Fix/set same seed should return the same interval

__tests__/fixed/same-seed.test.ts

@@ -0,0 +1,45 @@
+import { createEmptyCard, fsrs, Rating } from '../../src/fsrs'
+
+describe('fuzz same seed', () => {
+  const MOCK_NOW = new Date(2024, 7, 15)
+  const size = 100
+
+  // https://github.com/open-spaced-repetition/ts-fsrs/issues/113
+  it('should be the same[short-term]', () => {
+    const { card } = fsrs().next(createEmptyCard(), MOCK_NOW, Rating.Good)
+    const scheduler = fsrs({ enable_fuzz: true })
+    const MOCK_TOMORROW = new Date(2024, 7, 16)
+
+    const timestamp: number[] = []
+    for (let count = 0; count < size; count++) {
+      setTimeout(() => {
+        const _card = scheduler.next(card, MOCK_TOMORROW, Rating.Good).card
+        timestamp.push(_card.due.getTime())
+        if (timestamp.length === size) {
+          expect(timestamp.every((value) => value === timestamp[0])).toBe(true)
+        }
+      }, 50)
+    }
+  })
+
+  it('should be the same[long-term]', () => {
+    const { card } = fsrs({ enable_short_term: false }).next(
+      createEmptyCard(),
+      MOCK_NOW,
+      Rating.Good
+    )
+    const scheduler = fsrs({ enable_fuzz: true, enable_short_term: false })
+    const MOCK_TOMORROW = new Date(2024, 7, 18)
+
+    const timestamp: number[] = []
+    for (let count = 0; count < size; count++) {
+      setTimeout(() => {
+        const _card = scheduler.next(card, MOCK_TOMORROW, Rating.Good).card
+        timestamp.push(_card.due.getTime())
+        if (timestamp.length === size) {
+          expect(timestamp.every((value) => value === timestamp[0])).toBe(true)
+        }
+      }, 50)
+    }
+  })
+})

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-fsrs",
-  "version": "4.1.1",
+  "version": "4.1.2",
   "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/algorithm.ts

@@ -136,7 +136,7 @@ export class FSRSAlgorithm {
    **/
   apply_fuzz(ivl: number, elapsed_days: number, enable_fuzz?: boolean): int {
     if (!enable_fuzz || ivl < 2.5) return Math.round(ivl) as int
-    const generator = alea(this.seed)
+    const generator = alea(this._seed) // I do not want others to directly access the seed externally.
     const fuzz_factor = generator()
     const { min_ivl, max_ivl } = get_fuzz_range(
       ivl,

src/fsrs/default.ts

@@ -11,7 +11,7 @@ export const default_w = [
 export const default_enable_fuzz = false
 export const defualt_enable_short_term = true
 
-export const FSRSVersion: string = 'v4.1.1 using FSRS V5.0'
+export const FSRSVersion: string = 'v4.1.2 using FSRS V5.0'
 
 export const generatorParameters = (
   props?: Partial<FSRSParameters>