Add UTC-based date helpers for period calculations

desktop/src/lib/dates.ts

@@ -0,0 +1,50 @@
+const DAY_NAMES = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat']
+const MONTH_NAMES = [
+  'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
+  'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec',
+]
+
+function pad2(n: number): string {
+  return n < 10 ? `0${n}` : String(n)
+}
+
+export function todayKey(): string {
+  return formatDateKey(new Date())
+}
+
+export function formatDateKey(d: Date): string {
+  return `${d.getUTCFullYear()}-${pad2(d.getUTCMonth() + 1)}-${pad2(d.getUTCDate())}`
+}
+
+export function addDays(d: Date, n: number): Date {
+  const r = new Date(d.getTime())
+  r.setUTCDate(r.getUTCDate() + n)
+  return r
+}
+
+export function startOfDay(d: Date): Date {
+  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate()))
+}
+
+export function prettyDate(ymd: string): string {
+  const [y, m, d] = ymd.split('-').map(Number)
+  const dt = new Date(Date.UTC(y, m - 1, d))
+  return `${DAY_NAMES[dt.getUTCDay()]} ${MONTH_NAMES[dt.getUTCMonth()]} ${dt.getUTCDate()}`
+}
+
+export function shortDate(ymd: string): string {
+  const parts = ymd.split('-')
+  return `${parts[1]}/${parts[2]}`
+}
+
+export function firstOfMonth(d: Date): Date {
+  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), 1))
+}
+
+export function daysInMonth(d: Date): number {
+  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth() + 1, 0)).getUTCDate()
+}
+
+export function dayOfMonth(d: Date): number {
+  return d.getUTCDate()
+}