Migrate timezone/date utilities to Temporal (bundled polyfill)

deno.json

@@ -49,7 +49,6 @@
     "esbuild": "npm:esbuild@^0.28.0",
     "sass": "npm:sass@^1.101.0",
     "@bunny.net/edgescript-sdk": "npm:@bunny.net/edgescript-sdk@^0.12.1",
-    "@internationalized/date": "npm:@internationalized/date@^3.12.0",
     "@bunny.net/storage-sdk": "npm:@bunny.net/storage-sdk@^0.3.1",
     "@botpoison/browser": "npm:@botpoison/browser@^0.1.30",
     "jsqr": "npm:jsqr@^1.4.0",

src/shared/dates.ts

@@ -2,14 +2,14 @@
  * Date computation for daily listings
  */
 
-import { fromAbsolute } from "@internationalized/date";
 import { filter } from "#fp";
 import { settings } from "#shared/db/settings.ts";
 import {
   formatDatetimeInTz,
   formatDatetimeShortInTz,
   localToUtc,
   todayInTz,
+  utcToZoned,
 } from "#shared/timezone.ts";
 import {
   type Holiday,
@@ -449,14 +449,9 @@ export const formatTimeAgo = (
  * Used by the calendar view to map standard listing dates to calendar days.
  */
 export const listingDateToCalendarDate = (utcIso: string): string | null => {
-  const tz = settings.timezone;
   if (!utcIso) return null;
   try {
-    const ms = new Date(utcIso).getTime();
-    if (Number.isNaN(ms)) return null;
-    const zoned = fromAbsolute(ms, tz);
-    const pad = (n: number) => String(n).padStart(2, "0");
-    return `${zoned.year}-${pad(zoned.month)}-${pad(zoned.day)}`;
+    return utcToZoned(utcIso, settings.timezone).toPlainDate().toString();
   } catch {
     return null;
   }

src/shared/timezone.ts

@@ -1,17 +1,10 @@
 /**
- * Timezone conversion utilities using @internationalized/date.
+ * Timezone conversion utilities built on the standard Temporal API.
  *
- * Wraps the library to provide simple string-in/string-out functions
- * for the rest of the codebase, with correct DST handling and
- * explicit disambiguation.
+ * Provides simple string-in/string-out functions for the rest of the
+ * codebase, with correct DST handling and explicit disambiguation.
  */
 
-import {
-  fromAbsolute,
-  today as libToday,
-  parseDateTime,
-  toZoned,
-} from "@internationalized/date";
 import { formatIsoForPreview } from "#shared/bulk-replace.ts";
 
 /** Default timezone when none is configured */
@@ -21,13 +14,41 @@ export const DEFAULT_TIMEZONE = "Europe/London";
 const pad2 = (n: number): string => String(n).padStart(2, "0");
 
 /** Parse a UTC ISO string into a ZonedDateTime in the given timezone */
-const utcToZoned = (utcIso: string, tz: string) =>
-  fromAbsolute(new Date(utcIso).getTime(), tz);
+export const utcToZoned = (
+  utcIso: string,
+  tz: string,
+): Temporal.ZonedDateTime =>
+  Temporal.Instant.fromEpochMilliseconds(
+    new Date(utcIso).getTime(),
+  ).toZonedDateTimeISO(tz);
 
