refactor: Move the SM2 implementation to the backend

backend/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;
+}

backend/src/api/user.ts

@@ -8,7 +8,9 @@ import { authRoute } from "../security/token";
 import { userFromSession } from "../utils/user";
 
 import { IUser, IUserDBModel } from "../models/user";
-import { ISM2Metadata } from "../models/review";
+import {
+    ISchedulingData, AnswerType, updateSchedulingData
+} from "../algorithms/sm2";
 import { LRequest } from "../types/express";
 
 const userRouter = express.Router();
@@ -190,34 +192,31 @@ userRouter.post("/lastReview", async (req: LRequest, res) => {
         return;
     }
 
+    // NOTE: Oh oh
+    // Update the user's score based on what they sent us
     user.score += parseInt(req.body.delta);
 
+    // Itterate over all of the vocabulary that needs to have its
+    // metadata updated.
+    // Use our SM2 implementation to update the vocabulary and modify our
+    // copy of the user object, so that we can write the copied (and modified)
+    // user object back into the database.
     Object.keys(req.body.sm2).forEach((id: string) => {
         const vocabId = parseInt(id);
         const correct: boolean = req.body.sm2[id];
-        let vocab_sm2: ISM2Metadata = Object.assign({},
+        let vocab_sm2: ISchedulingData = Object.assign({},
             user.vocabMetadata[vocabId]);
 
-        // TODO: Tuning?
-        // TODO: Move into another module
-        const perf = correct ? 3 : 1;
-        vocab_sm2.easiness += -0.8 + 0.28 * perf + 0.02 * Math.pow(perf, 2);
-        // Update the consecutive correct answers and the due date
-        if (correct) {
-            vocab_sm2.consecutiveCorrectAnswers += 1;
-            vocab_sm2.nextDueDate = dateInNDays(6 * Math.pow(vocab_sm2.easiness, vocab_sm2.consecutiveCorrectAnswers - 1));
-        } else {
-            vocab_sm2.consecutiveCorrectAnswers = 0;
-            vocab_sm2.nextDueDate = dateInNDays(1);
-        }
-
-        user.vocabMetadata[vocabId] = vocab_sm2;
+        const answer = correct ? AnswerType.CORRECT : AnswerType.WRONG;
+        user.vocabMetadata[vocabId] = updateSchedulingData(vocab_sm2, answer);
     });
 
     // Update the last review
     user.lastReview = req.body.meta;
 
-    // TODO: Error handling
+    // NOTE: Error handling could be implemented here, but we can ensure that
+    //       the user exists, as we just got his username (and entire data)
+    //       from `userFromSession`.
     await db.collection("users").updateOne({
         username: user.username,
     }, {