {

    const aim = aimTouch || pointer;

    const me = worldToScreen(drawnMe.id ? drawnMe : snap.me);

    // The pointer is this view's aim, and it is ours the same way the mouse

    // is: with no pointer yet, keep the facing rather than the stale answer.

    if (aim) aimAt(head, Math.atan2(aim.y - me.y, aim.x - me.x));

    intent.angle = head.angle;

  }

  intent.fire = firing || keys.has("Space");

  intent.use = keys.has("KeyF");

  intent.reload = keys.has("KeyR");

  return intent;

}

// Twenty times a second the server hears it. Intent only — a direction, an

// angle, a held key — never a position: the guess below is for drawing.

setInterval(() => {

  if (!snap || !map) return;

  const now = readIntent();

  send({ t: "i", mx: now.mx, my: now.my, a: now.angle, f: now.fire, u: now.use, r: now.reload });

  // What we told it, so its echo is recognisable as ours when it comes back.

  told(head, now.angle, performance.now() / 1000);

}, 50);

// ------------------------------------------------------------------ drawing

function resize() {

  const box = view.getBoundingClientRect();

  const dpr = Math.min(devicePixelRatio || 1, 2);

  view.width = Math.round(box.width * dpr);

  view.height = Math.round(box.height * dpr);

}

addEventListener("resize", resize);

const scale = () => (map ? view.width / (map.rows[0].length * map.tile) : 1);

const worldToScreen = (p) => ({ x: p.x * scale(), y: p.y * scale() });

function smooth(id, x, y, angle) {

  const now = shown.get(id);

  if (!now) {

    const fresh = { x, y, angle };

    shown.set(id, fresh);

    return fresh;

  }

  now.x += (x - now.x) * 0.35;

  now.y += (y - now.y) * 0.35;

  const turn = ((angle - now.angle + Math.PI * 3) % (Math.PI * 2)) - Math.PI;

  now.angle += turn * 0.4;

  return now;

}

/**

 * Everybody else is smoothed toward the last position the server sent.

 * You are not: your own body is the one this browser can run forward

 * honestly, and smoothing it is what dragged the camera backwards.

 */

const look = (p) => (predicting() && p.id === snap.me.id ? drawnMe : smooth(p.id, p.x, p.y, p.angle));

/**

 * Your own movement is only guessed at while the round is live and you are

 * alive. The buy phase pens everybody in their own spawn — a rule of the

 * match, not of the map — and a guess that does not know it would spend the

 * phase being pulled back through the door.

 */

const predicting = () => snap !== null && world !== null && snap.phase !== "buy" && snap.me.alive;

/** The server's answer, caught up to now, then this frame of your own keys. */

function predict(dt, now) {

  if (!predicting()) {

    local.ready = false;

    drawnMe.id = "";

    return;

  }

  const held = readIntent();

  const speed = moveSpeed({

    haste: snap.me.haste > 0,

    slow: snap.me.slow > 0,

    stopped: snap.me.planting > 0 || snap.me.defusing,

    heavy: snap.me.weapon === "operator",

  });

  // The snapshot is a moment old and the keys held since have not reached

  // it; carry it that far forward and lean the drawn body onto it.

  const target = project(snap.me, held.mx, held.my, speed, (now - snapAt) / 1000, world);

  reconcile(local, target, dt);

  advance(local, held.mx, held.my, speed, dt, world);

  holdBack(local, target, held.mx, held.my);

  // A lean across a corner could put the drawn body in a wall; the server's

  // answer is never wrong, so take it rather than draw from inside one.

  if (insideWall(local, world)) anchor(local, snap.me);

  drawnMe.id = snap.me.id;

  drawnMe.x = local.x;

  drawnMe.y = local.y;

  drawnMe.angle = mode === "fp" ? head.angle : snap.me.angle;

}

function frame(now) {

  requestAnimationFrame(frame);

  const dt = Math.min(0.1, (now - last) / 1000);

  last = now;

  if (!map) return;

  gunTick(gun, dt);

  ctx.clearRect(0, 0, view.width, view.height);

  if (!snap) {

    drawTopdown(ctx, map, null, look, { x: 0, y: 0, w: view.width, h: view.height });

    return;

  }

  // Turning with the arrow keys belongs to the frame, at a rate a second,

  // rather than to whatever the input timer happens to do.

