refactor: database class singleton to use existing connection (#32)

This is a half-way fix for #31 so it does not close it. But it does solve the issue of `Too many connections` if the `Database` class when the `Database` class is instanced a lot. The issue of credentials still remain.

Reviewed-on: https://codeberg.org/vlw/scaffold/pulls/32

src/Database/Database.php

@@ -19,6 +19,8 @@
 		private const DEFAULT_USERNAME = "www-data";
 		private const DEFAULT_PASSWORD = "";
 
+		private static ?Database $instance = null;
+
 		/**
 		 * Create a new Database instance from credentials
 		 *
@@ -44,6 +46,16 @@
 			$_ENV["mariadb"]["user"] = $username;
 			$_ENV["mariadb"]["pass"] = $password;
 			$_ENV["mariadb"]["db"] = $database;
+
+			self::$instance = null;
+		}
+
+		public static function instance(): static {
+			if (self::$instance) {
+				return self::$instance;
+			}
+
+			return new static();
 		}
 
 		/**
@@ -56,6 +68,8 @@
 				$_ENV["mariadb"]["pass"],
 				$_ENV["mariadb"]["db"],
 			);
+
+			self::$instance = $this;
 		}
 
 		/**

src/Database/Model.php

@@ -27,7 +27,7 @@
 		 * @param string $table The target database table
 		 */
 		protected static function create(string $table, array $values): bool {
-			return new Database()->from($table)->insert($values);
+			return Database::instance()->from($table)->insert($values);
 		}
 
 		/**
@@ -42,7 +42,7 @@
 			public readonly array $columns,
 			public readonly array $where
 		) {
-			$this->db = new Database();
+			$this->db = Database::instance();
 		}
 
 		/**
@@ -75,7 +75,7 @@
 		 * @return bool Entity exists
 		 */
 		public function isset(): bool {
-			return $this->_isset ??= new Database()
+			return $this->_isset ??= Database::instance()
 				->from($this->table)
 				->where($this->where)
 				->limit(1)