Refactor code structure for improved readability and maintainability

server/lib/userService.js

@@ -10,6 +10,7 @@ function serializeUser(row) {
         username: row.username,
         name: row.name,
         email: row.email,
+        isAdmin: Boolean(row.is_admin),
         createdAt: row.created_at ? new Date(row.created_at).toISOString() : null
     };
 }
@@ -20,10 +21,12 @@ function signToken(userId) {
 
 export async function registerUser({ username, name, email, password }) {
     const passwordHash = await bcrypt.hash(password, 10);
+    const [[{ count }]] = await db.query("SELECT COUNT(*) AS count FROM users");
+    const isAdmin = count === 0 ? 1 : 0;
     try {
         const [result] = await db.query(
-            `INSERT INTO users (username, name, email, password_hash) VALUES (?, ?, ?, ?)`,
-            [username, name, email, passwordHash]
+            `INSERT INTO users (username, name, email, password_hash, is_admin) VALUES (?, ?, ?, ?, ?)`,
+            [username, name, email, passwordHash, isAdmin]
         );
         const user = await getUserById(result.insertId);
         const token = signToken(user.id);
@@ -64,6 +67,37 @@ export async function authenticateUser(identifier, password) {
 }
 
 export async function getUserById(id) {
-    const [rows] = await db.query(`SELECT id, username, name, email, created_at FROM users WHERE id = ? LIMIT 1`, [id]);
+    const [rows] = await db.query(
+        `SELECT id, username, name, email, is_admin, created_at FROM users WHERE id = ? LIMIT 1`,
+        [id]
+    );
     return serializeUser(rows[0]);
 }
+
+export async function listUsers() {
+    const [rows] = await db.query(
+        `SELECT id, username, name, email, is_admin, created_at FROM users ORDER BY created_at ASC`
+    );
+    return rows.map(serializeUser);
+}
+
+export async function adminCreateUser({ username, name, email, password, isAdmin = false }) {
+    const passwordHash = await bcrypt.hash(password, 10);
+    try {
+        const [result] = await db.query(
+            `INSERT INTO users (username, name, email, password_hash, is_admin) VALUES (?, ?, ?, ?, ?)`,
+            [username, name, email, passwordHash, isAdmin ? 1 : 0]
+        );
+        return await getUserById(result.insertId);
+    } catch (error) {
+        if (error?.code === "ER_DUP_ENTRY") {
+            const message = error.sqlMessage || "Duplicate";
+            if (message.includes("username")) {
+                error.meta = "USERNAME";
+            } else if (message.includes("email")) {
+                error.meta = "EMAIL";
+            }
+        }
+        throw error;
+    }
+}