fix(dateTime): calculate ralative time via duration (#75)

src/dateTime/dateTime.ts

@@ -377,11 +377,49 @@ class DateTimeImpl implements DateTime {
     fromNow(withoutSuffix?: boolean | undefined): string {
         return this.from(dateTime({timeZone: this._timeZone, lang: this._locale}), withoutSuffix);
     }
-    from(formaInput: DateTimeInput, withoutSuffix?: boolean): string {
+    from(fromInput: DateTimeInput, withoutSuffix?: boolean): string {
         if (!this.isValid()) {
             return this._localeData.invalidDate || INVALID_DATE_STRING;
         }
-        return fromTo(this, formaInput, this._localeData.relativeTime, withoutSuffix, true);
+
+        const value = DateTimeImpl.isDateTime(fromInput)
+            ? fromInput.timeZone(this._timeZone)
+            : createDateTime({
+                  ts: getTimestamp(fromInput, 'system', this._locale)[0],
+                  timeZone: this._timeZone,
+                  locale: this._locale,
+                  offset: this._offset,
+              });
+
+        if (!value.isValid()) {
+            return this._localeData.invalidDate || INVALID_DATE_STRING;
+        }
+
+        let a = value;
+        let b: DateTime = this;
+        let switched = false;
+        if (b.isBefore(a)) {
+            a = this;
+            b = value;
+            switched = true;
+        }
+
+        let months = b.month() - a.month() + (b.year() - a.year()) * 12;
+        if (a.add(months, 'months').isAfter(b)) {
+            months--;
+        }
+        let milliseconds = b.valueOf() - a.add(months, 'months').valueOf();
+
+        if (switched) {
+            months = -months;
+            milliseconds = -milliseconds;
+        }
+
+        return fromTo(
+            duration({months, milliseconds}),
+            this._localeData.relativeTime,
+            withoutSuffix,
+        );
     }
     locale(): string;
     locale(locale: string): DateTime;

src/dateTime/relative.ts

@@ -1,7 +1,5 @@
 import type {Locale, RelativeTime} from '../settings/types';
-import type {BaseUnit, DateTime, DateTimeInput} from '../typings';
-
-import {dateTime} from './dateTime';
+import type {BaseUnit, Duration} from '../typings';
 
 export interface RelativeTimeThreshold {
     l: Exclude<keyof RelativeTime, 'future' | 'past'>;
@@ -40,19 +38,18 @@ const relObj = {
 } satisfies RelativeTime;
 
 export function fromTo(
-    date: DateTime,
-    input: DateTimeInput,
+    duration: Duration,
     loc: Locale['relativeTime'] = relObj,
     withoutSuffix = false,
-    isFrom = true,
 ): string {
     let result = 0;
     let isFuture;
     let out = '';
+
     for (let i = 0; i < thresholds.length; i += 1) {
         let t = thresholds[i];
         if (t.d) {
-            result = isFrom ? date.diff(input, t.d, true) : dateTime({input}).diff(date, t.d, true);
+            result = duration.as(t.d);
         }
         const abs = Math.round(Math.abs(result));
         isFuture = result > 0;

src/duration/duration.ts

@@ -1,7 +1,7 @@
 // Copyright 2019 JS Foundation and other contributors
 // Copyright 2024 YANDEX LLC
 
-import {dateTimeUtc} from '../dateTime';
+import {fromTo} from '../dateTime/relative';
 import {settings} from '../settings';
 import type {
     Duration,
@@ -11,7 +11,7 @@ import type {
     FormatOptions,
 } from '../typings';
 import {normalizeDateComponents, normalizeDurationUnit} from '../utils';
-import {getListFormat, getNumberFormat} from '../utils/locale';
+import {getListFormat, getLocaleData, getNumberFormat} from '../utils/locale';
 
 import {createDuration} from './createDuration';
 import {normalizeValues, orderedUnits, rescale, shiftTo} from './normalize';
@@ -294,8 +294,8 @@ export class DurationImpl implements Duration {
         if (!this.isValid()) {
             return 'Invalid Duration';
         }
-        const now = dateTimeUtc({lang: this._locale});
-        return now.add(this.valueOf(), 'ms').from(now, !withSuffix);
+        const localeData = getLocaleData(this._locale);
+        return fromTo(this, localeData.relativeTime, !withSuffix);
     }
 
     humanizeIntl(

src/utils/locale.ts

@@ -1,3 +1,6 @@
+import dayjs from '../dayjs';
+import type {Locale} from '../settings/types';
+
 const dateTimeFormatCache = new Map<string, Intl.DateTimeFormat>();
 export function getDateTimeFormat(locale: string, options: Intl.DateTimeFormatOptions = {}) {
     const key = JSON.stringify([locale, options]);
@@ -33,3 +36,11 @@ export function getNumberFormat(locale: string, options: Intl.NumberFormatOption
     }
     return numberFormat;
 }
+
+export function getLocaleData(locale: string) {
+    const localeData = dayjs.Ls[locale];
+    if (!localeData) {
+        throw new Error(`Locale ${locale} is not loaded`);
+    }
+    return localeData as Locale;
+}