@tubular/astronomy/dist/index.min.cjs.map

Astronomical calculations for planetary positions, moon phases, eclipses, rise, transit, and set times, and more.

{"version":3,"file":"index.min.cjs","sources":["../node_modules/@tubular/time/src/common.ts","../node_modules/@tubular/time/src/calendar.ts","../node_modules/@tubular/time/src/locale-data.ts","../node_modules/@tubular/time/src/timezone.ts","../node_modules/@tubular/time/src/ut-converter.ts","../node_modules/@tubular/time/src/date-time.ts","../node_modules/@tubular/time/src/format-parse.ts","../node_modules/@tubular/time/src/timezone-small.ts","../node_modules/@tubular/time/src/timezone-large.ts","../node_modules/@tubular/time/src/timezone-large-alt.ts","../node_modules/@tubular/time/src/index.ts","../src/astro-constants.ts","../src/ecliptic.ts","../src/additional-orbiting-objects.ts","../src/astronomy-util.ts","../src/meeus-moon.ts","../src/pluto.ts","../src/vsop87-planets.ts","../src/solar-system.ts","../src/planetary-moons.ts","../src/jupiter-moons.ts","../src/event-finder.ts","../node_modules/@tubular/array-buffer-reader/src/array-buffer-reader.ts","../src/jupiter-info.ts","../src/saturn-moons.ts","../src/sky-observer.ts","../src/star-catalog.ts","../src/index.ts"],"sourcesContent":["import { floor } from '@tubular/math';\nimport { convertDigitsToAscii, isNumber, toNumber } from '@tubular/util';\n\nexport const MIN_YEAR = -271820;\nexport const MAX_YEAR =  275759;\n\nexport const MINUTE_MSEC =     60_000;\nexport const HOUR_MSEC   =  3_600_000;\nexport const DAY_MSEC    = 86_400_000;\nexport const DAY_SEC     =     86_400;\nexport const DAY_MINUTES =       1440;\n\nexport const UNIX_TIME_ZERO_AS_JULIAN_DAY = 2440587.5;\nexport const JD_J2000 = 2451545.0; // Julian date for the J2000.0 epoch.\nexport const DELTA_TDT_SEC = 32.184;\nexport const DELTA_TDT_MSEC = 32184;\nexport const DELTA_TDT_DAYS = DELTA_TDT_SEC / DAY_SEC;\nexport const DELTA_MJD = 2400000.5;\n\nexport const enEras = ['BC', 'AD', 'Before Christ', 'Anno Domini'];\nexport const enMonths = ['January', 'February', 'March', 'April', 'May', 'June',\n                         'July', 'August', 'September', 'October', 'November', 'December'];\nexport const enMonthsShort = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'];\nexport const enWeekdays = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];\nexport const enWeekdaysShort = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];\nexport const enWeekdaysMin = ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa'];\n\n// Hacks to eliminate circular dependencies.\ntype Formatter = (dt: any, fmt: string, localeOverride?: string | string[]) => string;\nexport let formatter: Formatter;\nexport const setFormatter = (fmt: Formatter): any => formatter = fmt;\n\ntype DeltaTUpdater = (post2019values?: number[], lastKnownLeapSecond?: YMDDate) => void;\nexport let deltaTUpdater: DeltaTUpdater;\nexport const setDeltaTUpdater = (dtu: DeltaTUpdater): any => deltaTUpdater = dtu;\n\n/**\n * Specifies a calendar date by year, month, and day. Optionally provides day number and boolean flag indicating Julian\n * or Gregorian.\n */\nexport interface YMDDate {\n  /** Year as signed integer (0 = 1 BCE, -1 = 2 BCE, etc.). */\n  y?: number;\n  year?: number;\n  /** Quarter as 1-4. */\n  q?: number;\n  quarter?: number;\n  /** Month as 1-12. */\n  m?: number;\n  month?: number;\n  /** Day of month. */\n  d?: number;\n  day?: number;\n  /** Day of week as 0-6 for Sunday-Saturday. */\n  dow?: number;\n  dayOfWeek?: number;\n  /** Day of week month index, 1-5, e.g. 2 for 2nd Tuesday of the month. */\n  dowmi?: number;\n  dayOfWeekMonthIndex?: number;\n  /** Day of year. */\n  dy?: number;\n  dayOfYear?: number;\n  /** Day number where 1970-01-01 = 0. */\n  n?: number;\n  epochDay?: number;\n  /** true if this is a Julian calendar date, false for Gregorian. */\n  j?: boolean;\n  isJulian?: boolean;\n  /** ISO year for week of year. */\n  yw?: number;\n  yearByWeek?: number;\n  /** ISO week of year. */\n  w?: number;\n  week?: number;\n  /** ISO day or week. */\n  dw?: number;\n  dayByWeek?: number;\n  /** Locale year for week of year. */\n  ywl?: number;\n  yearByWeekLocale?: number;\n  /** Locale week of year. */\n  wl?: number;\n  weekLocale?: number;\n  /** Locale day or week. */\n  dwl?: number;\n  dayByWeekLocale?: number;\n  /** Error, if any. */\n  error?: string;\n}\n\nexport interface DateAndTime extends YMDDate {\n  hrs?: number;\n  hour?: number;\n  min?: number;\n  minute?: number;\n  sec?: number;\n  second?: number;\n  millis?: number;\n  utcOffset?: number;\n  dstOffset?: number;\n  occurrence?: number;\n  deltaTai?: number;\n\n  /** Julian days, ephemeris. */\n  jde?: number;\n  /** Modified Julian days, ephemeris. */\n  mjde?: number;\n  /** Julian days, UT. */\n  jdu?: number;\n  /** Modified Julian days, UT. */\n  mjdu?: number;\n}\n\nconst altFields = [\n  ['y', 'year'], ['q', 'quarter'], ['m', 'month'], ['d', 'day'], ['dow', 'dayOfWeek'], ['dowmi', 'dayOfWeekMonthIndex'],\n  ['dy', 'dayOfYear'], ['n', 'epochDay'],\n  ['j', 'isJulian'], ['yw', 'yearByWeek'], ['w', 'week'], ['dw', 'dayByWeek'],\n  ['ywl', 'yearByWeekLocale'], ['wl', 'weekLocale'], ['dwl', 'dayByWeekLocale'],\n  ['hrs', 'hour'], ['min', 'minute'], ['sec', 'second']\n];\n\nconst fieldOrder = [\n  'y', 'q', 'm', 'd', 'dow', 'dowmi', 'dy', 'n', 'j',\n  'year', 'quarter', 'month', 'day', 'dayOfWeek', 'dayOfWeekMonthIndex', 'dayOfYear', 'epochDay', 'isJulian',\n  'yw', 'w', 'dw',\n  'yearByWeek', 'week', 'dayByWeek',\n  'ywl', 'wl', 'dwl',\n  'yearByWeekLocale', 'weekLocale', 'dayByWeekLocale',\n  'hrs', 'min', 'sec',\n  'hour', 'minute', 'second', 'millis',\n  'utcOffset', 'dstOffset', 'occurrence', 'deltaTai',\n  'jde', 'mjde', 'jdu', 'mjdu',\n  'error'\n];\n\nexport function syncDateAndTime<T extends YMDDate | DateAndTime>(obj: T): T {\n  for (const [key1, key2] of altFields) {\n    if (obj.hasOwnProperty(key1))\n      obj[key2] = obj[key1];\n    else if (obj.hasOwnProperty(key2))\n      obj[key1] = obj[key2];\n  }\n\n  return obj;\n}\n\nexport function purgeAliasFields<T extends YMDDate | DateAndTime>(obj: T, keepLongForm = false): T {\n  for (const [short, long] of altFields)\n    delete obj[keepLongForm ? short : long];\n\n  return obj;\n}\n\nconst minimalKeys =\n  new Set(['y', 'year', 'm', 'month', 'd', 'day', 'hrs', 'hour', 'min', 'minute', 'sec', 'second', 'millis']);\n\nexport function minimizeFields<T extends YMDDate | DateAndTime>(obj: T): T {\n  Object.keys(obj).forEach(key => {\n    if (!minimalKeys.has(key))\n      delete obj[key];\n  });\n\n  return obj;\n}\n\nexport function orderFields<T extends YMDDate | DateAndTime>(obj: T): T {\n  for (const key of fieldOrder) {\n    const value = obj[key];\n\n    delete obj[key];\n\n    if (value != null)\n      obj[key] = value;\n  }\n\n  return obj;\n}\n\nexport function validateDateAndTime(obj: YMDDate | DateAndTime): void {\n  const dt = obj as DateAndTime;\n\n  Object.keys(obj).forEach(key => {\n    if (key !