Jetpack Compose Simple calendar

Calendar.kt

@Composable
private fun Calendar(
  modifier: Modifier = Modifier,
  date: LocalDate
) {
  val firstDate = with(date) {
    val firstOfMonth = withDayOfMonth(1)
    val firstDayOfFirstWeek = firstOfMonth.dayOfWeek.value
    firstOfMonth.minusDays(firstDayOfFirstWeek.toLong())
  }
  val daysOfWeek = DateFormatSymbols().shortWeekdays.drop(1).run { 
    if (!isSundayFirstDayOfWeek()) this.rotateLeft(1) else this
  }

  Column(modifier = modifier.fillMaxWidth()) {
    Row(modifier = Modifier
      .fillMaxWidth()
      .padding(bottom = AppTheme.dimens.paddingSmall)) {
      daysOfWeek.forEach { dayOfWeek ->
        Text(
          text = dayOfWeek,
          modifier = Modifier.weight(1f),
          textAlign = TextAlign.Center,
          maxLines = 1,
          style = AppTheme.typography.caption
        )
      }
    }
    LazyVerticalGrid(columns = GridCells.Fixed(count = DAYS_IN_A_WEEK)) {
      items(DAYS_IN_A_WEEK * 6) { index -> // 6 rows
        val day = firstDate.plusDays(index.toLong()).run {
          if (!isSundayFirstDayOfWeek()) this.plusDays(1) else this
        }
        val isInCurrentMonth = day.month == date.month
        Text(
          text = day.dayOfMonth.toString(),
          textAlign = TextAlign.Center,
          color = when {
            day.isToday() -> AppTheme.colors.primary
            isInCurrentMonth -> Color.Unspecified
            else -> AppTheme.colors.outline
          },
          fontWeight = if (day.isToday()) FontWeight.Bold else null,
          style = AppTheme.typography.caption
        )
      }
    }
  }
}

private const val DAYS_IN_A_WEEK = 7

private fun isSundayFirstDayOfWeek(): Boolean = WeekFields.of(Locale.getDefault()).firstDayOfWeek.isSunday()
private fun DayOfWeek.isSunday(): Boolean = this == DayOfWeek.SUNDAY

private fun <TYPE> List<TYPE>.rotateLeft(n: Int): List<TYPE> = when {
  n.isGreaterThanZero() && n < this.size -> drop(n) + take(n)
  else -> this
}