/*
 * Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
 * and the EPL 1.0 (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */
package org.h2.engine;

import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import org.h2.api.ErrorCode;
import org.h2.command.CommandInterface;
import org.h2.command.dml.SetTypes;
import org.h2.message.DbException;
import org.h2.message.Trace;
import org.h2.security.auth.AuthenticationException;
import org.h2.security.auth.AuthenticationInfo;
import org.h2.security.auth.Authenticator;
import org.h2.store.FileLock;
import org.h2.store.FileLockMethod;
import org.h2.util.MathUtils;
import org.h2.util.ParserUtil;
import org.h2.util.ThreadDeadlockDetector;
import org.h2.util.Utils;

The engine contains a map of all open databases.
It is also responsible for opening and creating new databases.
This is a singleton class.
/**
 * The engine contains a map of all open databases.
 * It is also responsible for opening and creating new databases.
 * This is a singleton class.
 */
public class Engine implements SessionFactory {

    private static final Engine INSTANCE = new Engine();
    private static final Map<String, Database> DATABASES = new HashMap<>();

    private volatile long wrongPasswordDelay =
            SysProperties.DELAY_WRONG_PASSWORD_MIN;
    private boolean jmx;

    private Engine() {
        // use getInstance()
        if (SysProperties.THREAD_DEADLOCK_DETECTOR) {
            ThreadDeadlockDetector.init();
        }
    }

    public static Engine getInstance() {
        return INSTANCE;
    }

    private Session openSession(ConnectionInfo ci, boolean ifExists,
            String cipher) {
        String name = ci.getName();
        Database database;
        ci.removeProperty("NO_UPGRADE", false);
        boolean openNew = ci.getProperty("OPEN_NEW", false);
        boolean opened = false;
        User user = null;
        synchronized (DATABASES) {
            if (openNew || ci.isUnnamedInMemory()) {
                database = null;
            } else {
                database = DATABASES.get(name);
            }
            if (database == null) {
                if (ifExists && !Database.exists(name)) {
                    throw DbException.get(ErrorCode.DATABASE_NOT_FOUND_2, name);
                }
                database = new Database(ci, cipher);
                opened = true;
                if (database.getAllUsers().isEmpty()) {
                    // users is the last thing we add, so if no user is around,
                    // the database is new (or not initialized correctly)
                    user = new User(database, database.allocateObjectId(),
                            ci.getUserName(), false);
                    user.setAdmin(true);
                    user.setUserPasswordHash(ci.getUserPasswordHash());
                    database.setMasterUser(user);
                }
                if (!ci.isUnnamedInMemory()) {
                    DATABASES.put(name, database);
                }
            }
        }
        if (opened) {
            // start the thread when already synchronizing on the database
            // otherwise a deadlock can occur when the writer thread
            // opens a new database (as in recovery testing)
            database.opened();
        }
        if (database.isClosing()) {
            return null;
        }
        if (user == null) {
            if (database.validateFilePasswordHash(cipher, ci.getFilePasswordHash())) {
                if (ci.getProperty("AUTHREALM")== null) {
                    user = database.findUser(ci.getUserName());
                    if (user != null) {
                        if (!user.validateUserPasswordHash(ci.getUserPasswordHash())) {
                            user = null;
                        }
                    }
                } else {
                    Authenticator authenticator = database.getAuthenticator();
                    if (authenticator==null) {
                        throw DbException.get(ErrorCode.AUTHENTICATOR_NOT_AVAILABLE, name);
                    } else {
                        try {
                            AuthenticationInfo authenticationInfo=new AuthenticationInfo(ci);
                            user = database.getAuthenticator().authenticate(authenticationInfo, database);
                        } catch (AuthenticationException authenticationError) {
                            database.getTrace(Trace.DATABASE).error(authenticationError,
                                "an error occurred during authentication; user: \"" +
                                ci.getUserName() + "\"");
                        }
                    }
                }
            }
            if (opened && (user == null || !user.isAdmin())) {
                // reset - because the user is not an admin, and has no
                // right to listen to exceptions
                database.setEventListener(null);
            }
        }
        if (user == null) {
            DbException er = DbException.get(ErrorCode.WRONG_USER_OR_PASSWORD);
            database.getTrace(Trace.DATABASE).error(er, "wrong user or password; user: \"" +
                    ci.getUserName() + "\"");
            database.removeSession(null);
            throw er;
        }
        //Prevent to set _PASSWORD
        ci.cleanAuthenticationInfo();
        checkClustering(ci, database);
        Session session = database.createSession(user);
        if (session == null) {
            // concurrently closing
            return null;
        }
        if (ci.getProperty("JMX", false)) {
            try {
                Utils.callStaticMethod(
                        "org.h2.jmx.DatabaseInfo.registerMBean", ci, database);
            } catch (Exception e) {
                database.removeSession(session);
                throw DbException.get(ErrorCode.FEATURE_NOT_SUPPORTED_1, e, "JMX");
            }
            jmx = true;
        }
        return session;
    }

