perf: pagination, filter and sort on backend

pages/api/product/index.js

 
   await dbConnect();
 
-  const pageIndex = req.query.page;
+  const pageIndex = req.query.pageIndex;
+  const category = req.query.category === 'All' ? '' : req.query.category;
+  const filterType = req.query.filterType;
 
   if (pageIndex < 1) {
     res.status(422).json({
   switch (method) {
     case 'GET': {
       try {
-        const productCount = await Product.countDocuments();
+        const productCount = await Product.find({
+          category: { $regex: category },
+        }).countDocuments();
 
         if (productCount === 0) {
           res.status(200).json({
             message: 'There are currently no products in our database.',
             product: [],
             productCount: 0,
+            next: null,
+            previous: null,
           });
           break;
         }
           throw new Error('Page does not exist!');
         }
 
-        const product = await Product.find({})
+        const product = await Product.find({ category: { $regex: category } })
           .skip((pageIndex - 1) * 9)
-          .limit(9);
+          .limit(9)
+          .sort(filterType === 'asc' ? 'name' : '-name ');
 
         if (!product) {
           throw new Error('There are currently no products in our database.');
         }
 
+        const previousUrl =
+          pageIndex > 1
+            ? `https://localhost:3000/api/product?pageIndex=${
+                parseInt(pageIndex) - 1
+              }`
+            : null;
+        const nextUrl =
+          pageIndex * 9 < productCount
+            ? `https://localhost:3000/api/product?pageIndex=${
+                parseInt(pageIndex) + 1
+              }`
+            : null;
+
         res.status(200).json({
           message: 'All products from our database were fetched successfully.',
           product,
           productCount,
+          next: nextUrl,
+          previous: previousUrl,
         });
       } catch (error) {
         res.status(400).json({ message: error.message });