using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Diagnostics;
using System.IO;
using System.Linq;

namespace Umbraco.Core.Persistence
{
    /// <summary>
    /// Manages LocalDB databases.
    /// </summary>
    /// <remarks>
    /// <para>Latest version is SQL Server 2016 Express LocalDB,
    /// see https://docs.microsoft.com/en-us/sql/database-engine/configure-windows/sql-server-2016-express-localdb
    /// which can be installed by downloading the Express installer from https://www.microsoft.com/en-us/sql-server/sql-server-downloads
    /// (about 5MB) then select 'download media' to download SqlLocalDB.msi (about 44MB), which you can execute. This installs
    /// LocalDB only. Though you probably want to install the full Express. You may also want to install SQL Server Management
    /// Studio which can be used to connect to LocalDB databases.</para>
    /// <para>See also https://github.com/ritterim/automation-sql which is a somewhat simpler version of this.</para>
    /// </remarks>
    internal class LocalDb
    {
        private int _version;
        private bool _hasVersion;
        private string _exe;

        #region Availability & Version

        /// <summary>
        /// Gets the LocalDb installed version.
        /// </summary>
        /// <remarks>If more than one version is installed, returns the highest available. Returns
        /// the major version as an integer e.g. 11, 12...</remarks>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        public int Version
        {
            get
            {
                EnsureVersion();
                if (_version <= 0)
                    throw new InvalidOperationException("LocalDb is not available.");
                return _version;
            }
        }

        /// <summary>
        /// Ensures that the LocalDb version is detected.
        /// </summary>
        private void EnsureVersion()
        {
            if (_hasVersion) return;
            DetectVersion();
            _hasVersion = true;
        }

        /// <summary>
        /// Gets a value indicating whether LocalDb is available.
        /// </summary>
        public bool IsAvailable
        {
            get
            {
                EnsureVersion();
                return _version > 0;
            }
        }

        /// <summary>
        /// Ensures that LocalDb is available.
        /// </summary>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        private void EnsureAvailable()
        {
            if (IsAvailable == false)
                throw new InvalidOperationException("LocalDb is not available.");
        }

        /// <summary>
        /// Detects LocalDb installed version.
        /// </summary>
        /// <remarks>If more than one version is installed, the highest available is detected.</remarks>
        private void DetectVersion()
        {
            _hasVersion = true;
            _version = -1;
            _exe = null;

            var programFiles = Environment.GetEnvironmentVariable("ProgramFiles");

            // MS SQL Server installs in e.g. "C:\Program Files\Microsoft SQL Server", so
            // we want to detect it in "%ProgramFiles%\Microsoft SQL Server" - however, if
            // Umbraco runs as a 32bits process (e.g. IISExpress configured as 32bits)
            // on a 64bits system, %ProgramFiles% will point to "C:\Program Files (x86)"
            // and SQL Server cannot be found. But then, %ProgramW6432% will point to
            // the original "C:\Program Files". Using it to fix the path.
            // see also: MSDN doc for WOW64 implementation
            //
            var programW6432 = Environment.GetEnvironmentVariable("ProgramW6432");
            if (string.IsNullOrWhiteSpace(programW6432) == false && programW6432 != programFiles)
                programFiles = programW6432;

            if (string.IsNullOrWhiteSpace(programFiles)) return;

            // detect 14, 13, 12, 11
            for (var i = 14; i > 10; i--)
            {
                var exe = Path.Combine(programFiles, $@"Microsoft SQL Server\{i}0\Tools\Binn\SqlLocalDB.exe");
                if (File.Exists(exe) == false) continue;
                _version = i;
                _exe = exe;
                break;
            }
        }

        #endregion

        #region Instances

        /// <summary>
        /// Gets the name of existing LocalDb instances.
        /// </summary>
        /// <returns>The name of existing LocalDb instances.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        public string[] GetInstances()
        {
            EnsureAvailable();
            var rc = ExecuteSqlLocalDb("i", out var output, out var error); // info
            if (rc != 0 || error != string.Empty) return null;
            return output.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
        }

        /// <summary>
        /// Gets a value indicating whether a LocalDb instance exists.
        /// </summary>
        /// <param name="instanceName">The name of the instance.</param>
        /// <returns>A value indicating whether a LocalDb instance with the specified name exists.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        public bool InstanceExists(string instanceName)
        {
            EnsureAvailable();
            var instances = GetInstances();
            return instances != null && instances.Contains(instanceName, StringComparer.OrdinalIgnoreCase);
        }

