New apps Added

custom_components/maintenance_supporter/frontend-src/helpers/interval.ts

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+/**
+ * Unit-aware interval math (issue #59) for the frontend's progress bars and
+ * calendar projection stepping. Uses an AVERAGE day-span per unit (below), an
+ * intentional approximation — the backend `helpers/dates.add_interval` is
+ * calendar-exact (Jan+1mo = 31 days), so display-side spans can differ by a day
+ * or two. Cosmetic only. Pure functions — unit-tested in interval.test.ts.
+ */
+
+/** Approximate (average) days per interval unit — mean Gregorian month / Julian
+ *  year. NOT calendar-exact; see the module note above. */
+export const UNIT_DAYS: Record<string, number> = {
+  days: 1,
+  weeks: 7,
+  months: 30.4368,
+  years: 365.25,
+};
+
+/** Approximate length of `intervalDays` of `unit` in days; 0 when no interval. */
+export function intervalSpanDays(
+  intervalDays: number | null | undefined,
+  unit?: string | null,
+): number {
+  if (!intervalDays || intervalDays <= 0) return 0;
+  return intervalDays * (UNIT_DAYS[unit || "days"] ?? 1);
+}
+
+/**
+ * Progress through the current cycle, unit-aware.
+ * Returns a clamped 0–100 % plus `overflow` (raw % > 100, i.e. past due).
+ * Falls back to {0, false} when there is no usable interval/countdown.
+ */
+export function daysProgress(
+  intervalDays: number | null | undefined,
+  daysUntilDue: number | null | undefined,
+  unit?: string | null,
+): { pct: number; overflow: boolean } {
+  const span = intervalSpanDays(intervalDays, unit);
+  if (span <= 0 || daysUntilDue == null) return { pct: 0, overflow: false };
+  const raw = ((span - daysUntilDue) / span) * 100;
+  return { pct: Math.max(0, Math.min(100, raw)), overflow: raw > 100 };
+}