fix: prevent createCategory function from adding an existing category

Change `$push` operation to `$addToSet` in `createCategory` function for avoiding
duplicating existing categories, And make the function returns `null` if the incoming
category is already exist.

Add "if" statement to `products_createCategory_post` route handler to check if
the respond of `createCategory` function equals `null` for returning an error
with "The category already exist" message.

src/controllers/admin-controllers/createCategory.js

@@ -3,11 +3,15 @@ import SettingsModel from "../../models/Settings.js";
 export default async function createCategory(category, session) {
     try {
         const respond = await SettingsModel.updateOne(
-            {},
-            { $push: { productsCategories: [category] } },
+            { productsCategories: { $nin: [category] } },
+            { $addToSet: { productsCategories: [category] } },
             { session }
         );
-        return !!respond.modifiedCount;
+
+        if (respond.acknowledged && respond.modifiedCount === 0) {
+            return null
+        }
+        return !!respond.modifiedCount
     } catch (error) {
         console.log(error)
         return;

src/routes/admin_routes/products_createCategory_post.js

@@ -11,6 +11,9 @@ export default asyncRouteHandler(
             const session = await startSession();
             session.startTransaction();
             const dbUpdateResponse = await AdminController.createCategory(category, session);
+            if (dbUpdateResponse === null) {
+                return next(new ErrorGenerator("The category already exist", 400));
+            }
             const cacheUpdateResponse = await updateRedisCache("store-variables", (variablesObject) => {
                 variablesObject?.productsCategories.push(category)
                 return variablesObject
@@ -23,7 +26,7 @@ export default asyncRouteHandler(
                 res.status(400).json(false);
             }
         } else {
-            next(new ErrorGenerator("You didn't provide a valid category name", 400))
+            next(new ErrorGenerator("Ivalid Category Name", 400));
         }
     }
 )