  if (mode === "fp" && keys.has("ArrowLeft")) turn(head, -0.9 * dt);

  if (mode === "fp" && keys.has("ArrowRight")) turn(head, 0.9 * dt);

  predict(dt, now);

  beeper.update(snap.spike.planted, snap.spike.fuse, now / 1000);

  const eye = look(snap.me);

  const facing = mode === "fp" ? head.angle : eye.angle;

  if (mode === "fp" && !mapOpen) {

    drawScene(ctx, scene, { solid, tile: map.tile }, { x: eye.x, y: eye.y, angle: facing }, snap, {

      width: view.width,

      height: view.height,

      look,

    });

    drawGun(ctx, gun, view.width, view.height, snap);

    drawMinimap();

  } else {

    drawTopdown(ctx, map, snap, look, { x: 0, y: 0, w: view.width, h: view.height });

  }

  if (snap.me.planting > 0) bar(snap.me.planting / 4, "#e0a040", "planting");

  else if (snap.spike.planted && snap.spike.defuse > 0 && snap.me.side === "def")

    bar(snap.spike.defuse / 7, "#4fd6a0", "defusing");

  $("flash").style.opacity = Math.min(0.95, snap.me.blind * 0.8);

  $("dead").style.display = snap.me.alive ? "none" : "grid";

  $("aimhint").style.display = mode === "fp" && !locked && !COARSE ? "grid" : "none";

}

/** The same top-down drawing, small, in the corner, with you as an arrow. */

function drawMinimap() {

  const w = Math.min(view.width * 0.3, 260 * (view.width / 900));

  const h = (w * map.rows.length) / map.rows[0].length;

  const pad = 8;

  ctx.save();

  ctx.globalAlpha = 0.85;

  ctx.fillStyle = "#0b0d11";

  ctx.fillRect(pad - 2, pad - 2, w + 4, h + 4);

  drawTopdown(ctx, map, snap, look, { x: pad, y: pad, w, h }, { labels: false });

  ctx.restore();

  ctx.strokeStyle = "rgba(255,255,255,0.18)";

  ctx.lineWidth = 1;

  ctx.strokeRect(pad - 2, pad - 2, w + 4, h + 4);

}

function bar(fraction, colour, label) {

  const w = view.width * 0.4;

  const x = view.width / 2 - w / 2;

  const y = view.height * 0.86;

  ctx.fillStyle = "#0009";

  ctx.fillRect(x, y, w, 16);

  ctx.fillStyle = colour;

  ctx.fillRect(x, y, w * Math.min(1, fraction), 16);

  ctx.fillStyle = "#fff";

  ctx.font = "12px system-ui, sans-serif";

  ctx.textAlign = "center";

  ctx.fillText(label, view.width / 2, y + 12);

  ctx.textAlign = "left";

}

// --------------------------------------------------------------------- hud

// The buy opens itself every buy phase; closing it is remembered until the

// next one, so nobody has to fight the panel to watch the round start.

function toggleBuy() {

  const open = $("buy").classList.toggle("on");

  $("buy").dataset.closed = open ? "" : "1";

}

$("buytoggle").addEventListener("click", toggleBuy);

$("viewtoggle").addEventListener("click", () => setMode(mode === "fp" ? "top" : "fp"));

$("helptoggle").addEventListener("click", () => toggleHelp());

$("helpclose").addEventListener("click", () => toggleHelp(false));

for (const button of document.querySelectorAll("[data-buy]"))

  button.addEventListener("click", () => send({ t: "buy", what: button.dataset.buy }));

for (const button of document.querySelectorAll("[data-agent]"))

  button.addEventListener("click", () => send({ t: "agent", id: button.dataset.agent }));

function toggleHelp(force) {

  const open = force === undefined ? $("help").style.display !== "grid" : force;

  $("help").style.display = open ? "grid" : "none";

  if (!open) {

    helpShown = true;

    try {

      localStorage.setItem(HELP_SEEN, "1");

    } catch {

      // A browser that refuses storage still gets the card, every visit.

    }

  }

}

/** The first-run card, once per browser, and never over a round in progress. */

function maybeHelp(s) {

  if (helpShown) return;

  try {

    if (localStorage.getItem(HELP_SEEN) === "1") {

      helpShown = true;

      return;

    }

  } catch {

    /* no storage: show it and move on */

  }

  if (s.phase === "live" && s.me.alive) return;

  helpShown = true;

  $("help").style.display = "grid";

}

const KITS = {};

function paintHud(s) {

  $("clock").textContent = Math.ceil(s.phase === "live" && s.spike.planted ? s.spike.fuse : s.clock);

  document.querySelector("#scoreline .red").textContent = "red " + s.score.red;

  document.querySelector("#scoreline .blue").textContent = s.score.blue + " blue";

