OsAccountManager.java

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/*
 * Sleuth Kit Data Model
 *
 * Copyright 2020-2021 Basis Technology Corp.
 * Contact: carrier <at> sleuthkit <dot> org
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.sleuthkit.datamodel;

import com.google.common.base.Strings;
import org.apache.commons.lang3.StringUtils;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.Types;
import java.util.Collections;
import java.util.ArrayList;
import java.util.List;
import java.util.NavigableSet;
import java.util.Objects;
import java.util.Optional;
import java.util.UUID;
import java.util.concurrent.ConcurrentSkipListSet;
import java.util.stream.Collectors;
import org.sleuthkit.datamodel.BlackboardAttribute.TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE;
import org.sleuthkit.datamodel.OsAccount.OsAccountStatus;
import org.sleuthkit.datamodel.OsAccount.OsAccountType;
import org.sleuthkit.datamodel.OsAccount.OsAccountAttribute;
import org.sleuthkit.datamodel.SleuthkitCase.CaseDbConnection;
import org.sleuthkit.datamodel.SleuthkitCase.CaseDbTransaction;
import org.sleuthkit.datamodel.TskEvent.OsAccountsUpdatedTskEvent;
import static org.sleuthkit.datamodel.WindowsAccountUtils.getWindowsSpecialSidName;
import static org.sleuthkit.datamodel.WindowsAccountUtils.isWindowsSpecialSid;

public final class OsAccountManager {

        private final SleuthkitCase db;
        private final Object osAcctInstancesCacheLock;
        private final NavigableSet<OsAccountInstance> osAccountInstanceCache;

        OsAccountManager(SleuthkitCase skCase) {
                db = skCase;
                osAcctInstancesCacheLock = new Object();
                osAccountInstanceCache = new ConcurrentSkipListSet<>();
        }

        OsAccount newOsAccount(String uniqueAccountId, OsAccountRealm realm) throws TskCoreException {

                // ensure unique id is provided
                if (Strings.isNullOrEmpty(uniqueAccountId)) {
                        throw new TskCoreException("Cannot create OS account with null uniqueId.");
                }

                if (realm == null) {
                        throw new TskCoreException("Cannot create OS account without a realm.");
                }

                CaseDbTransaction trans = db.beginTransaction();
                try {

                        // try to create account
                        try {
                                OsAccount account = newOsAccount(uniqueAccountId, null, realm, OsAccount.OsAccountStatus.UNKNOWN, trans);
                                trans.commit();
                                trans = null;
                                return account;
                        } catch (SQLException ex) {
                                // Close the transaction before moving on
                                trans.rollback();
                                trans = null;

                                // Create may fail if an OsAccount already exists. 
                                Optional<OsAccount> osAccount = this.getOsAccountByAddr(uniqueAccountId, realm);
                                if (osAccount.isPresent()) {
                                        return osAccount.get();
                                }

                                // create failed for some other reason, throw an exception
                                throw new TskCoreException(String.format("Error creating OsAccount with uniqueAccountId = %s in realm id = %d", uniqueAccountId, realm.getRealmId()), ex);
                        }
                } finally {
                        if (trans != null) {
                                trans.rollback();
                        }
                }
        }

        public OsAccount newWindowsOsAccount(String sid, String loginName, String realmName, Host referringHost, OsAccountRealm.RealmScope realmScope) throws TskCoreException, NotUserSIDException {

                if (realmScope == null) {
                        throw new TskCoreException("RealmScope cannot be null. Use UNKNOWN if scope is not known.");
                }
                if (referringHost == null) {
                        throw new TskCoreException("A referring host is required to create an account.");
                }

                // ensure at least one of the two is supplied - unique id or a login name
                if (StringUtils.isBlank(sid) && StringUtils.isBlank(loginName)) {
                        throw new TskCoreException("Cannot create OS account with both uniqueId and loginName as null.");
                }
                // Realm name is required if the sid is null. 
                if (StringUtils.isBlank(sid) && StringUtils.isBlank(realmName)) {
                        throw new TskCoreException("Realm name or SID is required to create a Windows account.");
                }

                if (!StringUtils.isBlank(sid) && !WindowsAccountUtils.isWindowsUserSid(sid)) {
                        throw new OsAccountManager.NotUserSIDException(String.format("SID = %s is not a user SID.", sid));
                }

                // get the realm for the account, and update it if it is missing addr or name.
                Optional<OsAccountRealm> realmOptional;
                try (CaseDbConnection connection = db.getConnection()) {
                        realmOptional = db.getOsAccountRealmManager().getAndUpdateWindowsRealm(sid, realmName, referringHost, connection);
                }
                OsAccountRealm realm;
                if (realmOptional.isPresent()) {
                        realm = realmOptional.get();
                } else {
                        // realm was not found, create it.
                        realm = db.getOsAccountRealmManager().newWindowsRealm(sid, realmName, referringHost, realmScope);
                }

                return newWindowsOsAccount(sid, loginName, realm);
        }

        public OsAccount newWindowsOsAccount(String sid, String loginName, OsAccountRealm realm) throws TskCoreException, NotUserSIDException {

                // ensure at least one of the two is supplied - unique id or a login name
                if (StringUtils.isBlank(sid) && StringUtils.isBlank(loginName)) {
                        throw new TskCoreException("Cannot create OS account with both uniqueId and loginName as null.");
                }

                if (!StringUtils.isBlank(sid) && !WindowsAccountUtils.isWindowsUserSid(sid)) {
                        throw new OsAccountManager.NotUserSIDException(String.format("SID = %s is not a user SID.", sid));
                }

                CaseDbTransaction trans = db.beginTransaction();
                try {
                        // try to create account
                        try {
                                OsAccount account = newOsAccount(sid, loginName, realm, OsAccount.OsAccountStatus.UNKNOWN, trans);
                                
