File size: 2,748 Bytes
cf86710 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 | import {
daysInHebrewMonth,
monthsInHebrewYear,
roshHashanah,
} from "./calendarMath.js";
import { GREGORIAN_EPOCH, type HebrewDate, MS_PER_DAY } from "./constants.js";
/** Convert a Gregorian date to an absolute day number from the epoch. */
function dateToAbsolute(date: Date): number {
// Years < 100 must use UTC components to avoid JS's 1900 offset; for normal
// years keep local components so we don't reintroduce UTC/local skew in the
// rendered month grid.
const useUTC = date.getFullYear() < 100;
const year = useUTC ? date.getUTCFullYear() : date.getFullYear();
const month = useUTC ? date.getUTCMonth() : date.getMonth();
const day = useUTC ? date.getUTCDate() : date.getDate();
const normalized = new Date(0);
normalized.setUTCFullYear(year, month, day);
normalized.setUTCHours(0, 0, 0, 0);
return Math.floor((normalized.getTime() - GREGORIAN_EPOCH) / MS_PER_DAY) + 1;
}
/** Convert an absolute day number back to a Gregorian date. */
function absoluteToDate(absolute: number): Date {
const utc = new Date(GREGORIAN_EPOCH + (absolute - 1) * MS_PER_DAY);
const result = new Date(0);
result.setFullYear(utc.getUTCFullYear(), utc.getUTCMonth(), utc.getUTCDate());
result.setHours(0, 0, 0, 0);
return result;
}
/** Convert a Hebrew date to an absolute day number so it can be compared. */
function absoluteFromHebrew({ year, monthIndex, day }: HebrewDate): number {
let days = day - 1;
for (let index = 0; index < monthIndex; index += 1) {
days += daysInHebrewMonth(year, index);
}
return roshHashanah(year) + days;
}
/** Convert an absolute day number to the equivalent Hebrew date. */
function hebrewFromAbsolute(absolute: number): HebrewDate {
const date = new Date(GREGORIAN_EPOCH + (absolute - 1) * MS_PER_DAY);
let year = date.getUTCFullYear() + 3760;
if (date.getUTCMonth() >= 8) {
year += 1;
}
while (absolute >= roshHashanah(year + 1)) {
year += 1;
}
while (absolute < roshHashanah(year)) {
year -= 1;
}
let dayOfYear = absolute - roshHashanah(year);
const monthCount = monthsInHebrewYear(year);
let monthIndex = 0;
while (monthIndex < monthCount) {
const monthDays = daysInHebrewMonth(year, monthIndex);
if (dayOfYear < monthDays) {
break;
}
dayOfYear -= monthDays;
monthIndex += 1;
}
return {
year,
monthIndex,
day: dayOfYear + 1,
};
}
/** Converts a Gregorian date to the corresponding Hebrew date. */
export function toHebrewDate(date: Date): HebrewDate {
return hebrewFromAbsolute(dateToAbsolute(date));
}
/** Converts a Hebrew date back to the Gregorian calendar. */
export function toGregorianDate(hebrew: HebrewDate): Date {
return absoluteToDate(absoluteFromHebrew(hebrew));
}
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