== 'j' && key !== 'isJulian') {\n      const value = obj[key];\n\n      if (value != null) {\n        if (/^(m?(deltaTai|jde|jdu))$/.test(key)) {\n          if (!isNumber(value))\n            throw new Error(`${key} must be a numeric value (${value})`);\n        }\n        else if (!isNumber(value) || value !== floor(value))\n          throw new Error(`${key} must be an integer value (${value})`);\n      }\n    }\n  });\n\n  if (obj.y == null && obj.year == null && obj.yw == null && obj.yearByWeek == null &&\n      obj.ywl == null && obj.yearByWeekLocale == null && obj.n == null && obj.epochDay == null &&\n      dt.hrs == null && dt.hour == null && dt.jde == null && dt.mjde == null && dt.jdu == null && dt.mjdu == null)\n    throw new Error('A year value, an epoch day, an hour value, or a Julian date value must be specified');\n}\n\nconst invalidDateTime = new Error('Invalid ISO date/time');\n\nexport function parseISODateTime(date: string, allowLeapSecond = false): DateAndTime {\n  date = date.trim();\n\n  let time: DateAndTime;\n  let $ = /^([-+]?\\d+)-(\\d{1,2}(?=\\D|$))(?:-(\\d{1,2}))?/.exec(date);\n\n  if ($ || ($ = /^([-+]?\\d{1,5}(?=[^-+:.Ww\\d]|$))/.exec(date)) || ($ = /^([-+]?\\d{4,})(\\d\\d)(\\d\\d)/.exec(date)))\n    time = { y: toNumber($[1]), m: Number($[2] ?? 1), d: Number($[3] ?? 1) };\n  else if (($ = /^([-+]?\\d+)-(W)(\\d+)(?:-(\\d))?/i.exec(date)) || ($ = /^([-+]?\\d{4,})(W)(\\d\\d)(\\d)?/i.exec(date))) {\n    if ($[2] === 'W')\n      time = { yw: toNumber($[1]), w: Number($[3]), dw: Number($[4] ?? 1) };\n    else\n      time = { ywl: toNumber($[1]), wl: Number($[3]), dwl: Number($[4] ?? 1) };\n  }\n  else if (($ = /^(\\d+)-(\\d+)/.exec(date)) || ($ = /^(\\d{4})(\\d{3})/.exec(date))) {\n    time = { y: toNumber($[1]), dy: Number($[2]) };\n  }\n  else {\n    $ = [''] as RegExpExecArray; // Keep trying to parse as time-only string\n    time = {};\n  }\n\n  date = date.substr($[0].length).trim().replace(/^T\\s*/i, '');\n\n  if (!date)\n    Object.assign(time, { hrs: 0, min: 0, sec: 0 });\n  else if (($ = /^(\\d{1,2})(?::(\\d{1,2}))(?::(?:(\\d{1,2})(?:[.,](\\d+))?))?(?=\\D|$)/.exec(date)) ||\n           ($ = /^(\\d\\d)(?:(\\d\\d)(?:(\\d\\d)(?:[.,](\\d+))?)?)?(?=\\D|$)/.exec(date))) {\n    Object.assign(time, {\n      hrs: Number($[1]), min: Number($[2] ?? 0),\n      sec: Number($[3] ?? 0), millis: Number(($[4] ?? '0').padEnd(3, '0').substr(0, 3)) });\n\n    if ($[4] == null && time.millis === 0)\n      delete time.millis;\n\n    date = date.substr($[0].length).trim();\n  }\n\n  $ = /^([-+]\\d\\d(\\d{4}|\\d\\d|:\\d\\d(:\\d\\d)?)?)$/i.exec(date);\n\n  if ($)\n    time.utcOffset = parseTimeOffset($[1]);\n  else if (date)\n    throw invalidDateTime;\n\n  const y = time.y ?? time.yw ?? time.ywl ?? 0;\n  const m = time.m ?? 1;\n  const w = time.w ?? time.wl ?? 1;\n  const d = time.d ?? 1;\n\n  if (y < MIN_YEAR || y > MAX_YEAR)\n    throw new Error(`Invalid year: ${y}`);\n  else if (m > 13)\n    throw new Error(`Invalid month: ${m}`);\n  else if (w > 53)\n    throw new Error(`Invalid week: ${w}`);\n  else if (d > 32)\n    throw new Error(`Invalid day of month: ${d}`);\n  else if (time.hrs > 23)\n    throw new Error(`Invalid hour: ${time.hrs}`);\n  else if (time.min > 59)\n    throw new Error(`Invalid minute: ${time.min}`);\n  else if (time.sec > 59 + +allowLeapSecond)\n    throw new Error(`Invalid second: ${time.sec}`);\n  else if (time.utcOffset && (time.utcOffset < -57600 || time.utcOffset > 57600))\n    throw new Error(`Invalid UTC offset: ${$[1]}`);\n\n  if (time.m != null)\n    time.q = floor((time.m - 1) / 3) + 1;\n\n  return syncDateAndTime(time);\n}\n\nexport function parseTimeOffset(offset: string, roundToMinutes = false): number {\n  let sign = 1;\n\n  if (offset.startsWith('-')) {\n    sign = -1;\n    offset = offset.substr(1);\n  }\n  else if (offset.startsWith('+'))\n    offset = offset.substr(1);\n\n  const parts = offset.includes(':') ?\n    offset.split(':') :\n    offset.match(/../g) ?? ['0'];\n  let offsetSeconds = 60 * (60 * Number(parts[0]) + Number(parts[1] ?? 0));\n\n  if (parts[2]) {\n    const seconds = Number(parts[2]);\n\n    if (roundToMinutes)\n      offsetSeconds += (seconds < 30 ? 0 : 60);\n    else\n      offsetSeconds += seconds;\n  }\n\n  return sign * offsetSeconds;\n}\n\nexport function getDatePart(format: Intl.DateTimeFormat, date: number, partName: string): string;\nexport function getDatePart(fields: Intl.DateTimeFormatPart[], partName: string): string;\nexport function getDatePart(source: Intl.DateTimeFormat | Intl.DateTimeFormatPart[],\n                            dateOrPart: number | string, partName?: string): string {\n  const parts = (source instanceof Intl.DateTimeFormat ? source.formatToParts(dateOrPart as number) : source);\n  partName = partName ?? dateOrPart as string;\n  const part = parts.find(part => part.type === partName);\n\n  if (part)\n    return part.value;\n  else\n    return '???';\n}\n\nexport function getDateValue(format: Intl.DateTimeFormat, date: number, partName: string): number;\nexport function getDateValue(fields: Intl.DateTimeFormatPart[], partName: string): number;\nexport function getDateValue(source: Intl.DateTimeFormat | Intl.DateTimeFormatPart[],\n                            dateOrPart: number | string, partName?: string): number {\n  return toNumber(convertDigitsToAscii(getDatePart(source as any, dateOrPart as any, partName)));\n}\n","import { div_rd, div_tt0, floor, mod } from '@tubular/math';\nimport { isArray, isNumber, isObject, isString, padLeft } from '@tubular/util';\nimport { DateAndTime, DAY_MSEC, HOUR_MSEC, MINUTE_MSEC, syncDateAndTime, YMDDate } from './common';\n\nexport enum CalendarType { PURE_GREGORIAN, PURE_JULIAN }\nexport const GREGORIAN_CHANGE_MIN_YEAR = 300;\nexport const GREGORIAN_CHANGE_MAX_YEAR = 3900;\n\nexport const SUNDAY    = 0;\nexport const MONDAY    = 1;\nexport const TUESDAY   = 2;\nexport const WEDNESDAY = 3;\nexport const THURSDAY  = 4;\nexport const FRIDAY    = 5;\nexport const SATURDAY  = 6;\n\n// noinspection JSUnusedGlobalSymbols\nexport enum DayOfWeek { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }\n// noinspection JSUnusedGlobalSymbols\nexport enum Month { JANUARY = 1, FEBRUARY, MARCH, APRIL, MAY, JUNE, JULY, AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER }\n\n/**\n * Constant for indicating the last occurrence of a particular day of the week (e.g. the last Tuesday) of a given month.\n */\nexport const LAST = 6;\n\n/** @hidden */\nconst DISTANT_YEAR_PAST = -9999999;\n/** @hidden */\nconst DISTANT_YEAR_FUTURE = 9999999;\nconst FIRST_GREGORIAN_DAY_SGC = -141427; // 1582-10-15\n\n/**\n * Type allowing a year alone to be specified, a full date as a [[YMDDate]], or a full date as a numeric array in the\n * form [year, month, date].\n */\nexport type YearOrDate = number | YMDDate | number[];\n/**\n * Type for specifying the date when a calendar switches from Julian to Gregorian, or if the calendar is purely Julian\n * or purely Gregorian. As a string, the letters 'J' or 'G' can be used.\n */\nexport type GregorianChange = YMDDate | CalendarType | string | number[];\n\nfunction hasYearField(obj: any): boolean {\n  return obj.y != null || obj.yw != null || obj.ywl != null ||\n         obj.year != null || obj.yearByWeek != null || obj.yearByWeekLocale != null;\n}\n\n/** @hidden */\nexport function isGregorianType(obj: any): obj is GregorianChange {\n  return isNumber(obj) ||\n         (isArray(obj) && obj.length === 3 && obj.findIndex(n => !isNumber(n)) < 0) ||\n         (isString(obj) && /^(g|j|(\\d+)-(\\d+)-(\\d+)|\\d{8})$/i.test(obj)) ||\n         (isObject(obj) && hasYearField(obj));\n}\n\nconst lockError = new Error('This DateTime instance is locked and immutable');\n\n/** @hidden */\nexport function handleVariableDateArgs(yearOrDate: YearOrDate, month?: number, day?: number,\n                                       calendar?: Calendar | 'g' | 'j', ignoreJ = false): number[] {\n  let n: number;\n  let j: boolean;\n  let year: number;\n  let dy: number;\n\n  if (isNumber(yearOrDate))\n    year = yearOrDate;\n  else if (isArray(yearOrDate) && yearOrDate.length >= 3 && isNumber(yearOrDate[0]))\n    return yearOrDate;\n  else if (isArray(yearOrDate)) {\n    year = yearOrDate[0];\n    month = yearOrDate[1];\n  }\n  else if (isObject(yearOrDate)) {\n    syncDateAndTime(yearOrDate);\n    n     = yearOrDate.n;\n    j     = ignoreJ ? undefined : yearOrDate.j;\n    year  = yearOrDate.y;\n    dy    = yearOrDate.dy;\n    month = yearOrDate.m;\n    day   = yearOrDate.d;\n  }\n\n  if (year != null) {\n    if (month == null && day == null && dy != null) {\n      if (calendar === 'g' || j === false)\n        return handleVariableDateArgs(getDateFromDayNumberGregorian(getDayNumberGregorian(year, 1, 0) + dy));\n      else if (calendar === 'j' || j === true)\n        return handleVariableDateArgs(getDateFromDayNumberJulian(getDayNumberJulian(year, 1, 0) + dy));\n      else\n        return handleVariableDateArgs(getDateFromDayNumber_SGC(getDayNumber_SGC(year, 1, 0) + dy));\n    }\n    else {\n      month = month ?? 1;\n      day = day ?? 1;\n    }\n  }\n  else if (n != null) {\n    if (calendar === 'g' || j === false)\n      return handleVariableDateArgs(getDateFromDayNumberGregorian(n));\n    else if (calendar === 'j' || j === true)\n      return handleVariableDateArgs(getDateFromDayNumberJulian(n));\n    else if (calendar) {\n      ++(calendar as any).computeWeekValues;\n      const ymd = handleVariableDateArgs(calendar.getDateFromDayNumber(n));\n      --(calendar as any).computeWeekValues;\n      return ymd;\n    }\n    else\n      return handleVariableDateArgs(getDateFromDayNumber_SGC(n));\n  }\n  else\n    throw new Error('Calendar: Invalid date arguments');\n\n  return [year, month, day, j == null ? -1 : +j];\n}\n\n/**\n * Determine if a given date falls during the Julian calendar or the Gregorian calendar, given the standard\n * Gregorian change date of 1582-10-15.\n *\n * @param {YearOrDate} yearOrDate\n * @param {number} month\n * @param {number} day\n * @returns True if the date is Julian.\n */\nexport function isJulianCalendarDate_SGC(yearOrDate: YearOrDate, month?: number, day?: number): boolean {\n  let year: number, j: number; [year, month, day, j] = handleVariableDateArgs(yearOrDate, month, day);\n\n  return (j === 1 || year < 1582 || (year === 1582 && (month < 10 || month === 10 && day < 15)));\n}\n\n/**\n * Gets the day number for the given date, relative to 1970-01-01, using the standard Gregorian change date 1582-10-15.\n * @param yearOrDate\n * @param month\n * @param day\n * @returns Day number.\n */\nexport function getDayNumber_SGC(yearOrDate: YearOrDate, month?: number, day?: number): number {\n  let year: number, j: number; [year, month, day, j] = handleVariableDateArgs(yearOrDate, month, day);\n\n  while (month <  1) { month += 12; --year; }\n  while (month > 12) { month -= 12; ++year; }\n\n  if (j === 1 || (j !== 0 && isJulianCalendarDate_SGC(year, month, day)))\n    return getDayNumberJulian(year, month, day);\n  else\n    return getDayNumberGregorian(year, month, day);\n}\n\n/**\n * Gets the day number for the given Gregorian calendar date, relative to 1970-01-01.\n * @param yearOrDate\n * @param month\n * @param day\n * @returns Day number.\n */\nexport function getDayNumberGregorian(yearOrDate: YearOrDate, month?: number, day?: number): number {\n  let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, 'g');\n\n  while (month <  1) { month += 12; --year; }\n  while (month > 12) { month -= 12; ++year; }\n\n  return 367 * year - div_rd(7 * (year + div_tt0(month + 9, 12)), 4) - div_tt0(3 * (div_tt0(year + div_tt0(month - 9, 7), 100) + 1), 4) +\n    div_tt0(275 * month, 9) + day - 719559;\n}\n\n/**\n * Gets the day number for the given Julian calendar date, relative to 1970-01-01 Gregorian.