chrono-node

import dayjs from "dayjs"; import { TimezoneAbbrMap, Weekday, Month } from "./types"; export const TIMEZONE_ABBR_MAP: TimezoneAbbrMap = { ACDT: 630, ACST: 570, ADT: -180, AEDT: 660, AEST: 600, AFT: 270, AKDT: -480, AKST: -540, ALMT: 360, AMST: -180, AMT: -240, ANAST: 720, ANAT: 720, AQTT: 300, ART: -180, AST: -240, AWDT: 540, AWST: 480, AZOST: 0, AZOT: -60, AZST: 300, AZT: 240, BNT: 480, BOT: -240, BRST: -120, BRT: -180, BST: 60, BTT: 360, CAST: 480, CAT: 120, CCT: 390, CDT: -300, CEST: 120, // Note: Many sources define CET as a constant UTC+1. In common usage, however, // CET usually refers to the time observed in most of Europe, be it standard time or daylight saving time. CET: { timezoneOffsetDuringDst: 2 * 60, timezoneOffsetNonDst: 60, dstStart: (year: number) => getLastWeekdayOfMonth(year, Month.MARCH, Weekday.SUNDAY, 2), dstEnd: (year: number) => getLastWeekdayOfMonth(year, Month.OCTOBER, Weekday.SUNDAY, 3), }, CHADT: 825, CHAST: 765, CKT: -600, CLST: -180, CLT: -240, COT: -300, CST: -360, CT: { timezoneOffsetDuringDst: -5 * 60, timezoneOffsetNonDst: -6 * 60, dstStart: (year: number) => getNthWeekdayOfMonth(year, Month.MARCH, Weekday.SUNDAY, 2, 2), dstEnd: (year: number) => getNthWeekdayOfMonth(year, Month.NOVEMBER, Weekday.SUNDAY, 1, 2), }, CVT: -60, CXT: 420, ChST: 600, DAVT: 420, EASST: -300, EAST: -360, EAT: 180, ECT: -300, EDT: -240, EEST: 180, EET: 120, EGST: 0, EGT: -60, EST: -300, ET: { timezoneOffsetDuringDst: -4 * 60, timezoneOffsetNonDst: -5 * 60, dstStart: (year: number) => getNthWeekdayOfMonth(year, Month.MARCH, Weekday.SUNDAY, 2, 2), dstEnd: (year: number) => getNthWeekdayOfMonth(year, Month.NOVEMBER, Weekday.SUNDAY, 1, 2), }, FJST: 780, FJT: 720, FKST: -180, FKT: -240, FNT: -120, GALT: -360, GAMT: -540, GET: 240, GFT: -180, GILT: 720, GMT: 0, GST: 240, GYT: -240, HAA: -180, HAC: -300, HADT: -540, HAE: -240, HAP: -420, HAR: -360, HAST: -600, HAT: -90, HAY: -480, HKT: 480, HLV: -210, HNA: -240, HNC: -360, HNE: -300, HNP: -480, HNR: -420, HNT: -150, HNY: -540, HOVT: 420, ICT: 420, IDT: 180, IOT: 360, IRDT: 270, IRKST: 540, IRKT: 540, IRST: 210, IST: 330, JST: 540, KGT: 360, KRAST: 480, KRAT: 480, KST: 540, KUYT: 240, LHDT: 660, LHST: 630, LINT: 840, MAGST: 720, MAGT: 720, MART: -510, MAWT: 300, MDT: -360, MESZ: 120, MEZ: 60, MHT: 720, MMT: 390, MSD: 240, MSK: 180, MST: -420, MT: { timezoneOffsetDuringDst: -6 * 60, timezoneOffsetNonDst: -7 * 60, dstStart: (year: number) => getNthWeekdayOfMonth(year, Month.MARCH, Weekday.SUNDAY, 2, 2), dstEnd: (year: number) => getNthWeekdayOfMonth(year, Month.NOVEMBER, Weekday.SUNDAY, 1, 2), }, MUT: 240, MVT: 300, MYT: 480, NCT: 660, NDT: -90, NFT: 690, NOVST: 420, NOVT: 360, NPT: 345, NST: -150, NUT: -660, NZDT: 780, NZST: 720, OMSST: 420, OMST: 420, PDT: -420, PET: -300, PETST: 720, PETT: 720, PGT: 600, PHOT: 780, PHT: 480, PKT: 300, PMDT: -120, PMST: -180, PONT: 660, PST: -480, PT: { timezoneOffsetDuringDst: -7 * 60, timezoneOffsetNonDst: -8 * 60, dstStart: (year: number) => getNthWeekdayOfMonth(year, Month.MARCH, Weekday.SUNDAY, 2, 2), dstEnd: (year: number) => getNthWeekdayOfMonth(year, Month.NOVEMBER, Weekday.SUNDAY, 1, 2), }, PWT: 540, PYST: -180, PYT: -240, RET: 240, SAMT: 240, SAST: 120, SBT: 660, SCT: 240, SGT: 480, SRT: -180, SST: -660, TAHT: -600, TFT: 300, TJT: 300, TKT: 780, TLT: 540, TMT: 300, TVT: 720, ULAT: 480, UTC: 0, UYST: -120, UYT: -180, UZT: 300, VET: -210, VLAST: 660, VLAT: 660, VUT: 660, WAST: 120, WAT: 60, WEST: 60, WESZ: 60, WET: 0, WEZ: 0, WFT: 720, WGST: -120, WGT: -180, WIB: 420, WIT: 540, WITA: 480, WST: 780, WT: 0, YAKST: 600, YAKT: 600, YAPT: 600, YEKST: 360, YEKT: 360, }; /** * Get the date which is the nth occurence