DayOfWeekParser.kt

import kotlinx.datetime.DayOfWeek
import java.time.DayOfWeek.*


private val enFull = Regex("""^(mon|tues?|wed(nes)?|thurs?|fri|sat(ur)?|sun)(day|\.)?$""", RegexOption.IGNORE_CASE)

fun parseDayOfWeek(expr: String): DayOfWeek? {
  if (expr.isBlank()) return null
  val trim = expr.trim()

  trim.toIntOrNull()?.toDayOfWeek()?.let { return it }
  matchEn(trim)?.let { return it }
  matchZh(trim)?.let { return it }

  return null
}

private fun matchZh(expr: String): DayOfWeek? {
  if (expr.length == 1) {
    return expr.first().zhCharToWeek()
  }
  if (expr.length == 2 && expr.startsWith("周")) {
    expr[1].toString().toIntOrNull()?.toDayOfWeek()?.let { return it }
    expr[1].zhCharToWeek()?.let { return it }
  }
  if (expr.length == 3 && expr.startsWith("星期")) {
    expr[2].toString().toIntOrNull()?.toDayOfWeek()?.let { return it }
    expr[2].zhCharToWeek()?.let { return it }
  }
  return null
}

private fun matchEn(expr: String): DayOfWeek? {
  val full = enFull.find(expr) ?: return null
  val g1 = full.groups[1]?.value?.lowercase() ?: return null
  return when {
    g1 == "mon" -> DayOfWeek.MONDAY
    g1.startsWith("tue") -> DayOfWeek.TUESDAY
    g1.startsWith("wed") -> DayOfWeek.WEDNESDAY
    g1.startsWith("thur") -> DayOfWeek.THURSDAY
    g1 == "fri" -> DayOfWeek.FRIDAY
    g1.startsWith("sat") -> DayOfWeek.SATURDAY
    g1 == "sun" -> DayOfWeek.SUNDAY
    else -> null
  }
}

private fun Int.toDayOfWeek(): DayOfWeek? = when (this) {
  1 -> MONDAY
  2 -> TUESDAY
  3 -> WEDNESDAY
  4 -> THURSDAY
  5 -> FRIDAY
  6 -> SATURDAY
  7 -> SUNDAY
  else -> null
}

private fun Char.zhCharToWeek(): DayOfWeek? = when (this) {
  '一' -> MONDAY
  '二' -> TUESDAY
  '三' -> WEDNESDAY
  '四' -> THURSDAY
  '五' -> FRIDAY
  '六' -> SATURDAY
  '日' -> SUNDAY
  '七' -> SUNDAY
  else -> null
}

DayOfWeekParserTest.kt

import io.kotest.matchers.shouldBe
import org.junit.jupiter.api.Test
import java.time.DayOfWeek.*

class DayOfWeekParserTest {
  @Test
  fun `parse number day of week`() {
    parseDayOfWeek("1") shouldBe MONDAY
    parseDayOfWeek("2") shouldBe TUESDAY
    parseDayOfWeek("3") shouldBe WEDNESDAY
    parseDayOfWeek("4") shouldBe THURSDAY
    parseDayOfWeek("5") shouldBe FRIDAY
    parseDayOfWeek("6") shouldBe SATURDAY
    parseDayOfWeek("7") shouldBe SUNDAY
    parseDayOfWeek("8") shouldBe null
  }

  @Test
  fun `parse English full week`() {
    parseDayOfWeek("MONDAY") shouldBe MONDAY
    parseDayOfWeek("TUESDAY") shouldBe TUESDAY
    parseDayOfWeek("WEDNESDAY") shouldBe WEDNESDAY
    parseDayOfWeek("THURSDAY") shouldBe THURSDAY
    parseDayOfWeek("FRIDAY") shouldBe FRIDAY
    parseDayOfWeek("SATURDAY") shouldBe SATURDAY
    parseDayOfWeek("SUNDAY") shouldBe SUNDAY
    parseDayOfWeek("Staurn") shouldBe null

    parseDayOfWeek("Monday") shouldBe MONDAY
    parseDayOfWeek("Tuesday") shouldBe TUESDAY
    parseDayOfWeek("Wednesday") shouldBe WEDNESDAY
    parseDayOfWeek("Thursday") shouldBe THURSDAY
    parseDayOfWeek("Friday") shouldBe FRIDAY
    parseDayOfWeek("Saturday") shouldBe SATURDAY
    parseDayOfWeek("Sunday") shouldBe SUNDAY
    parseDayOfWeek("Fritm") shouldBe null

    parseDayOfWeek("monday") shouldBe MONDAY
    parseDayOfWeek("tuesday") shouldBe TUESDAY
    parseDayOfWeek("wednesday") shouldBe WEDNESDAY
    parseDayOfWeek("thursday") shouldBe THURSDAY
    parseDayOfWeek("friday") shouldBe FRIDAY
    parseDayOfWeek("saturday") shouldBe SATURDAY
    parseDayOfWeek("sunday") shouldBe SUNDAY
    parseDayOfWeek("fritm") shouldBe null
  }

