/* The panel. Every control acts immediately and reconciles with what the
   speakers report a moment later, because a remote that waits for a
   network round trip before it looks like it did anything feels broken. */

const STEP = Number(document.documentElement.dataset.step) || 2;
// Where the app is mounted: "/" on its own port, "/heos/" behind a proxy.
const BASE = document.documentElement.dataset.base || '/';
// The commit this page was rendered from, so a resumed iOS home-screen
// session can tell the Pi has moved on and reload itself.
const VERSION = document.documentElement.dataset.version || '';
const POLL_MS = 5000;
// How long a dropped cursor waits for the player to report it got there.
const SEEK_HOLD_MS = 10000;
// How far an arrow key moves the progress cursor.
const SEEK_KEY_MS = 10000;
// And how long a pressed play or pause on the AVR waits for the same. The
// Zidoo acknowledges the key press at once but takes a moment to act on it.
const PLAY_HOLD_MS = 6000;

// Which way each arrow key moves a slider.
const ARROWS = { ArrowRight: 1, ArrowUp: 1, ArrowLeft: -1, ArrowDown: -1 };

const el = (sel, root = document) => root.querySelector(sel);
const els = (sel, root = document) => Array.from(root.querySelectorAll(sel));

const SPEAKER = { viewbox: '0 0 384 512', path: 'M0 64C0 28.7 28.7 0 64 0L320 0c35.3 0 64 28.7 64 64l0 384c0 35.3-28.7 64-64 64L64 512c-35.3 0-64-28.7-64-64L0 64zM304 336a112 112 0 1 0 -224 0 112 112 0 1 0 224 0zM192 272a64 64 0 1 1 0 128 64 64 0 1 1 0-128zm0-112a48 48 0 1 0 0-96 48 48 0 1 0 0 96z' };
const SPEAKERS = { viewbox: '0 -32 448 576', path: 'M160-32C124.7-32 96-3.3 96 32l0 352c0 35.3 28.7 64 64 64l224 0c35.3 0 64-28.7 64-64l0-352c0-35.3-28.7-64-64-64L160-32zM272 184a104 104 0 1 1 0 208 104 104 0 1 1 0-208zm56 104a56 56 0 1 0 -112 0 56 56 0 1 0 112 0zM240 64a32 32 0 1 1 64 0 32 32 0 1 1 -64 0zM48 88c0-13.3-10.7-24-24-24S0 74.7 0 88L0 480c0 35.3 28.7 64 64 64l264 0c13.3 0 24-10.7 24-24s-10.7-24-24-24L64 496c-8.8 0-16-7.2-16-16L48 88z' };
const TV = { viewbox: '0 0 576 512', path: 'M64 96l0 240 448 0 0-240-448 0zM0 96C0 60.7 28.7 32 64 32l448 0c35.3 0 64 28.7 64 64l0 240c0 35.3-28.7 64-64 64L64 400c-35.3 0-64-28.7-64-64L0 96zM160 448l256 0c17.7 0 32 14.3 32 32s-14.3 32-32 32l-256 0c-17.7 0-32-14.3-32-32s14.3-32 32-32z' };

