Fix/wrong calc elapsed days (#144)

* Fix/incorrect calc of elapsed_days

* add test

* bump version to 4.5.2

__tests__/fixed/calc-elapsed-days.test.ts

@@ -0,0 +1,26 @@
+import { createEmptyCard, fsrs, Grade, Rating } from '../../src/fsrs'
+
+/**
+ * @see https://forums.ankiweb.net/t/feature-request-estimated-total-knowledge-over-time/53036/58?u=l.m.sherlock
+ * @see https://ankiweb.net/shared/info/1613056169
+ */
+test('TS-FSRS-Simulator', () => {
+  const f = fsrs({
+    w: [
+      1.1596, 1.7974, 13.1205, 49.3729, 7.2303, 0.5081, 1.5371, 0.001, 1.5052,
+      0.1261, 0.9735, 1.8924, 0.1486, 0.2407, 2.1937, 0.1518, 3.0699, 0.4636,
+      0.6048,
+    ],
+  })
+  const rids = [1704468957000, 1704469645000, 1704599572000, 1705509507000]
+
+  const expected = [13.1205, 17.3668145, 21.28550751, 39.63452215]
+  let card = createEmptyCard(new Date(rids[0]))
+  const grades: Grade[] = [Rating.Good, Rating.Good, Rating.Good, Rating.Good]
+  for (let i = 0; i < rids.length; i++) {
+    const now = new Date(rids[i])
+    const log = f.next(card, now, grades[i])
+    card = log.card
+    expect(card.stability).toBeCloseTo(expected[i], 4)
+  }
+})

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-fsrs",
-  "version": "4.5.1",
+  "version": "4.5.2",
   "description": "ts-fsrs is a versatile package based on TypeScript that supports ES modules, CommonJS, and UMD. It implements the Free Spaced Repetition Scheduler (FSRS) algorithm, enabling developers to integrate FSRS into their flashcard applications to enhance the user learning experience.",
   "main": "dist/index.cjs",
   "umd": "dist/index.umd.js",

src/fsrs/abstract_scheduler.ts

@@ -1,6 +1,6 @@
 import { FSRSAlgorithm } from './algorithm'
 import { TypeConvert } from './convert'
-import { Grades } from './help'
+import { dateDiffInDays, Grades } from './help'
 import {
   type Card,
   type Grade,
@@ -46,7 +46,7 @@ export abstract class AbstractScheduler implements IScheduler {
     const { state, last_review } = this.current
     let interval = 0 // card.state === State.New => 0
     if (state !== State.New && last_review) {
-      interval = this.review_time.diff(last_review as Date, 'days')
+      interval = dateDiffInDays(last_review, this.review_time)
     }
     this.current.last_review = this.review_time
     this.current.elapsed_days = interval

src/fsrs/default.ts

@@ -11,7 +11,7 @@ export const default_w = [
 export const default_enable_fuzz = false
 export const default_enable_short_term = true
 
-export const FSRSVersion: string = 'v4.5.1 using FSRS-5.0'
+export const FSRSVersion: string = 'v4.5.2 using FSRS-5.0'
 
 export const generatorParameters = (
   props?: Partial<FSRSParameters>

src/fsrs/help.ts

@@ -191,3 +191,19 @@ export function get_fuzz_range(
 export function clamp(value: number, min: number, max: number): number {
   return Math.min(Math.max(value, min), max)
 }
+
+export function dateDiffInDays(last: Date, cur: Date) {
+  // Discard the time and time-zone information.
+  const utc1 = Date.UTC(
+    last.getUTCFullYear(),
+    last.getUTCMonth(),
+    last.getUTCDate()
+  )
+  const utc2 = Date.UTC(
+    cur.getUTCFullYear(),
+    cur.getUTCMonth(),
+    cur.getUTCDate()
+  )
+
+  return Math.floor((utc2 - utc1) / 86400000 /** 1000 * 60 * 60 * 24*/)
+}