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date-cache.ts
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date-cache.ts
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import dayjs, { Dayjs } from 'dayjs';
import isoWeek from 'dayjs/plugin/isoWeek'; // eslint-disable-line -- tell the type system that Dayjs::isoWeekYear is available
import { assert } from './assert';
export interface UnifiedDay {
string: string;
dayjs: Dayjs;
isoWeek: UnifiedIsoWeek;
}
export interface UnifiedIsoWeek {
isoYear: number;
isoWeek: number;
yearWeekString: string;
firstDay: UnifiedDay;
}
// parseYearWeekString extracts the ISO week and year from a string.
// It will **not check** whether there is actually a week 53 in the specified year.
function parseYearWeekString(yearWeek: string): { year: number; week: number } {
const yearWeekRegex = /^(\d{4})-(\d{1,2})$/;
const m = yearWeek.match(yearWeekRegex);
if (!m) {
throw new Error('invalid YearWeek string');
}
const parsed = { year: +m[1], week: +m[2] };
if (!(parsed.week >= 1 && parsed.week <= 53)) {
throw new Error('invalid week in YearWeek string');
}
return parsed;
}
function yearWeekStringToDayjs(yearWeek: string): Dayjs {
const { year, week } = parseYearWeekString(yearWeek);
// "The first week of the year, hence, always contains 4 January." https://en.wikipedia.org/wiki/ISO_week_date
const output = dayjs().year(year).month(1).date(4).isoWeek(week).startOf('isoWeek');
assert(output.isoWeek() === week && output.isoWeekYear() === year, 'conversion to dayjs was wrong');
return output;
}
function dayjsToYearWeekString(yearWeek: Dayjs): string {
return `${yearWeek.isoWeekYear()}-${yearWeek.isoWeek().toString().padStart(2, '0')}`;
}
class DateCache {
private dayCache = new Map<string, UnifiedDay>();
private isoWeekCache = new Map<string, UnifiedIsoWeek>();
private nextWeekCache = new WeakMap<UnifiedIsoWeek, UnifiedIsoWeek>();
getDay(dayString: string): UnifiedDay {
return this._getDay(dayString, undefined, undefined);
}
getDayUsingDayjs(dayjsDay: Dayjs): UnifiedDay {
return this.getDay(dayjsDay.format('YYYY-MM-DD'));
}
today(): UnifiedDay {
return this.getDayUsingDayjs(dayjs());
}
getIsoWeek(nonNormalizedYearWeekString: string): UnifiedIsoWeek {
let yearWeekString =
nonNormalizedYearWeekString.length === 7
? nonNormalizedYearWeekString
: nonNormalizedYearWeekString.slice(0, 5) + '0' + nonNormalizedYearWeekString.slice(5);
const cachedIsoWeek = this.isoWeekCache.get(yearWeekString);
if (cachedIsoWeek) {
return cachedIsoWeek;
}
assert(!!yearWeekString.match(/^\d{4}-\d{2}$/));
const { year, week } = parseYearWeekString(yearWeekString);
const firstDayDayjs = yearWeekStringToDayjs(yearWeekString);
const firstDayString = firstDayDayjs.format('YYYY-MM-DD');
const output: UnifiedIsoWeek = {
isoYear: year,
isoWeek: week,
yearWeekString,
firstDay: undefined as any as UnifiedDay,
};
output.firstDay = this._getDay(firstDayString, firstDayDayjs, output);
assert(output.firstDay.isoWeek === output);
this.isoWeekCache.set(yearWeekString, output);
return output;
}
rangeFromDays(days: Iterable<UnifiedDay>): { min: UnifiedDay; max: UnifiedDay } | undefined {
let min: UnifiedDay | undefined;
let max: UnifiedDay | undefined;
for (const day of days) {
if (!min) {
min = day;
} else if (day.dayjs.isBefore(min.dayjs)) {
min = day;
}
if (!max) {
max = day;
} else if (day.dayjs.isAfter(max.dayjs)) {
max = day;
}
}
assert((min === undefined) === (max === undefined));
