Timezone related functions

index.ts

import {
  fromUnixTime,
  format,
} from "date-fns"

/**
 * Checks if a timezone string is valid or not
 *
 * We do this to catch typos.
 *
 * Source: https://stackoverflow.com/a/44118363/3015595
 **/
export function isValidTimezone(tz: string) {
  if (!tz) {
    console.error(`No timezone provided: ${tz}`)
    return false
  }

  if (!Intl || !Intl.DateTimeFormat().resolvedOptions().timeZone) {
    throw "Time zones are not available in this environment"
  }

  try {
    Intl.DateTimeFormat(undefined, { timeZone: tz })
    return true
  } catch (e) {
    console.info(`Invalid timezone: ${tz}`)
    return false
  }
}

/**
 * Gets the date from the unix timestamp
 * Returns null if no date
 **/
export function getDateFromUnixTimestamp(date: number | undefined) {
  if (!date) {
    return null
  }

  return fromUnixTime(date)
}

declare const _date: unique symbol
export type DateInTimezone = Date & { readonly [_date]: Date }

// Source: https://stackoverflow.com/a/54127122/3015595
export function convertTZ(
  date: Date | string,
  tzString: string
): DateInTimezone {
  return new Date(
    (typeof date === "string" ? new Date(date) : date).toLocaleString("en-US", {
      timeZone: tzString,
    })
  ) as DateInTimezone
}

export function isSameDay(messageDate: Date, expectedDate: Date) {
  return messageDate.getDate() === expectedDate.getDate()
}