 /**
  * Get today's date as YYYY-MM-DD in the given timezone.
  */
-export const todayInTz = (tz: string): string => libToday(tz).toString();
+export const todayInTz = (tz: string): string =>
+  Temporal.Now.plainDateISO(tz).toString();
+
+/**
+ * Strict datetime-local shape: a calendar date optionally followed by a
+ * wall-clock time. Deliberately excludes any UTC designator (`Z`), numeric
+ * offset, or bracketed IANA zone — the rest of the app interprets these values
+ * in the configured timezone, and `Temporal.PlainDateTime.from` would silently
+ * *discard* such a suffix rather than reject it, storing a different instant.
+ */
+const NAIVE_DATETIME = /^\d{4}-\d{2}-\d{2}(T\d{2}:\d{2}(:\d{2}(\.\d+)?)?)?$/;
+
+/**
+ * Parse a naive datetime-local value into a PlainDateTime, rejecting
+ * offset/zone-bearing input up front, then delegating real calendar-validity
+ * checks to Temporal (`overflow: "reject"` catches impossible dates like
+ * 2026-02-30 rather than silently clamping them).
+ */
+const parseNaiveDateTime = (value: string): Temporal.PlainDateTime => {
+  if (!NAIVE_DATETIME.test(value)) {
+    throw new RangeError(`Non-naive datetime: ${value}`);
+  }
+  return Temporal.PlainDateTime.from(value, { overflow: "reject" });
+};
 
 /**
  * Convert a naive datetime-local value (YYYY-MM-DDTHH:MM) to a UTC ISO string,
@@ -38,9 +59,10 @@ export const todayInTz = (tz: string): string => libToday(tz).toString();
  */
 export const localToUtc = (naive: string, tz: string): string => {
   try {
-    const dt = parseDateTime(naive);
-    const zoned = toZoned(dt, tz, "compatible");
-    return zoned.toAbsoluteString();
+    return parseNaiveDateTime(naive)
+      .toZonedDateTime(tz, { disambiguation: "compatible" })
+      .toInstant()
+      .toString({ fractionalSecondDigits: 3 });
   } catch {
     throw new Error(`Invalid datetime: ${naive}`);
   }
@@ -107,7 +129,7 @@ export const isValidTimezone = (tz: string): boolean => {
  */
 export const isValidDatetime = (value: string): boolean => {
   try {
-    parseDateTime(value);
+    parseNaiveDateTime(value);
     return true;
   } catch {
     return false;

test/lib/timezone.test.ts

@@ -84,6 +84,27 @@ describe("timezone", () => {
       expect(() => localToUtc("not-a-date", "UTC")).toThrow("Invalid datetime");
     });
 
+    test("rejects a datetime carrying a numeric offset", () => {
+      // Input must be naive: an offset would otherwise be silently discarded
+      // and the wall-clock time reinterpreted in the target timezone, storing
+      // a different instant than the string implies.
+      expect(() =>
+        localToUtc("2026-06-15T14:30+09:00", "Europe/London"),
+      ).toThrow("Invalid datetime");
+    });
+
+    test("rejects a datetime carrying a bracketed IANA zone", () => {
+      expect(() =>
+        localToUtc("2026-06-15T14:30[Asia/Tokyo]", "Europe/London"),
+      ).toThrow("Invalid datetime");
+    });
+
+    test("rejects a datetime carrying a UTC designator", () => {
+      expect(() => localToUtc("2026-06-15T14:30Z", "Europe/London")).toThrow(
+        "Invalid datetime",
+      );
+    });
+
     test("handles DST spring-forward gap with 'compatible' disambiguation", () => {
       // 2026-03-29 01:30 Europe/London doesn't exist (clocks skip from 01:00 GMT to 02:00 BST)
       // 'compatible' maps to the later (post-transition) interpretation: 02:30 BST = 01:30 UTC
@@ -253,6 +274,19 @@ describe("timezone", () => {
     test("rejects empty string", () => {
       expect(isValidDatetime("")).toBe(false);
     });
+
+    test("rejects an impossible calendar date", () => {
+      // overflow: "reject" must not clamp 2026-02-30 to a real day.
+      expect(isValidDatetime("2026-02-30T00:00")).toBe(false);
+    });
+
+    test("rejects a datetime carrying a numeric offset", () => {
+      expect(isValidDatetime("2026-06-15T14:30+09:00")).toBe(false);
+    });
+
+    test("rejects a datetime carrying a bracketed IANA zone", () => {
+      expect(isValidDatetime("2026-06-15T14:30[Asia/Tokyo]")).toBe(false);
+    });
   });
 
   describe("round-trip: localToUtc -> utcToLocalInput", () => {