/**
 * Utility functions for timezone-aware datetime formatting.
 */

/**
 * Format a datetime string in the user's timezone.
 *
 * @param datetime - ISO datetime string from API (in UTC)
 * @param timezone - IANA timezone string (e.g., "Europe/Bucharest")
 * @param options - Intl.DateTimeFormat options
 * @returns Formatted datetime string
 */
export const formatDateTime = (
  datetime: string,
  timezone: string = 'UTC',
  options?: Intl.DateTimeFormatOptions
): string => {
  const date = new Date(datetime)

  const defaultOptions: Intl.DateTimeFormatOptions = {
    timeZone: timezone,
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    ...options
  }

  return new Intl.DateTimeFormat('ro-RO', defaultOptions).format(date)
}

/**
 * Format date only (no time) in user's timezone.
 */
export const formatDate = (datetime: string, timezone: string = 'UTC'): string => {
  return formatDateTime(datetime, timezone, {
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: undefined,
    minute: undefined
  })
}

/**
 * Format time only in user's timezone.
 */
export const formatTime = (datetime: string, timezone: string = 'UTC'): string => {
  const date = new Date(datetime)
  return new Intl.DateTimeFormat('ro-RO', {
    timeZone: timezone,
    hour: '2-digit',
    minute: '2-digit'
  }).format(date)
}

/**
 * Format datetime with timezone abbreviation.
 */
export const formatDateTimeWithTZ = (datetime: string, timezone: string = 'UTC'): string => {
  const date = new Date(datetime)

  const formatted = new Intl.DateTimeFormat('ro-RO', {
    timeZone: timezone,
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    timeZoneName: 'short'
  }).format(date)

  return formatted
}

/**
 * Get timezone abbreviation (e.g., "EET", "EEST").
 */
export const getTimezoneAbbr = (timezone: string = 'UTC'): string => {
  const date = new Date()
  const formatted = new Intl.DateTimeFormat('en-US', {
    timeZone: timezone,
    timeZoneName: 'short'
  }).format(date)

  // Extract timezone abbreviation from formatted string
  const match = formatted.match(/,\s*(.+)/)
  return match ? match[1] : timezone.split('/').pop() || 'UTC'
}

/**
 * Convert local datetime-local input to ISO string (for API).
 * The input from datetime-local is in user's local time, so we just add seconds and Z.
 */
export const localDateTimeToISO = (localDateTime: string): string => {
  // datetime-local format: "YYYY-MM-DDTHH:mm"
  // We need to send it as is to the API (API will handle timezone conversion)
  return localDateTime + ':00'
}

/**
 * Convert ISO datetime to datetime-local format for input field.
 */
export const isoToLocalDateTime = (isoDateTime: string, timezone: string = 'UTC'): string => {
  const date = new Date(isoDateTime)

  // Get the date components in the user's timezone
  const year = date.toLocaleString('en-US', { timeZone: timezone, year: 'numeric' })
  const month = date.toLocaleString('en-US', { timeZone: timezone, month: '2-digit' })
  const day = date.toLocaleString('en-US', { timeZone: timezone, day: '2-digit' })
  const hour = date.toLocaleString('en-US', { timeZone: timezone, hour: '2-digit', hour12: false })
  const minute = date.toLocaleString('en-US', { timeZone: timezone, minute: '2-digit' })

  // Format as YYYY-MM-DDTHH:mm for datetime-local input
  return `${year}-${month}-${day}T${hour.padStart(2, '0')}:${minute}`
}