feat(auth): add UserStore with bcryptjs password hashing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/data/users.ts

@@ -0,0 +1,84 @@
+import { randomUUID } from "node:crypto";
+import type Database from "better-sqlite3";
+import bcrypt from "bcryptjs";
+
+const BCRYPT_ROUNDS = 12;
+
+export interface UserRow {
+  id: string;
+  username: string;
+  passwordHash: string;
+  createdAt: number;
+  updatedAt: number;
+}
+
+export interface UserStore {
+  countUsers(): number;
+  createUser(username: string, password: string): Promise<UserRow>;
+  findByUsername(username: string): UserRow | null;
+  findById(id: string): UserRow | null;
+  verifyPassword(plain: string, hash: string): Promise<boolean>;
+  changePassword(userId: string, newPassword: string): Promise<void>;
+}
+
+export class UsernameTakenError extends Error {
+  constructor(username: string) {
+    super(`username taken: ${username}`);
+    this.name = "UsernameTakenError";
+  }
+}
+
+export function createUserStore(db: Database.Database): UserStore {
+  const countStmt = db.prepare("SELECT COUNT(*) AS n FROM users");
+  const insertStmt = db.prepare(
+    "INSERT INTO users (id, username, passwordHash, createdAt, updatedAt) VALUES (?, ?, ?, ?, ?)"
+  );
+  const findByUsernameStmt = db.prepare(
+    "SELECT id, username, passwordHash, createdAt, updatedAt FROM users WHERE username = ? COLLATE NOCASE"
+  );
+  const findByIdStmt = db.prepare(
+    "SELECT id, username, passwordHash, createdAt, updatedAt FROM users WHERE id = ?"
+  );
+  const updatePasswordStmt = db.prepare(
+    "UPDATE users SET passwordHash = ?, updatedAt = ? WHERE id = ?"
+  );
+
+  return {
+    countUsers() {
+      return (countStmt.get() as { n: number }).n;
+    },
+
+    async createUser(username, password) {
+      const hash = await bcrypt.hash(password, BCRYPT_ROUNDS);
+      const id = randomUUID();
+      const now = Date.now();
+      try {
+        insertStmt.run(id, username, hash, now, now);
+      } catch (err) {
+        const msg = (err as Error).message;
+        if (msg.includes("UNIQUE") && msg.includes("users.username")) {
+          throw new UsernameTakenError(username);
+        }
+        throw err;
+      }
+      return { id, username, passwordHash: hash, createdAt: now, updatedAt: now };
+    },
+
+    findByUsername(username) {
+      return (findByUsernameStmt.get(username) as UserRow | undefined) ?? null;
+    },
+
+    findById(id) {
+      return (findByIdStmt.get(id) as UserRow | undefined) ?? null;
+    },
+
+    verifyPassword(plain, hash) {
+      return bcrypt.compare(plain, hash);
+    },
+
+    async changePassword(userId, newPassword) {
+      const hash = await bcrypt.hash(newPassword, BCRYPT_ROUNDS);
+      updatePasswordStmt.run(hash, Date.now(), userId);
+    },
+  };
+}