\n * @param yearOrDate\n * @param month\n * @param day\n * @returns Day number.\n */\nexport function getDayNumberJulian(yearOrDate: YearOrDate, month?: number, day?: number): number {\n  let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, 'j');\n\n  while (month <  1) { month += 12; --year; }\n  while (month > 12) { month -= 12; ++year; }\n\n  return 367 * year - div_rd(7 * (year + div_tt0(month + 9, 12)), 4) + div_tt0(275 * month, 9) + day - 719561;\n}\n\n// noinspection JSUnusedLocalSymbols\n/**\n * Always returns 1. This function exists only to parallel getFirstDateInMonth, which isn't always 1 when the\n * Gregorian change date is not fixed.\n * @returns First date of calendar month.\n */\nexport function getFirstDateInMonth_SGC(_year: number, _month: number): number {\n  return 1;\n}\n\n/**\n * The last date of the given calendar month, using the standard Gregorian change date 1582-10-15, e.g. 31 for\n * any January, 28 for non-leap-year February, 29 for leap-year February, etc.\n * @param year\n * @param month\n * @returns Last date of calendar month.\n */\nexport function getLastDateInMonth_SGC(year: number, month: number): number {\n  if (month === 9 || month === 4 || month === 6 || month === 11)\n    return 30;\n  else if (month !== 2)\n    return 31; // Works for pseudo-months 0 and 13 as well.\n  else if (year % 4 === 0 && (year < 1583 || year % 100 !== 0 || year % 400 === 0))\n    return 29;\n  else\n    return 28;\n}\n\n/**\n * The last date of the given Gregorian calendar month.\n * @param year\n * @param month\n * @returns Last date of calendar month.\n */\nexport function getLastDateInMonthGregorian(year: number, month: number): number {\n  if (month === 9 || month === 4 || month === 6 || month === 11)\n    return 30;\n  else if (month !== 2)\n    return 31; // Works for pseudo-months 0 and 13 as well.\n  else if (year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0))\n    return 29;\n  else\n    return 28;\n}\n\n/**\n * The last date of the given Gregorian calendar month.\n * @param year\n * @param month\n * @returns Last date of calendar month.\n */\nexport function getLastDateInMonthJulian(year: number, month: number): number {\n  if (month === 9 || month === 4 || month === 6 || month === 11)\n    return 30;\n  else if (month !== 2)\n    return 31; // Works for pseudo-months 0 and 13 as well.\n  else if (year % 4 === 0)\n    return 29;\n  else\n    return 28;\n}\n\n/**\n * Returns the number of days in the given calendar month. Since this\n * function is for the standard Gregorian change date of 1582-10-15,\n * it returns 21 for 1582/10, otherwise it returns the same value as\n * [[getLastDateInMonth_SGC]].\n * @param year\n * @param month\n * @returns Total number of days in the given month.\n */\nexport function getDaysInMonth_SGC(year: number, month: number): number {\n  if (year === 1582 && month === 10)\n    return 21;\n  else if (month === 9 || month === 4 || month === 6 || month === 11)\n    return 30;\n  else if (month !== 2)\n    return 31; // Works for pseudo-months 0 and 13 as well.\n  else\n    return getDayNumber_SGC(year, 3, 1) - getDayNumber_SGC(year, 2, 1);\n}\n\n/**\n * This typically returns 365, or 366 for a leap year, but for the year\n * 1582 it returns 355.\n * @param year\n * @returns Total number of days in the given year.\n */\nexport function getDaysInYear_SGC(year: number): number {\n  return getDayNumber_SGC(year + 1, 1, 1) - getDayNumber_SGC(year, 1, 1);\n}\n\n/**\n * Get day of week for a given 1970-01-01-based day number.\n * @param dayNum 1970-01-01-based day number.\n * @return Day of week as 0-6: 0 for Sunday, 1 for Monday... 6 for Saturday.\n */\nexport function getDayOfWeek(dayNum: number): number {\n  return mod(dayNum + 4, 7);\n}\n\n/**\n * Get day of week for a given date, assuming standard Gregorian change.\n * @param yearOrDateOrDayNum 1970-01-01-based day number (month and date must be left undefined) - OR -\n *                           YMDDate form y/m/d - OR - [y, m, d].\n * @param month\n * @param day\n * @return Day of week as 0-6: 0 for Sunday, 1 for Monday... 6 for Saturday.\n */\nexport function getDayOfWeek_SGC(yearOrDateOrDayNum: YearOrDate, month?: number, day?: number): number {\n  if (isNumber(yearOrDateOrDayNum) && month == null)\n    return mod(yearOrDateOrDayNum + 4, 7);\n  else\n    return getDayOfWeek(getDayNumber_SGC(yearOrDateOrDayNum, month, day));\n}\n\n/**\n * Get the date of the index-th day of the week of a given month, e.g. the date of the\n * first Wednesday or the third Monday or the last Friday of the month.\n * @param year Year.\n * @param month Month.\n * @param dayOfTheWeek The day of the week (e.g. 0 for Sunday, 2 for Tuesday, 6 for Saturday) for\n *                     which you wish to find the date.\n * @param index A value of 1-5, or LAST (6), for the occurrence of the specified day of the week.\n * @return 0 if the described day does not exist (e.g. there is no fifth Monday in the given month) or\n *         the date of the specified day.\n */\nexport function getDateOfNthWeekdayOfMonth_SGC(year: number, month: number, dayOfTheWeek: number, index: number): number {\n  const last: boolean = (index >= LAST);\n  const day = 1;\n  let dayNum: number = getDayNumber_SGC(year, month, day);\n  const dayOfWeek = getDayOfWeek(dayNum);\n  let ymd: YMDDate;\n  let lastDay = 0;\n\n  if (dayOfWeek === dayOfTheWeek && index === 1)\n    return day;\n\n  dayNum += mod(dayOfTheWeek - dayOfWeek, 7);\n  ymd = getDateFromDayNumber_SGC(dayNum);\n\n  while (ymd.m === month) {\n    lastDay = ymd.d;\n\n    if (--index === 0)\n      return lastDay;\n\n    dayNum += 7;\n    ymd = getDateFromDayNumber_SGC(dayNum);\n  }\n\n  if (last)\n    return lastDay;\n  else\n    return 0;\n}\n\nexport function getDayOfWeekInMonthCount_SGC(year: number, month: number, dayOfTheWeek: number): number {\n  const firstDay = getDayNumber_SGC(year, month, getDateOfNthWeekdayOfMonth_SGC(year, month, dayOfTheWeek, 1));\n  const nextMonth = getDayNumber_SGC(year, month + 1, 1);\n\n  return div_tt0(nextMonth - firstDay - 1, 7) + 1;\n}\n\nexport function getDayOnOrAfter_SGC(year: number, month: number, dayOfTheWeek: number, minDate: number): number {\n  const dayNum = getDayNumber_SGC(year, month, minDate);\n  const dayOfWeek = getDayOfWeek(dayNum);\n  const delta = mod(dayOfTheWeek - dayOfWeek, 7);\n\n  if (year === 1582 && month === 10) {\n    const ymd = getDateFromDayNumber_SGC(dayNum + delta);\n\n    if (ymd.y !