    
Open a database connection with the given connection information.
Params:
ci – the connection information
Returns:
the session/**
     * Open a database connection with the given connection information.
     *
     * @param ci the connection information
     * @return the session
     */
    @Override
    public Session createSession(ConnectionInfo ci) {
        return INSTANCE.createSessionAndValidate(ci);
    }

    private Session createSessionAndValidate(ConnectionInfo ci) {
        try {
            ConnectionInfo backup = null;
            String lockMethodName = ci.getProperty("FILE_LOCK", null);
            FileLockMethod fileLockMethod = FileLock.getFileLockMethod(lockMethodName);
            if (fileLockMethod == FileLockMethod.SERIALIZED) {
                // In serialized mode, database instance sharing is not possible
                ci.setProperty("OPEN_NEW", "TRUE");
                try {
                    backup = ci.clone();
                } catch (CloneNotSupportedException e) {
                    throw DbException.convert(e);
                }
            }
            Session session = openSession(ci);
            validateUserAndPassword(true);
            if (backup != null) {
                session.setConnectionInfo(backup);
            }
            return session;
        } catch (DbException e) {
            if (e.getErrorCode() == ErrorCode.WRONG_USER_OR_PASSWORD) {
                validateUserAndPassword(false);
            }
            throw e;
        }
    }

    private synchronized Session openSession(ConnectionInfo ci) {
        boolean ifExists = ci.removeProperty("IFEXISTS", false);
        boolean ignoreUnknownSetting = ci.removeProperty(
                "IGNORE_UNKNOWN_SETTINGS", false);
        String cipher = ci.removeProperty("CIPHER", null);
        String init = ci.removeProperty("INIT", null);
        Session session;
        long start = System.nanoTime();
        for (;;) {
            session = openSession(ci, ifExists, cipher);
            if (session != null) {
                break;
            }
            // we found a database that is currently closing
            // wait a bit to avoid a busy loop (the method is synchronized)
            if (System.nanoTime() - start > 60_000_000_000L) {
                // retry at most 1 minute
                throw DbException.get(ErrorCode.DATABASE_ALREADY_OPEN_1,
                        "Waited for database closing longer than 1 minute");
            }
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                throw DbException.get(ErrorCode.DATABASE_CALLED_AT_SHUTDOWN);
            }
        }
        synchronized (session) {
            session.setAllowLiterals(true);
            DbSettings defaultSettings = DbSettings.getDefaultSettings();
            for (String setting : ci.getKeys()) {
                if (defaultSettings.containsKey(setting)) {
                    // database setting are only used when opening the database
                    continue;
                }
                String value = ci.getProperty(setting);
                if (!ParserUtil.isSimpleIdentifier(setting, false, false)) {
                    throw DbException.get(ErrorCode.UNSUPPORTED_SETTING_1, setting);
                }
                try {
                    CommandInterface command = session.prepareCommand(
                            "SET " + setting + ' ' + value,
                            Integer.MAX_VALUE);
                    command.executeUpdate(false);
                } catch (DbException e) {
                    if (e.getErrorCode() == ErrorCode.ADMIN_RIGHTS_REQUIRED) {
                        session.getTrace().error(e, "admin rights required; user: \"" +
                                ci.getUserName() + "\"");
                    } else {
                        session.getTrace().error(e, "");
                    }
                    if (!ignoreUnknownSetting) {
                        session.close();
                        throw e;
                    }
                }
            }
            if (init != null) {
                try {
                    CommandInterface command = session.prepareCommand(init,
                            Integer.MAX_VALUE);
                    command.executeUpdate(false);
                } catch (DbException e) {
                    if (!ignoreUnknownSetting) {
                        session.close();
                        throw e;
                    }
                }
            }
            session.setAllowLiterals(false);
            session.commit(true);
        }
        return session;
    }