                                // If the SID indicates a special windows account, then set its full name. 
                                if (!StringUtils.isBlank(sid) && isWindowsSpecialSid(sid)) {
                                        String fullName = getWindowsSpecialSidName(sid);
                                        if (StringUtils.isNotBlank(fullName)) {
                                                OsAccountUpdateResult updateResult = updateStandardOsAccountAttributes(account, fullName, null, null, null, trans);
                                                if (updateResult.getUpdatedAccount().isPresent()) {
                                                        account = updateResult.getUpdatedAccount().get();
                                                }
                                        }
                                }
                                trans.commit();
                                trans = null;
                                return account;
                        } catch (SQLException ex) {
                                // Rollback the transaction before proceeding
                                trans.rollback();
                                trans = null;

                                // Create may fail if an OsAccount already exists. 
                                Optional<OsAccount> osAccount;

                                // First search for account by uniqueId
                                if (!Strings.isNullOrEmpty(sid)) {
                                        osAccount = getOsAccountByAddr(sid, realm);
                                        if (osAccount.isPresent()) {
                                                return osAccount.get();
                                        }
                                }

                                // search by loginName
                                if (!Strings.isNullOrEmpty(loginName)) {
                                        osAccount = getOsAccountByLoginName(loginName, realm);
                                        if (osAccount.isPresent()) {
                                                return osAccount.get();
                                        }
                                }

                                // create failed for some other reason, throw an exception
                                throw new TskCoreException(String.format("Error creating OsAccount with sid = %s, loginName = %s, realm = %s, referring host = %s",
                                                (sid != null) ? sid : "Null",
                                                (loginName != null) ? loginName : "Null",
                                                (!realm.getRealmNames().isEmpty()) ? realm.getRealmNames().get(0) : "Null",
                                                realm.getScopeHost().isPresent() ? realm.getScopeHost().get().getName() : "Null"), ex);

                        }
                } finally {
                        if (trans != null) {
                                trans.rollback();
                        }
                }
        }

        private OsAccount newOsAccount(String uniqueId, String loginName, OsAccountRealm realm, OsAccount.OsAccountStatus accountStatus, CaseDbTransaction trans) throws TskCoreException, SQLException {

                if (Objects.isNull(realm)) {
                        throw new TskCoreException("Cannot create an OS Account, realm is NULL.");
                }

                String signature = getOsAccountSignature(uniqueId, loginName);
                OsAccount account;

                CaseDbConnection connection = trans.getConnection();

                // first create a tsk_object for the OsAccount.
                // RAMAN TODO: need to get the correct parent obj id.  
                //            Create an Object Directory parent and used its id.
                long parentObjId = 0;

                int objTypeId = TskData.ObjectType.OS_ACCOUNT.getObjectType();
                long osAccountObjId = db.addObject(parentObjId, objTypeId, connection);

                String accountInsertSQL = "INSERT INTO tsk_os_accounts(os_account_obj_id, login_name, realm_id, addr, signature, status)"
                                + " VALUES (?, ?, ?, ?, ?, ?)"; // NON-NLS

                PreparedStatement preparedStatement = connection.getPreparedStatement(accountInsertSQL, Statement.NO_GENERATED_KEYS);
                preparedStatement.clearParameters();

                preparedStatement.setLong(1, osAccountObjId);

                preparedStatement.setString(2, loginName);
                preparedStatement.setLong(3, realm.getRealmId());

                preparedStatement.setString(4, uniqueId);
                preparedStatement.setString(5, signature);
                preparedStatement.setInt(6, accountStatus.getId());

                connection.executeUpdate(preparedStatement);

                account = new OsAccount(db, osAccountObjId, realm.getRealmId(), loginName, uniqueId, signature,
                                null, null, null, accountStatus, OsAccount.OsAccountDbStatus.ACTIVE);

                trans.registerAddedOsAccount(account);
                return account;
        }

        private Optional<OsAccount> getOsAccountByAddr(String addr, Host host) throws TskCoreException {

                try (CaseDbConnection connection = db.getConnection()) {
                        return getOsAccountByAddr(addr, host, connection);
                }
        }

        private Optional<OsAccount> getOsAccountByAddr(String uniqueId, Host host, CaseDbConnection connection) throws TskCoreException {

                String whereHostClause = (host == null)
                                ? " 1 = 1 "
                                : " ( realms.scope_host_id = " + host.getHostId() + " OR realms.scope_host_id IS NULL) ";

                String queryString = "SELECT accounts.os_account_obj_id as os_account_obj_id, accounts.login_name, accounts.full_name, "
                                + " accounts.realm_id, accounts.addr, accounts.signature, "
                                + "     accounts.type, accounts.status, accounts.admin, accounts.created_date, accounts.db_status, "
                                + " realms.realm_name as realm_name, realms.realm_addr as realm_addr, realms.realm_signature, realms.scope_host_id, realms.scope_confidence, realms.db_status as realm_db_status "
                                + " FROM tsk_os_accounts as accounts"
                                + "             LEFT JOIN tsk_os_account_realms as realms"
                                + " ON accounts.realm_id = realms.id"
                                + " WHERE " + whereHostClause
                                + "     AND accounts.db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId()
                                + "             AND LOWER(accounts.addr) = LOWER('" + uniqueId + "')";

                db.acquireSingleUserCaseReadLock();
                try (Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        if (!rs.next()) {
                                return Optional.empty();        // no match found
                        } else {
                                return Optional.of(osAccountFromResultSet(rs));
                        }
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS account for unique id = %s and host = %s", uniqueId, (host != null ? host.getName() : "null")), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        Optional<OsAccount> getOsAccountByAddr(String uniqueId, OsAccountRealm realm) throws TskCoreException {

                String queryString = "SELECT * FROM tsk_os_accounts"
                                + " WHERE LOWER(addr) = LOWER('" + uniqueId + "')"
                                + " AND db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId()
                                + " AND realm_id = " + realm.getRealmId();

                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = this.db.getConnection();
                                Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        if (!rs.next()) {
                                return Optional.empty();        // no match found
                        } else {
                                return Optional.of(osAccountFromResultSet(rs));
                        }
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS account for realm = %s and uniqueId = %s.", (realm != null) ? realm.getSignature() : "NULL", uniqueId), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        Optional<OsAccount> getOsAccountByLoginName(String loginName, OsAccountRealm realm) throws TskCoreException {