// Keyed on a room's kind (config.IN_ROOM_GROUPS, or "avr") or an input's
// HEOS id, straight from data-icon or GET /api/avr/inputs' "code" -- not
// something a room name or a renamed input label could change. "plug" is
// the fallback for an input HEOS reports that none of these name.
const ICONS = {
  avr: { viewbox: '0 0 448 512', path: 'M64 32C28.7 32 0 60.7 0 96l0 64c0 35.3 28.7 64 64 64l320 0c35.3 0 64-28.7 64-64l0-64c0-35.3-28.7-64-64-64L64 32zm216 72a24 24 0 1 1 0 48 24 24 0 1 1 0-48zm56 24a24 24 0 1 1 48 0 24 24 0 1 1 -48 0zM64 288c-35.3 0-64 28.7-64 64l0 64c0 35.3 28.7 64 64 64l320 0c35.3 0 64-28.7 64-64l0-64c0-35.3-28.7-64-64-64L64 288zm216 72a24 24 0 1 1 0 48 24 24 0 1 1 0-48zm56 24a24 24 0 1 1 48 0 24 24 0 1 1 -48 0z' },
  'none': SPEAKER,
  'stereo-pair': SPEAKERS,
  'lcr-fronts': SPEAKERS,
  'surround-sound-system': SPEAKERS,
  'subwoofer': SPEAKER,
  mediaplayer: { viewbox: '0 -16 576 512', path: 'M0 112c0 70.7 57.3 128 128 128l224 0c70.7 0 128-57.3 128-128S422.7-16 352-16c-48.2 0-90.2 26.6-112 66-21.8-39.4-63.8-66-112-66-70.7 0-128 57.3-128 128zm304 0a48 48 0 1 1 96 0 48 48 0 1 1 -96 0zM128 64a48 48 0 1 1 0 96 48 48 0 1 1 0-96zM64 352l0 64c0 35.3 28.7 64 64 64l224 0c35.3 0 64-28.7 64-64l0-64c0-35.3-28.7-64-64-64l-224 0c-35.3 0-64 28.7-64 64zM537.5 490.8c4.2 3.4 9.4 5.2 14.8 5.2 13.1 0 23.7-10.6 23.7-23.7l0-240.6c0-13.1-10.6-23.7-23.7-23.7-5.4 0-10.6 1.8-14.8 5.2l-73.5 58.8 0 160 73.5 58.8z' },
  game: { viewbox: '0 0 640 512', path: 'M448 64c106 0 192 86 192 192S554 448 448 448l-256 0C86 448 0 362 0 256S86 64 192 64l256 0zM192 176c-13.3 0-24 10.7-24 24l0 32-32 0c-13.3 0-24 10.7-24 24s10.7 24 24 24l32 0 0 32c0 13.3 10.7 24 24 24s24-10.7 24-24l0-32 32 0c13.3 0 24-10.7 24-24s-10.7-24-24-24l-32 0 0-32c0-13.3-10.7-24-24-24zm240 96a32 32 0 1 0 0 64 32 32 0 1 0 0-64zm64-96a32 32 0 1 0 0 64 32 32 0 1 0 0-64z' },
  tv: TV,
  tvaudio: TV,
  bluray: { viewbox: '0 0 512 512', path: 'M0 256a256 256 0 1 1 512 0 256 256 0 1 1 -512 0zm256 32a32 32 0 1 1 0-64 32 32 0 1 1 0 64zm-96-32a96 96 0 1 0 192 0 96 96 0 1 0 -192 0zm-56-16c0-32.4 16.3-66.6 42.8-93.2S207.6 104 240 104c13.3 0 24-10.7 24-24s-10.7-24-24-24c-47.9 0-93.7 23.5-127.1 56.9S56 192.1 56 240c0 13.3 10.7 24 24 24s24-10.7 24-24z' },
  plug: { viewbox: '0 -32 448 544', path: 'M128-32c17.7 0 32 14.3 32 32l0 96 128 0 0-96c0-17.7 14.3-32 32-32s32 14.3 32 32l0 96 64 0c17.7 0 32 14.3 32 32s-14.3 32-32 32l0 64c0 95.1-69.2 174.1-160 189.3l0 66.7c0 17.7-14.3 32-32 32s-32-14.3-32-32l0-66.7C101.2 398.1 32 319.1 32 224l0-64c-17.7 0-32-14.3-32-32S14.3 96 32 96l64 0 0-96c0-17.7 14.3-32 32-32z' }
};

function inputIcon(code) {
  return ICONS[(code || '').replace('inputs/', '')] || ICONS.plug;
}

/* Repaints an inline <svg><path/></svg> in place -- cheaper than replacing
   the node, and there is no library here to lose track of the change. */
function paintIcon(svg, icon) {
  svg.setAttribute('viewBox', icon.viewbox);
  svg.firstElementChild.setAttribute('d', icon.path);
}

// Room and AVR cards carry their icon as a fixed kind (data-icon="avr", set
// server-side from config -- see index.html) rather than the AVR input's
// live one, so these paint once, not on every poll.
els('[data-icon]').forEach((svg) => paintIcon(svg, ICONS[svg.dataset.icon]));

const ui = {
  foot: el('[data-role="foot"]'),
  toast: el('[data-role="toast"]'),
  inputButton: el('[data-role="input-button"]'),
  inputName: el('[data-role="input-name"]'),
  inputIcon: el('[data-role="input-icon"]'),
  sheet: el('[data-role="sheet"]'),
  options: el('[data-role="options"]'),
  app: el('.app'),
  avr: el('.card.avr'),
  joined: el('[data-role="joined"]'),
};

// The AVR is one of the rooms below, so its key comes off its card like
// theirs do. Which one it is, everything that only it can do goes through.
const HOST = ui.avr.dataset.room;

const rooms = {};
let inputs = [];
let currentInput = null;

/* --- transport -------------------------------------------------------- */
async function api(path, body) {
  const options = body === undefined
    ? {}
    : { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify(body) };
  const response = await fetch(BASE + path.replace(/^\//, ''), options);
  let data = {};
  try { data = await response.json(); } catch (_) { /* empty or not JSON */ }
  if (!response.ok) throw new Error(data.error || `${response.status} ${response.statusText}`);
  return data;
}

let toastTimer;
/* Red by default, since most toasts report trouble; 'ok' for a confirmation. */
function toast(message, kind = 'error') {
  ui.toast.textContent = message;
  ui.toast.classList.toggle('ok', kind === 'ok');
  ui.toast.hidden = false;
  clearTimeout(toastTimer);
  toastTimer = setTimeout(() => { ui.toast.hidden = true; }, 4000);
}