    private static void checkClustering(ConnectionInfo ci, Database database) {
        String clusterSession = ci.getProperty(SetTypes.CLUSTER, null);
        if (Constants.CLUSTERING_DISABLED.equals(clusterSession)) {
            // in this case, no checking is made
            // (so that a connection can be made to disable/change clustering)
            return;
        }
        String clusterDb = database.getCluster();
        if (!Constants.CLUSTERING_DISABLED.equals(clusterDb)) {
            if (!Constants.CLUSTERING_ENABLED.equals(clusterSession)) {
                if (!Objects.equals(clusterSession, clusterDb)) {
                    if (clusterDb.equals(Constants.CLUSTERING_DISABLED)) {
                        throw DbException.get(
                                ErrorCode.CLUSTER_ERROR_DATABASE_RUNS_ALONE);
                    }
                    throw DbException.get(
                            ErrorCode.CLUSTER_ERROR_DATABASE_RUNS_CLUSTERED_1,
                            clusterDb);
                }
            }
        }
    }

    
Called after a database has been closed, to remove the object from the
list of open databases.
Params:
name – the database name/**
     * Called after a database has been closed, to remove the object from the
     * list of open databases.
     *
     * @param name the database name
     */
    void close(String name) {
        if (jmx) {
            try {
                Utils.callStaticMethod("org.h2.jmx.DatabaseInfo.unregisterMBean", name);
            } catch (Exception e) {
                throw DbException.get(ErrorCode.FEATURE_NOT_SUPPORTED_1, e, "JMX");
            }
        }
        synchronized (DATABASES) {
            DATABASES.remove(name);
        }
    }

    
This method is called after validating user name and password. If user
name and password were correct, the sleep time is reset, otherwise this
method waits some time (to make brute force / rainbow table attacks
harder) and then throws a 'wrong user or password' exception. The delay
is a bit randomized to protect against timing attacks. Also the delay
doubles after each unsuccessful logins, to make brute force attacks
harder.
There is only one exception message both for wrong user and for
wrong password, to make it harder to get the list of user names. This
method must only be called from one place, so it is not possible from the
stack trace to see if the user name was wrong or the password.
Params:
correct – if the user name or the password was correct
Throws:
DbException – the exception 'wrong user or password'/**
     * This method is called after validating user name and password. If user
     * name and password were correct, the sleep time is reset, otherwise this
     * method waits some time (to make brute force / rainbow table attacks
     * harder) and then throws a 'wrong user or password' exception. The delay
     * is a bit randomized to protect against timing attacks. Also the delay
     * doubles after each unsuccessful logins, to make brute force attacks
     * harder.
     *
     * There is only one exception message both for wrong user and for
     * wrong password, to make it harder to get the list of user names. This
     * method must only be called from one place, so it is not possible from the
     * stack trace to see if the user name was wrong or the password.
     *
     * @param correct if the user name or the password was correct
     * @throws DbException the exception 'wrong user or password'
     */
    private void validateUserAndPassword(boolean correct) {
        int min = SysProperties.DELAY_WRONG_PASSWORD_MIN;
        if (correct) {
            long delay = wrongPasswordDelay;
            if (delay > min && delay > 0) {
                // the first correct password must be blocked,
                // otherwise parallel attacks are possible
                synchronized (INSTANCE) {
                    // delay up to the last delay
                    // an attacker can't know how long it will be
                    delay = MathUtils.secureRandomInt((int) delay);
                    try {
                        Thread.sleep(delay);
                    } catch (InterruptedException e) {
                        // ignore
                    }
                    wrongPasswordDelay = min;
                }
            }
        } else {
            // this method is not synchronized on the Engine, so that
            // regular successful attempts are not blocked
            synchronized (INSTANCE) {
                long delay = wrongPasswordDelay;
                int max = SysProperties.DELAY_WRONG_PASSWORD_MAX;
                if (max <= 0) {
                    max = Integer.MAX_VALUE;
                }
                wrongPasswordDelay += wrongPasswordDelay;
                if (wrongPasswordDelay > max || wrongPasswordDelay < 0) {
                    wrongPasswordDelay = max;
                }
                if (min > 0) {
                    // a bit more to protect against timing attacks
                    delay += Math.abs(MathUtils.secureRandomLong() % 100);
                    try {
                        Thread.sleep(delay);
                    } catch (InterruptedException e) {
                        // ignore
                    }
                }
                throw DbException.get(ErrorCode.WRONG_USER_OR_PASSWORD);
            }
        }
    }

}