                String queryString = "SELECT * FROM tsk_os_accounts"
                                + " WHERE LOWER(login_name) = LOWER('" + loginName + "')"
                                + " AND db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId()
                                + " AND realm_id = " + realm.getRealmId();

                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = this.db.getConnection();
                                Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        if (!rs.next()) {
                                return Optional.empty();        // no match found
                        } else {
                                return Optional.of(osAccountFromResultSet(rs));
                        }
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS account for realm = %s and loginName = %s.", (realm != null) ? realm.getSignature() : "NULL", loginName), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        public OsAccount getOsAccountByObjectId(long osAccountObjId) throws TskCoreException {

                try (CaseDbConnection connection = this.db.getConnection()) {
                        return getOsAccountByObjectId(osAccountObjId, connection);
                }
        }

        OsAccount getOsAccountByObjectId(long osAccountObjId, CaseDbConnection connection) throws TskCoreException {

                String queryString = "SELECT * FROM tsk_os_accounts"
                                + " WHERE os_account_obj_id = " + osAccountObjId;

                db.acquireSingleUserCaseReadLock();
                try (Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        if (!rs.next()) {
                                throw new TskCoreException(String.format("No account found with obj id = %d ", osAccountObjId));
                        } else {
                                return osAccountFromResultSet(rs);
                        }
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting account with obj id = %d ", osAccountObjId), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        public OsAccountInstance newOsAccountInstance(OsAccount osAccount, DataSource dataSource, OsAccountInstance.OsAccountInstanceType instanceType) throws TskCoreException {
                if (osAccount == null) {
                        throw new TskCoreException("Cannot create account instance with null account.");
                }
                if (dataSource == null) {
                        throw new TskCoreException("Cannot create account instance with null data source.");
                }

                /*
                 * Check the cache of OS account instances for an existing instance for
                 * this OS account and data source. Note that the account instance
                 * created here has a bogus instance ID. This is possible since the
                 * instance ID is not considered in the equals() and hashCode() methods
                 * of this class.
                 */
                OsAccountInstance bogus = new OsAccountInstance(db, 0, osAccount.getId(), dataSource.getId(), instanceType);
                synchronized (osAcctInstancesCacheLock) {
                        if (osAccountInstanceCache.contains(bogus)) {
                                // since we checked for contains(bogus), floor(bogus) should return the exact match and not a less than match.
                                return osAccountInstanceCache.floor(bogus);
                        }
                }

                try (CaseDbConnection connection = this.db.getConnection()) {
                        return newOsAccountInstance(osAccount.getId(), dataSource.getId(), instanceType, connection);
                }
        }

        OsAccountInstance newOsAccountInstance(long osAccountId, long dataSourceObjId, OsAccountInstance.OsAccountInstanceType instanceType, CaseDbConnection connection) throws TskCoreException {
                /*
                 * Check the cache of OS account instances for an existing instance for
                 * this OS account and data source. Note that the account instance
                 * created here has a bogus instance ID. This is possible since the
                 * instance ID is not considered in the equals() and hashCode() methods
                 * of this class.
                 */
                OsAccountInstance bogus = new OsAccountInstance(db, 0, osAccountId, dataSourceObjId, instanceType);
                synchronized (osAcctInstancesCacheLock) {
                        if (osAccountInstanceCache.contains(bogus)) {
                                // since we checked for contains(bogus), floor(bogus) should return the exact match and not a less than match.
                                return osAccountInstanceCache.floor(bogus);
                        }
                }

                /*
                 * Create the OS account instance.
                 */
                db.acquireSingleUserCaseWriteLock();
                try {
                        String accountInsertSQL = db.getInsertOrIgnoreSQL("INTO tsk_os_account_instances(os_account_obj_id, data_source_obj_id, instance_type)"
                                        + " VALUES (?, ?, ?)"); // NON-NLS
                        PreparedStatement preparedStatement = connection.getPreparedStatement(accountInsertSQL, Statement.RETURN_GENERATED_KEYS);
                        preparedStatement.clearParameters();
                        preparedStatement.setLong(1, osAccountId);
                        preparedStatement.setLong(2, dataSourceObjId);
                        preparedStatement.setInt(3, instanceType.getId());
                        connection.executeUpdate(preparedStatement);
                        try (ResultSet resultSet = preparedStatement.getGeneratedKeys();) {
                                if (resultSet.next()) {
                                        OsAccountInstance accountInstance = new OsAccountInstance(db, resultSet.getLong(1), osAccountId, dataSourceObjId, instanceType);
                                        synchronized (osAcctInstancesCacheLock) {
                                                osAccountInstanceCache.add(accountInstance);
                                        }
                                        /*
                                         * There is a potential issue here. The cache of OS account
                                         * instances is an optimization and was not intended to be
                                         * used as an authoritative indicator of whether or not a
                                         * particular OS account instance was already added to the
                                         * case. In fact, the entire cache is flushed during merge
                                         * operations. But regardless, there is a check-then-act
                                         * race condition for multi-user cases, with or without the
                                         * cache. And although the case database schema and the SQL
                                         * returned by getInsertOrIgnoreSQL() seamlessly prevents
                                         * duplicates in the case database, a valid row ID is
                                         * returned here even if the INSERT is not done. So the
                                         * bottom line is that a redundant event may be published
                                         * from time to time.
                                         */
                                        db.fireTSKEvent(new TskEvent.OsAcctInstancesAddedTskEvent(Collections.singletonList(accountInstance)));
                                        
                                        return accountInstance;
                                } else {
                                        throw new TskCoreException(String.format("Could not get autogen key after row insert for OS account instance. OS account object id = %d, data source object id = %d", osAccountId, dataSourceObjId));
                                }
                        }
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error adding OS account instance for OS account object id = %d, data source object id = %d", osAccountId, dataSourceObjId), ex);
                } finally {
                        db.releaseSingleUserCaseWriteLock();
                }
        }

        public List<OsAccount> getOsAccounts(Host host) throws TskCoreException {

                String queryString = "SELECT * FROM tsk_os_accounts as accounts "
                                + " JOIN tsk_os_account_instances as instances "
                                + "             ON instances.os_account_obj_id = accounts.os_account_obj_id "
                                + " JOIN data_source_info as datasources "
                                + "             ON datasources.obj_id = instances.data_source_obj_id "
                                + " WHERE datasources.host_id = " + host.getHostId()
                                + " AND accounts.db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId();

