feat: initial foundation for collaborative canteen ordering system in vanilla PHP

app/Models/User.php

@@ -0,0 +1,59 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Models;
+
+use App\Core\Database\Database;
+use PDO;
+
+class User
+{
+    public static function all(): array
+    {
+        $db = Database::getConnection();
+        $stmt = $db->query("
+            SELECT u.id, u.name, u.username, u.email, u.created_at,
+                   (SELECT COUNT(*) FROM employee_orders WHERE user_id = u.id) as total_orders,
+                   (SELECT COALESCE(SUM(total_bill), 0) FROM employee_orders WHERE user_id = u.id AND status = 'unpaid') as unpaid_balance
+            FROM users u
+            ORDER BY u.name ASC
+        ");
+        return $stmt->fetchAll();
+    }
+
+    public static function find(int $id): ?array
+    {
+        $db = Database::getConnection();
+        $stmt = $db->prepare("SELECT id, name, username, email, created_at FROM users WHERE id = ?");
+        $stmt->execute([$id]);
+        $res = $stmt->fetch();
+        return $res ?: null;
+    }
+
+    public static function findByIdentifier(string $identifier): ?array
+    {
+        $db = Database::getConnection();
+        $identifier = trim($identifier);
+        $stmt = $db->prepare("SELECT * FROM users WHERE LOWER(username) = LOWER(?) OR LOWER(email) = LOWER(?)");
+        $stmt->execute([$identifier, $identifier]);
+        $res = $stmt->fetch();
+        return $res ?: null;
+    }
+
+    public static function create(string $name, string $username, string $email, string $password): int
+    {
+        $db = Database::getConnection();
+        $hash = password_hash($password, PASSWORD_DEFAULT);
+
+        $stmt = $db->prepare("INSERT INTO users (name, username, email, password_hash) VALUES (?, ?, ?, ?)");
+        $stmt->execute([
+            trim($name),
+            strtolower(trim($username)),
+            strtolower(trim($email)),
+            $hash
+        ]);
+
+        return (int)$db->lastInsertId();
+    }
+}