chore: import upstream snapshot with attribution

apps/sim/lib/core/utils/timezone.test.ts

@@ -0,0 +1,123 @@
+import { describe, expect, it } from 'vitest'
+import {
+  getSupportedTimezones,
+  getTimezoneOptions,
+  wallClockNow,
+  zonedClockDate,
+  zonedWallClockToUtc,
+} from './timezone'
+
+describe('zonedWallClockToUtc', () => {
+  it('treats a UTC wall-clock as the same instant', () => {
+    expect(zonedWallClockToUtc('2026-06-15T09:00', 'UTC').toISOString()).toBe(
+      '2026-06-15T09:00:00.000Z'
+    )
+  })
+
+  it('applies a positive (east-of-UTC) offset (Asia/Kolkata, UTC+5:30)', () => {
+    expect(zonedWallClockToUtc('2026-06-15T09:00', 'Asia/Kolkata').toISOString()).toBe(
+      '2026-06-15T03:30:00.000Z'
+    )
+  })
+
+  it('honors DST: America/New_York is UTC-4 in summer, UTC-5 in winter', () => {
+    expect(zonedWallClockToUtc('2026-06-15T09:00', 'America/New_York').toISOString()).toBe(
+      '2026-06-15T13:00:00.000Z'
+    )
+    expect(zonedWallClockToUtc('2026-01-15T09:00', 'America/New_York').toISOString()).toBe(
+      '2026-01-15T14:00:00.000Z'
+    )
+  })
+
+  it('preserves seconds when present', () => {
+    expect(zonedWallClockToUtc('2026-07-01T23:59:59', 'UTC').toISOString()).toBe(
+      '2026-07-01T23:59:59.000Z'
+    )
+  })
+
+  it('resolves a wall-clock on the autumn DST fall-back day at the correct offset', () => {
+    // America/New_York falls back EDT(-4)→EST(-5) at 2026-11-01 06:00Z. A naive
+    // single-pass offset read lands these an hour early; the two-pass resolve
+    // settles on EST (-5) for these post-transition wall clocks.
+    expect(zonedWallClockToUtc('2026-11-01T02:00', 'America/New_York').toISOString()).toBe(
+      '2026-11-01T07:00:00.000Z'
+    )
+    expect(zonedWallClockToUtc('2026-11-01T05:00', 'America/New_York').toISOString()).toBe(
+      '2026-11-01T10:00:00.000Z'
+    )
+  })
+
+  it('resolves a spring-forward gap wall-clock forward by the DST shift', () => {
+    // 2026-03-08 02:00–02:59 does not exist in America/New_York (EST→EDT).
+    expect(zonedWallClockToUtc('2026-03-08T02:30', 'America/New_York').toISOString()).toBe(
+      '2026-03-08T07:30:00.000Z'
+    )
+  })
+})
+
+describe('wallClockNow', () => {
+  it('returns a naive yyyy-MM-ddTHH:mm string', () => {
+    expect(wallClockNow('UTC')).toMatch(/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}$/)
+  })
+})
+
+describe('getSupportedTimezones', () => {
+  it('always returns a non-empty list including UTC', () => {
+    const zones = getSupportedTimezones()
+    expect(zones.length).toBeGreaterThan(0)
+    expect(zones).toContain('UTC')
+  })
+})
+
+describe('getTimezoneOptions', () => {
+  it('renders every zone as "City (GMT±HH:MM)"', () => {
+    const options = getTimezoneOptions()
+    expect(options.length).toBeGreaterThan(0)
+    for (const option of options) {
+      expect(option.label).toMatch(/^.+ \(GMT[+-]\d{2}:\d{2}\)$/)
+    }
+  })
+
+  it('orders zones alphabetically by city', () => {
+    const cities = getTimezoneOptions().map((option) =>
+      option.label.replace(/ \(GMT[+-]\d{2}:\d{2}\)$/, '')
+    )
+    expect(cities).toEqual([...cities].sort((a, b) => a.localeCompare(b)))
+  })
+
+  it('uses a live DST-aware offset and a friendly city', () => {
+    const options = getTimezoneOptions()
+    expect(options.find((o) => o.value === 'UTC')?.label).toBe('UTC (GMT+00:00)')
+    // India has no DST, so this offset is stable regardless of when the test runs.
+    expect(
+      options.find((o) => o.value === 'Asia/Kolkata' || o.value === 'Asia/Calcutta')?.label
+    ).toMatch(/^(Kolkata|Calcutta) \(GMT\+05:30\)$/)
+  })
+
+  it('has no duplicate values', () => {
+    const values = getTimezoneOptions().map((o) => o.value)
+    expect(new Set(values).size).toBe(values.length)
+  })
+})
+
+describe('zonedClockDate', () => {
+  const instant = new Date('2026-06-15T13:00:00.000Z')
+
+  it('exposes the zone wall-clock through device-local fields', () => {
+    const ny = zonedClockDate(instant, 'America/New_York')
+    expect(ny.getHours()).toBe(9)
+    expect(ny.getMinutes()).toBe(0)
+    expect(ny.getDate()).toBe(15)
+  })
+
+  it('rolls the date when the zone is on the other side of midnight', () => {
+    const tokyo = zonedClockDate(instant, 'Asia/Tokyo')
+    expect(tokyo.getDate()).toBe(15)
+    expect(tokyo.getHours()).toBe(22)
+
+    const earlyUtc = new Date('2026-06-15T01:00:00.000Z')
+    const la = zonedClockDate(earlyUtc, 'America/Los_Angeles')
+    expect(la.getDate()).toBe(14)
+    expect(la.getHours()).toBe(18)
+  })
+})