                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = this.db.getConnection();
                                Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        List<OsAccount> accounts = new ArrayList<>();
                        while (rs.next()) {
                                accounts.add(osAccountFromResultSet(rs));
                        }
                        return accounts;
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS accounts for host id = %d", host.getHostId()), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        void mergeOsAccountsForRealms(OsAccountRealm sourceRealm, OsAccountRealm destRealm, CaseDbTransaction trans) throws TskCoreException {
                List<OsAccount> destinationAccounts = getOsAccounts(destRealm, trans.getConnection());
                List<OsAccount> sourceAccounts = getOsAccounts(sourceRealm, trans.getConnection());

                for (OsAccount sourceAccount : sourceAccounts) {

                        // First a check for the case where the source account has both the login name and unique ID set and
                        // we have separate matches in the destination account for both. If we find this case, we need to first merge
                        // the two accounts in the destination realm. This will ensure that all source accounts match at most one
                        // destination account.
                        // Note that we only merge accounts based on login name if the unique ID is empty.
                        if (sourceAccount.getAddr().isPresent() && sourceAccount.getLoginName().isPresent()) {
                                List<OsAccount> duplicateDestAccounts = destinationAccounts.stream()
                                                .filter(p -> p.getAddr().equals(sourceAccount.getAddr())
                                                || (p.getLoginName().equals(sourceAccount.getLoginName()) && (!p.getAddr().isPresent())))
                                                .collect(Collectors.toList());
                                if (duplicateDestAccounts.size() > 1) {
                                        OsAccount combinedDestAccount = duplicateDestAccounts.get(0);
                                        duplicateDestAccounts.remove(combinedDestAccount);
                                        for (OsAccount dupeDestAccount : duplicateDestAccounts) {
                                                mergeOsAccounts(dupeDestAccount, combinedDestAccount, trans);
                                        }
                                }
                        }

                        // Look for matching destination account
                        OsAccount matchingDestAccount = null;

                        // First look for matching unique id
                        if (sourceAccount.getAddr().isPresent()) {
                                List<OsAccount> matchingDestAccounts = destinationAccounts.stream()
                                                .filter(p -> p.getAddr().equals(sourceAccount.getAddr()))
                                                .collect(Collectors.toList());
                                if (!matchingDestAccounts.isEmpty()) {
                                        matchingDestAccount = matchingDestAccounts.get(0);
                                }
                        }

                        // If a match wasn't found yet, look for a matching login name.
                        // We will merge only if:
                        // - We didn't already find a unique ID match
                        // - The source account has no unique ID OR the destination account has no unique ID
                        if (matchingDestAccount == null && sourceAccount.getLoginName().isPresent()) {
                                List<OsAccount> matchingDestAccounts = destinationAccounts.stream()
                                                .filter(p -> (p.getLoginName().equals(sourceAccount.getLoginName())
                                                && ((!sourceAccount.getAddr().isPresent()) || (!p.getAddr().isPresent()))))
                                                .collect(Collectors.toList());
                                if (!matchingDestAccounts.isEmpty()) {
                                        matchingDestAccount = matchingDestAccounts.get(0);
                                }
                        }

                        // If we found a match, merge the accounts. Otherwise simply update the realm id
                        if (matchingDestAccount != null) {
                                mergeOsAccounts(sourceAccount, matchingDestAccount, trans);
                        } else {
                                String query = "UPDATE tsk_os_accounts SET realm_id = " + destRealm.getRealmId() + " WHERE os_account_obj_id = " + sourceAccount.getId();
                                try (Statement s = trans.getConnection().createStatement()) {
                                        s.executeUpdate(query);
                                } catch (SQLException ex) {
                                        throw new TskCoreException("Error executing SQL update: " + query, ex);
                                }
                                trans.registerChangedOsAccount(sourceAccount);
                        }
                }
        }

        private void mergeOsAccounts(OsAccount sourceAccount, OsAccount destAccount, CaseDbTransaction trans) throws TskCoreException {

                String query = "";
                try (Statement s = trans.getConnection().createStatement()) {

                        // Update all references
                        query = makeOsAccountUpdateQuery("tsk_os_account_attributes", sourceAccount, destAccount);
                        s.executeUpdate(query);

                        // tsk_os_account_instances has a unique constraint on os_account_obj_id, data_source_obj_id, host_id,
                        // so delete any rows that would be duplicates.
                        query = "DELETE FROM tsk_os_account_instances "
                                        + "WHERE id IN ( "
                                        + "SELECT "
                                        + "  sourceAccountInstance.id "
                                        + "FROM "
                                        + "  tsk_os_account_instances destAccountInstance "
                                        + "INNER JOIN tsk_os_account_instances sourceAccountInstance ON destAccountInstance.data_source_obj_id = sourceAccountInstance.data_source_obj_id "
                                        + "WHERE destAccountInstance.os_account_obj_id = " + destAccount.getId()
                                        + " AND sourceAccountInstance.os_account_obj_id = " + sourceAccount.getId() + " )";
                        s.executeUpdate(query);

                        query = makeOsAccountUpdateQuery("tsk_os_account_instances", sourceAccount, destAccount);
                        s.executeUpdate(query);
                        synchronized (osAcctInstancesCacheLock) {
                                osAccountInstanceCache.clear();
                        }

                        query = makeOsAccountUpdateQuery("tsk_files", sourceAccount, destAccount);
                        s.executeUpdate(query);

                        query = makeOsAccountUpdateQuery("tsk_data_artifacts", sourceAccount, destAccount);
                        s.executeUpdate(query);

                        // Update the source account. Make a dummy signature to prevent problems with the unique constraint.
                        String mergedSignature = makeMergedOsAccountSignature();
                        query = "UPDATE tsk_os_accounts SET merged_into = " + destAccount.getId()
                                        + ", db_status = " + OsAccount.OsAccountDbStatus.MERGED.getId()
                                        + ", signature = '" + mergedSignature + "' "
                                        + " WHERE os_account_obj_id = " + sourceAccount.getId();

