clamp displayed skill in [0,1]... (#849)

Author: NiloCK

packages/courseware/src/typing/questions/single-letter/index.ts

@@ -71,8 +71,9 @@ export class TypeLetterQuestion extends Question {
       if (t < 3000) {
         return 1.0;
       } else {
-        // scale from 1 at 3s to 0.25 at 10s
-        return 1 - ((t - 3000) / 7000) * 0.75;
+        // scale from 1 at 3s to 0.25 at 10s, clamped to [0.25, 1]
+        const skill = 1 - ((t - 3000) / 7000) * 0.75;
+        return Math.max(0.25, skill);
       }
     }
     return 0;

packages/db/src/study/SpacedRepetition.ts

@@ -39,7 +39,7 @@ function newQuestionInterval(user: DocumentUpdater, cardHistory: CardHistory<Que
   }
 
   if (currentAttempt.isCorrect) {
-    const skill = currentAttempt.performance as number;
+    const skill = Math.min(1.0, Math.max(0.0, currentAttempt.performance as number));
     logger.debug(`Demontrated skill: \t${skill}`);
     const interval: number = lastInterval * (0.75 + skill);
     cardHistory.lapses = getLapses(cardHistory.records);