Implement mattertimesync: one-shot Matter time synchronization CLIHEADmain

A standalone CLI Matter controller that joins Matter devices' existing
setups as a secondary administrator (multi-admin) and sets their clocks
via the standard Time Synchronization cluster. Built on matter.js 0.17.6
using the CommissioningController API. One-shot runs from a systemd
timer, no daemon: being a secondary controller is fabric membership, not
a running process, so each invocation loads the persisted keys,
discovers the device via operational DNS-SD, opens a fresh CASE session,
does its work, and exits.

- TypeScript scaffold: strict tsc, oxlint, prettier, vitest (66 tests:
  Matter epoch conversion, config validation, IANA timezone offsets and
  exact DST transition search, atomic state writes, pairing-code
  parsing, clock-delta reporting, capability planning against the
  captured device fixture)
- Validated JSON configuration with bigint-safe values; unknown fields
  rejected loudly
- Persistent controller fabric with the same identity across restarts.
  The fabric doubles as the device registry: every node commissioned
  onto it is kept in sync, and membership changes only through
  commission and decommission, so no separate device list can drift
- On-network multi-admin commissioning from a manual or QR pairing code;
  any number of devices, one per-device pairing code each. A device
  already on the fabric rejects re-commissioning via fabric conflict
- sync, validated against real hardware (IKEA ALPSTUGA air quality
  monitor over Thread, commissioned alongside Apple Home): refuses to
  run unless the host is NTP-synchronized, then per node reads utcTime,
  reports the correction with direction ("device clock was 1m 23s
  behind", handling unset clocks in exact bigint microseconds), writes
  SetUTCTime, SetTimeZone (standard offset plus IANA name), and
  SetDSTOffset (transition list bounded by the device's capacity), and
  verifies by reading the clock back. Capability-driven throughout:
  UTC-only devices degrade gracefully, cluster-less devices are skipped
  with a warning. Devices whose firmware encodes Unix-epoch time on the
  wire are detected by the exact 946684800s shift and reported
  corrected. Note matter.js's TlvEpochUs API convention: values are
  Unix-epoch microseconds at the API boundary; the library converts to
  Matter epoch on the wire
- Commands: nodes, inspect (human/JSON; also reads the fabric table
  fabric-unfiltered, matching our own entry by fabric ID plus root
  public key and flagging likely-stale orphans; strictly read-only,
  since this tool never uses its admin rights against other fabrics'
  entries), status, and decommission (each device drops our fabric
  while staying paired to its primary ecosystem; targets all devices
  unless --node narrows it)
- Logs (service and matter.js library, plain format) go to stderr;
  stdout carries only command output, so --json (available on nodes,
  inspect, sync, status, fabrics) is always clean parseable JSON with
  64-bit values as decimal strings. Node's node:sqlite
  ExperimentalWarning is filtered before matter.js loads
- systemd oneshot service (dedicated non-root user, hardening) plus
  hourly timer with randomized delay
- Deployment as a single esbuild bundle (mattertimesync.mjs, ~4.5 MB):
  all runtime deps are pure JavaScript, so the target needs only
  Node 20+, with no npm, registry access, or build toolchain. The Bun
  sqlite driver stays external behind its runtime guard and node:sqlite
  is aliased to a lazy shim so the bundle runs under plain Node. npm
  pack remains an alternative install path

1 files changed, 190 insertions, 0 deletions

diff --git a/src/timezone.ts b/src/timezone.ts
new file mode 100644
index 0000000..062a811
--- /dev/null
+++ b/src/timezone.ts
@@ -0,0 +1,190 @@
+/**
+ * IANA time-zone helpers: validation and offset introspection (config
+ * validation, status output) plus Matter TimeZone/DSTOffset structure
+ * generation for the sync command.
