add Redis for cache and Mysqli for database query

classes/interface_db.php

@@ -0,0 +1,25 @@
+<?php
+
+interface DBInterface
+{
+    public function connect($host, $username, $password, $database, $port);
+
+    public function query(string $sql);
+
+    public function error(): string;
+
+    public function errno(): int;
+
+    public function numRows($result): int;
+
+    public function selectDb($database);
+
+    public function fetchAssoc($result): array|null;
+
+    public function fetchRow($result): array|null;
+
+    public function affectedRows(): int;
+
+    public function escapeString(string $string): string;
+
+}