return min && max && { min, max };
}
daysFromRange(range: { min: UnifiedDay; max: UnifiedDay } | undefined): UnifiedDay[] {
if (!range) {
return [];
}
const { min, max } = range;
assert(min.dayjs.isBefore(max.dayjs) || min === max);
const diff = max.dayjs.diff(min.dayjs, 'day');
const output: UnifiedDay[] = [min];
for (let i = 0; i < diff; i++) {
output.push(this.getDayUsingDayjs(min.dayjs.add(i, 'day')));
}
return output;
}
middleDay({ min, max }: { min: UnifiedDay; max: UnifiedDay }): UnifiedDay {
const diff = Math.abs(min.dayjs.diff(max.dayjs, 'days'));
const middle = min.dayjs.add(Math.floor(diff / 2), 'days');
return this.getDayUsingDayjs(middle);
}
rangeFromWeeks(weeks: Iterable<UnifiedIsoWeek>): { min: UnifiedIsoWeek; max: UnifiedIsoWeek } | undefined {
let min: UnifiedIsoWeek | undefined;
let max: UnifiedIsoWeek | undefined;
for (const week of weeks) {
if (!min) {
min = week;
} else if (this.weekIsBefore(week, min)) {
min = week;
}
if (!max) {
max = week;
} else if (this.weekIsBefore(max, week)) {
max = week;
}
}
assert((min === undefined) === (max === undefined));
return min && max && { min, max };
}
weeksFromRange(range: { min: UnifiedIsoWeek; max: UnifiedIsoWeek } | undefined): UnifiedIsoWeek[] {
if (!range) {
return [];
}
const { min, max } = range;
assert(this.weekIsBefore(min, max) || min === max);
const maxOutputSize = (max.isoYear - min.isoYear + 1) * 53;
assert(maxOutputSize > 0);
const output: UnifiedIsoWeek[] = [min];
let last = min;
while (last !== max) {
const next = this.getNextWeek(last);
last = next;
output.push(next);
assert(output.length <= maxOutputSize);
}
return output;
}
// a < b
weekIsBefore(a: UnifiedIsoWeek, b: UnifiedIsoWeek) {
return a.isoYear < b.isoYear || (a.isoYear === b.isoYear && a.isoWeek < b.isoWeek);
}
private getNextWeek(week: UnifiedIsoWeek): UnifiedIsoWeek {
let nextWeek = this.nextWeekCache.get(week);
if (nextWeek) {
return nextWeek;
}
// this is good enough for most weeks of the year
nextWeek = this.isoWeekCache.get(`${week.isoYear}-${week.isoWeek + 1}`);
// cover the case where "week.isoWeek + 1" is out of range at the end of the year
if (!nextWeek) {
const firstDayOfNextWeek = week.firstDay.dayjs.endOf('isoWeek').add(1, 'day').startOf('isoWeek');
nextWeek = this.getDayUsingDayjs(firstDayOfNextWeek).isoWeek;
}
assert(this.weekIsBefore(week, nextWeek));
this.nextWeekCache.set(week, nextWeek);
return nextWeek;
}
private _getDay(
dayString: string,
_dayDayjs: Dayjs | undefined,
_isoWeek: UnifiedIsoWeek | undefined
): UnifiedDay {
const cachedDay = this.dayCache.get(dayString);
if (cachedDay) {
return cachedDay;
}
assert(!!dayString.match(/^\d{4}-\d{2}-\d{2}$/));
const dayDayjs = _dayDayjs || dayjs(dayString, 'YYYY-MM-DD');
const isoWeek = _isoWeek || this.getIsoWeek(dayjsToYearWeekString(dayDayjs));
// Since getDay and getIsoWeek are mutually recursive, we may already have created
// the requested day. If that is the case, return that instance to prevent duplicates.
if (isoWeek.firstDay?.string === dayString) {
return isoWeek.firstDay;
}
const output: UnifiedDay = {
string: dayString,
dayjs: dayDayjs,
isoWeek,
};
this.dayCache.set(dayString, output);
return output;
}
}
// It is important that there is only one DateCache instance, so that all UnifiedDay (etc.)
// objects are reference equal when they describe the same day
export const globalDateCache = new DateCache();
export const DateCacheClassForTests = DateCache;