+ */
+
+import { MATTER_EPOCH_AS_UNIX_MICROS } from "./sync.js";
+
+/** Returns true when the host's ICU data recognizes the IANA time-zone name. */
+export function isValidTimeZone(timezone: string): boolean {
+  if (typeof timezone !== "string" || timezone.length === 0) return false;
+  try {
+    new Intl.DateTimeFormat("en-US", { timeZone: timezone });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Current UTC offset of `timezone` at `date`, in seconds.
+ *
+ * Derived from ICU rules, never from a hard-coded offset, so daylight-saving
+ * transitions are honored automatically.
+ */
+export function utcOffsetSeconds(timezone: string, date: Date = new Date()): number {
+  const formatter = new Intl.DateTimeFormat("en-US", {
+    timeZone: timezone,
+    timeZoneName: "longOffset",
+  });
+  const offsetPart = formatter.formatToParts(date).find(part => part.type === "timeZoneName")?.value;
+  if (offsetPart === undefined) {
+    throw new Error(`Unable to determine UTC offset for time zone ${timezone}`);
+  }
+  // Formats look like "GMT-05:00", "GMT+05:30", or plain "GMT" for UTC itself.
+  const match = /^GMT(?:([+-])(\d{2}):(\d{2})(?::(\d{2}))?)?$/.exec(offsetPart);
+  if (!match) {
+    throw new Error(`Unrecognized UTC offset format "${offsetPart}" for time zone ${timezone}`);
+  }
+  if (match[1] === undefined) return 0;
+  const sign = match[1] === "-" ? -1 : 1;
+  const hours = Number(match[2]);
+  const minutes = Number(match[3]);
+  const seconds = match[4] === undefined ? 0 : Number(match[4]);
+  return sign * (hours * 3600 + minutes * 60 + seconds);
+}
+
+/** Formats an offset in seconds as "UTC-05:00" style text for logs and status output. */
+export function formatUtcOffset(offsetSeconds: number): string {
+  const sign = offsetSeconds < 0 ? "-" : "+";
+  const absolute = Math.abs(offsetSeconds);
+  const hours = String(Math.floor(absolute / 3600)).padStart(2, "0");
+  const minutes = String(Math.floor((absolute % 3600) / 60)).padStart(2, "0");
+  return `UTC${sign}${hours}:${minutes}`;
+}
+
+/**
+ * Finds the next instant at which the zone's UTC offset changes, scanning up
+ * to `horizonDays` ahead. Returns null when no transition occurs in the
+ * window (e.g. fixed-offset zones).
+ *
+ * Uses day-granularity scan plus binary search, so it is exact to the second
+ * without iterating minute-by-minute.
+ */
+export function nextOffsetTransition(
+  timezone: string,
+  from: Date = new Date(),
+  horizonDays = 400,
+): { at: Date; offsetBeforeSeconds: number; offsetAfterSeconds: number } | null {
+  const startOffset = utcOffsetSeconds(timezone, from);
+  const dayMs = 24 * 60 * 60 * 1000;
+  // Probe on whole-second boundaries so the binary search converges on the
+  // exact transition instant (transitions occur at whole seconds).
+  const startMs = Math.ceil(from.getTime() / 1000) * 1000;
+
+  let previous = startMs;
+  let changedAtOrBefore: number | null = null;
+  for (let day = 1; day <= horizonDays; day++) {
+    const probe = startMs + day * dayMs;
+    if (utcOffsetSeconds(timezone, new Date(probe)) !== startOffset) {
+      changedAtOrBefore = probe;
+      break;
+    }
+    previous = probe;
+  }
+  if (changedAtOrBefore === null) return null;
+
+  // Binary search the exact transition instant between the last unchanged
+  // probe and the first changed probe.
