From a3d4e5d9c671106b9ae6202b6e4dc7092e16f72a Mon Sep 17 00:00:00 2001
From: Sara <sarak.works@gmail.com>
Date: Thu, 5 Dec 2024 09:38:38 +0000
Subject: [PATCH] [WOM-5333] Wrap BpkCalendar format date methods with memoize
 (#3689)

* Wrap BpkCalendar format date methods with memoize

* Improvements

* Improvement

* Add memoize for formatMonth only to avoid double calls

* Add TS doc

* Add licence header to test file
---
 .../src/BpkCalendarGrid.tsx                   |  3 +-
 .../src/composeCalendar.tsx                   |  5 +-
 .../bpk-component-calendar/src/utils-test.ts  | 70 +++++++++++++++++++
 packages/bpk-component-calendar/src/utils.ts  | 50 +++++++++++++
 4 files changed, 125 insertions(+), 3 deletions(-)
 create mode 100644 packages/bpk-component-calendar/src/utils-test.ts

diff --git a/packages/bpk-component-calendar/src/BpkCalendarGrid.tsx b/packages/bpk-component-calendar/src/BpkCalendarGrid.tsx
index 60808f2982..77085f5319 100644
--- a/packages/bpk-component-calendar/src/BpkCalendarGrid.tsx
+++ b/packages/bpk-component-calendar/src/BpkCalendarGrid.tsx
@@ -30,6 +30,7 @@ import {
   getCalendarMonthWeeks,
   isSameMonth,
 } from './date-utils';
+import { memoize } from './utils';
 
 import type { DateModifiers, SelectionConfiguration } from './custom-proptypes';
 
@@ -170,7 +171,7 @@ class BpkCalendarGrid extends Component<Props, State> {
               dates={dates}
               onDateClick={onDateClick}
               onDateKeyDown={onDateKeyDown}
-              formatDateFull={formatDateFull}
+              formatDateFull={memoize(formatDateFull)}
               DateComponent={DateComponent}
               dateModifiers={dateModifiers!}
               preventKeyboardFocus={preventKeyboardFocus}
diff --git a/packages/bpk-component-calendar/src/composeCalendar.tsx b/packages/bpk-component-calendar/src/composeCalendar.tsx
index ec2bfc10c7..178f3e618b 100644
--- a/packages/bpk-component-calendar/src/composeCalendar.tsx
+++ b/packages/bpk-component-calendar/src/composeCalendar.tsx
@@ -21,6 +21,7 @@ import type { ComponentType } from 'react';
 import { cssModules } from '../../bpk-react-utils';
 
 import { CALENDAR_SELECTION_TYPE } from './custom-proptypes';
+import { memoize } from './utils';
 
