adam-acs/app/utils/schedule_window.ts

import type { ScheduleWindow } from '../domain/configuration/configuration.js'

/**
 * Checks if the current time (or provided time) falls within the schedule window.
 * Returns true if no schedule is defined (no restriction).
 *
 * Handles:
 * - IANA timezone conversion (uses the timezone to get local hour and day)
 * - Midnight-spanning windows (startHour > endHour means spans midnight)
 * - Day-of-week filtering (daysOfWeek array, 0=Sunday)
 */
export function isWithinSchedule(schedule: ScheduleWindow | undefined, now?: Date): boolean {
  if (!schedule) {
    return true
  }

  const currentTime = now ?? new Date()

  // Get the local hour and day in the schedule's timezone
  const localParts = getLocalTimeParts(currentTime, schedule.timezone)
  const localHour = localParts.hour
  const localDay = localParts.dayOfWeek // 0=Sunday

  // Check day-of-week filter
  if (schedule.daysOfWeek.length > 0 && !schedule.daysOfWeek.includes(localDay)) {
    return false
  }

  // Check time window
  const { startHour, endHour } = schedule

  if (startHour <= endHour) {
    // Normal window (e.g., 2-6 means 02:00 to 06:00)
    return localHour >= startHour && localHour < endHour
  } else {
    // Midnight-spanning window (e.g., 22-6 means 22:00 to 06:00 next day)
    return localHour >= startHour || localHour < endHour
  }
}

/**
 * Gets the local hour and day-of-week for a given Date in a specific IANA timezone.
 */
function getLocalTimeParts(
  date: Date,
  timezone: string
): { hour: number; dayOfWeek: number } {
  const formatter = new Intl.DateTimeFormat('en-US', {
    timeZone: timezone,
    hour: 'numeric',
    weekday: 'short',
    hour12: false,
  })

  const parts = formatter.formatToParts(date)

  let hour = 0
  let dayOfWeek = 0

  for (const part of parts) {
    if (part.type === 'hour') {
      // Intl may return "24" for midnight in some locales, normalize to 0
      hour = Number.parseInt(part.value, 10) % 24
    }
    if (part.type === 'weekday') {
      dayOfWeek = weekdayToNumber(part.value)
    }
  }

  return { hour, dayOfWeek }
}

/**
 * Converts a short weekday name (from Intl) to a number (0=Sunday).
 */
function weekdayToNumber(weekday: string): number {
  const map: Record<string, number> = {
    Sun: 0,
    Mon: 1,
    Tue: 2,
    Wed: 3,
    Thu: 4,
    Fri: 5,
    Sat: 6,
  }
  return map[weekday] ?? 0
}