        /// <summary>
        /// Creates a LocalDb instance.
        /// </summary>
        /// <param name="instanceName">The name of the instance.</param>
        /// <returns>A value indicating whether the instance was created without errors.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        public bool CreateInstance(string instanceName)
        {
            EnsureAvailable();
            return ExecuteSqlLocalDb($"c \"{instanceName}\"", out _, out var error) == 0 && error == string.Empty;
        }

        /// <summary>
        /// Drops a LocalDb instance.
        /// </summary>
        /// <param name="instanceName">The name of the instance.</param>
        /// <returns>A value indicating whether the instance was dropped without errors.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        /// <remarks>
        /// When an instance is dropped all the attached database files are deleted.
        /// Successful if the instance does not exist.
        /// </remarks>
        public bool DropInstance(string instanceName)
        {
            EnsureAvailable();
            var instance = GetInstance(instanceName);
            if (instance == null) return true;
            instance.DropDatabases(); // else the files remain

            // -i force NOWAIT, -k kills
            return ExecuteSqlLocalDb($"p \"{instanceName}\" -i", out _, out var error) == 0 && error == string.Empty
                   && ExecuteSqlLocalDb($"d \"{instanceName}\"", out _, out error) == 0 && error == string.Empty;
        }

        /// <summary>
        /// Stops a LocalDb instance.
        /// </summary>
        /// <param name="instanceName">The name of the instance.</param>
        /// <returns>A value indicating whether the instance was stopped without errors.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        /// <remarks>
        /// Successful if the instance does not exist.
        /// </remarks>
        public bool StopInstance(string instanceName)
        {
            EnsureAvailable();
            if (InstanceExists(instanceName) == false) return true;

            // -i force NOWAIT, -k kills
            return ExecuteSqlLocalDb($"p \"{instanceName}\" -i", out _, out var error) == 0 && error == string.Empty;
        }

        /// <summary>
        /// Stops a LocalDb instance.
        /// </summary>
        /// <param name="instanceName">The name of the instance.</param>
        /// <returns>A value indicating whether the instance was started without errors.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        /// <remarks>
        /// Failed if the instance does not exist.
        /// </remarks>
        public bool StartInstance(string instanceName)
        {
            EnsureAvailable();
            if (InstanceExists(instanceName) == false) return false;
            return ExecuteSqlLocalDb($"s \"{instanceName}\"", out _, out var error) == 0 && error == string.Empty;
        }

        /// <summary>
        /// Gets a LocalDb instance.
        /// </summary>
        /// <param name="instanceName">The name of the instance.</param>
        /// <returns>The instance with the specified name if it exists, otherwise null.</returns>
        /// <exception cref="InvalidOperationException">Thrown when LocalDb is not available.</exception>
        public Instance GetInstance(string instanceName)
        {
            EnsureAvailable();
            return InstanceExists(instanceName) ? new Instance(instanceName) : null;
        }

        #endregion

        #region Databases

        /// <summary>
        /// Represents a LocalDb instance.
        /// </summary>
        /// <remarks>
        /// LocalDb is assumed to be available, and the instance is assumed to exist.
        /// </remarks>
        public class Instance
        {
            private readonly string _masterCstr;

            /// <summary>
            /// Gets the name of the instance.
            /// </summary>
            public string InstanceName { get; }

            /// <summary>
            /// Initializes a new instance of the <see cref="Instance"/> class.
            /// </summary>
            /// <param name="instanceName"></param>
            public Instance(string instanceName)
            {
                InstanceName = instanceName;
                _masterCstr = $@"Server=(localdb)\{instanceName};Integrated Security=True;";
            }

            /// <summary>
            /// Gets a LocalDb connection string.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <returns>The connection string for the specified database.</returns>
            /// <remarks>
            /// The database should exist in the LocalDb instance.
            /// </remarks>
            public string GetConnectionString(string databaseName)
            {
                return _masterCstr + $@"Database={databaseName};";
            }