                        s.executeUpdate(query);
                        trans.registerDeletedOsAccount(sourceAccount.getId());

                        // Merge and update the destination account. Note that this must be done after updating
                        // the source account to prevent conflicts when merging two accounts in the
                        // same realm.
                        mergeOsAccountObjectsAndUpdateDestAccount(sourceAccount, destAccount, trans);
                } catch (SQLException ex) {
                        throw new TskCoreException("Error executing SQL update: " + query, ex);
                }
        }

        private String makeMergedOsAccountSignature() {
                return "MERGED " + UUID.randomUUID().toString();
        }

        private String makeOsAccountUpdateQuery(String tableName, OsAccount sourceAccount, OsAccount destAccount) {
                return "UPDATE " + tableName + " SET os_account_obj_id = " + destAccount.getId() + " WHERE os_account_obj_id = " + sourceAccount.getId();
        }

        private OsAccount mergeOsAccountObjectsAndUpdateDestAccount(OsAccount sourceAccount, OsAccount destAccount, CaseDbTransaction trans) throws TskCoreException {

                OsAccount mergedDestAccount = destAccount;

                String destLoginName = null;
                String destAddr = null;

                // Copy any fields that aren't set in the destination to the value from the source account.
                if (!destAccount.getLoginName().isPresent() && sourceAccount.getLoginName().isPresent()) {
                        destLoginName = sourceAccount.getLoginName().get();
                }

                if (!destAccount.getAddr().isPresent() && sourceAccount.getAddr().isPresent()) {
                        destAddr = sourceAccount.getAddr().get();
                }

                // update the dest account core 
                OsAccountUpdateResult updateStatus = this.updateOsAccountCore(destAccount, destAddr, destLoginName, trans);

                if (updateStatus.getUpdateStatusCode() == OsAccountUpdateStatus.UPDATED && updateStatus.getUpdatedAccount().isPresent()) {
                        mergedDestAccount = updateStatus.getUpdatedAccount().get();
                }

                String destFullName = null;
                Long destCreationTime = null;
                if (!destAccount.getFullName().isPresent() && sourceAccount.getFullName().isPresent()) {
                        destFullName = sourceAccount.getFullName().get();
                }

                if (!destAccount.getCreationTime().isPresent() && sourceAccount.getCreationTime().isPresent()) {
                        destCreationTime = sourceAccount.getCreationTime().get();
                }

                // update the dest account properties 
                updateStatus = this.updateStandardOsAccountAttributes(destAccount, destFullName, null, null, destCreationTime, trans);

                if (updateStatus.getUpdateStatusCode() == OsAccountUpdateStatus.UPDATED && updateStatus.getUpdatedAccount().isPresent()) {
                        mergedDestAccount = updateStatus.getUpdatedAccount().get();
                }

                return mergedDestAccount;
        }

        private List<OsAccount> getOsAccounts(OsAccountRealm realm, CaseDbConnection connection) throws TskCoreException {
                String queryString = "SELECT * FROM tsk_os_accounts"
                                + " WHERE realm_id = " + realm.getRealmId()
                                + " AND db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId()
                                + " ORDER BY os_account_obj_id";

                try (Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        List<OsAccount> accounts = new ArrayList<>();
                        while (rs.next()) {
                                accounts.add(osAccountFromResultSet(rs));
                        }
                        return accounts;
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS accounts for realm id = %d", realm.getRealmId()), ex);
                }
        }

        public List<OsAccount> getOsAccounts() throws TskCoreException {
                String queryString = "SELECT * FROM tsk_os_accounts"
                                + " WHERE db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId();

                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = this.db.getConnection();
                                Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        List<OsAccount> accounts = new ArrayList<>();
                        while (rs.next()) {
                                accounts.add(osAccountFromResultSet(rs));
                        }
                        return accounts;
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS accounts"), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        public Optional<OsAccount> getWindowsOsAccount(String sid, String loginName, String realmName, Host referringHost) throws TskCoreException, NotUserSIDException {

                if (referringHost == null) {
                        throw new TskCoreException("A referring host is required to get an account.");
                }

                // ensure at least one of the two is supplied - sid or a login name
                if (StringUtils.isBlank(sid) && StringUtils.isBlank(loginName)) {
                        throw new TskCoreException("Cannot get an OS account with both SID and loginName as null.");
                }

                // first get the realm for the given sid
                Optional<OsAccountRealm> realm = db.getOsAccountRealmManager().getWindowsRealm(sid, realmName, referringHost);
                if (!realm.isPresent()) {
                        return Optional.empty();
                }

                // search by SID
                if (!Strings.isNullOrEmpty(sid)) {
                        if (!WindowsAccountUtils.isWindowsUserSid(sid)) {
                                throw new OsAccountManager.NotUserSIDException(String.format("SID = %s is not a user SID.", sid));
                        }

                        Optional<OsAccount> account = this.getOsAccountByAddr(sid, realm.get());
                        if (account.isPresent()) {
                                return account;
                        }
                }

                // search by login name
                return this.getOsAccountByLoginName(loginName, realm.get());
        }

        public void addExtendedOsAccountAttributes(OsAccount account, List<OsAccountAttribute> accountAttributes) throws TskCoreException {

                synchronized (account) {  // synchronized to prevent multiple threads trying to add osAccount attributes concurrently to the same osAccount.
                        db.acquireSingleUserCaseWriteLock();

                        try (CaseDbConnection connection = db.getConnection()) {
                                for (OsAccountAttribute accountAttribute : accountAttributes) {

                                        String attributeInsertSQL = "INSERT INTO tsk_os_account_attributes(os_account_obj_id, host_id, source_obj_id, attribute_type_id, value_type, value_byte, value_text, value_int32, value_int64, value_double)"
                                                        + " VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"; // NON-NLS

                                        PreparedStatement preparedStatement = connection.getPreparedStatement(attributeInsertSQL, Statement.RETURN_GENERATED_KEYS);
                                        preparedStatement.clearParameters();

