refactor: extract cron schedule and test runner helpers

src/infra/format-time/parse-offsetless-zoned-datetime.test.ts

@@ -0,0 +1,34 @@
+import { describe, expect, it } from "vitest";
+import {
+  isOffsetlessIsoDateTime,
+  parseOffsetlessIsoDateTimeInTimeZone,
+} from "./parse-offsetless-zoned-datetime.js";
+
+describe("parseOffsetlessIsoDateTimeInTimeZone", () => {
+  it("detects offset-less ISO datetimes", () => {
+    expect(isOffsetlessIsoDateTime("2026-03-23T23:00:00")).toBe(true);
+    expect(isOffsetlessIsoDateTime("2026-03-23T23:00:00+02:00")).toBe(false);
+    expect(isOffsetlessIsoDateTime("+20m")).toBe(false);
+  });
+
+  it("converts offset-less datetimes in the requested timezone", () => {
+    expect(parseOffsetlessIsoDateTimeInTimeZone("2026-03-23T23:00:00", "Europe/Oslo")).toBe(
+      "2026-03-23T22:00:00.000Z",
+    );
+  });
+
+  it("keeps DST boundary conversions on the intended wall-clock time", () => {
+    expect(parseOffsetlessIsoDateTimeInTimeZone("2026-03-29T01:30:00", "Europe/Oslo")).toBe(
+      "2026-03-29T00:30:00.000Z",
+    );
+  });
+
+  it("returns null for invalid input", () => {
+    expect(parseOffsetlessIsoDateTimeInTimeZone("2026-03-23T23:00:00+02:00", "Europe/Oslo")).toBe(
+      null,
+    );
+    expect(parseOffsetlessIsoDateTimeInTimeZone("2026-03-23T23:00:00", "Invalid/Timezone")).toBe(
+      null,
+    );
+  });
+});

src/infra/format-time/parse-offsetless-zoned-datetime.ts

@@ -0,0 +1,58 @@
+const OFFSETLESS_ISO_DATETIME_RE = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(:\d{2})?(\.\d+)?$/;
+
+export function isOffsetlessIsoDateTime(raw: string): boolean {
+  return OFFSETLESS_ISO_DATETIME_RE.test(raw);
+}
+
+export function parseOffsetlessIsoDateTimeInTimeZone(raw: string, timeZone: string): string | null {
+  if (!isOffsetlessIsoDateTime(raw)) {
+    return null;
+  }
+  try {
+    new Intl.DateTimeFormat("en-US", { timeZone }).format(new Date());
+
+    const naiveMs = new Date(`${raw}Z`).getTime();
+    if (Number.isNaN(naiveMs)) {
+      return null;
+    }
+
+    // Re-check the offset at the first candidate instant so DST boundaries
+    // land on the intended wall-clock time instead of drifting by one hour.
+    const firstOffsetMs = getTimeZoneOffsetMs(naiveMs, timeZone);
+    const candidateMs = naiveMs - firstOffsetMs;
+    const finalOffsetMs = getTimeZoneOffsetMs(candidateMs, timeZone);
+    return new Date(naiveMs - finalOffsetMs).toISOString();
+  } catch {
+    return null;
+  }
+}
+
+function getTimeZoneOffsetMs(utcMs: number, timeZone: string): number {
+  const utcDate = new Date(utcMs);
+  const parts = new Intl.DateTimeFormat("en-US", {
+    timeZone,
+    year: "numeric",
+    month: "2-digit",
+    day: "2-digit",
+    hour: "2-digit",
+    minute: "2-digit",
+    second: "2-digit",
+    hour12: false,
+  }).formatToParts(utcDate);
+
+  const getNumericPart = (type: string) => {
+    const part = parts.find((candidate) => candidate.type === type);
+    return Number.parseInt(part?.value ?? "0", 10);
+  };
+
+  const localAsUtc = Date.UTC(
+    getNumericPart("year"),
+    getNumericPart("month") - 1,
+    getNumericPart("day"),
+    getNumericPart("hour"),
+    getNumericPart("minute"),
+    getNumericPart("second"),
+  );
+
+  return localAsUtc - utcMs;
+}