== year || ymd.m !== month)\n      minDate = 0;\n    else\n      minDate = ymd.d;\n  }\n  else {\n    minDate += delta;\n\n    if (minDate > getLastDateInMonth_SGC(year, month))\n      minDate = 0;\n  }\n\n  return minDate;\n}\n\nexport function getDayOnOrBefore_SGC(year: number, month: number, dayOfTheWeek: number, maxDate: number): number {\n  const dayNum = getDayNumber_SGC(year, month, maxDate);\n  const dayOfWeek = getDayOfWeek(dayNum);\n  const delta = mod(dayOfWeek - dayOfTheWeek, 7);\n\n  if (year === 1582 && month === 10) {\n    const ymd = getDateFromDayNumber_SGC(dayNum - delta);\n\n    if (ymd.y !== year || ymd.m !== month)\n      maxDate = 0;\n    else\n      maxDate = ymd.d;\n  }\n  else {\n    maxDate -= delta;\n\n    if (maxDate < 0)\n      maxDate = 0;\n  }\n\n  return maxDate;\n}\n\nexport function addDaysToDate_SGC(deltaDays: number, yearOrDate: YearOrDate, month?: number, day?: number): YMDDate {\n  return getDateFromDayNumber_SGC(getDayNumber_SGC(yearOrDate, month, day) + deltaDays);\n}\n\nexport function getDateFromDayNumber_SGC(dayNum: number): YMDDate {\n  if (dayNum >= FIRST_GREGORIAN_DAY_SGC)\n    return getDateFromDayNumberGregorian(dayNum);\n  else\n    return getDateFromDayNumberJulian(dayNum);\n}\n\nexport function getDateFromDayNumberGregorian(dayNum: number): YMDDate {\n  let year: number;\n  let month: number;\n  let day: number;\n  let dayOfYear: number;\n  let lastDay: number;\n\n  year = Math.floor((dayNum + 719528) / 365.2425);\n\n  while (dayNum < getDayNumberGregorian(year, 1, 1))\n    --year;\n\n  while (dayNum >= getDayNumberGregorian(year + 1, 1, 1))\n    ++year;\n\n  day = dayOfYear = dayNum - getDayNumberGregorian(year, 1, 1) + 1;\n\n  for (month = 1; day > (lastDay = getLastDateInMonthGregorian(year, month)); ++month)\n    day -= lastDay;\n\n  return syncDateAndTime({ y: year, m: month, d: day, dy: dayOfYear, n: dayNum, j: false });\n}\n\nfor (let i = -207084; i <= 205084; ++i) {\n  getDateFromDayNumberJulian(i);\n}\n\nexport function getDateFromDayNumberJulian(dayNum: number): YMDDate {\n  let year: number;\n  let month: number;\n  let day: number;\n  let lastDay: number;\n\n  year = Math.floor((dayNum + 719530) / 365.25);\n  day = dayNum - getDayNumberJulian(year, 1, 1) + 1;\n\n  for (month = 1; day > (lastDay = getLastDateInMonthJulian(year, month)); ++month)\n    day -= lastDay;\n\n  return syncDateAndTime({ y: year, m: month, d: day, n: dayNum, j: true });\n}\n\nexport function millisFromDateTime_SGC(year: number, month: number, day: number, hour: number, minute: number, second?: number, millis?: number): number {\n  millis = millis || 0;\n  second = second || 0;\n\n  return millis +\n         second * 1000 +\n         minute * MINUTE_MSEC +\n         hour * HOUR_MSEC +\n         getDayNumber_SGC(year, month, day) * DAY_MSEC;\n}\n\nexport function dateAndTimeFromMillis_SGC(ticks: number): DateAndTime {\n  const wallTime = getDateFromDayNumber_SGC(div_rd(ticks, DAY_MSEC)) as DateAndTime;\n\n  wallTime.millis = mod(ticks, 1000);\n  ticks = div_rd(ticks, 1000);\n  wallTime.sec = mod(ticks, 60);\n  ticks = div_rd(ticks, 60);\n  wallTime.min = mod(ticks, 60);\n  ticks = div_rd(ticks, 60);\n  wallTime.hrs = mod(ticks, 24);\n  wallTime.utcOffset = 0;\n  wallTime.dstOffset = 0;\n  wallTime.occurrence = 1;\n\n  return syncDateAndTime(wallTime);\n}\n\nexport function isValidDate_SGC(yearOrDate: YearOrDate, month?: number, day?: number): boolean {\n  const [y, m, d, j] = handleVariableDateArgs(yearOrDate, month, day);\n  let ymd: YMDDate;\n  const n = getDayNumber_SGC({ y, m, d, j: j < 0 ? null : !!j });\n\n  if (j < 0)\n    ymd = getDateFromDayNumber_SGC(n);\n  else if (j === 0)\n    ymd = getDateFromDayNumberGregorian(n);\n  else\n    ymd = getDateFromDayNumberJulian(n);\n\n  return (y === ymd.y && m === ymd.m && d === ymd.d);\n}\n\nexport function isValidDateGregorian(yearOrDate: YearOrDate, month?: number, day?: number): boolean {\n  let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, 'g');\n  const ymd: YMDDate = getDateFromDayNumberGregorian(getDayNumberGregorian(year, month, day));\n\n  return (year === ymd.y && month === ymd.m && day === ymd.d);\n}\n\nexport function isValidDateJulian(yearOrDate: YearOrDate, month?: number, day?: number): boolean {\n  let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, 'j');\n  const ymd: YMDDate = getDateFromDayNumberJulian(getDayNumberJulian(year, month, day));\n\n  return (year === ymd.y && month === ymd.m && day === ymd.d);\n}\n\nexport function getISOFormatDate(yearOrDate: YearOrDate, month?: number, day?: number): string {\n  let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day);\n\n  const yyyy = (year < 0 ? '-' : '') + padLeft(Math.abs(year), 4, '0');\n  const mm   = padLeft(month, 2, '0');\n  const dd   = padLeft(day, 2, '0');\n\n  return yyyy + '-' + mm + '-' + dd;\n}\n\nexport function parseISODate(date: string): YMDDate {\n  let sign = 1;\n\n  date = date.trim();\n\n  if (date.startsWith('-')) {\n    sign = -1;\n    date = date.substring(1).trim();\n  }\n\n  let $ = /^(\\d+)-(\\d{1,2}(?=\\D))(?:-(\\d+))?$/.exec(date);\n\n  if (!$)\n    $ = /^(\\d{1,5})$/.exec(date);\n\n  if (!$)\n    $ = /^(\\d{4,})(\\d\\d)(\\d\\d)$/.exec(date);\n\n  if (!$)\n    throw new Error('Invalid ISO date');\n\n  return syncDateAndTime({ y: Number($[1]) * sign, m: Number($[2] ?? 1), d: Number($[3] ?? 