  @Test
  fun `parse English abbr week`() {
    parseDayOfWeek("MON") shouldBe MONDAY
    parseDayOfWeek("TUES") shouldBe TUESDAY
    parseDayOfWeek("WEDNES") shouldBe WEDNESDAY
    parseDayOfWeek("WED") shouldBe WEDNESDAY
    parseDayOfWeek("THURS") shouldBe THURSDAY
    parseDayOfWeek("THUR") shouldBe THURSDAY
    parseDayOfWeek("FRI") shouldBe FRIDAY
    parseDayOfWeek("SATUR") shouldBe SATURDAY
    parseDayOfWeek("SAT") shouldBe SATURDAY
    parseDayOfWeek("SUN") shouldBe SUNDAY
    parseDayOfWeek("FRl") shouldBe null

    parseDayOfWeek("Mon.") shouldBe MONDAY
    parseDayOfWeek("Tues.") shouldBe TUESDAY
    parseDayOfWeek("Wednes.") shouldBe WEDNESDAY
    parseDayOfWeek("Wed.") shouldBe WEDNESDAY
    parseDayOfWeek("Thurs.") shouldBe THURSDAY
    parseDayOfWeek("Thur.") shouldBe THURSDAY
    parseDayOfWeek("Fri.") shouldBe FRIDAY
    parseDayOfWeek("Satur.") shouldBe SATURDAY
    parseDayOfWeek("Sat.") shouldBe SATURDAY
    parseDayOfWeek("Sun.") shouldBe SUNDAY
    parseDayOfWeek("Saturn.") shouldBe null

    parseDayOfWeek("mon.") shouldBe MONDAY
    parseDayOfWeek("tues.") shouldBe TUESDAY
    parseDayOfWeek("tue.") shouldBe TUESDAY
    parseDayOfWeek("wednes.") shouldBe WEDNESDAY
    parseDayOfWeek("wed.") shouldBe WEDNESDAY
    parseDayOfWeek("thurs.") shouldBe THURSDAY
    parseDayOfWeek("thur.") shouldBe THURSDAY
    parseDayOfWeek("fri.") shouldBe FRIDAY
    parseDayOfWeek("sat.") shouldBe SATURDAY
    parseDayOfWeek("sun.") shouldBe SUNDAY
    parseDayOfWeek("7hur.") shouldBe null
  }

  @Test
  fun `zh char test`() {
    parseDayOfWeek("一") shouldBe MONDAY
    parseDayOfWeek("二") shouldBe TUESDAY
    parseDayOfWeek("三") shouldBe WEDNESDAY
    parseDayOfWeek("四") shouldBe THURSDAY
    parseDayOfWeek("五") shouldBe FRIDAY
    parseDayOfWeek("六") shouldBe SATURDAY
    parseDayOfWeek("七") shouldBe SUNDAY
    parseDayOfWeek("日") shouldBe SUNDAY
    parseDayOfWeek("八") shouldBe null
  }

  @Test
  fun `zh word test`() {
    parseDayOfWeek("周一") shouldBe MONDAY
    parseDayOfWeek("周二") shouldBe TUESDAY
    parseDayOfWeek("周三") shouldBe WEDNESDAY
    parseDayOfWeek("周四") shouldBe THURSDAY
    parseDayOfWeek("周五") shouldBe FRIDAY
    parseDayOfWeek("周六") shouldBe SATURDAY
    parseDayOfWeek("周七") shouldBe SUNDAY
    parseDayOfWeek("周日") shouldBe SUNDAY
    parseDayOfWeek("周八") shouldBe null

    parseDayOfWeek("星期一") shouldBe MONDAY
    parseDayOfWeek("星期二") shouldBe TUESDAY
    parseDayOfWeek("星期三") shouldBe WEDNESDAY
    parseDayOfWeek("星期四") shouldBe THURSDAY
    parseDayOfWeek("星期五") shouldBe FRIDAY
    parseDayOfWeek("星期六") shouldBe SATURDAY
    parseDayOfWeek("星期七") shouldBe SUNDAY
    parseDayOfWeek("星期日") shouldBe SUNDAY
    parseDayOfWeek("星期八") shouldBe null

    parseDayOfWeek("星期1") shouldBe MONDAY
    parseDayOfWeek("星期2") shouldBe TUESDAY
    parseDayOfWeek("星期3") shouldBe WEDNESDAY
    parseDayOfWeek("星期4") shouldBe THURSDAY
    parseDayOfWeek("星期5") shouldBe FRIDAY
    parseDayOfWeek("星期6") shouldBe SATURDAY
    parseDayOfWeek("星期7") shouldBe SUNDAY
    parseDayOfWeek("星期8") shouldBe null

    parseDayOfWeek("周1") shouldBe MONDAY
    parseDayOfWeek("周2") shouldBe TUESDAY
    parseDayOfWeek("周3") shouldBe WEDNESDAY
    parseDayOfWeek("周4") shouldBe THURSDAY
    parseDayOfWeek("周5") shouldBe FRIDAY
    parseDayOfWeek("周6") shouldBe SATURDAY
    parseDayOfWeek("周7") shouldBe SUNDAY
    parseDayOfWeek("周8") shouldBe null
  }
}