/* --- rooms ------------------------------------------------------------ */
els('.card[data-room]').forEach((node) => {
  const key = node.dataset.room;
  const room = {
    key,
    node,
    avr: node.classList.contains('avr'),
    level: el('[data-role="level"]', node),
    meter: el('[data-role="meter"]', node),
    navigation: el('[data-role="navigation"]', node),
    toggle: el('[data-role="group"]', node),
    toggleLabel: el('[data-role="group-label"]', node),
    prev: el('[data-role="prev"]', node),
    play: el('[data-role="play"]', node),
    next: el('[data-role="next"]', node),
    sources: el('.sources', node),   // the resume buttons and the host toggle
    media: el('[data-role="media"]', node),
    cover: el('[data-role="cover"]', node),
    song: el('[data-role="song"]', node),
    artist: el('[data-role="artist"]', node),
    progress: el('[data-role="progress"]', node),
    steps: els('.step', node),
    queue: el('[data-role="queue"]', node),
    queueList: el('[data-role="queue-list"]', node),
    queueFor: null,     // the song the queue on show was fetched behind
    queueLoading: false,
    volume: null,
    playState: null,
    track: null,    // {song, artist, image} while something is loaded
    onSpotify: false,
    spotifyAccount: null,   // the account playing here, whose button gets a border
    grouped: false,
    available: false,
    taps: 0,        // button presses not yet sent
    wanted: null,   // a level dragged to, not yet sent
    dragging: false,
    inflight: false,
    busy: false,    // a grouping change is in flight
    playBusy: false,
    wantedPlay: null,   // {state, sentAt} from a press until the player reports it
    // HEOS cannot seek, so only a stream Spotify can be asked to seek in: the
    // same one the transport buttons show for (see paintTransport). Only a
    // Zidoo ever fills the AVR's card in, and it can always seek.
    canSeek: () => room.avr || (room.onSpotify && room.spotifyAccount && !room.grouped),
    playing: () => shownPlayState(room) === 'play',
    seek: null,     // {ms, stage, ...} from a drag of the cursor until the player catches up
  };
  rooms[key] = room;

  room.steps.forEach((button) => {
    const direction = Number(button.dataset.delta);
    holdable(button, () => nudge(key, direction));
  });
  draggable(room);
  seekable(room);

  // A cover that will not load (gone, or plain http on an https page) is
  // dropped rather than left as a broken-image box. Its src stays put, so
  // the next poll does not try it again until the track changes.
  room.cover.addEventListener('error', () => { room.cover.hidden = true; });

  // Asked for afresh on every unfold: songs queued from the Spotify app in
  // the meantime would not otherwise turn up until the track changed.
  if (room.queue) room.queue.addEventListener('toggle', () => { if (room.queue.open) loadQueue(room); });
  if (room.toggle) room.toggle.addEventListener('click', () => setGrouped(key, !room.grouped));
  if (room.prev) room.prev.addEventListener('click', () => skipTrack(key, 'previous'));
  room.play.addEventListener('click', () => togglePlay(key));
  if (room.next) room.next.addEventListener('click', () => skipTrack(key, 'next'));
});

function paintVolume(room) {
  const known = room.volume !== null && room.volume !== undefined;
  room.level.textContent = known ? room.volume : '—';
  // The fill and the knob riding it both size themselves off this.
  room.meter.style.setProperty('--level', known ? room.volume : 0);
  // The knob is a slider to VoiceOver, which reads these rather than its digits.
  if (known) room.level.setAttribute('aria-valuenow', room.volume);
  else room.level.removeAttribute('aria-valuenow');
  room.level.setAttribute('aria-disabled', String(!room.available));
  room.steps.forEach((button) => { button.disabled = !room.available; });
}

function paintTransport(room) {
  const state = shownPlayState(room);
  const playing = state === 'play';
  room.node.classList.toggle('playing', playing);
  room.play.classList.toggle('playing', playing);
  room.play.disabled = !room.available || !state;
  room.play.setAttribute(
    'aria-label', `${room.node.querySelector('h2').textContent}: ${playing ? 'pause' : 'play'}`);
  room.navigation.hidden = room.avr
    ? !state
    : !(room.onSpotify && room.spotifyAccount && !room.grouped);
  if (room.prev) room.prev.disabled = !room.available;
  if (room.next) room.next.disabled = !room.available;
}

function paintSources(room) {
  if (!room.sources) return;
  // Grouped, the room plays whatever the AVR does, so resuming Spotify on it
  // is not on offer. They hide one by one rather than the row hiding with
  // them, because the row also holds the host toggle, which stays put and
  // merely disables.
  els('.spotify', room.sources).forEach((button) => {
    const holding = button.dataset.account === room.spotifyAccount;
    button.hidden = !room.available || room.grouped;
    button.setAttribute('aria-pressed', String(holding));
    // Bordered, the button is the way back out of the room rather than into
    // it, so its label has to say that and not "Resume".
    button.setAttribute(
      'aria-label',
      `${holding ? 'Disconnect' : 'Resume'} ${button.querySelector('span').textContent}'s Spotify`);
  });

  room.toggle.disabled = !room.available || room.busy;
  room.toggle.classList.toggle('loading', room.busy);
  room.toggle.setAttribute('aria-pressed', String(room.grouped));
  // Out of the group the button names where tapping it sends the room; in it,
  // where the card sits already says so, so the button says what it does.
  room.toggleLabel.textContent = room.grouped ? 'Ungroup' : 'Cinema';
}

function paintRoom(room) {
  room.node.classList.toggle('offline', !room.available);
  renderTrack(room.available ? room.track : null, room);
  paintVolume(room);
  paintTransport(room);
  paintSources(room);
  paintQueue(room);
  placeRoom(room);
}