1) });\n}\n\nexport class Calendar {\n  private gcYear  = 1582;\n  private gcMonth = 10;\n  private gcDate  = 15;\n  private firstGregorianDay: number = FIRST_GREGORIAN_DAY_SGC;\n  private firstDateInGCChangeMonth = 1;\n  private lengthOfGCChangeMonth = 21;\n  private lastJulianYear: number = Number.MIN_SAFE_INTEGER;\n  private lastJulianMonth: number = Number.MIN_SAFE_INTEGER;\n  private lastJulianDate = 4;\n\n  protected _locked = false;\n\n  constructor(gcYearOrDateOrType?: YearOrDate | CalendarType | string, gcMonth?: number, gcDate?: number) {\n    if (gcYearOrDateOrType === CalendarType.PURE_GREGORIAN)\n      this.setGregorianChange(DISTANT_YEAR_PAST, 0, 0);\n    else if (gcYearOrDateOrType === CalendarType.PURE_JULIAN)\n      this.setGregorianChange(DISTANT_YEAR_FUTURE, 0, 0);\n    else if (arguments.length === 0 || gcYearOrDateOrType == null)\n      this.setGregorianChange(1582, 10, 15);\n    else\n      this.setGregorianChange(gcYearOrDateOrType as YearOrDate | string, gcMonth, gcDate);\n  }\n\n  lock = (): this => this._lock();\n  protected _lock(doLock = true): this {\n    this._locked = this._locked || doLock;\n    return this;\n  }\n\n  get locked(): boolean { return this._locked; }\n\n  setPureGregorian(pureGregorian: boolean): this {\n    if (this.locked)\n      throw lockError;\n\n    if (pureGregorian)\n      this.setGregorianChange(DISTANT_YEAR_PAST, 0, 0);\n    else\n      this.setGregorianChange(1582, 10, 15);\n\n    return this;\n  }\n\n  isPureGregorian(): boolean {\n    return (this.gcYear <= DISTANT_YEAR_PAST);\n  }\n\n  setPureJulian(pureJulian: boolean): this {\n    if (this.locked)\n      throw lockError;\n\n    if (pureJulian)\n      this.setGregorianChange(DISTANT_YEAR_FUTURE, 0, 0);\n    else\n      this.setGregorianChange(1582, 10, 15);\n\n    return this;\n  }\n\n  isPureJulian(): boolean {\n    return (this.gcYear >= DISTANT_YEAR_FUTURE);\n  }\n\n  setGregorianChange(gcYearOrDate: YearOrDate | string, gcMonth?: number, gcDate?: number): this {\n    if (this.locked)\n      throw lockError;\n\n    if (gcYearOrDate === 'g' || gcYearOrDate === 'G') {\n      this.setPureGregorian(true);\n\n      return this;\n    }\n    else if (gcYearOrDate === 'j' || gcYearOrDate === 'J') {\n      this.setPureJulian(true);\n\n      return this;\n    }\n    else if (isString(gcYearOrDate))\n      gcYearOrDate = parseISODate(gcYearOrDate);\n    else if (isObject(gcYearOrDate) && !isArray(gcYearOrDate) && (gcYearOrDate.y == null ||\n             gcYearOrDate.m == null || gcYearOrDate.d == null || gcYearOrDate.j))\n      throw new Error('Gregorian change date must be an explicit non-Julian y-m-d date');\n\n    let gcYear: number; [gcYear, gcMonth, gcDate] = handleVariableDateArgs(gcYearOrDate as YearOrDate, gcMonth, gcDate, this);\n\n    if (gcYear < GREGORIAN_CHANGE_MIN_YEAR) {\n      if ((gcMonth !== 0 || gcDate !== 0) && gcYear > DISTANT_YEAR_PAST)\n        throw new Error('Calendar: Gregorian change year cannot be less than ' + GREGORIAN_CHANGE_MIN_YEAR);\n\n      this.firstGregorianDay = Number.MIN_SAFE_INTEGER;\n      this.gcYear = DISTANT_YEAR_PAST;\n    }\n    else if (gcYear > GREGORIAN_CHANGE_MAX_YEAR) {\n      if ((gcMonth !== 0 || gcDate !== 0) && gcYear < DISTANT_YEAR_FUTURE)\n        throw new Error('Calendar: Gregorian change year cannot be greater than ' + GREGORIAN_CHANGE_MAX_YEAR);\n\n      this.firstGregorianDay = Number.MAX_SAFE_INTEGER;\n      this.gcYear = DISTANT_YEAR_FUTURE;\n    }\n    else if (!isValidDateGregorian(gcYear, gcMonth, gcDate))\n      throw new Error('Calendar: Invalid Gregorian date: ' + getISOFormatDate(gcYear, gcMonth, gcDate));\n\n    this.gcYear  = gcYear;\n    this.gcMonth = gcMonth;\n    this.gcDate  = gcDate;\n    this.firstGregorianDay = getDayNumberGregorian(gcYear, gcMonth, gcDate);\n\n    const lastJDay: YMDDate = getDateFromDayNumberJulian(this.firstGregorianDay - 1);\n\n    this.lastJulianDate = lastJDay.d;\n    this.lengthOfGCChangeMonth = getLastDateInMonthGregorian(gcYear, gcMonth);\n\n    if (lastJDay.y === gcYear && lastJDay.m === gcMonth) {\n      this.lastJulianYear = Number.MIN_SAFE_INTEGER; // Number.MIN_SAFE_INTEGER used to indicate mixed Julian/Gregorian transition month\n      this.lastJulianMonth = Number.MIN_SAFE_INTEGER;\n      this.firstDateInGCChangeMonth = 1;\n      this.lengthOfGCChangeMonth -= gcDate - this.lastJulianDate - 1;\n    }\n    else {\n      this.lastJulianYear = lastJDay.y;\n      this.lastJulianMonth = lastJDay.m;\n      this.firstDateInGCChangeMonth = gcDate;\n      this.lengthOfGCChangeMonth -= gcDate - 1;\n    }\n\n    return this;\n  }\n\n  getGregorianChange(): YMDDate {\n    return syncDateAndTime({ y: this.gcYear, m: this.gcMonth, d: this.gcDate, n: this.firstGregorianDay, j: false });\n  }\n\n  isJulianCalendarDate(yearOrDate: YearOrDate, month?: number, day?: number): boolean {\n    let year: number, j: number; [year, month, day, j] = handleVariableDateArgs(yearOrDate, month, day, this);\n\n    return (j === 1 || year < this.gcYear || (year === this.gcYear && (month < this.gcMonth ||\n            month === this.gcMonth && day < this.gcDate)));\n  }\n\n  getDayNumber(yearOrDate: YearOrDate, month?: number, day?: number): number {\n    // Note: month/day can be used internally to pass startOfWeek/minDaysInWeek.\n    if (isObject(yearOrDate) && !isArray(yearOrDate)) {\n      syncDateAndTime(yearOrDate);\n\n      if (yearOrDate.y == null && (yearOrDate.yw != null || yearOrDate.ywl != null)) {\n        const localeWeek = (yearOrDate.ywl != null);\n        const year = yearOrDate.ywl ?? yearOrDate.yw;\n        const startOfWeek = (localeWeek && month != null ? month : 1);\n        const minDaysInWeek = (localeWeek && day != null ? day : 4);\n        const week = (localeWeek ? yearOrDate.wl : yearOrDate.w) ?? /* istanbul ignore next: unreached sanity check */ 1;\n        const dayOfWeek = (localeWeek ? yearOrDate.dwl : yearOrDate.dw) ?? /* istanbul ignore next: unreached sanity check */ 1;\n        ++this.computeWeekValues;\n\n        const w = this.getStartDateOfFirstWeekOfYear(year, startOfWeek, minDaysInWeek);\n        const dayNum = w.n + (week - 1) * 7 + dayOfWeek - 1;\n\n        yearOrDate = this.getDateFromDayNumber(dayNum);\n        --this.computeWeekValues;\n      }\n      else if (yearOrDate.y != null && yearOrDate.m == null && yearOrDate.dy != null)\n        yearOrDate = this.addDaysToDate(yearOrDate.dy - 1, { y: yearOrDate.y, m: 1, d: 1 });\n    }\n\n    let year: number, j: number; [year, month, day, j] = handleVariableDateArgs(yearOrDate, month, day, this);\n\n    while (month <  1) { month += 12; --year; }\n    while (month > 12) { month -= 12; ++year; }\n\n    if (j < 0) {\n      if (year === this.lastJulianYear && month === this.lastJulianMonth) {\n        if (day > this.lastJulianDate)\n          day = this.lastJulianDate + 1;\n      }\n      else if (year === this.gcYear && month === this.gcMonth && (day > this.lastJulianDate ||\n               (this.lastJulianMonth !