            /// <summary>
            /// Gets a LocalDb connection string for an attached database.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="filesPath">The directory containing database files.</param>
            /// <returns>The connection string for the specified database.</returns>
            /// <remarks>
            /// The database should not exist in the LocalDb instance.
            /// It will be attached with its name being its MDF filename (full path), uppercased, when
            /// the first connection is opened, and remain attached until explicitely detached.
            /// </remarks>
            public string GetAttachedConnectionString(string databaseName, string filesPath)
            {
                GetDatabaseFiles(databaseName, filesPath, out _, out _, out _, out var mdfFilename, out _);

                return _masterCstr + $@"AttachDbFileName='{mdfFilename}';";
            }

            /// <summary>
            /// Gets the name of existing databases.
            /// </summary>
            /// <returns>The name of existing databases.</returns>
            public string[] GetDatabases()
            {
                var userDatabases = new List<string>();

                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    var databases = new Dictionary<string, string>();

                    SetCommand(cmd, @"
                        SELECT name, filename FROM sys.sysdatabases");

                    using (var reader = cmd.ExecuteReader())
                    {
                        while (reader.Read())
                        {
                            databases[reader.GetString(0)] = reader.GetString(1);
                        }
                    }

                    foreach (var database in databases)
                    {
                        var dbname = database.Key;

                        if (dbname == "master" || dbname == "tempdb" || dbname == "model" || dbname == "msdb")
                            continue;

                        // fixme - shall we deal with stale databases?
                        // fixme - is it always ok to assume file names?
                        //var mdf = database.Value;
                        //var ldf = mdf.Replace(".mdf", "_log.ldf");
                        //if (staleOnly && File.Exists(mdf) && File.Exists(ldf))
                        //    continue;

                        //ExecuteDropDatabase(cmd, dbname, mdf, ldf);
                        //count++;

                        userDatabases.Add(dbname);
                    }
                }

                return userDatabases.ToArray();
            }

            /// <summary>
            /// Gets a value indicating whether a database exists.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <returns>A value indicating whether a database with the specified name exists.</returns>
            /// <remarks>
            /// A database exists if it is registered in the instance, and its files exist. If the database
            /// is registered but some of its files are missing, the database is dropped.
            /// </remarks>
            public bool DatabaseExists(string databaseName)
            {
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    var mdf = GetDatabase(cmd, databaseName);
                    if (mdf == null) return false;

                    // it can exist, even though its files have been deleted
                    // if files exist assume all is ok (should we try to connect?)
                    var ldf = GetLogFilename(mdf);
                    if (File.Exists(mdf) && File.Exists(ldf))
                        return true;

                    ExecuteDropDatabase(cmd, databaseName, mdf, ldf);
                }

                return false;
            }

            /// <summary>
            /// Creates a new database.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="filesPath">The directory containing database files.</param>
            /// <returns>A value indicating whether the database was created without errors.</returns>
            /// <remarks>
            /// Failed if a database with the specified name already exists in the instance,
            /// or if the database files already exist in the specified directory.
            /// </remarks>
            public bool CreateDatabase(string databaseName, string filesPath)
            {
                GetDatabaseFiles(databaseName, filesPath, out var logName, out _, out _, out var mdfFilename, out var ldfFilename);

                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    var mdf = GetDatabase(cmd, databaseName);
                    if (mdf != null) return false;

                    // cannot use parameters on CREATE DATABASE
                    // ie "CREATE DATABASE @0 ..." does not work
                    SetCommand(cmd, $@"
                        CREATE DATABASE {QuotedName(databaseName)}
                            ON (NAME=N{QuotedName(databaseName, '\'')}, FILENAME={QuotedName(mdfFilename, '\'')})
                            LOG ON (NAME=N{QuotedName(logName, '\'')}, FILENAME={QuotedName(ldfFilename, '\'')})");

                    var unused = cmd.ExecuteNonQuery();
                }
                return true;
            }

            /// <summary>
            /// Drops a database.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <returns>A value indicating whether the database was dropped without errors.</returns>
            /// <remarks>
            /// Successful if the database does not exist.
            /// Deletes the database files.
            /// </remarks>
            public bool DropDatabase(string databaseName)
            {
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    SetCommand(cmd, @"
                        SELECT name, filename FROM master.dbo.sysdatabases WHERE ('[' + name + ']' = @0 OR name = @0)",
                        databaseName);

                    var mdf = GetDatabase(cmd, databaseName);
                    if (mdf == null) return true;

