/**
 * Get the number of days between two dates (calendar days in the viewer's
 * local timezone, not 24-hour periods). Uses local days so the bucket a
 * message falls into always agrees with the locale-formatted output
 * (time of day, weekday name, date), which is also rendered in local time.
 */
const getDaysDifference = (date1: Date, date2: Date): number => {
  const d1 = Date.UTC(date1.getFullYear(), date1.getMonth(), date1.getDate())
  const d2 = Date.UTC(date2.getFullYear(), date2.getMonth(), date2.getDate())
  return Math.floor((d2 - d1) / (1000 * 60 * 60 * 24))
}

/**
 * Format a date - shows time for today, relative time for older messages
 * (e.g., "Just now", "2:08 PM" for today, "Yesterday" for yesterday,
 * "Mon" for 2-6 days ago, "Jul 14" for older dates this year,
 * "Jul 14, 2025" for previous years)
 */
export const formatRelativeTime = (date: Date): string => {
  const now = new Date()
  const diffInSeconds = Math.floor((now.getTime() - date.getTime()) / 1000)

  // Less than 1 minute
  if (diffInSeconds < 60) {
    return 'Just now'
  }

  // Check if it's today (same calendar day)
  const daysDiff = getDaysDifference(date, now)

  // If today, show time in 12-hour format (e.g., "8:40 PM")
  if (daysDiff === 0) {
    return date.toLocaleTimeString([], {
      hour: 'numeric',
      minute: '2-digit',
      hour12: true,
    })
  }

  // Yesterday
  if (daysDiff === 1) {
    return 'Yesterday'
  }

  // 2-6 days ago - show short weekday name (e.g., "Mon")
  if (daysDiff < 7) {
    return date.toLocaleDateString(undefined, { weekday: 'short' })
  }

  // 7+ days ago, same local year - show month and day (e.g., "Jul 14")
  if (date.getFullYear() === now.getFullYear()) {
    return date.toLocaleDateString(undefined, {
      month: 'short',
      day: 'numeric',
    })
  }

  // Previous years - include the year (e.g., "Jul 14, 2025")
  return date.toLocaleDateString(undefined, {
    month: 'short',
    day: 'numeric',
    year: 'numeric',
  })
}