== this.gcMonth && this.lastJulianMonth > 0)) && day < this.gcDate) {\n        day = this.gcDate;\n      }\n    }\n\n    if (j === 1 || (j !== 0 && this.isJulianCalendarDate(year, month, day)))\n      return getDayNumberJulian(year, month, day);\n    else\n      return getDayNumberGregorian(year, month, day);\n  }\n\n  protected computeWeekValues = 0; // To prevent infinite recursion, compute week values only when this is 0.\n\n  /** @hidden */\n  getDateFromDayNumber(dayNum: number, startingDayOfWeek?: number, minDaysInCalendarYear?: number): YMDDate {\n    let result: YMDDate;\n\n    if (dayNum >= this.firstGregorianDay)\n      result = getDateFromDayNumberGregorian(dayNum);\n    else\n      result = getDateFromDayNumberJulian(dayNum);\n\n    if (this.computeWeekValues === 0)\n      [result.yw, result.w, result.dw] = this.getYearWeekAndWeekday(result, startingDayOfWeek, minDaysInCalendarYear);\n\n    return syncDateAndTime(result);\n  }\n\n  getFirstDateInMonth(year: number, month: number): number {\n    if (year === this.gcYear && month === this.gcMonth)\n      return this.firstDateInGCChangeMonth;\n    else\n      return 1;\n  }\n\n  getLastDateInMonth(year: number, month: number): number {\n    if (month === 0) {\n      month = 12;\n      --year;\n    }\n    else if (month === 13) {\n      month = 1;\n      ++year;\n    }\n\n    if (year === this.lastJulianYear && month === this.lastJulianMonth)\n      return this.lastJulianDate;\n    else if (month === 9 || month === 4 || month === 6 || month === 11)\n      return 30;\n    else if (month !== 2)\n      return 31;\n    else if (year % 4 === 0 && (year < this.gcYear || (year === this.gcYear && this.gcMonth > 2) || year % 100 !== 0 || year % 400 === 0))\n      return 29;\n    else\n      return 28;\n  }\n\n  getDaysInMonth(year: number, month: number): number {\n    if (month === 0) {\n      month = 12;\n      --year;\n    }\n    else if (month === 13) {\n      month = 1;\n      ++year;\n    }\n\n    if (year === this.gcYear && month === this.gcMonth)\n      return this.lengthOfGCChangeMonth;\n    else if (year === this.lastJulianYear && month === this.lastJulianMonth)\n      return this.lastJulianDate;\n    else if (month === 9 || month === 4 || month === 6 || month === 11)\n      return 30;\n    else if (month !== 2)\n      return 31;\n    else\n      return this.getDayNumber(year, 3, 1) - this.getDayNumber(year, 2, 1);\n  }\n\n  getDaysInYear(year: number): number {\n    return this.getDayNumber(year + 1, 1, 1) - this.getDayNumber(year, 1, 1);\n  }\n\n  getDayOfWeek(yearOrDateOrDayNum: YearOrDate, month?: number, day?: number): number {\n    if (isNumber(yearOrDateOrDayNum) && month == null)\n      return getDayOfWeek(yearOrDateOrDayNum);\n    else\n      return getDayOfWeek(this.getDayNumber(yearOrDateOrDayNum, month, day));\n  }\n\n  /**\n   * @description Get the date of the index-th day of the week of a given month, e.g. the date of the\n   * first Wednesday or the third Monday or the last Friday of the month.\n   *\n   * @param {number} year - Year.\n   * @param {number} month - Month.\n   * @param {number} dayOfTheWeek - The day of the week (e.g. 0 for Sunday, 2 for Tuesday, 6 for Saturday) for\n   *                                which you wish to find the date.\n   * @param {number} index - A value of 1-5, or LAST (6), for the occurrence of the specified day of the week.\n   *\n   * @return {number} 0 if the described day does not exist (e.g. there is no fifth Monday in the given month) or\n   *                  the date of the specified day.\n   */\n  getDateOfNthWeekdayOfMonth(year: number, month: number, dayOfTheWeek: number, index: number): number {\n    const last: boolean = (index >= LAST);\n    const day = 1;\n    let dayNum: number = this.getDayNumber(year, month, day);\n    const dayOfWeek = getDayOfWeek(dayNum);\n    let ymd: YMDDate;\n    let lastDay = 0;\n\n    if (dayOfWeek === dayOfTheWeek && index === 1)\n      return day;\n\n    dayNum += mod(dayOfTheWeek - dayOfWeek, 7);\n    ymd = this.getDateFromDayNumber(dayNum);\n\n    while (ymd.m === month) {\n      lastDay = ymd.d;\n\n      if (--index === 0)\n        return lastDay;\n\n      dayNum += 7;\n      ymd = this.getDateFromDayNumber(dayNum);\n    }\n\n    if (last)\n      return lastDay;\n    else\n      return 0;\n  }\n\n  getDayOfWeekInMonthCount(year: number, month: number, dayOfTheWeek: number): number {\n    const firstDay = this.getDayNumber(year, month, this.getDateOfNthWeekdayOfMonth(year, month, dayOfTheWeek, 1));\n    const nextMonth = this.getDayNumber(year, month + 1, 1);\n\n    return div_tt0(nextMonth - firstDay - 1, 7) + 1;\n  }\n\n  getDayOfWeekInMonthIndex(yearOrDate: YearOrDate, month?: number, day?: number): number {\n    let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, this);\n    const firstDay = this.getDayNumber(year, month, 1);\n    const dayNumber = this.getDayNumber(year, month, day);\n\n    return div_rd(dayNumber - firstDay, 7) + 1;\n  }\n\n  getDayOnOrAfter(year: number, month: number, dayOfTheWeek: number, minDate: number): number {\n    const dayNum = this.getDayNumber(year, month, minDate);\n    const dayOfWeek = getDayOfWeek(dayNum);\n    const delta = mod(dayOfTheWeek - dayOfWeek, 7);\n\n    if (year === this.gcYear && month === this.gcMonth) {\n      const ymd = this.getDateFromDayNumber(dayNum + delta);\n\n      if (ymd.y !== year || ymd.m !== month)\n        minDate = 0;\n      else\n        minDate = ymd.d;\n    }\n    else {\n      minDate += delta;\n\n      if (minDate > this.getLastDateInMonth(year, month))\n        minDate = 0;\n    }\n\n    return minDate;\n  }\n\n  getDayOnOrBefore(year: number, month: number, dayOfTheWeek: number, maxDate: number): number {\n    const dayNum = this.getDayNumber(year, month, maxDate);\n    const dayOfWeek = getDayOfWeek(dayNum);\n    const delta = mod(dayOfWeek - dayOfTheWeek, 7);\n\n    if (year === this.gcYear && month === this.gcMonth) {\n      const ymd = this.getDateFromDayNumber(dayNum - delta);\n\n      if (ymd.y !