/* --- Spotify queue: what comes next, folded at the foot of a room's card.
   It costs a Spotify call, so it is only fetched while unfolded -- on the
   unfold, and again whenever the song changes under it. ------------------ */
function queueKey(room) {
  return room.track ? `${room.spotifyAccount}|${room.track.song}|${room.track.artist}` : room.spotifyAccount;
}

function paintQueue(room) {
  if (!room.queue) return;
  // Shown for the same stream the transport buttons are: one of your accounts'.
  const shown = room.available && room.onSpotify && Boolean(room.spotifyAccount) && !room.grouped;
  room.queue.hidden = !shown;
  if (!shown) {
    // Folded again for next time, rather than reopening on a stale list.
    room.queue.open = false;
    room.queueFor = null;
    return;
  }
  if (room.queue.open && room.queueFor !== queueKey(room)) loadQueue(room);
}

async function loadQueue(room) {
  if (room.queueLoading) return;
  room.queueLoading = true;
  const wanted = queueKey(room);
  room.queueFor = wanted;
  // Only an empty box says it is loading; a list already there stays put
  // until the new one replaces it.
  if (!room.queueList.children.length) renderQueueLoading(room);
  try {
    const data = await api(`/api/spotify/queue?target=${encodeURIComponent(room.key)}`);
    renderQueue(room, data.queue || []);
  } catch (error) {
    renderQueueNote(room, error.message);
    room.queueFor = null;   // so the next poll tries again
  } finally {
    room.queueLoading = false;
  }
  // The song moved on while this was in flight.
  if (room.queueFor !== null && room.queueFor !== queueKey(room)) paintQueue(room);
}

function renderQueueNote(room, text) {
  const note = document.createElement('li');
  note.className = 'queue-note';
  note.textContent = text;
  room.queueList.replaceChildren(note);
}

/* Font Awesome's ellipsis, one path per dot so panel.css can blink them in turn. */
function renderQueueLoading(room) {
  const note = document.createElement('li');
  note.className = 'queue-note';
  note.setAttribute('aria-label', 'Loading');
  note.innerHTML = '<svg class="queue-loading" viewBox="0 0 448 512" aria-hidden="true">'
    + '<path d="M0 256a56 56 0 1 1 112 0 56 56 0 1 1 -112 0z"/>'
    + '<path d="M168 256a56 56 0 1 1 112 0 56 56 0 1 1 -112 0z"/>'
    + '<path d="M336 256a56 56 0 1 1 112 0 56 56 0 1 1 -112 0z"/></svg>';
  room.queueList.replaceChildren(note);
}

function renderQueue(room, items) {
  if (!items.length) {
    renderQueueNote(room, 'Nothing queued');
    return;
  }
  room.queueList.replaceChildren(...items.map((item) => {
    const row = document.createElement('li');
    row.className = 'queue-item';
    row.innerHTML = '<img class="cover" alt="" loading="lazy"><div class="track"><span class="song"></span><span class="artist"></span></div><span class="queue-time"></span>';
    const cover = el('.cover', row);
    if (item.image) {
      cover.addEventListener('error', () => { cover.style.visibility = 'hidden'; });
      cover.src = item.image;
    }
    el('.song', row).textContent = item.song;
    el('.artist', row).textContent = item.artist || '';
    el('.artist', row).hidden = !item.artist;
    el('.queue-time', row).textContent = item.duration_ms ? clock(Math.floor(item.duration_ms / 1000)) : '';
    return row;
  }));
}

/* Song, artist, cover and progress, each only when there is one. The
   cover's src is only touched when the track changes, so a poll never makes
   it flicker. */
function renderTrack(track, refs) {
  renderProgress(track, refs);
  refs.media.hidden = !track;
  if (!track) return;
  refs.song.textContent = track.song;
  refs.artist.textContent = track.artist || '';
  refs.artist.hidden = !track.artist;
  if (!track.image) {
    refs.cover.hidden = true;
    refs.cover.removeAttribute('src');
  } else if (refs.cover.getAttribute('src') !== track.image) {
    refs.cover.hidden = false;
    refs.cover.src = track.image;
  }
}

function renderProgress(track, refs) {
  refs.shown = null;
  refs.tick = null;
  if (!track) return;
  const { duration_ms: duration } = track;
  const position = seekPosition(track, refs);
  const known = typeof duration === 'number' && duration > 0 && typeof position === 'number';
  if (known) {
    refs.shown = track;
    refs.shownMs = position;
    refs.tick = { ms: position, at: Date.now(), duration };
  }
  paintProgress(refs, known, position, duration);
}

/* Just the painting, shared with tickProgress() below so a between-polls
   nudge repaints exactly the same way a real sync does. */
function paintProgress(refs, known, position, duration) {
  const { progress } = refs;
  // Whole seconds on both sides, so elapsed and remaining always add up to
  // the total shown at the end of the line -- and the knob is placed off
  // these same whole seconds, not the raw fractional position, so it never
  // creeps past where the digits still say it is.
  const total = known ? Math.floor(duration / 1000) : 0;
  const elapsed = known ? Math.min(total, Math.max(0, Math.floor(position / 1000))) : 0;
  const percent = known ? Math.min(100, Math.max(0, (elapsed / total) * 100)) : 0;
  progress.classList.toggle('known', known);
  progress.classList.toggle('seekable', known && Boolean(refs.canSeek()));
  progress.style.setProperty('--progress', percent);
  const labels = {
    elapsed: known ? '+' + clock(elapsed) : '',
    remaining: known ? '−' + clock(total - elapsed) : '',
  };
  Object.entries(labels).forEach(([role, text]) => {
    const label = el(`[data-role="progress-${role}"]`, progress);
    label.textContent = text;
    // Read back once the new text is in, for panel.css to clamp it by.
    if (known) label.style.setProperty('--half', `${label.offsetWidth / 2}px`);
  });
  el('[data-role="progress-total"]', progress).textContent = known ? clock(total) : '';

