clock-site/seth.js

// Seth Calendar
//
// Structure:
//   - Same year numbers and Jan 1 epoch as Gregorian
//   - 10 months of 36 days (6 weeks of 6 days each)
//   - 5 holiday days at year end (6 on leap years)
//   - Total: 365 or 366 days
//
// Gregorian alignment (non-leap year):
//   Month 1 Day 1   = Jan 1
//   Month 10 Day 35 = Dec 25 (Christmas)
//   Month 10 Day 36 = Dec 26 (Boxing Day)
//   Holiday 1       = Dec 27
//   Holiday 5       = Dec 31 (New Year's Eve)
//
// Gregorian alignment (leap year):
//   Month 10 Day 35 = Dec 24 (Christmas Eve)
//   Month 10 Day 36 = Dec 25 (Christmas)
//   Holiday 1       = Dec 26 (Boxing Day)
//   Holiday 6       = Dec 31 (New Year's Eve)

function isLeapYear(year) {
  return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
}

function toSethDate(year, dayOfYear) {
  // dayOfYear: 1-indexed (Jan 1 = 1)
  const leap = isLeapYear(year);

  // Leap Day: DOY 60 in a leap year — sits between M1 W3 D4 and M1 W3 D5
  if (leap && dayOfYear === 60) {
    return { type: "leapday", year, dayOfYear };
  }

  // After leap day, subtract 1 so the rest of the calendar stays pegged
  const idx = (leap && dayOfYear > 60 ? dayOfYear - 1 : dayOfYear) - 1;

  if (idx < 360) {
    const month  = Math.floor(idx / 36);    // 0..9
    const dayInM = idx % 36;               // 0..35
    const week   = Math.floor(dayInM / 6); // 0..5
    const dayInW = dayInM % 6;             // 0..5
    return { type: "month", year, month, day: dayInM, week, weekDay: dayInW, dayOfYear };
  } else {
    const holiday = idx - 360;              // 0..4 (or 0..5 leap)
    return { type: "holiday", year, holiday, leap, dayOfYear };
  }
}

function getDayOfYear(date, zone) {
  const fmt = new Intl.DateTimeFormat("en-US", {
    timeZone: zone,
    year: "numeric", month: "numeric", day: "numeric"
  });
  const parts = fmt.formatToParts(date).reduce((acc, p) => {
    if (p.type !== "literal") acc[p.type] = parseInt(p.value, 10);
    return acc;
  }, {});

  const { year, month, day } = parts;

  // Day of year calculation
  const cumDays = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
  const leap = isLeapYear(year);
  let doy = cumDays[month - 1] + day;
  if (leap && month > 2) doy++;

  return { year, doy };
}

function formatSethDate(sd) {
  if (sd.type === "leapday") return "Leap Day";
  if (sd.type === "holiday") {
    const total = sd.leap ? 6 : 5;
    return `Holiday ${sd.holiday} of ${total}`;
  }
  return `Month ${sd.month}, Week ${sd.week}, Day ${sd.weekDay}`;
}

function formatSethLong(sd) {
  if (sd.type === "leapday") return `${sd.year} Leap Day — Feb 29`;
  if (sd.type === "holiday") {
    const lastHoliday = sd.leap ? 5 : 4;
    const isNYE       = sd.holiday === lastHoliday;
    const isBoxingDay = sd.leap && sd.holiday === 0;
    let note = "";
    if (isNYE)            note = " — New Year's Eve";
    else if (isBoxingDay) note = " — Boxing Day";
    return `${sd.year} Holiday ${sd.holiday}${note}`;
  }
  return `${sd.year} M${sd.month} W${sd.week} D${sd.weekDay}  (Month ${sd.month}, Day ${sd.day})`;
}

