From 4d6f784cd2c7ffcc497e56469dd9f930b9f9752c Mon Sep 17 00:00:00 2001
From: Stephen Mwangi <mail@stephenmwangi.com>
Date: Sun, 20 Oct 2024 10:52:11 +0300
Subject: [PATCH] fix(load balancer): update due dates histogram after review

---
 src/algorithms/osr/note-scheduling.ts |  3 +--
 src/flashcard-review-sequencer.ts     | 14 ++++++++++++++
 tests/unit/scheduling.test.ts         |  6 +++---
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/algorithms/osr/note-scheduling.ts b/src/algorithms/osr/note-scheduling.ts
index 3272ffb7..3df9ef7c 100644
--- a/src/algorithms/osr/note-scheduling.ts
+++ b/src/algorithms/osr/note-scheduling.ts
@@ -43,8 +43,7 @@ export function osrSchedule(
             else if (interval < 30) fuzz = Math.max(2, Math.floor(interval * 0.15));
             else fuzz = Math.max(4, Math.floor(interval * 0.05));
 
-            const fuzzedInterval = dueDateHistogram.findLeastUsedIntervalOverRange(interval, fuzz);
-            interval = fuzzedInterval;
+            interval = dueDateHistogram.findLeastUsedIntervalOverRange(interval, fuzz);
         }
     }
 
diff --git a/src/flashcard-review-sequencer.ts b/src/flashcard-review-sequencer.ts
index fb7ff813..558022c6 100644
--- a/src/flashcard-review-sequencer.ts
+++ b/src/flashcard-review-sequencer.ts
@@ -2,6 +2,7 @@ import { ISrsAlgorithm } from "src/algorithms/base/isrs-algorithm";
 import { RepItemScheduleInfo } from "src/algorithms/base/rep-item-schedule-info";
 import { ReviewResponse } from "src/algorithms/base/repetition-item";
 import { Card } from "src/card";
+import { TICKS_PER_DAY } from "src/constants";
 import { DataStore } from "src/data-stores/base/data-store";
 import { CardListType, Deck } from "src/deck";
 import { IDeckTreeIterator } from "src/deck-tree-iterator";
@@ -11,6 +12,7 @@ import { Question, QuestionText } from "src/question";
 import { IQuestionPostponementList } from "src/question-postponement-list";
 import { SRSettings } from "src/settings";
 import { TopicPath } from "src/topic-path";
+import { globalDateProvider } from "src/utils/dates";
 
 export interface IFlashcardReviewSequencer {
     get hasCurrentCard(): boolean;
@@ -146,6 +148,8 @@ export class FlashcardReviewSequencer implements IFlashcardReviewSequencer {
 
     async processReviewReviewMode(response: ReviewResponse): Promise<void> {
         if (response != ReviewResponse.Reset || this.currentCard.hasSchedule) {
+            const oldSchedule = this.currentCard.scheduleInfo;
+
             // We need to update the schedule if:
             //  (1) the user reviewed with easy/good/hard (either a new or due card),
             //  (2) or reset a due card
@@ -154,6 +158,16 @@ export class FlashcardReviewSequencer implements IFlashcardReviewSequencer {
 
             // Update the source file with the updated schedule
             await DataStore.getInstance().questionWriteSchedule(this.currentQuestion);
+
+            if (oldSchedule) {
+                const today: number = globalDateProvider.today.valueOf();
+                const nDays: number = Math.ceil(
+                    (oldSchedule.dueDateAsUnix - today) / TICKS_PER_DAY,
+                );
+
+                this.dueDateFlashcardHistogram.decrement(nDays);
+            }
+            this.dueDateFlashcardHistogram.increment(this.currentCard.scheduleInfo.interval);
         }
 
         // Move/delete the card
diff --git a/tests/unit/scheduling.test.ts b/tests/unit/scheduling.test.ts
index b73e90fb..984f9dcb 100644
--- a/tests/unit/scheduling.test.ts
+++ b/tests/unit/scheduling.test.ts
@@ -99,7 +99,7 @@ test("Test load balancing, small interval (load balancing disabled)", () => {
     const newInterval: number = 3;
     const dueDates = new DueDateHistogram({
         0: 1,
-        1: 1, // key = originalInterval
+        1: 1,
         2: 1,
         3: 4,
     });
@@ -121,9 +121,9 @@ test("Test load balancing, small interval (load balancing disabled)", () => {
     expect(dueDates).toEqual(
         new DueDateHistogram({
             0: 1,
-            1: 0, // One less than before
+            1: 0,
             2: 1,
-            3: 5, // One more than before
+            3: 5,
         }),
     );
 });