  const cursor = el('[data-role="progress-cursor"]', progress);
  const seekable = progress.classList.contains('seekable');
  cursor.tabIndex = seekable ? 0 : -1;
  cursor.setAttribute('aria-readonly', String(!seekable));
  if (known) {
    cursor.setAttribute('aria-valuemax', total);
    cursor.setAttribute('aria-valuenow', elapsed);
    cursor.setAttribute('aria-valuetext', `${clock(elapsed)} of ${clock(total)}`);
  }
}

function tickProgress(refs) {
  if (!refs.tick || !refs.shown || refs.seek || !refs.playing()) return;
  const { ms, at, duration } = refs.tick;
  const position = Math.min(duration, ms + (Date.now() - at));
  paintProgress(refs, true, position, duration);
}

setInterval(() => Object.values(rooms).forEach(tickProgress), 250);

function seekable(refs) {
  const { progress } = refs;
  const line = el('.progress-line', progress);
  let startX = 0;
  let startMs = 0;
  let moved = false;

  let held = null;   // a previous seek still waiting on the player, back if this drag goes nowhere

  line.addEventListener('pointerdown', (event) => {
    if (event.button > 0 || seeking(refs) || !refs.shown || !progress.classList.contains('seekable')) return;
    if (!event.target.closest('.progress-cursor, .progress-time')) return;
    event.preventDefault();
    line.setPointerCapture(event.pointerId);
    startX = event.clientX;
    startMs = refs.shownMs;   // where the cursor is, even if the player has not caught up with it yet
    moved = false;
    held = refs.seek;
    refs.seek = { ms: startMs, stage: 'drag', song: refs.shown.song };
    progress.classList.add('dragging');
  });

  line.addEventListener('pointermove', (event) => {
    if (!refs.seek || refs.seek.stage !== 'drag' || !refs.shown) return;
    const dx = event.clientX - startX;
    // A few pixels of slack, so a tap that wobbles is still just a tap.
    if (!moved && Math.abs(dx) < 6) return;
    moved = true;
    const { duration_ms: duration } = refs.shown;
    const ms = startMs + (dx / line.clientWidth) * duration;
    refs.seek.ms = Math.round(Math.max(0, Math.min(duration, ms)));
    renderProgress(refs.shown, refs);
  });

  const stop = (event) => {
    if (!refs.seek || refs.seek.stage !== 'drag') return;
    progress.classList.remove('dragging');
    if (event.type === 'pointerup' && moved) {
      sendSeek(refs);
    } else {
      refs.seek = held;
      if (refs.shown) renderProgress(refs.shown, refs);
    }
  };
  line.addEventListener('pointerup', stop);
  line.addEventListener('pointercancel', stop);

  // The arrow keys, and VoiceOver's swipe up and down on a slider, move the
  // cursor a step at a time, each one its own seek.
  el('[data-role="progress-cursor"]', progress).addEventListener('keydown', (event) => {
    const direction = ARROWS[event.key];
    if (!direction || seeking(refs) || !refs.shown || !progress.classList.contains('seekable')) return;
    event.preventDefault();
    const { duration_ms: duration } = refs.shown;
    const ms = refs.shownMs + direction * SEEK_KEY_MS;
    refs.seek = { ms: Math.round(Math.max(0, Math.min(duration, ms))), stage: 'drag', song: refs.shown.song };
    renderProgress(refs.shown, refs);
    sendSeek(refs);
  });
}

/* A seek that fails snaps the cursor back; one that works holds it where it
   was dropped (see seekPosition). */
async function sendSeek(refs) {
  const { seek } = refs;
  seek.stage = 'send';
  seek.sentAt = Date.now();
  try {
    await api('/api/seek', { target: refs.key, position_ms: seek.ms });
    seek.stage = 'hold';
    // The player takes a moment to report where it has got to.
    setTimeout(refresh, 1500);
  } catch (error) {
    toast(error.message);
    refs.seek = null;
  }
  // Unless a poll in the meantime found nothing left to seek in.
  if (refs.shown) renderProgress(refs.shown, refs);
}

function seekPosition(track, refs) {
  const { seek } = refs;
  if (!seek) return track.position_ms;
  if (seek.stage !== 'hold') return seek.ms;
  const since = Date.now() - seek.sentAt;
  const slack = 2000;
  const caughtUp = track.position_ms >= seek.ms - slack && track.position_ms <= seek.ms + since + slack;
  if (caughtUp || track.song !== seek.song || since > SEEK_HOLD_MS) {
    refs.seek = null;
    return track.position_ms;
  }
  return seek.ms;
}

function seeking(refs) {
  return Boolean(refs.seek) && refs.seek.stage !== 'hold';
}