  $("phase").textContent =

    `round ${s.round} · ${s.phase === "buy" ? "buy phase" : s.phase === "live" ? (s.spike.planted ? "spike down" : "live") : s.phase === "end" ? "round over" : "match over"} · ${s.attackers} attacking · you are ${s.me.side === "atk" ? "attacking" : "defending"}${s.result ? " · " + s.result : ""}`;

  $("hp").textContent = `${s.me.hp} hp${s.me.armour ? " +" + s.me.armour : ""}`;

  $("gun").textContent = `${s.me.weapon}${s.me.reloading ? " reloading" : " " + s.me.ammo}`;

  $("creds").textContent = `${s.me.credits} cr`;

  $("ultmeter").textContent = `ult ${s.me.ult}/${s.me.ultNeeds}`;

  $("buy").classList.toggle("on", s.phase === "buy" && $("buy").dataset.closed !== "1");

  if (s.phase !== "buy") $("buy").dataset.closed = "";

  const text = choosePrompt(s, {

    onSite: onSite(s.me),

    nearSpike: s.spike.x !== null && Math.hypot(s.spike.x - s.me.x, s.spike.y - s.me.y) < REACH,

  });

  if ($("prompt").textContent !== text) $("prompt").textContent = text;

  paintKit(s);

  paintBuy(s);

  paintRoster(s);

  paintFeed(s);

  const log = $("log");

  const lines = s.events.slice(0, 3).join("\n");

  if (log.dataset.text !== lines) {

    log.dataset.text = lines;

    log.replaceChildren();

    for (const line of s.events.slice(0, 3)) {

      const div = document.createElement("div");

      div.textContent = line;

      log.append(div);

    }

  }

  for (const side of ["atk", "def"]) {

    const body = $(side + "board");

    const rows = s.board.filter((p) => p.side === side).sort((a, b) => b.kills - a.kills);

    const key = rows.map((p) => `${p.name}${p.kills}${p.deaths}${p.alive}${p.credits}`).join();

    if (body.dataset.key === key) continue;

    body.dataset.key = key;

    body.replaceChildren();

    for (const player of rows) {

      const tr = document.createElement("tr");

      const cells = [

        player.name + (player.bot ? " (bot)" : "") + (player.alive ? "" : " ✕"),

        player.agent + (player.credits !== null ? ` · ${player.credits}cr` : ""),

        String(player.kills),

        String(player.deaths),

      ];

      for (const value of cells) {

        const td = document.createElement("td");

        td.textContent = value;

        tr.append(td);

      }

      if (player.id === s.me.id) tr.style.fontWeight = "700";

      body.append(tr);

    }

  }

}

/** Is this player standing where the spike arms? The grid says so. */

function onSite(me) {

  if (!map) return false;

  const row = map.rows[Math.floor(me.y / map.tile)];

  const cell = row ? row[Math.floor(me.x / map.tile)] : "";

  return cell === "A" || cell === "B";

}

/**

 * What just happened to whom: newest first, and gone a few seconds later.

 * The server sends names and a gun and nothing else, so there is nothing

 * here to read a position out of.

 */

function paintFeed(s) {

  const box = $("feed");

  const lines = (s.feed ?? []).slice().reverse();

  // The age is bucketed into the key: an entry fades once on its way out

  // rather than rebuilding the panel every frame.

  const key = lines.map((l) => `${l.k}>${l.v}:${l.w}:${l.h}:${l.t > 6 ? "old" : "new"}`).join("|");

  if (box.dataset.key === key) return;

  box.dataset.key = key;

  box.replaceChildren();

  for (const line of lines) {

    const row = document.createElement("div");

    row.style.opacity = line.t > 6 ? "0.5" : "1";

    const killer = document.createElement("span");

    killer.className = "k";

    killer.textContent = line.k ?? "—";

    const victim = document.createElement("span");

    victim.className = "v";

    victim.textContent = line.v;

    const how = document.createElement("span");

    how.className = "w";

    how.textContent = `${line.w ? " " + line.w : " ability"}${line.h ? " ✧" : ""}`;

    const arrow = document.createElement("span");

    arrow.textContent = " ▸ ";

    row.append(killer, arrow, victim, how);

    box.append(row);

  }

}

/**

 * Your team, always on screen: five slots, health, and struck through when

 * somebody is dead. The one place both questions — who is with me, who is

 * still up — are answered whether anybody is in sight or not.

