feat: Implement SM2

src/algorithms/sm2/index.ts

@@ -0,0 +1,35 @@
+import { dayInNDays } from "../../utils/date";
+
+export interface ISchedulingData {
+    easiness: number;
+    consecutiveCorrectAnswers: number;
+    nextDueDate: number;
+};
+
+export enum AnswerType {
+    CORRECT,
+    WRONG,
+};
+
+function performanceRating(answer: AnswerType): number {
+    switch (answer) {
+        case AnswerType.WRONG:
+            return 1;
+        case AnswerType.CORRECT:
+            return 4;
+    }
+}
+
+export function updateSchedulingData(data: ISchedulingData, answer: AnswerType): ISchedulingData {
+    const perfRating = performanceRating(answer);
+
+    data.easiness += -0.8 + 0.28 * perfRating + 0.02 * Math.pow(perfRating, 2);
+    data.consecutiveCorrectAnswers = answer === AnswerType.CORRECT ? (
+        data.consecutiveCorrectAnswers + 1
+    ) : 0;
+    data.nextDueDate = answer === AnswerType.CORRECT ? (
+        dayInNDays(6 * Math.pow(data.easiness, data.consecutiveCorrectAnswers - 1))
+    ) : dayInNDays(1);
+
+    return data;
+}

src/utils/date.ts

@@ -0,0 +1,9 @@
+export const DAY_IN_MILLI = 24 * 60 * 60 * 1000;
+
+export function daysToMilli(n: number): number {
+    return DAY_IN_MILLI * n;
+};
+
+export function dayInNDays(n: number): number {
+    return Date.now() * daysToMilli(n);
+}