// --- Decimal time (same as decimal page) ---

function getLocalParts(date, zone) {
  const fmt = new Intl.DateTimeFormat("en-US", {
    timeZone: zone,
    hour12: false,
    year: "numeric", month: "2-digit", day: "2-digit",
    hour: "2-digit", minute: "2-digit", second: "2-digit"
  });
  return fmt.formatToParts(date).reduce((acc, p) => {
    if (p.type !== "literal") acc[p.type] = parseInt(p.value, 10);
    return acc;
  }, {});
}

function toDecimalTime(date, zone) {
  const p = getLocalParts(date, zone);
  const msIntoDay =
    p.hour   * 3_600_000 +
    p.minute * 60_000 +
    p.second * 1_000 +
    date.getMilliseconds();

  const dayFraction = msIntoDay / 86_400_000;
  const totalDecimalSeconds = dayFraction * 100_000;

  const dHour   = Math.floor(totalDecimalSeconds / 10_000);
  const rem1    = totalDecimalSeconds % 10_000;
  const dMin    = Math.floor(rem1 / 100);
  const dSec    = rem1 % 100;
  const dCenti  = Math.floor((dSec % 1) * 100);
  const dSecInt = Math.floor(dSec);

  return `\u00a0${dHour}:${String(dMin).padStart(2,"0")}:${String(dSecInt).padStart(2,"0")}.${String(dCenti).padStart(2,"0")}`;
}

// --- DOM & sync ---

const zoneSelect    = document.getElementById("zoneSelect");
const zoneLabel     = document.getElementById("zoneLabel");
const offsetLabel   = document.getElementById("offsetLabel");
const decimalTime   = document.getElementById("decimalTime");
const gregorianTime = document.getElementById("gregorianTime");
const dayOfYear     = document.getElementById("dayOfYear");
const weekOfYear    = document.getElementById("weekOfYear");
const utcLabel      = document.getElementById("utcLabel");
const dateLine      = document.getElementById("dateLine");
const digital       = document.getElementById("digital");

const zones = [
  "America/New_York",
  "America/Chicago",
  "America/Denver",
  "America/Los_Angeles",
  "America/Anchorage",
  "Pacific/Honolulu",
  "UTC"
];

let selectedZone = Intl.DateTimeFormat().resolvedOptions().timeZone || "America/New_York";
if (!zones.includes(selectedZone)) selectedZone = "America/New_York";

for (const zone of zones) {
  const option = document.createElement("option");
  option.value = zone;
  option.textContent = zone;
  if (zone === selectedZone) option.selected = true;
  zoneSelect.appendChild(option);
}

zoneSelect.addEventListener("change", () => {
  selectedZone = zoneSelect.value;
  zoneLabel.textContent = selectedZone;
});

let serverOffsetMs = 0;

async function syncWithServer() {
  const start = Date.now();
  try {
    const response = await fetch(`/api/time?ts=${start}`, { cache: "no-store" });
    const end = Date.now();
    const data = await response.json();
    const rtt = end - start;
    serverOffsetMs = (data.epoch_ms + rtt / 2) - end;
    offsetLabel.textContent = `Synchronized (${serverOffsetMs >= 0 ? "+" : ""}${serverOffsetMs.toFixed(0)} ms, RTT ${rtt} ms)`;
  } catch (_) {
    offsetLabel.textContent = "Sync failed";
  }
}

function toGregorianTime(date, zone) {
  const p = getLocalParts(date, zone);
  // Format as HH:MM:SS.cc to match decimal time width
  const cs = String(Math.floor(date.getMilliseconds() / 10)).padStart(2, "0");
  return `${String(p.hour).padStart(2,"0")}:${String(p.minute).padStart(2,"0")}:${String(p.second).padStart(2,"0")}.${cs}`;
}

function render() {
  const now = new Date(Date.now() + serverOffsetMs);
  const { year, doy } = getDayOfYear(now, selectedZone);
  const sd = toSethDate(year, doy);
  const dt = toDecimalTime(now, selectedZone);
  const gt = toGregorianTime(now, selectedZone);

  dateLine.textContent        = formatSethLong(sd);
  digital.textContent         = dt;
  decimalTime.textContent     = dt;
  gregorianTime.textContent   = gt;
  dayOfYear.textContent       = `${doy} of ${isLeapYear(year) ? 366 : 365}`;
  const totalWeeks = 60; // 10 months × 6 weeks
  const woy = sd.type === "month" ? sd.month * 6 + sd.week : "—";
  const woyTotal = sd.type === "month" ? `${woy} of ${totalWeeks}`
                 : sd.type === "leapday" ? "— (leap day)"
                 : `— (holiday days)`;
  weekOfYear.textContent      = woyTotal;
  zoneLabel.textContent       = selectedZone;
  utcLabel.textContent        = now.toISOString().replace("T", " ").replace("Z", " UTC");

  requestAnimationFrame(render);
}

syncWithServer();
setInterval(syncWithServer, 20_000);
render();