/* 83 -> "1:23", 4000 -> "1:06:40": hours only for what runs that long. */
function clock(seconds) {
  const h = Math.floor(seconds / 3600);
  const m = Math.floor(seconds / 60) % 60;
  const s = String(seconds % 60).padStart(2, '0');
  return h ? `${h}:${String(m).padStart(2, '0')}:${s}` : `${m}:${s}`;
}

function placeRoom(room) {
  // The host's card is where the column ends, and every room placed above
  // measures from it, so it is the one card that never moves.
  if (room.avr) return;
  if (room.grouped) {
    if (room.node.parentElement !== ui.joined) ui.joined.appendChild(room.node);
  } else if (room.node.parentElement !== ui.app) {
    const order = Object.keys(rooms);
    const next = order.slice(order.indexOf(room.key) + 1)
      .map((key) => rooms[key].node)
      .find((node) => node.parentElement === ui.app);
    // Nothing left in the column below it means it goes last, before the host.
    ui.app.insertBefore(room.node, next || ui.avr);
  }
}

function paintGrouping() {
  const order = Object.keys(rooms);
  const inside = Array.from(ui.joined.children);
  // Keep them in the order the cards are declared, not the order they joined.
  inside
    .slice()
    .sort((a, b) => order.indexOf(a.dataset.room) - order.indexOf(b.dataset.room))
    .forEach((node) => ui.joined.appendChild(node));
  ui.joined.hidden = inside.length === 0;
  // Grouped rooms share the host's transport, so one of them playing means
  // the whole group is -- and the tint goes on the group's card.
  // A film running on the Zidoo counts as the AVR playing too, grouped rooms or not.
  const playing = inside.some((node) => node.classList.contains('playing'))
    || shownPlayState(rooms[HOST]) === 'play';
  ui.avr.classList.toggle('playing', playing);
}

/* Press and hold to keep moving, accelerating as you hold. */
function holdable(node, action) {
  let timer = null;
  let delay = 420;

  // A press by pointer acts on pointerdown and preventDefault()s, so the
  // click behind it is not meant to act again. One with no pointer press
  // just before it -- Enter or Space on a focused button, VoiceOver's
  // double-tap -- is the only way in for those, and acts once.
  let pressed = false;
  const stop = () => { clearTimeout(timer); timer = null; delay = 420; };
  const tick = () => {
    action();
    delay = Math.max(130, delay * 0.72);
    timer = setTimeout(tick, delay);
  };

  node.addEventListener('pointerdown', (event) => {
    if (event.button > 0 || node.disabled) return;
    event.preventDefault();   // also suppresses the click that would double-fire
    pressed = true;
    action();
    timer = setTimeout(tick, delay);
  });
  ['pointerup', 'pointercancel', 'pointerleave'].forEach((type) => node.addEventListener(type, stop));
  ['pointerup', 'pointercancel'].forEach((type) => node.addEventListener(type, () => setTimeout(() => { pressed = false; }, 500)));
  node.addEventListener('click', () => {
    if (!pressed && !node.disabled) action();
  });
}

function nextLevel(current, direction) {
  if (direction > 0) return Math.min(100, (Math.floor(current / STEP) + 1) * STEP);
  const aligned = Math.floor(current / STEP) * STEP;
  return Math.max(0, aligned === current ? current - STEP : aligned);
}

function nudge(key, direction) {
  const room = rooms[key];
  if (!room.available) return;
  room.volume = nextLevel(room.volume ?? 0, direction);
  room.taps += direction;
  paintRoom(room);
  if (room.taps === 0) refresh();   // taps cancelled out; take the real level
  else flushVolume(key);
}

/* A burst of taps collapses into one call, so holding + does not queue up
   thirty requests the speakers then have to chew through. */
async function flushVolume(key) {
  const room = rooms[key];
  if (room.inflight) return;
  // A dragged level goes first: any taps still waiting were pressed after it,
  // so they are meant to move on from it.
  let body;
  if (room.wanted !== null) {
    body = { target: key, level: room.wanted };
    room.wanted = null;
  } else if (room.taps) {
    body = { target: key, steps: room.taps };
    room.taps = 0;
  } else {
    return;
  }
  room.inflight = true;
  try {
    const data = await api('/api/volume', body);
    if (!room.taps && room.wanted === null && !room.dragging) {
      room.volume = data.level;
      paintRoom(room);
    }
  } catch (error) {
    toast(error.message);
    refresh();
  } finally {
    room.inflight = false;
    if (room.taps || room.wanted !== null) flushVolume(key);
  }
}

function draggable(room) {
  const knob = room.level;
  let startX = 0;
  let startLevel = 0;
  let travel = 0;

  knob.addEventListener('pointerdown', (event) => {
    if (event.button > 0 || !room.available) return;
    event.preventDefault();
    knob.setPointerCapture(event.pointerId);
    startX = event.clientX;
    startLevel = room.volume ?? 0;
    travel = room.meter.clientWidth - knob.offsetWidth;   // how far the knob itself can go
    room.dragging = true;
    room.meter.classList.add('dragging');
  });

  knob.addEventListener('pointermove', (event) => {
    if (!room.dragging || travel <= 0) return;
    const moved = ((event.clientX - startX) / travel) * 100;
    const level = Math.round(Math.max(0, Math.min(100, startLevel + moved)));
    if (level === room.volume) return;
    room.volume = level;
    room.wanted = level;
    room.taps = 0;   // an absolute level supersedes any taps not yet sent
    paintRoom(room);
    flushVolume(room.key);
  });

  const stop = () => {
    room.dragging = false;
    room.meter.classList.remove('dragging');
  };
  knob.addEventListener('pointerup', stop);
  knob.addEventListener('pointercancel', stop);