+  let low = previous;
+  let high = changedAtOrBefore;
+  while (high - low > 1000) {
+    const middle = low + Math.floor((high - low) / 2 / 1000) * 1000;
+    if (utcOffsetSeconds(timezone, new Date(middle)) === startOffset) {
+      low = middle;
+    } else {
+      high = middle;
+    }
+  }
+  return {
+    at: new Date(high),
+    offsetBeforeSeconds: startOffset,
+    offsetAfterSeconds: utcOffsetSeconds(timezone, new Date(high)),
+  };
+}
+
+/**
+ * Matter TimeZoneStruct and DSTOffsetStruct as passed to matter.js. All
+ * timestamps here are Unix-epoch microseconds: matter.js's TlvEpochUs
+ * converts to Matter-epoch on the wire and rejects pre-converted values.
+ * "Valid since the beginning of time" is therefore Matter epoch zero
+ * expressed in Unix microseconds, not 0.
+ */
+export interface MatterTimeZoneEntry {
+  /** Standard (non-DST) UTC offset in seconds. */
+  offset: number;
+  /** Unix-epoch microseconds at which the entry takes effect. */
+  validAt: bigint;
+  name?: string;
+}
+
+/** One DST period; offset is added on top of the TimeZone offset. */
+export interface MatterDstOffsetEntry {
+  offset: number;
+  validStarting: bigint;
+  /** Unix-epoch microseconds; null = valid until further notice (last entry only). */
+  validUntil: bigint | null;
+}
+
+/**
+ * The zone's standard (non-DST) UTC offset in seconds: the smaller of the
+ * mid-January and mid-July offsets of the year. DST increases the offset in
+ * every zone as reported by ICU (including Europe/Dublin, which ICU models
+ * as +00:00 standard / +01:00 summer despite IANA's negative-SAVE encoding).
+ */
+export function standardOffsetSeconds(timezone: string, at: Date = new Date()): number {
+  const year = at.getUTCFullYear();
+  const january = utcOffsetSeconds(timezone, new Date(Date.UTC(year, 0, 15)));
+  const july = utcOffsetSeconds(timezone, new Date(Date.UTC(year, 6, 15)));
+  return Math.min(january, july);
+}
+
+/**
+ * The TimeZone attribute list for SetTimeZone: a single entry carrying the
+ * zone's standard offset and IANA name, valid from the beginning of time.
+ */
+export function buildTimeZoneList(timezone: string, at: Date = new Date()): MatterTimeZoneEntry[] {
+  return [
+    {
+      offset: standardOffsetSeconds(timezone, at),
+      validAt: MATTER_EPOCH_AS_UNIX_MICROS,
+      name: timezone.slice(0, 64),
+    },
+  ];
+}
+
+/**
+ * The DSTOffset list for SetDstOffset: the DST state in effect at `from`
+ * followed by upcoming transitions, at most `maxEntries` entries (the
+ * device's DSTOffsetListMaxSize; spec minimum 1). Entries carry concrete
+ * validUntil bounds where a next transition is known, so a device left
+ * unrefreshed falls back to standard time rather than trusting stale DST;
+ * the periodic sync refreshes the list long before it expires. Zones
+ * without transitions yield a single open-ended zero entry.
+ */
+export function buildDstOffsetList(
+  timezone: string,
+  maxEntries: number,
+  from: Date = new Date(),
+): MatterDstOffsetEntry[] {
+  const standard = standardOffsetSeconds(timezone, from);
+  const entries: MatterDstOffsetEntry[] = [];
+  let cursor = from;
+  let currentDst = utcOffsetSeconds(timezone, cursor) - standard;
+  let validStarting = MATTER_EPOCH_AS_UNIX_MICROS;
+  const limit = Math.max(1, maxEntries);
+  while (entries.length < limit) {
+    const transition = nextOffsetTransition(timezone, cursor);
+    if (transition === null) {
+      entries.push({ offset: currentDst, validStarting, validUntil: null });
+      break;
+    }
+    const untilMicros = BigInt(transition.at.getTime()) * 1_000n;
+    entries.push({ offset: currentDst, validStarting, validUntil: untilMicros });
+    validStarting = untilMicros;
+    currentDst = transition.offsetAfterSeconds - standard;
+    cursor = new Date(transition.at.getTime() + 1000);
+  }
+  return entries;
+}