 import type {
   DaysOfWeek,
@@ -184,7 +185,7 @@ const composeCalendar = (
         {Nav && (
           <Nav
             changeMonthLabel={changeMonthLabel}
-            formatMonth={formatMonth}
+            formatMonth={memoize(formatMonth)}
             id={`${id}__bpk_calendar_nav`}
             maxDate={maxDate}
             minDate={minDate}
@@ -211,7 +212,7 @@ const composeCalendar = (
           dateModifiers={dateModifiers}
           daysOfWeek={daysOfWeek}
           formatDateFull={formatDateFull}
-          formatMonth={formatMonth}
+          formatMonth={memoize(formatMonth)}
           month={month}
           onDateClick={onDateClick}
           onDateKeyDown={onDateKeyDown}
diff --git a/packages/bpk-component-calendar/src/utils-test.ts b/packages/bpk-component-calendar/src/utils-test.ts
new file mode 100644
index 0000000000..17c9ed4782
--- /dev/null
+++ b/packages/bpk-component-calendar/src/utils-test.ts
@@ -0,0 +1,70 @@
+/*
+ * Backpack - Skyscanner's Design System
+ *
+ * Copyright 2016 Skyscanner Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { describe, it, expect, jest } from '@jest/globals';
+
+import { memoize } from './utils';
+
+describe('memoize', () => {
+  it('should call the original function for new arguments', () => {
+    const mockFn = jest.fn((x: number) => x * 2);
+    const memoizedFn = memoize(mockFn);
+
+    expect(memoizedFn(2)).toBe(4);
+    expect(mockFn).toHaveBeenCalledTimes(1);
+
+    expect(memoizedFn(3)).toBe(6);
+    expect(mockFn).toHaveBeenCalledTimes(2);
+  });
+
+  it('should return cached results for repeated arguments', () => {
+    const mockFn = jest.fn((x: number) => x * 2);
+    const memoizedFn = memoize(mockFn);
+
+    memoizedFn(2); // Original function called
+    memoizedFn(2); // Result from cache
+    memoizedFn(2); // Result from cache
+
+    expect(mockFn).toHaveBeenCalledTimes(1); // Function called only once
+  });
+
+  it('should handle functions with multiple arguments', () => {
+    const mockFn = jest.fn((x: number, y: number) => x + y);
+    const memoizedFn = memoize(mockFn);
+
+    expect(memoizedFn(2, 3)).toBe(5); // Original function called
+    expect(mockFn).toHaveBeenCalledTimes(1);
+
+    expect(memoizedFn(2, 3)).toBe(5); // Result from cache
+    expect(mockFn).toHaveBeenCalledTimes(1); // No additional calls
+
+    expect(memoizedFn(3, 2)).toBe(5); // New arguments, original function called
+    expect(mockFn).toHaveBeenCalledTimes(2);
+  });
+
+  it('should handle functions with no arguments', () => {
+    const mockFn = jest.fn(() => 42);
+    const memoizedFn = memoize(mockFn);
+
+    expect(memoizedFn()).toBe(42); // Original function called
+    expect(mockFn).toHaveBeenCalledTimes(1);
+
+    expect(memoizedFn()).toBe(42); // Result from cache
+    expect(mockFn).toHaveBeenCalledTimes(1); // No additional calls
+  });
+});
diff --git a/packages/bpk-component-calendar/src/utils.ts b/packages/bpk-component-calendar/src/utils.ts
index 218c80e2a5..4cbff4497e 100644
--- a/packages/bpk-component-calendar/src/utils.ts
+++ b/packages/bpk-component-calendar/src/utils.ts
@@ -60,3 +60,53 @@ export const getTransformStyles = (transformValue: string) => {
 
 export const isTransitionEndSupported = () =>
   !!(typeof window !== 'undefined' && 'TransitionEvent' in window);
+
+/**
+ * Memoizes a given function to optimize performance by caching its results based on input arguments.
+ *
+ * @template T - The type of the function to be memoized. Must be a function.
+ * @param {T} fn - The function to be memoized.
+ * @returns {T} - The memoized version of the input function. Subsequent calls with the same arguments
+ *                will return the cached result, avoiding redundant computations.
+ *
+ * @example
+ * // Simple usage:
+ * const add = (a: number, b: number) => a + b;
+ * const memoizedAdd = memoize(add);
+ *
+ * console.log(memoizedAdd(1, 2)); // Computes and caches result: 3
+ * console.log(memoizedAdd(1, 2)); // Fetches from cache: 3
+ *
+ * @example
+ * // With a more complex function:
+ * const slowFunction = (num: number) => {
+ *   console.log('Computing...');
+ *   return num * 2;
+ * };
+ * const memoizedSlowFunction = memoize(slowFunction);
+ *
+ * console.log(memoizedSlowFunction(5)); // Logs "Computing...", returns 10
+ * console.log(memoizedSlowFunction(5)); // Fetches from cache: 10
+ *
+ * @remarks
+ * - This implementation uses a `Map` object and `JSON.stringify` to create cache keys.
+ * - Functions with non-primitive or cyclic arguments may not work as expected due to
+ *   `JSON.stringify` limitations.
+ * - The cache is stored in memory and will grow indefinitely unless manually managed or
+ *   the function goes out of scope.
+ */
+export function memoize<T extends (...args: any[]) => any>(fn: T): T {
+  const cache = new Map<string, ReturnType<T>>();
+
+  function memoizedFunction(...args: Parameters<T>): ReturnType<T> {
+    const key = JSON.stringify(args);
+    if (cache.has(key)) {
+      return cache.get(key) as ReturnType<T>;
+    }
+    const result = fn(...args);
+    cache.set(key, result);
+    return result;
+  }
+
+  return memoizedFunction as T;
+}