of a given weekday in a given month and year. * * @param year The year for which to find the date * @param month The month in which the date occurs * @param weekday The weekday on which the date occurs * @param n The nth occurence of the given weekday on the month to return * @param hour The hour of day which should be set on the returned date * @return The date which is the nth occurence of a given weekday in a given * month and year, at the given hour of day */ export function getNthWeekdayOfMonth(year: number, month: Month, weekday: Weekday, n: 1 | 2 | 3 | 4, hour = 0): Date { let dayOfMonth = 0; let i = 0; while (i < n) { dayOfMonth++; const date = new Date(year, month - 1, dayOfMonth); if (date.getDay() === weekday) i++; } return new Date(year, month - 1, dayOfMonth, hour); } /** * Get the date which is the last occurence of a given weekday in a given month and year. * * @param year The year for which to find the date * @param month The month in which the date occurs * @param weekday The weekday on which the date occurs * @param hour The hour of day which should be set on the returned date * @return The date which is the last occurence of a given weekday in a given * month and year, at the given hour of day */ export function getLastWeekdayOfMonth(year: number, month: Month, weekday: Weekday, hour = 0): Date { // Procedure: Find the first weekday of the next month, compare with the given weekday, // and use the difference to determine how many days to subtract from the first of the next month. const oneIndexedWeekday = weekday === 0 ? 7 : weekday; const date = new Date(year, month - 1 + 1, 1, 12); const firstWeekdayNextMonth = date.getDay() === 0 ? 7 : date.getDay(); let dayDiff; if (firstWeekdayNextMonth === oneIndexedWeekday) dayDiff = 7; else if (firstWeekdayNextMonth < oneIndexedWeekday) dayDiff = 7 + firstWeekdayNextMonth - oneIndexedWeekday; else dayDiff = firstWeekdayNextMonth - oneIndexedWeekday; date.setDate(date.getDate() - dayDiff); return new Date(year, month - 1, date.getDate(), hour); } /** * Finds and returns timezone offset. If timezoneInput is numeric, it is returned. Otherwise, look for timezone offsets * in the following order: timezoneOverrides -> {@link TIMEZONE_ABBR_MAP}. * * @param timezoneInput Uppercase timezone abbreviation or numeric offset in minutes * @param date The date to use to determine whether to return DST offsets for ambiguous timezones * @param timezoneOverrides Overrides for timezones * @return timezone offset in minutes */ export function toTimezoneOffset( timezoneInput?: string | number, date?: Date, timezoneOverrides: TimezoneAbbrMap = {} ): number | null { if (timezoneInput == null) { return null; } if (typeof timezoneInput === "number") { return timezoneInput; } const matchedTimezone = timezoneOverrides[timezoneInput] ?? TIMEZONE_ABBR_MAP[timezoneInput]; if (matchedTimezone == null) { return null; } // This means that we have matched an unambiguous timezone if (typeof matchedTimezone == "number") { return matchedTimezone; } // The matched timezone is an ambiguous timezone, where the offset depends on whether the context (refDate) // is during daylight savings or not. // Without refDate as context, there's no way to know if DST or non-DST offset should be used. Return null instead. if (date == null) { return null; } // Return DST offset if the refDate is during daylight savings if ( dayjs(date).isAfter(matchedTimezone.dstStart(date.getFullYear())) && !dayjs(date).isAfter(matchedTimezone.dstEnd(date.getFullYear())) ) { return matchedTimezone.timezoneOffsetDuringDst; } // refDate is not during DST => return non-DST offset return matchedTimezone.timezoneOffsetNonDst; }