                                        preparedStatement.setLong(1, account.getId());
                                        if (accountAttribute.getHostId().isPresent()) {
                                                preparedStatement.setLong(2, accountAttribute.getHostId().get());
                                        } else {
                                                preparedStatement.setNull(2, java.sql.Types.NULL);
                                        }
                                        if (accountAttribute.getSourceObjectId().isPresent()) {
                                                preparedStatement.setLong(3, accountAttribute.getSourceObjectId().get());
                                        } else {
                                                preparedStatement.setNull(3, java.sql.Types.NULL);
                                        }

                                        preparedStatement.setLong(4, accountAttribute.getAttributeType().getTypeID());
                                        preparedStatement.setLong(5, accountAttribute.getAttributeType().getValueType().getType());

                                        if (accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.BYTE) {
                                                preparedStatement.setBytes(6, accountAttribute.getValueBytes());
                                        } else {
                                                preparedStatement.setBytes(6, null);
                                        }

                                        if (accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.STRING
                                                        || accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.JSON) {
                                                preparedStatement.setString(7, accountAttribute.getValueString());
                                        } else {
                                                preparedStatement.setString(7, null);
                                        }
                                        if (accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.INTEGER) {
                                                preparedStatement.setInt(8, accountAttribute.getValueInt());
                                        } else {
                                                preparedStatement.setNull(8, java.sql.Types.NULL);
                                        }

                                        if (accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.DATETIME
                                                        || accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.LONG) {
                                                preparedStatement.setLong(9, accountAttribute.getValueLong());
                                        } else {
                                                preparedStatement.setNull(9, java.sql.Types.NULL);
                                        }

                                        if (accountAttribute.getAttributeType().getValueType() == TSK_BLACKBOARD_ATTRIBUTE_VALUE_TYPE.DOUBLE) {
                                                preparedStatement.setDouble(10, accountAttribute.getValueDouble());
                                        } else {
                                                preparedStatement.setNull(10, java.sql.Types.NULL);
                                        }

                                        connection.executeUpdate(preparedStatement);
                                }
                        } catch (SQLException ex) {
                                throw new TskCoreException(String.format("Error adding OS Account attribute for account id = %d", account.getId()), ex);
                        } finally {
                                db.releaseSingleUserCaseWriteLock();
                        }
                        // set the atrribute list in account to the most current list from the database
                        List<OsAccountAttribute> currentAttribsList = getOsAccountAttributes(account);
                        account.setAttributesInternal(currentAttribsList);
                }
                fireChangeEvent(account);
        }

        List<OsAccountAttribute> getOsAccountAttributes(OsAccount account) throws TskCoreException {

                String queryString = "SELECT attributes.os_account_obj_id as os_account_obj_id, attributes.host_id as host_id, attributes.source_obj_id as source_obj_id, "
                                + " attributes.attribute_type_id as attribute_type_id,  attributes.value_type as value_type, attributes.value_byte as value_byte, "
                                + " attributes.value_text as value_text, attributes.value_int32 as value_int32, attributes.value_int64 as value_int64, attributes.value_double as value_double, "
                                + " hosts.id, hosts.name as host_name, hosts.db_status as host_status "
                                + " FROM tsk_os_account_attributes as attributes"
                                + "             LEFT JOIN tsk_hosts as hosts "
                                + " ON attributes.host_id = hosts.id "
                                + " WHERE os_account_obj_id = " + account.getId();

                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = this.db.getConnection();
                                Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, queryString)) {

                        List<OsAccountAttribute> attributes = new ArrayList<>();
                        while (rs.next()) {

                                Host host = null;
                                long hostId = rs.getLong("host_id");
                                if (!rs.wasNull()) {
                                        host = new Host(hostId, rs.getString("host_name"), Host.HostDbStatus.fromID(rs.getInt("host_status")));
                                }

                                Content sourceContent = null;
                                long sourceObjId = rs.getLong("source_obj_id");
                                if (!rs.wasNull()) {
                                        sourceContent = this.db.getContentById(sourceObjId);
                                }
                                BlackboardAttribute.Type attributeType = db.getAttributeType(rs.getInt("attribute_type_id"));
                                OsAccountAttribute attribute = account.new OsAccountAttribute(attributeType, rs.getInt("value_int32"), rs.getLong("value_int64"),
                                                rs.getDouble("value_double"), rs.getString("value_text"), rs.getBytes("value_byte"),
                                                db, account, host, sourceContent);

                                attributes.add(attribute);
                        }
                        return attributes;
                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error getting OS account attributes for account obj id = %d", account.getId()), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
        }

        List<OsAccountInstance> getOsAccountInstances(OsAccount account) throws TskCoreException {
                String whereClause = "tsk_os_account_instances.os_account_obj_id = " + account.getId();
                return getOsAccountInstances(whereClause);
        }

        public List<OsAccountInstance> getOsAccountInstances(List<Long> instanceIDs) throws TskCoreException {
                String instanceIds = instanceIDs.stream().map(id -> id.toString()).collect(Collectors.joining(","));
                String whereClause = "tsk_os_account_instances.id IN (" + instanceIds + ")";
                return getOsAccountInstances(whereClause);
        }

        private List<OsAccountInstance> getOsAccountInstances(String whereClause) throws TskCoreException {
                List<OsAccountInstance> osAcctInstances = new ArrayList<>();
                String querySQL = "SELECT * FROM tsk_os_account_instances WHERE " + whereClause;
                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = db.getConnection();
                                PreparedStatement preparedStatement = connection.getPreparedStatement(querySQL, Statement.NO_GENERATED_KEYS);
                                ResultSet results = connection.executeQuery(preparedStatement)) {
                        while (results.next()) {
                                long instanceId = results.getLong("id");
                                long osAccountObjID = results.getLong("os_account_obj_id");
                                long dataSourceObjId = results.getLong("data_source_obj_id");
                                int instanceType = results.getInt("instance_type");
                                osAcctInstances.add(new OsAccountInstance(db, instanceId, osAccountObjID, dataSourceObjId, OsAccountInstance.OsAccountInstanceType.fromID(instanceType)));
                        }
                } catch (SQLException ex) {
                        throw new TskCoreException("Failed to get OsAccountInstances (SQL = " + querySQL + ")", ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
                return osAcctInstances;
        }

        public OsAccountUpdateResult updateStandardOsAccountAttributes(OsAccount osAccount, String fullName, OsAccountType accountType, OsAccountStatus accountStatus, Long creationTime) throws TskCoreException {

