Function getTimezoneAbbreviation

packages/utils/src/formatting.ts:7–52

(timezone: string, date: Date = new Date())

 * @returns A simplified timezone string (e.g., "PST" instead of "America/Los_Angeles")
 */
export function getTimezoneAbbreviation(timezone: string, date: Date = new Date()): string {
  if (timezone === 'UTC') return 'UTC'

  const timezoneMap: Record<string, { standard: string; daylight: string }> = {
    'America/Los_Angeles': { standard: 'PST', daylight: 'PDT' },
    'America/Denver': { standard: 'MST', daylight: 'MDT' },
    'America/Chicago': { standard: 'CST', daylight: 'CDT' },
    'America/New_York': { standard: 'EST', daylight: 'EDT' },
    'Europe/London': { standard: 'GMT', daylight: 'BST' },
    'Europe/Paris': { standard: 'CET', daylight: 'CEST' },
    'Asia/Tokyo': { standard: 'JST', daylight: 'JST' }, // Japan doesn't use DST
    'Australia/Sydney': { standard: 'AEST', daylight: 'AEDT' },
    'Asia/Singapore': { standard: 'SGT', daylight: 'SGT' }, // Singapore doesn't use DST
  }

  if (timezone in timezoneMap) {
    const januaryDate = new Date(date.getFullYear(), 0, 1)
    const julyDate = new Date(date.getFullYear(), 6, 1)

    const januaryFormatter = new Intl.DateTimeFormat('en-US', {
      timeZone: timezone,
      timeZoneName: 'short',
    })

    const julyFormatter = new Intl.DateTimeFormat('en-US', {
      timeZone: timezone,
      timeZoneName: 'short',
    })

    const isDSTObserved = januaryFormatter.format(januaryDate) !== julyFormatter.format(julyDate)

    if (isDSTObserved) {
      const currentFormatter = new Intl.DateTimeFormat('en-US', {
        timeZone: timezone,
        timeZoneName: 'short',
      })

      const isDST = currentFormatter.format(date) !== januaryFormatter.format(januaryDate)
      return isDST ? timezoneMap[timezone].daylight : timezoneMap[timezone].standard
    }

    return timezoneMap[timezone].standard
  }

  return timezone
}

/**
 * Format a date into a human-readable format