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frontend/utils/UserDao.java

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+package ins.frontend.utils;
+
+import org.openautonomousconnection.webserver.utils.Sha256;
+
+import java.sql.*;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.UUID;
+
+/**
+ * DAO for users table:
+ * users(id, uid(uuid string), username(sha256 hex or plain), password(pbkdf2...))
+ */
+public final class UserDao {
+
+    private final DataSourceProvider dataSource;
+
+    /**
+     * Creates a UserDao.
+     *
+     * @param dataSource connection provider
+     */
+    public UserDao(DataSourceProvider dataSource) {
+        this.dataSource = Objects.requireNonNull(dataSource, "dataSource");
+    }
+
+    /**
+     * Finds a user by username.
+     *
+     * @param uid exact uid match
+     * @return optional row
+     * @throws SQLException on SQL errors
+     */
+    public Optional<UserRow> findByUid(UUID uid) throws SQLException {
+        if (uid == null) return Optional.empty();
+
+        String sql = "SELECT id, uid, username, password FROM users WHERE uid = ? LIMIT 1";
+
+        try (Connection c = dataSource.getConnection();
+             PreparedStatement ps = c.prepareStatement(sql)) {
+
+            ps.setString(1, uid.toString());
+
+            try (ResultSet rs = ps.executeQuery()) {
+                if (!rs.next()) return Optional.empty();
+                return Optional.of(new UserRow(
+                        rs.getInt("id"),
+                        rs.getString("uid"),
+                        rs.getString("username"),
+                        rs.getString("password")
+                ));
+            }
+        }
+    }
+
+    /**
+     * Creates a new user.
+     *
+     * @param uid             uuid string (36 chars)
+     * @param username        username string (your choice: raw or sha256 hex)
+     * @param passwordEncoded encoded password
+     * @return generated users.id
+     * @throws SQLException on SQL errors
+     */
+    public int createUser(String uid, String username, String passwordEncoded) throws SQLException {
+        if (uid == null || uid.isBlank()) throw new IllegalArgumentException("uid must not be blank");
+        if (username == null || username.isBlank()) throw new IllegalArgumentException("username must not be blank");
+        if (passwordEncoded == null || passwordEncoded.isBlank())
+            throw new IllegalArgumentException("passwordEncoded must not be blank");
+
+        String sql = "INSERT INTO users (uid, username, password) VALUES (?, ?, ?)";
+
+        try (Connection c = dataSource.getConnection();
+             PreparedStatement ps = c.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
+
+            ps.setString(1, uid);
+            ps.setString(2, Sha256.hex(username));
+            ps.setString(3, passwordEncoded);
+            ps.executeUpdate();
+
+            try (ResultSet rs = ps.getGeneratedKeys()) {
+                if (rs.next()) return rs.getInt(1);
+            }
+        }
+
+        throw new SQLException("No generated key returned for users.id");
+    }
+
+    /**
+     * Convenience: creates a user with a new random UUID.
+     *
+     * @param username        username
+     * @param passwordEncoded encoded password
+     * @return generated users.id
+     * @throws SQLException on SQL errors
+     */
+    public int createUserWithNewUuid(String username, String passwordEncoded) throws SQLException {
+        UUID uuid = UUID.randomUUID();
+        while (findByUid(uuid).isPresent()) uuid = UUID.randomUUID();
+        return createUser(uuid.toString(), username, passwordEncoded);
+    }
+
+    /**
+     * Finds a user by username.
+     *
+     * @param username exact username match
+     * @return optional row
+     * @throws SQLException on SQL errors
+     */
+    public Optional<UserRow> findByUsername(String username) throws SQLException {
+        if (username == null || username.isBlank()) return Optional.empty();
+        username = Sha256.hex(username);
+
+        String sql = "SELECT id, uid, username, password FROM users WHERE username = ? LIMIT 1";
+
+        try (Connection c = dataSource.getConnection();
+             PreparedStatement ps = c.prepareStatement(sql)) {
+
+            ps.setString(1, username);
+
+            try (ResultSet rs = ps.executeQuery()) {
+                if (!rs.next()) return Optional.empty();
+                return Optional.of(new UserRow(
+                        rs.getInt("id"),
+                        rs.getString("uid"),
+                        rs.getString("username"),
+                        rs.getString("password")
+                ));
+            }
+        }
+    }
+
+    /**
+     * Connection provider abstraction.
+     */
+    public interface DataSourceProvider {
+        /**
+         * @return open SQL connection
+         * @throws SQLException on errors
+         */
+        Connection getConnection() throws SQLException;
+    }
+
+    /**
+     * User row.
+     *
+     * @param id              users.id
+     * @param uid             users.uid (uuid)
+     * @param username        users.username
+     * @param passwordEncoded users.password
+     */
+    public record UserRow(int id, String uid, String username, String passwordEncoded) {
+    }
+}