feat: Add new vocabulary to the review queue

When a level is finished, the vocabulary of that item will be
converted into SM2 metadata, which will be appended to the
user's vocabMetadata.

backend/src/api/user.ts

@@ -261,9 +261,27 @@ userRouter.post("/level/:id", async (req: LRequest, res) => {
             levels: user.levels.concat(id),
         };
         if (id > Math.max(...user.levels)) {
-            // TODO: Add the levels vocabulary to the users review queue
+            // TODO: if (!level)
+            const level = await db.collection("levels").findOne({
+                level: id,
+            });
+
+            // Convert the level's vocabulary to SM2 metadata
+            let sm2: { [id: number]: ISM2Metadata } = {};
+            level.vocab.forEach((id: number) => {
+                sm2[id] = {
+                    easiness: 1.3,
+                    consecutiveCorrectAnswers: 0,
+                    nextDueDate: Date.parse((new Date()).toString()),
+                };
+            });
+            const newVocabMetadata = Object.assign({}, user.vocabMetadata, sm2);
+
             // Also update the lastLevel attribute
-            Object.assign(update, { lastLevel: id });
+            Object.assign(update, {
+                lastLevel: id,
+                vocabMetadata: newVocabMetadata,
+            });
         }
         await db.collection("users").updateOne({
             username: user.username,