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Align timer/stopwatch start to the next whole second #7

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Align timer/stopwatch start to the next whole second #7

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32 changes: 28 additions & 4 deletions server.js
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,12 @@ let ntpOffset = 0;
let ntpSynced = false;
function ntpNow() { return Date.now() + ntpOffset; }

// ms until the next whole wall-clock second, so timers/stopwatches can be
// kicked off exactly on a second boundary — same boundary the digital clock
// ticks over on for every connected viewer — instead of at an arbitrary
// mid-second offset determined by click timing.
function msUntilNextSecond() { return (1000 - (ntpNow() % 1000)) % 1000; }

function syncNTP() {
const server = NTP_SERVERS[Math.floor(Math.random() * NTP_SERVERS.length)];
const client = dgram.createSocket('udp4');
Expand Down Expand Up @@ -143,6 +149,11 @@ const RESET_SLOT_COLORS = { slot1: '#ffd600', slot2: '#4fc3f7', slot3: '#ffffff'

let flashTimeout = null;
const expiredTimeouts = new Map(); // slot id -> Timeout
const pendingStartTimeouts = new Map(); // slot id -> Timeout, aligned start/resume awaiting the next second boundary

function clearPendingStart(id) {
if (pendingStartTimeouts.has(id)) { clearTimeout(pendingStartTimeouts.get(id)); pendingStartTimeouts.delete(id); }
}

// ── SSE broadcast ─────────────────────────────────────────────────────────
let sseClients = [];
Expand Down Expand Up @@ -448,18 +459,31 @@ const server = http.createServer((req, res) => {
const [, id, action] = slotMatch;
const slot = getSlot(id);
return parseBody(req, body => {
if (action === 'start' || action === 'resume') {
// Align the actual start to the next whole second so the countdown/
// count-up ticks over in sync with the clock and other slots, rather
// than at whatever mid-second instant the button was clicked.
clearPendingStart(slot.id);
pendingStartTimeouts.set(slot.id, setTimeout(() => {
pendingStartTimeouts.delete(slot.id);
if (action === 'start') slotStart(slot, body); else slotResume(slot);
saveState();
broadcast(snapshot());
}, msUntilNextSecond()));
return noContent(res);
}

switch (action) {
case 'type':
clearPendingStart(slot.id);
if (['timer', 'stopwatch', 'targetTime'].includes(body.type)) {
clearExpiredTimeout(slot.id);
slot.type = body.type;
slot.mode = 'idle'; slot.endAt = null; slot.startedAt = null;
}
break;
case 'start': slotStart(slot, body); break;
case 'pause': slotPause(slot); break;
case 'resume': slotResume(slot); break;
case 'reset': slotReset(slot, body); break;
case 'pause': clearPendingStart(slot.id); slotPause(slot); break;
case 'reset': clearPendingStart(slot.id); slotReset(slot, body); break;
case 'config': slotConfig(slot, body); break;
}
saveState();
Expand Down