fix(billing): compute plan expiry with Jalali months

Server/plugin/support charges used Gregorian Date#setMonth, so 3 months from 1405/06/01 became 1405/09/02. Now add N Jalali months minus one day (1405/08/30).

src/common/iran-time.util.ts

@@ -1,5 +1,7 @@
 /** Shared Iran timezone helpers for SuperAdmin API. */
 
+import { toGregorian, jalaaliMonthLength } from 'jalaali-js';
+
 export const IRAN_TZ = 'Asia/Tehran';
 
 /** Gregorian YYYY-MM-DD for the calendar day in Asia/Tehran. */
@@ -38,3 +40,71 @@ export function iranDaysUntil(expiresAt: Date, now: Date = new Date()): number {
   const end = Date.parse(`${iranYmd(expiresAt)}T12:00:00+03:30`);
   return Math.round((end - start) / 86_400_000);
 }
+
+export type IranJalaliYmd = { year: number; month: number; day: number };
+
+/** Jalali Y/M/D for a Date in Asia/Tehran. */
+export function iranJalaliParts(date: Date): IranJalaliYmd {
+  const parts = new Intl.DateTimeFormat('en-u-ca-persian', {
+    timeZone: IRAN_TZ,
+    year: 'numeric',
+    month: 'numeric',
+    day: 'numeric',
+  }).formatToParts(date);
+
+  const num = (type: Intl.DateTimeFormatPartTypes) => {
+    const raw = parts.find((p) => p.type === type)?.value ?? '';
+    const n = Number(raw);
+    if (!Number.isFinite(n)) {
+      throw new Error(`Cannot read Jalali ${type} from ${date.toISOString()}`);
+    }
+    return n;
+  };
+
+  return { year: num('year'), month: num('month'), day: num('day') };
+}
+
+/** Noon Iran (+03:30) for a Jalali calendar day. */
+export function iranDateFromJalali(year: number, month: number, day: number): Date {
+  const g = toGregorian(year, month, day);
+  const iso = `${pad2(g.gy)}-${pad2(g.gm)}-${pad2(g.gd)}T12:00:00+03:30`;
+  const d = new Date(iso);
+  if (Number.isNaN(d.getTime())) {
+    throw new Error(`Invalid Jalali date ${year}/${month}/${day}`);
+  }
+  return d;
+}
+
+/** Add calendar days on the Iran civil day (noon Tehran). */
+export function addIranDays(from: Date, days: number): Date {
+  const ymd = iranYmd(from);
+  const base = Date.parse(`${ymd}T12:00:00+03:30`);
+  return new Date(base + days * 86_400_000);
+}
+
+/**
+ * Add Jalali months (same day-of-month, clamped to month length).
+ * Example: 1405/06/01 + 3 → 1405/09/01.
+ */
+export function addIranMonths(from: Date, months: number): Date {
+  const { year, month, day } = iranJalaliParts(from);
+  const total = year * 12 + (month - 1) + months;
+  const nextYear = Math.floor(total / 12);
+  const nextMonth = (total % 12) + 1;
+  const maxDay = jalaaliMonthLength(nextYear, nextMonth);
+  const nextDay = Math.min(day, maxDay);
+  return iranDateFromJalali(nextYear, nextMonth, nextDay);
+}
+
+/**
+ * Plan expiry for server / plugin / support charges.
+ * Start day + N Jalali months, then minus 1 day (last inclusive day of the period).
+ * Example: 1405/06/01 + 3 months → expires 1405/08/30.
+ */
+export function addIranPlanExpiry(from: Date, months: number): Date {
+  return addIranDays(addIranMonths(from, months), -1);
+}
+
+function pad2(n: number) {
+  return String(n).padStart(2, '0');
+}