Add scheduled invoice delivery

packages/domain/src/time-zone.ts

@@ -0,0 +1,44 @@
+const FALLBACK_TIME_ZONE = "UTC";
+
+export function isValidTimeZone(value: string): boolean {
+  if (!value.trim()) return false;
+  try {
+    new Intl.DateTimeFormat("en-US", { timeZone: value }).format(0);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+export function getLocalTimeZone(): string {
+  const resolved = Intl.DateTimeFormat().resolvedOptions().timeZone;
+  return resolved && isValidTimeZone(resolved) ? resolved : FALLBACK_TIME_ZONE;
+}
+
+export function formatZonedDateTime(
+  value: Date | string | number,
+  timeZone = getLocalTimeZone(),
+  options: Intl.DateTimeFormatOptions = {},
+): string {
+  const date = value instanceof Date ? value : new Date(value);
+  if (Number.isNaN(date.getTime())) return "Invalid date";
+
+  return new Intl.DateTimeFormat("en-US", {
+    dateStyle: "medium",
+    timeStyle: "short",
+    ...options,
+    timeZone: isValidTimeZone(timeZone) ? timeZone : FALLBACK_TIME_ZONE,
+  }).format(date);
+}
+
+export function getDefaultScheduledSendAt(now = new Date()): Date {
+  const result = new Date(now);
+  result.setMinutes(0, 0, 0);
+  result.setHours(result.getHours() + 1);
+  return result;
+}
+
+export function toLocalDateTimeInputValue(value: Date): string {
+  const pad = (part: number) => String(part).padStart(2, "0");
+  return `${value.getFullYear()}-${pad(value.getMonth() + 1)}-${pad(value.getDate())}T${pad(value.getHours())}:${pad(value.getMinutes())}`;
+}