                    ExecuteDropDatabase(cmd, databaseName, mdf);
                }

                return true;
            }

            /// <summary>
            /// Drops stale databases.
            /// </summary>
            /// <returns>The number of databases that were dropped.</returns>
            /// <remarks>
            /// A database is considered stale when its files cannot be found.
            /// </remarks>
            public int DropStaleDatabases()
            {
                return DropDatabases(true);
            }

            /// <summary>
            /// Drops databases.
            /// </summary>
            /// <param name="staleOnly">A value indicating whether to delete only stale database.</param>
            /// <returns>The number of databases that were dropped.</returns>
            /// <remarks>
            /// A database is considered stale when its files cannot be found.
            /// </remarks>
            public int DropDatabases(bool staleOnly = false)
            {
                var count = 0;
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    var databases = new Dictionary<string, string>();

                    SetCommand(cmd, @"
                        SELECT name, filename FROM sys.sysdatabases");

                    using (var reader = cmd.ExecuteReader())
                    {
                        while (reader.Read())
                        {
                            databases[reader.GetString(0)] = reader.GetString(1);
                        }
                    }

                    foreach (var database in databases)
                    {
                        var dbname = database.Key;

                        if (dbname == "master" || dbname == "tempdb" || dbname == "model" || dbname == "msdb")
                            continue;

                        var mdf = database.Value;
                        var ldf = mdf.Replace(".mdf", "_log.ldf");
                        if (staleOnly && File.Exists(mdf) && File.Exists(ldf))
                            continue;

                        ExecuteDropDatabase(cmd, dbname, mdf, ldf);
                        count++;
                    }
                }

                return count;
            }

            /// <summary>
            /// Detaches a database.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <returns>The directory containing the database files.</returns>
            /// <exception cref="InvalidOperationException">Thrown when a database with the specified name does not exist.</exception>
            public string DetachDatabase(string databaseName)
            {
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    var mdf = GetDatabase(cmd, databaseName);
                    if (mdf == null)
                        throw new InvalidOperationException("Database does not exist.");

                    DetachDatabase(cmd, databaseName);

                    return Path.GetDirectoryName(mdf);
                }
            }

            /// <summary>
            /// Attaches a database.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="filesPath">The directory containing database files.</param>
            /// <exception cref="InvalidOperationException">Thrown when a database with the specified name already exists.</exception>
            public void AttachDatabase(string databaseName, string filesPath)
            {
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    var mdf = GetDatabase(cmd, databaseName);
                    if (mdf != null)
                        throw new InvalidOperationException("Database already exists.");

                    AttachDatabase(cmd, databaseName, filesPath);
                }
            }

            /// <summary>
            /// Gets the file names of a database.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="mdfName">The MDF logical name.</param>
            /// <param name="ldfName">The LDF logical name.</param>
            /// <param name="mdfFilename">The MDF filename.</param>
            /// <param name="ldfFilename">The LDF filename.</param>
            public void GetFilenames(string databaseName,
                out string mdfName, out string ldfName,
                out string mdfFilename, out string ldfFilename)
            {
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    GetFilenames(cmd, databaseName, out mdfName, out ldfName, out mdfFilename, out ldfFilename);
                }
            }

            /// <summary>
            /// Kills all existing connections.
            /// </summary>
            /// <param name="databaseName">The name of the database.</param>
            public void KillConnections(string databaseName)
            {
                using (var conn = new SqlConnection(_masterCstr))
                using (var cmd = conn.CreateCommand())
                {
                    conn.Open();

                    SetCommand(cmd, @"
                        DECLARE @sql VARCHAR(MAX);
                        SELECT @sql = COALESCE(@sql,'') + 'kill ' + CONVERT(VARCHAR, SPId) + ';'
                            FROM master.sys.sysprocesses
                            WHERE DBId = DB_ID(@0) AND SPId <> @@SPId;
                        EXEC(@sql);",
                        databaseName);
                    cmd.ExecuteNonQuery();
                }
            }

