started working on updateItem function at firebase.js, implemented ge…

…tDaysBetweenDates at dates.js

package.json

@@ -7,6 +7,7 @@
 		"npm": ">=8.19.0"
 	},
 	"dependencies": {
+		"@the-collab-lab/shopping-list-utils": "^2.2.0",
 		"firebase": "^10.1.0",
 		"react": "^18.2.0",
 		"react-dom": "^18.2.0",

src/api/firebase.js

@@ -10,7 +10,12 @@ import {
 } from 'firebase/firestore';
 import { useEffect, useState } from 'react';
 import { db } from './config';
-import { getFutureDate, isMoreThanADayAgo } from '../utils';
+import {
+	getFutureDate,
+	getDaysBetweenDates,
+	isMoreThanADayAgo,
+} from '../utils';
+import { calculateEstimate } from '@the-collab-lab/shopping-list-utils';
 
 /**
  * A custom hook that subscribes to the user's shopping lists in our Firestore
@@ -184,8 +189,24 @@ export async function updateItem(listPath, itemId) {
 	const itemDocumentRef = doc(listCollectionRef, itemId);
 	const item = await getDoc(itemDocumentRef);
 	const itemTotalPurchases = item.data().totalPurchases;
+	const dateLastPurchased = item.data().dateLastPurchased.toDate();
+	const prevDateNextPurchased = item.data().dateNextPurchased.toDate();
+	const now = new Date();
+	const daysSinceLastPurchase = getDaysBetweenDates(now, dateLastPurchased); // First buy: 0.
+	const prevEstimate = getDaysBetweenDates(
+		prevDateNextPurchased,
+		dateLastPurchased,
+	);
+	const nextEstimate = calculateEstimate(
+		prevEstimate,
+		daysSinceLastPurchase,
+		itemTotalPurchases,
+	);
+	const dateNextPurchased = getFutureDate(nextEstimate);
+
 	await updateDoc(itemDocumentRef, {
-		dateLastPurchased: new Date(),
+		dateLastPurchased: now,
+		dateNextPurchased: dateNextPurchased,
 		totalPurchases: itemTotalPurchases + 1,
 	});
 	return itemDocumentRef;

src/utils/dates.js

@@ -21,3 +21,14 @@ export const isMoreThanADayAgo = (date) => {
 	const diff = now - dateInMiliseconds;
 	return ONE_DAY_IN_MILLISECONDS < diff;
 };
+
+/**
+ * .
+ * @example
+ * //
+ *
+ * @param {Date} date
+ */
+export function getDaysBetweenDates(dateFuture, datePast = dateFuture) {
+	return Math.ceil((dateFuture.getTime() - datePast.getTime()) / 86400000);
+}