                CaseDbTransaction trans = db.beginTransaction();
                try {
                        OsAccountUpdateResult updateStatus = updateStandardOsAccountAttributes(osAccount, fullName, accountType, accountStatus, creationTime, trans);

                        trans.commit();
                        trans = null;

                        return updateStatus;
                } finally {
                        if (trans != null) {
                                trans.rollback();
                        }
                }
        }

        OsAccountUpdateResult updateStandardOsAccountAttributes(OsAccount osAccount, String fullName, OsAccountType accountType, OsAccountStatus accountStatus, Long creationTime, CaseDbTransaction trans) throws TskCoreException {

                OsAccountUpdateStatus updateStatusCode = OsAccountUpdateStatus.NO_CHANGE;

                try {
                        CaseDbConnection connection = trans.getConnection();

                        if (!StringUtils.isBlank(fullName)) {
                                updateAccountColumn(osAccount.getId(), "full_name", fullName, connection);
                                updateStatusCode = OsAccountUpdateStatus.UPDATED;
                        }

                        if (Objects.nonNull(accountType)) {
                                updateAccountColumn(osAccount.getId(), "type", accountType, connection);
                                updateStatusCode = OsAccountUpdateStatus.UPDATED;
                        }

                        if (Objects.nonNull(accountStatus)) {
                                updateAccountColumn(osAccount.getId(), "status", accountStatus, connection);
                                updateStatusCode = OsAccountUpdateStatus.UPDATED;
                        }

                        if (Objects.nonNull(creationTime)) {
                                updateAccountColumn(osAccount.getId(), "created_date", creationTime, connection);
                                updateStatusCode = OsAccountUpdateStatus.UPDATED;
                        }

                        // if nothing has been changed, return
                        if (updateStatusCode == OsAccountUpdateStatus.NO_CHANGE) {
                                return new OsAccountUpdateResult(updateStatusCode, null);
                        }

                        // get the updated account from database
                        OsAccount updatedAccount = getOsAccountByObjectId(osAccount.getId(), connection);

                        // register the updated account with the transaction to fire off an event
                        trans.registerChangedOsAccount(updatedAccount);

                        return new OsAccountUpdateResult(updateStatusCode, updatedAccount);

                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error updating account with addr = %s, account id = %d", osAccount.getAddr().orElse("Unknown"), osAccount.getId()), ex);
                }
        }

        private <T> void updateAccountColumn(long accountObjId, String colName, T colValue, CaseDbConnection connection) throws SQLException, TskCoreException {

                String updateSQL = "UPDATE tsk_os_accounts "
                                + " SET " + colName + " = ? "
                                + " WHERE os_account_obj_id = ?";

                db.acquireSingleUserCaseWriteLock();
                try {
                        PreparedStatement preparedStatement = connection.getPreparedStatement(updateSQL, Statement.NO_GENERATED_KEYS);
                        preparedStatement.clearParameters();

                        if (Objects.isNull(colValue)) {
                                preparedStatement.setNull(1, Types.NULL); // handle null value
                        } else {
                                if (colValue instanceof String) {
                                        preparedStatement.setString(1, (String) colValue);
                                } else if (colValue instanceof Long) {
                                        preparedStatement.setLong(1, (Long) colValue);
                                } else if (colValue instanceof Integer) {
                                        preparedStatement.setInt(1, (Integer) colValue);
                                } else {
                                        throw new TskCoreException(String.format("Unhandled column data type received while updating the account (%d) ", accountObjId));
                                }
                        }

                        preparedStatement.setLong(2, accountObjId);

                        connection.executeUpdate(preparedStatement);
                } finally {
                        db.releaseSingleUserCaseWriteLock();
                }
        }

        private void updateAccountSignature(long accountObjId, String signature, CaseDbConnection connection) throws SQLException {

                String updateSQL = "UPDATE tsk_os_accounts SET "
                                + "             signature = "
                                + "       CASE WHEN db_status = " + OsAccount.OsAccountDbStatus.ACTIVE.getId() + " THEN ? ELSE signature END  "
                                + " WHERE os_account_obj_id = ?";       // 8

                PreparedStatement preparedStatement = connection.getPreparedStatement(updateSQL, Statement.NO_GENERATED_KEYS);
                preparedStatement.clearParameters();

                preparedStatement.setString(1, signature);
                preparedStatement.setLong(2, accountObjId);

                connection.executeUpdate(preparedStatement);
        }

        public OsAccountUpdateResult updateCoreWindowsOsAccountAttributes(OsAccount osAccount, String accountSid, String loginName, String realmName, Host referringHost) throws TskCoreException, NotUserSIDException {
                CaseDbTransaction trans = db.beginTransaction();
                try {
                        OsAccountUpdateResult updateStatus = this.updateCoreWindowsOsAccountAttributes(osAccount, accountSid, loginName, realmName, referringHost, trans);

                        trans.commit();
                        trans = null;
                        return updateStatus;
                } finally {
                        if (trans != null) {
                                trans.rollback();
                        }
                }
        }

        private OsAccountUpdateResult updateCoreWindowsOsAccountAttributes(OsAccount osAccount, String accountSid, String loginName, String realmName, Host referringHost, CaseDbTransaction trans) throws TskCoreException, NotUserSIDException {

                // first get and update the realm - if we have the info to find the realm
                if (!StringUtils.isBlank(accountSid) || !StringUtils.isBlank(realmName)) {
                        db.getOsAccountRealmManager().getAndUpdateWindowsRealm(accountSid, realmName, referringHost, trans.getConnection());
                }

                // now update the account core data
                OsAccountUpdateResult updateStatus = this.updateOsAccountCore(osAccount, accountSid, loginName, trans);

                return updateStatus;
        }

        private OsAccountUpdateResult updateOsAccountCore(OsAccount osAccount, String address, String loginName, CaseDbTransaction trans) throws TskCoreException {