== year || ymd.m !== month)\n        maxDate = 0;\n      else\n        maxDate = ymd.d;\n    }\n    else {\n      maxDate -= delta;\n\n      if (maxDate < 0)\n        maxDate = 0;\n    }\n\n    return maxDate;\n  }\n\n  addDaysToDate(deltaDays: number, yearOrDate: YearOrDate, month?: number, day?: number): YMDDate {\n    return this.getDateFromDayNumber(this.getDayNumber(yearOrDate, month, day) + deltaDays);\n  }\n\n  getCalendarMonth(year: number, month: number, startingDayOfWeek = SUNDAY): YMDDate[] {\n    const dates: YMDDate[] = [];\n    let dateOffset: number;\n    let dayNum = this.getDayNumber(year, month, this.getFirstDateInMonth(year, month));\n    let ymd: YMDDate;\n    let currMonth: number;\n\n    // Step back (if necessary) to the nearest prior day matching the requested starting day of the week.\n    dateOffset = mod(startingDayOfWeek - getDayOfWeek(dayNum), -7); // First time I recall ever wanting to use a negative modulus.\n    dayNum += dateOffset; // dateOffset will be 0 or negative\n\n    ymd = this.getDateFromDayNumber(dayNum, startingDayOfWeek);\n\n    // This loop will fill in a calendar month's full set of dates in such a way as to obtain dates which\n    // should be shown from previous and subsequent months, while also skipping over Julian-to-Gregorian\n    // calendar switch-over dates.\n    do {\n      dates.push(ymd);\n      ++dayNum;\n      ++dateOffset;\n      ymd = this.getDateFromDayNumber(dayNum);\n      currMonth = ymd.m;\n      // We've reached the end of the calendar when we're at a positive date offset, in a different month\n      // than the requested month, and the day of week is back to the first day of the week of the calendar.\n      // The first date to meet these criteria is just past the end of the calendar, and is not added to it.\n    } while (dateOffset < 1 || currMonth === month || getDayOfWeek(dayNum) !== startingDayOfWeek);\n\n    return dates;\n  }\n\n  isValidDate(year: number, month: number, day: number): boolean;\n  isValidDate(yearOrDate: YMDDate | number[]): boolean;\n  isValidDate(yearOrDate: YearOrDate, month?: number, day?: number): boolean {\n    let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, this, true);\n    const ymd = this.getDateFromDayNumber(this.getDayNumber(year, month, day));\n\n    return (year === ymd.y && month === ymd.m && day === ymd.d);\n  }\n\n  normalizeDate(year: number, month: number, day: number): YMDDate;\n  normalizeDate(yearOrDate: YMDDate | number[]): YMDDate;\n  normalizeDate(yearOrDate: YearOrDate, month?: number, day?: number): YMDDate {\n    let year: number; [year, month, day] = handleVariableDateArgs(yearOrDate, month, day, this, true);\n\n    if (month < 1) {\n      month += 12;\n      year -= 1;\n    }\n    else if (month > 12) {\n      month -= 12;\n      year += 1;\n    }\n\n    if (!this.isValidDate(year, month, day)) {\n      let d: number;\n\n      if (day < (d = this.getFirstDateInMonth(year, month)))\n        day = d;\n      else if (day > (d = this.getLastDateInMonth(year, month)))\n        day = d;\n      else {\n        const range = this.getMissingDateRange(year, month);\n\n        if (range != null)\n          day = range[1] + 1;\n      }\n    }\n\n    return syncDateAndTime({ y: year, m: month, d: day });\n  }\n\n  getMissingDateRange(year: number, month: number): number[] | null {\n    if (year === this.lastJulianYear && month === this.lastJulianMonth) {\n      const lastDate = getLastDateInMonthJulian(year, month);\n\n      if (lastDate > this.lastJulianDate)\n        return [this.lastJulianDate + 1, lastDate];\n    }\n    else if (year === this.gcYear && month === this.gcMonth && this.gcDate > 1 && this.gcDate > this.lastJulianDate + 1)\n      return [this.lastJulianDate + 1, this.gcDate - 1];\n\n    return null;\n  }\n\n  getStartDateOfFirstWeekOfYear(year: number, startingDayOfWeek = 1, minDaysInCalendarYear = 4): YMDDate {\n    let day = 1;\n\n    // 7 is a special case, where start week is first full week *after* January 1st.\n    if (minDaysInCalendarYear === 7) {\n      ++day;\n      --minDaysInCalendarYear;\n    }\n\n    const daysIntoWeek = mod(this.getDayOfWeek(year, 1, day) - startingDayOfWeek, 7);\n\n    return this.addDaysToDate(-daysIntoWeek + (daysIntoWeek > 7 - minDaysInCalendarYear ? 7 : 0), year, 1, day);\n  }\n\n  getWeeksInYear(year: number, startingDayOfWeek = 1, minDaysInCalendarYear = 4): number {\n    const w1 = this.getStartDateOfFirstWeekOfYear(year, startingDayOfWeek, minDaysInCalendarYear);\n    const w2 = this.getStartDateOfFirstWeekOfYear(year + 1, startingDayOfWeek, minDaysInCalendarYear);\n\n    return (w2.n - w1.n) / 7;\n  }\n\n  getYearWeekAndWeekday(year: number, month: number, day: number,\n    startingDayOfWeek?: number, minDaysInCalendarYear?: number): number[];\n\n  getYearWeekAndWeekday(date: YearOrDate | number,\n    startingDayOfWeek?: number, minDaysInCalendarYear?: number): number[];\n\n  getYearWeekAndWeekday(yearOrDate: YearOrDate, monthOrSDW: number, dayOrMDiCY: number,\n                      startingDayOfWeek?: number, minDaysInCalendarYear?: number): number[] {\n    const [year, month, day] = handleVariableDateArgs(yearOrDate, monthOrSDW, dayOrMDiCY, this, true);\n\n    if (isObject(yearOrDate)) {\n      startingDayOfWeek = monthOrSDW;\n      minDaysInCalendarYear = dayOrMDiCY;\n    }\n\n    startingDayOfWeek = startingDayOfWeek ?? 1;\n    minDaysInCalendarYear = minDaysInCalendarYear ?? 4;\n    ++this.computeWeekValues;\n\n    let resultYear = year;\n    let w = this.getStartDateOfFirstWeekOfYear(year, startingDayOfWeek, minDaysInCalendarYear);\n    const w2 = this.getStartDateOfFirstWeekOfYear(year + 1, startingDayOfWeek, minDaysInCalendarYear);\n    const dayNum = this.getDayNumber(year, month, day);\n\n    if (w.n > dayNum) {\n      w = this.getStartDateOfFirstWeekOfYear(year - 1, startingDayOfWeek, minDaysInCalendarYear);\n      --resultYear;\n    }\n    else if (w2.n <= dayNum) {\n      w = w2;\n      ++resultYear;\n    }\n\n    --this.computeWeekValues;\n\n    return [resultYear, floor((dayNum - w.n) / 7) +