feat: adding to cart php script

server/controllers/add_cart.php

+<?php
+    session_start();
+    require_once "connect_database.php";
+    global $conn; $conn = connect_database();
+    if ($_SERVER["REQUEST_METHOD"] == "POST") {
+        global $conn;
+        $insert_query = "INSERT INTO `cart` (`item_id`, `cart_username`, `item_quantity`) VALUES ((?), (?), (?))
+        ";
+        $item_id = $_POST["item_id"];
+        $cart_username = $_SESSION["username"];
+        $item_quantity = $_POST["item_quantity"];
+
+        $stmt = $conn->prepare($insert_query);
+        if (!$stmt) {
+            die("Error in query preparation". $conn->error);
+        }
+
+        $stmt->bind_param("sss", $item_id, $cart_username, $item_quantity);
+        $result = $stmt->execute();
+        if (!$result) {
+            $response = array("success" => "false", "message" => $stmt.error);
+            die ("Error in query execution: " . $stmt->error);
+        } else {
+            $response = array("success" => "true", "message" => "item has been added");
+        }
+        echo json_encode($response);
+        mysqli_close($conn);
+    }
+?>
\ No newline at end of file