                OsAccountUpdateStatus updateStatusCode = OsAccountUpdateStatus.NO_CHANGE;
                OsAccount updatedAccount;

                try {
                        CaseDbConnection connection = trans.getConnection();

                        // if a new addr is provided and the account already has an address, and they are not the same, throw an exception
                        if (!StringUtils.isBlank(address) && !StringUtils.isBlank(osAccount.getAddr().orElse(null)) && !address.equalsIgnoreCase(osAccount.getAddr().orElse(""))) {
                                throw new TskCoreException(String.format("Account (%d) already has an address (%s), address cannot be updated.", osAccount.getId(), osAccount.getAddr().orElse("NULL")));
                        }

                        if (StringUtils.isBlank(osAccount.getAddr().orElse(null)) && !StringUtils.isBlank(address)) {
                                updateAccountColumn(osAccount.getId(), "addr", address, connection);
                                updateStatusCode = OsAccountUpdateStatus.UPDATED;
                        }

                        if (StringUtils.isBlank(osAccount.getLoginName().orElse(null)) && !StringUtils.isBlank(loginName)) {
                                updateAccountColumn(osAccount.getId(), "login_name", loginName, connection);
                                updateStatusCode = OsAccountUpdateStatus.UPDATED;
                        }

                        // if nothing is changed, return
                        if (updateStatusCode == OsAccountUpdateStatus.NO_CHANGE) {
                                return new OsAccountUpdateResult(updateStatusCode, osAccount);
                        }

                        // update signature if needed, based on the most current addr/loginName
                        OsAccount currAccount = getOsAccountByObjectId(osAccount.getId(), connection);
                        String newAddress = currAccount.getAddr().orElse(null);
                        String newLoginName = currAccount.getLoginName().orElse(null);

                        String newSignature = getOsAccountSignature(newAddress, newLoginName);
                        updateAccountSignature(osAccount.getId(), newSignature, connection);

                        // get the updated account from database
                        updatedAccount = getOsAccountByObjectId(osAccount.getId(), connection);

                        // register the updated account with the transaction to fire off an event
                        trans.registerChangedOsAccount(updatedAccount);

                        return new OsAccountUpdateResult(updateStatusCode, updatedAccount);

                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Error updating account with unique id = %s, account id = %d", osAccount.getAddr().orElse("Unknown"), osAccount.getId()), ex);
                }
        }

        public List<Host> getHosts(OsAccount account) throws TskCoreException {
                List<Host> hostList = new ArrayList<>();

                String query = "SELECT tsk_hosts.id AS hostId, name, db_status FROM tsk_hosts "
                                + " JOIN data_source_info ON tsk_hosts.id = data_source_info.host_id"
                                + "     JOIN tsk_os_account_instances ON data_source_info.obj_id = tsk_os_account_instances.data_source_obj_id"
                                + " WHERE os_account_obj_id = " + account.getId();

                db.acquireSingleUserCaseReadLock();
                try (CaseDbConnection connection = db.getConnection();
                                Statement s = connection.createStatement();
                                ResultSet rs = connection.executeQuery(s, query)) {

                        while (rs.next()) {
                                hostList.add(new Host(rs.getLong("hostId"), rs.getString("name"), Host.HostDbStatus.fromID(rs.getInt("db_status"))));
                        }

                } catch (SQLException ex) {
                        throw new TskCoreException(String.format("Failed to get host list for os account %d", account.getId()), ex);
                } finally {
                        db.releaseSingleUserCaseReadLock();
                }
                return hostList;
        }

        private OsAccount osAccountFromResultSet(ResultSet rs) throws SQLException {

                OsAccountType accountType = null;
                int typeId = rs.getInt("type");
                if (!rs.wasNull()) {
                        accountType = OsAccount.OsAccountType.fromID(typeId);
                }

                Long creationTime = rs.getLong("created_date"); // getLong returns 0 if value is null
                if (rs.wasNull()) {
                        creationTime = null;
                }

                return new OsAccount(db, rs.getLong("os_account_obj_id"), rs.getLong("realm_id"), rs.getString("login_name"), rs.getString("addr"),
                                rs.getString("signature"), rs.getString("full_name"), creationTime, accountType, OsAccount.OsAccountStatus.fromID(rs.getInt("status")),
                                OsAccount.OsAccountDbStatus.fromID(rs.getInt("db_status")));

        }

        private void fireChangeEvent(OsAccount account) {
                db.fireTSKEvent(new OsAccountsUpdatedTskEvent(Collections.singletonList(account)));
        }

        static String getOsAccountSignature(String uniqueId, String loginName) throws TskCoreException {
                // Create a signature. 
                String signature;
                if (Strings.isNullOrEmpty(uniqueId) == false) {
                        signature = uniqueId;
                } else if (Strings.isNullOrEmpty(loginName) == false) {
                        signature = loginName;
                } else {
                        throw new TskCoreException("OS Account must have either a uniqueID or a login name.");
                }
                return signature;
        }

        public static class NotUserSIDException extends TskException {

                private static final long serialVersionUID = 1L;

                public NotUserSIDException() {
                        super("No error message available.");
                }

                public NotUserSIDException(String msg) {
                        super(msg);
                }

                public NotUserSIDException(String msg, Exception ex) {
                        super(msg, ex);
                }
        }

        public enum OsAccountUpdateStatus {

                NO_CHANGE, 
                UPDATED, 
                MERGED          
        }

        public final static class OsAccountUpdateResult {

                private final OsAccountUpdateStatus updateStatus;
                private final OsAccount updatedAccount;

                OsAccountUpdateResult(OsAccountUpdateStatus updateStatus, OsAccount updatedAccount) {
                        this.updateStatus = updateStatus;
                        this.updatedAccount = updatedAccount;
                }

                public OsAccountUpdateStatus getUpdateStatusCode() {
                        return updateStatus;
                }

                public Optional<OsAccount> getUpdatedAccount() {
                        return Optional.ofNullable(updatedAccount);
                }
        }
}