Function createDateWithTimezone

apps/sim/lib/workflows/schedules/utils.ts:212–306

(
  dateInput: string | Date,
  timeStr: string,
  timezone = 'UTC'
)

 * @returns Date object representing the absolute point in time (UTC).
 */
export function createDateWithTimezone(
  dateInput: string | Date,
  timeStr: string,
  timezone = 'UTC'
): Date {
  try {
    // 1. Parse the base date and target time
    const baseDate = typeof dateInput === 'string' ? new Date(dateInput) : new Date(dateInput)
    const [targetHours, targetMinutes] = parseTimeString(timeStr)

    // Ensure baseDate reflects the date part only, setting time to 00:00:00 in UTC
    // This prevents potential issues if dateInput string includes time/timezone info.
    const year = baseDate.getUTCFullYear()
    const monthIndex = baseDate.getUTCMonth() // 0-based
    const day = baseDate.getUTCDate()

    // 2. Create a tentative UTC Date object using the target date and time components
    // This assumes, for a moment, that the target H:M were meant for UTC.
    const tentativeUTCDate = new Date(
      Date.UTC(year, monthIndex, day, targetHours, targetMinutes, 0)
    )

    // 3. If the target timezone is UTC, we're done.
    if (timezone === 'UTC') {
      return tentativeUTCDate
    }

    // 4. Format the tentative UTC date into the target timezone's local time components.
    // Use 'en-CA' locale for unambiguous YYYY-MM-DD and 24-hour format.
    const formatter = new Intl.DateTimeFormat('en-CA', {
      timeZone: timezone,
      year: 'numeric',
      month: '2-digit',
      day: '2-digit',
      hour: '2-digit', // Use 2-digit for consistency
      minute: '2-digit',
      second: '2-digit',
      hourCycle: 'h23', // Use 24-hour format (00-23)
    })

    const parts = formatter.formatToParts(tentativeUTCDate)
    const getPart = (type: Intl.DateTimeFormatPartTypes) =>
      parts.find((p) => p.type === type)?.value

    const formattedYear = Number.parseInt(getPart('year') || '0', 10)
    const formattedMonth = Number.parseInt(getPart('month') || '0', 10) // 1-based
    const formattedDay = Number.parseInt(getPart('day') || '0', 10)
    const formattedHour = Number.parseInt(getPart('hour') || '0', 10)
    const formattedMinute = Number.parseInt(getPart('minute') || '0', 10)

    // Create a Date object representing the local time *in the target timezone*
    // when the tentative UTC date occurs.
    // Note: month needs to be adjusted back to 0-based for Date.UTC()
    const actualLocalTimeInTargetZone = Date.UTC(
      formattedYear,
      formattedMonth - 1,
      formattedDay,
      formattedHour,