fix(website/ta): Prevent duplicate TA lesson in reducer (#3940)

Co-authored-by: Zhao Wei Liew <[email protected]>

Author: leslieyip02

website/src/reducers/timetables.test.ts

@@ -171,6 +171,17 @@ describe('TA module reducer', () => {
       },
     });
   });
+
+  test('should not add duplicate TA lessons', () => {
+    expect(
+      reducer(withTaModules, addTaLessonInTimetable(1, 'CS1010S', 'Tutorial', '1')),
+    ).toMatchObject({
+      ta: {
+        [1]: { CS1010S: [['Tutorial', '1']] },
+        [2]: { CS1010S: [['Tutorial', '1']] },
+      },
+    });
+  });
 });
 
 describe('lesson reducer', () => {

website/src/reducers/timetables.ts

@@ -3,7 +3,7 @@ import { produce } from 'immer';
 import { createMigrate } from 'redux-persist';
 
 import { PersistConfig } from 'storage/persistReducer';
-import { ModuleCode } from 'types/modules';
+import { ClassNo, LessonType, ModuleCode } from 'types/modules';
 import { ModuleLessonConfig, SemTimetableConfig, TaModulesConfig } from 'types/timetables';
 import { ColorMapping, TimetablesState } from 'types/reducers';
 
@@ -192,9 +192,13 @@ function semTaModules(state = DEFAULT_TA_STATE, action: Actions): TaModulesConfi
     case ADD_TA_LESSON_IN_TIMETABLE: {
       const { moduleCode, lessonType, classNo } = action.payload;
       if (!(moduleCode && lessonType && classNo)) return state;
+      const newLesson: [LessonType, ClassNo] = [lessonType, classNo];
+      const curLessons = state[moduleCode] ?? [];
+      // Prevent duplicate lessons
+      if (curLessons.some((lesson) => isEqual(lesson, newLesson))) return state;
       return {
         ...state,
-        [moduleCode]: [...(state[moduleCode] ?? []), [lessonType, classNo]],
+        [moduleCode]: [...curLessons, newLesson],
       };
     }
     case REMOVE_TA_LESSON_IN_TIMETABLE: {