  // The arrow keys, and VoiceOver's swipe up and down on a slider.
  knob.addEventListener('keydown', (event) => {
    const direction = ARROWS[event.key];
    if (!direction) return;
    event.preventDefault();
    nudge(room.key, direction);
  });
}

async function setGrouped(key, joined) {
  const room = rooms[key];
  if (room.busy || !room.available) return;
  room.busy = true;
  room.grouped = joined;      // show the new state while the speakers catch up
  paintRoom(room);
  paintGrouping();
  try {
    const data = await api('/api/group', { target: key, joined });
    applyJoined(data.joined || []);
  } catch (error) {
    toast(error.message);
  } finally {
    room.busy = false;
    refresh();
  }
}

function shownPlayState(room) {
  const reported = room.playState;
  if (!room.wantedPlay) return reported;
  // Nothing loaded any more -- the film ended, or the AVR changed input --
  // leaves nothing to hold; so does the player reporting the state asked for.
  if (!reported || reported === room.wantedPlay.state
      || Date.now() - room.wantedPlay.sentAt > PLAY_HOLD_MS) {
    room.wantedPlay = null;
  }
  return room.wantedPlay ? room.wantedPlay.state : reported;
}

/* Sends the state it wants rather than "toggle", so a stale idea of what the
   room is doing cannot flip it the wrong way. For the AVR this reaches the
   Zidoo rather than HEOS, which can no more pause a device on one of the
   AVR's inputs than it can seek in it -- app.py routes it there. */
async function togglePlay(key) {
  const room = rooms[key];
  const state = shownPlayState(room);
  if (!room.available || !state || room.playBusy) return;
  const wanted = state === 'play' ? 'pause' : 'play';
  room.playBusy = true;
  room.wantedPlay = { state: wanted, sentAt: Date.now() };
  paintRoom(room);
  paintGrouping();
  try {
    const data = await api('/api/playback', { target: key, state: wanted });
    // HEOS answers with the state the room is now in, which lets the hold go
    // at once. The Zidoo only says the key press was taken, so the AVR's card
    // keeps holding until a poll sees the film itself move.
    if (!room.avr) room.playState = data.state;
  } catch (error) {
    toast(error.message);
    room.wantedPlay = null;
  } finally {
    room.playBusy = false;
    paintRoom(room);
    paintGrouping();
    // The Zidoo takes a moment to report that it has started or stopped.
    if (room.avr) setTimeout(refresh, 1500);
  }
}

/* Nothing to optimistically flip the way play/pause does -- the panel
   cannot guess which song comes up -- so it looks again once HEOS has
   moved on, rather than showing the old song until the next poll. */
async function skipTrack(key, direction) {
  const room = rooms[key];
  if (!room.available) return;
  try {
    await api('/api/skip', { target: key, direction });
    setTimeout(refresh, 1000);
  } catch (error) {
    toast(error.message);
  }
}

function applyJoined(joined) {
  Object.values(rooms).forEach((room) => {
    room.grouped = joined.includes(room.key);
    paintRoom(room);
  });
  paintGrouping();
}

/* --- Spotify: one button per account, asking the card's own Connect
   receiver to resume that account, instead of always connecting to it
   from the Spotify app -------------------------------------------------- */
els('.spotify').forEach((button) => {
  button.addEventListener('click', () => {
    // The bordered button is the account already playing here, and resuming
    // it again would do nothing, so that tap is the opposite request: let
    // the room go, so another account can have it.
    const room = rooms[button.dataset.target];
    if (room && room.spotifyAccount === button.dataset.account) disconnectSpotify(button);
    else resumeSpotify(button);
  });
});

async function resumeSpotify(button) {
  const { target, account } = button.dataset;
  const who = button.querySelector('span').textContent;
  button.disabled = true;
  button.classList.add('loading');
  try {
    const data = await api('/api/spotify/resume', { target, account });
    toast(`Resuming ${who}'s Spotify on ${data.device}`, 'ok');
    const room = rooms[target];
    room.spotifyAccount = account;   // show it straight away; the refresh below confirms it
    paintRoom(room);
    // HEOS takes a moment to notice the new stream; look again once it
    // has, so play/pause turns up without waiting for the next poll.
    setTimeout(refresh, 1500);
  } catch (error) {
    toast(error.message);
  } finally {
    button.disabled = false;
    button.classList.remove('loading');
  }
}

async function disconnectSpotify(button) {
  const { target, account } = button.dataset;
  const who = button.querySelector('span').textContent;
  const room = rooms[target];
  button.disabled = true;
  button.classList.add('loading');
  try {
    const data = await api('/api/spotify/disconnect', { target, account });
    // The speaker not answering on the LAN is not a failure -- the room
    // still stops -- but it does leave the account signed in to it, and
    // that is the difference between "let go of" and "stopped".
    // A stereo pair is only ever paused -- signing it out can leave one
    // half silent -- so it staying signed in is the plan, not a failure.
    toast(data.signed_out
      ? `${data.device} let go of ${who}'s Spotify`
      : data.paired
        ? `Paused ${who}'s Spotify on ${data.device}`
        : `Stopped ${who}'s Spotify on ${data.device} — the speaker did not answer, so it stays signed in`,
      'ok');
    // The room stops with it, so drop the border, the transport row and the
    // song now rather than leaving a card that still claims to be playing;
    // the refresh below confirms it.
    room.spotifyAccount = null;
    room.playState = 'stop';
    room.track = null;
    paintRoom(room);
    setTimeout(refresh, 1500);
  } catch (error) {
    toast(error.message);
  } finally {
    button.disabled = false;
    button.classList.remove('loading');
  }
}