 */

function paintRoster(s) {

  const rows = roster(s);

  const panel = $("roster");

  const key = rosterKey(rows);

  if (panel.dataset.key === key) return;

  panel.dataset.key = key;

  panel.replaceChildren();

  for (const row of rows) {

    const slot = document.createElement("div");

    slot.className = `slot${row.mine ? " mine" : ""}${row.alive ? "" : " down"}`;

    slot.style.borderLeftColor = AGENT_COLOUR[row.agent] || "#4a5162";

    const who = document.createElement("span");

    who.className = "who";

    who.textContent = row.name;

    const agent = document.createElement("span");

    agent.className = "agent";

    agent.textContent = row.alive ? row.agent : `${row.agent} · dead`;

    if (row.spike) {

      const spike = document.createElement("span");

      spike.className = "spike";

      spike.textContent = " spike";

      agent.append(spike);

    }

    const bar = document.createElement("span");

    bar.className = "hp";

    const fill = document.createElement("i");

    fill.style.width = `${row.hp}%`;

    fill.style.background = row.hp > 40 ? "#6fcf6f" : "#e0a040";

    bar.append(fill);

    slot.append(who, agent, bar);

    panel.append(slot);

  }

}

const kitOf = (id) => (agents ? agents.find((a) => a.id === id) : null);

/** The four ability buttons, each saying what it does and what it has left. */

function paintKit(s) {

  const kit = $("kit");

  const agent = kitOf(s.me.agent);

  const shape =

    ["c", "q", "e", "x"].map((slot) => `${slot}${s.me.charges[slot]}${Math.ceil(s.me.cooldown[slot])}`).join("|") +

    s.me.agent +

    s.me.ult +

    (agent ? "k" : "");

  if (KITS.shape === shape) return;

  KITS.shape = shape;

  kit.replaceChildren();

  for (const slot of ["c", "q", "e", "x"]) {

    const ability = agent ? agent.abilities[slot] : null;

    const button = document.createElement("button");

    const ready = slot === "x" ? s.me.ult >= s.me.ultNeeds : s.me.charges[slot] > 0 && s.me.cooldown[slot] <= 0;

    button.disabled = !ready;

    button.type = "button";

    const count =

      slot === "x"

        ? `${s.me.ult}/${s.me.ultNeeds}`

        : s.me.cooldown[slot] > 0

          ? `${Math.ceil(s.me.cooldown[slot])}s`

          : s.me.charges[slot];

    const name = document.createElement("span");

    name.textContent = `${slot.toUpperCase()}${ability ? " " + ability.name : ""}`;

    const tally = document.createElement("b");

    tally.textContent = String(count);

    button.append(name, tally);

    if (ability) button.title = `${ability.name} — ${ability.text}`;

    button.addEventListener("click", () => send({ t: "i", c: slot }));

    kit.append(button);

  }

}

/** Prices on every button, greyed when you cannot afford it. */

function paintBuy(s) {

  const agent = kitOf(s.me.agent);

  for (const button of document.querySelectorAll("[data-buy]")) {

    const what = button.dataset.buy;

    let cost = Number(button.dataset.cost ?? 0);

    if ((what === "c" || what === "q") && agent) {

      const ability = agent.abilities[what];

      cost = ability.cost;

      button.replaceChildren();

      const name = document.createElement("span");

      name.textContent = `${what.toUpperCase()} ${ability.name}`;

      const price = document.createElement("b");

      price.textContent = `${ability.cost} · ${s.me.charges[what]}/${ability.charges}`;

      button.append(name, price);

      button.title = `${ability.text} (${ability.charges} charge${ability.charges === 1 ? "" : "s"} a round)`;

    }

    button.disabled = cost > s.me.credits;

  }

  for (const button of document.querySelectorAll("[data-agent]")) {

    const picked = button.dataset.agent === s.me.agent;

    button.style.outline = picked ? "2px solid #6fcf9f" : "";

  }

}

// ------------------------------------------------------------------- start

Promise.all([fetch("/map.json").then((r) => r.json()), fetch("/agents.json").then((r) => r.json())])

  .then(([mapData, kit]) => {

    map = mapData;

    agents = kit.agents;

    const rows = map.rows;

    const cols = rows[0].length;

    solid = (col, row) =>

      col < 0 || row < 0 || row >= rows.length || col >= cols || rows[row][col] === "#";

    // The same grid the server collides against, so a guess about your own

    // movement lands where the server's answer is about to.

    world = { solid, tile: map.tile, r: BODY_R };

    $("stage").dataset.mode = mode;

    fillHelp();

    resize();

    connect();

  })

  .catch(() => ($("conn").textContent = "offline"));

/** The card says the round, the sides, the keys and the kit, in that order. */

function fillHelp() {

  const list = $("helpagents");

  if (!list || !agents) return;

  list.replaceChildren();

  for (const agent of agents) {

    const li = document.createElement("li");

    li.textContent = `${agent.name} (${agent.role}) — ${agent.blurb}`;

    list.append(li);

  }

}

requestAnimationFrame(frame);