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)
  })
})