/* --- the input picker -------------------------------------------------- */
ui.inputButton.addEventListener('click', openSheet);
el('[data-role="scrim"]').addEventListener('click', closeSheet);
el('[data-role="sheet-close"]').addEventListener('click', closeSheet);

function sheetOpen() { return !ui.sheet.hidden; }

function setInputIcon(code) {
  paintIcon(ui.inputIcon, inputIcon(code));
}

function openSheet() {
  if (!inputs.length) {
    toast('No inputs reported by the AVR yet');
    return;
  }
  ui.options.innerHTML = '';
  inputs.forEach((source) => {
    const option = document.createElement('button');
    option.className = 'option';
    option.setAttribute('aria-current', String(currentInput && currentInput.code === source.code));
    option.innerHTML = '<span class="option-label"><svg viewBox="0 0 512 512" aria-hidden="true"><path d=""/></svg><span></span></span><span class="code"></span>';
    paintIcon(option.querySelector('svg'), inputIcon(source.code));
    option.querySelector('.option-label span').textContent = source.name;
    option.querySelector('.code').textContent = source.code;
    option.addEventListener('click', () => chooseInput(source));
    ui.options.appendChild(option);
  });
  ui.sheet.hidden = false;
  // Into the sheet, on the input already selected, so a keyboard or VoiceOver
  // starts there rather than on the page behind it.
  (el('[aria-current="true"]', ui.options) || ui.options.firstElementChild).focus();
}

function closeSheet() {
  ui.sheet.hidden = true;
  ui.inputButton.focus();
}

document.addEventListener('keydown', (event) => {
  if (event.key === 'Escape' && sheetOpen()) closeSheet();
});

async function chooseInput(source) {
  closeSheet();
  currentInput = source;
  ui.inputName.textContent = source.name;
  setInputIcon(source.code);
  try {
    const data = await api('/api/avr/input', { code: source.code });
    currentInput = data;
    ui.inputName.textContent = data.name;
    setInputIcon(data.code);
  } catch (error) {
    toast(error.message);
    refresh();
  }
}

/* --- state ------------------------------------------------------------- */
function applyRoom(room, incoming) {
  if (!room) return;
  room.available = Boolean(incoming.available);
  room.grouped = Boolean(incoming.grouped);
  // Do not stomp on a volume the user is in the middle of changing.
  if (!room.taps && !room.inflight && !room.dragging && room.wanted === null) {
    room.volume = incoming.volume;
  }
  if (!room.playBusy) room.playState = incoming.play_state || null;
  room.track = incoming.now_playing || null;
  room.onSpotify = Boolean(incoming.spotify);
  room.spotifyAccount = incoming.spotify_account || null;
  paintRoom(room);
}

function render(state) {
  // The Pi shipped a newer version while this tab (or a resumed iOS
  // home-screen session) was still showing an old one -- catch up rather
  // than keep polling a page that no longer matches the server.
  if (VERSION && state.version && state.version !== VERSION && !busy()) {
    location.reload();
    return;
  }

  (state.rooms || []).forEach((incoming) => applyRoom(rooms[incoming.key], incoming));

  const avr = state.avr || {};
  inputs = avr.inputs || [];
  currentInput = avr.input || null;
  ui.inputName.textContent = currentInput ? currentInput.name : '—';
  setInputIcon(currentInput ? currentInput.code : null);
  // Whatever is on one of its inputs is what the AVR is playing, and its own
  // play state is that device's -- HEOS has none to give for an input.
  applyRoom(rooms[HOST], {
    available: avr.connected !== false,
    volume: avr.volume,
    now_playing: avr.now_playing || null,
    play_state: (avr.now_playing || {}).play_state || null,
  });
  paintGrouping();   // after the AVR's card, which decides where it sits

  const problems = state.errors || [];
  ui.foot.textContent = problems.length ? problems[0] : (state.demo ? 'demo mode — no real speakers' : '');
  ui.foot.classList.toggle('bad', problems.length > 0);
}

let refreshing = false;
async function refresh() {
  if (refreshing) return;
  refreshing = true;
  try {
    render(await api('/api/state'));
  } catch (error) {
    ui.foot.textContent = error.message;
    ui.foot.classList.add('bad');
  } finally {
    refreshing = false;
  }
}

function busy() {
  return sheetOpen()
    || Object.values(rooms).some((r) => r.taps || r.inflight || r.dragging || r.busy || r.playBusy || seeking(r));
}

setInterval(() => {
  if (document.visibilityState === 'visible' && !busy()) refresh();
}, POLL_MS);

document.addEventListener('visibilitychange', () => {
  if (document.visibilityState === 'visible') refresh();
});

Object.values(rooms).forEach(paintRoom);
paintGrouping();
refresh();