            /// <summary>
            /// Gets a database.
            /// </summary>
            /// <param name="cmd">The Sql Command.</param>
            /// <param name="databaseName">The name of the database.</param>
            /// <returns>The full filename of the MDF file, if the database exists, otherwise null.</returns>
            private static string GetDatabase(SqlCommand cmd, string databaseName)
            {
                SetCommand(cmd, @"
                    SELECT name, filename FROM master.dbo.sysdatabases WHERE ('[' + name + ']' = @0 OR name = @0)",
                    databaseName);

                string mdf = null;
                using (var reader = cmd.ExecuteReader())
                {
                    if (reader.Read())
                        mdf = reader.GetString(1) ?? string.Empty;
                    while (reader.Read())
                    {
                    }
                }

                return mdf;
            }

            /// <summary>
            /// Drops a database and its files.
            /// </summary>
            /// <param name="cmd">The Sql command.</param>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="mdf">The name of the database (MDF) file.</param>
            /// <param name="ldf">The name of the log (LDF) file.</param>
            private static void ExecuteDropDatabase(SqlCommand cmd, string databaseName, string mdf, string ldf = null)
            {
                try
                {
                    // cannot use parameters on ALTER DATABASE
                    // ie "ALTER DATABASE @0 ..." does not work
                    SetCommand(cmd, $@"
                        ALTER DATABASE {QuotedName(databaseName)} SET SINGLE_USER WITH ROLLBACK IMMEDIATE");

                    var unused1 = cmd.ExecuteNonQuery();
                }
                catch (SqlException e)
                {
                    if (e.Message.Contains("Unable to open the physical file") && e.Message.Contains("Operating system error 2:"))
                    {
                        // quite probably, the files were missing
                        // yet, it should be possible to drop the database anyways
                        // but we'll have to deal with the files
                    }
                    else
                    {
                        // no idea, throw
                        throw;
                    }
                }

                // cannot use parameters on DROP DATABASE
                // ie "DROP DATABASE @0 ..." does not work
                SetCommand(cmd, $@"
                    DROP DATABASE {QuotedName(databaseName)}");

                var unused2 = cmd.ExecuteNonQuery();

                // be absolutely sure
                if (File.Exists(mdf)) File.Delete(mdf);
                ldf = ldf ?? GetLogFilename(mdf);
                if (File.Exists(ldf)) File.Delete(ldf);
            }

            /// <summary>
            /// Gets the log (LDF) filename corresponding to a database (MDF) filename.
            /// </summary>
            /// <param name="mdfFilename">The MDF filename.</param>
            /// <returns></returns>
            private static string GetLogFilename(string mdfFilename)
            {
                if (mdfFilename.EndsWith(".mdf") == false)
                    throw new ArgumentException("Not a valid MDF filename (no .mdf extension).", nameof(mdfFilename));
                return mdfFilename.Substring(0, mdfFilename.Length - ".mdf".Length) + "_log.ldf";
            }

            /// <summary>
            /// Detaches a database.
            /// </summary>
            /// <param name="cmd">The Sql command.</param>
            /// <param name="databaseName">The name of the database.</param>
            private static void DetachDatabase(SqlCommand cmd, string databaseName)
            {
                // cannot use parameters on ALTER DATABASE
                // ie "ALTER DATABASE @0 ..." does not work
                SetCommand(cmd, $@"
                    ALTER DATABASE {QuotedName(databaseName)} SET SINGLE_USER WITH ROLLBACK IMMEDIATE");

                var unused1 = cmd.ExecuteNonQuery();

                SetCommand(cmd, @"
                    EXEC sp_detach_db @dbname=@0",
                    databaseName);

                var unused2 = cmd.ExecuteNonQuery();
            }

            /// <summary>
            /// Attaches a database.
            /// </summary>
            /// <param name="cmd">The Sql command.</param>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="filesPath">The directory containing database files.</param>
            private static void AttachDatabase(SqlCommand cmd, string databaseName, string filesPath)
            {
                GetDatabaseFiles(databaseName, filesPath,
                    out var logName, out _, out _, out var mdfFilename, out var ldfFilename);

                // cannot use parameters on CREATE DATABASE
                // ie "CREATE DATABASE @0 ..." does not work
                SetCommand(cmd, $@"
                        CREATE DATABASE {QuotedName(databaseName)}
                            ON (NAME=N{QuotedName(databaseName, '\'')}, FILENAME={QuotedName(mdfFilename, '\'')})
                            LOG ON (NAME=N{QuotedName(logName, '\'')}, FILENAME={QuotedName(ldfFilename, '\'')})
                            FOR ATTACH");

                var unused = cmd.ExecuteNonQuery();
            }

            /// <summary>
            /// Sets a database command.
            /// </summary>
            /// <param name="cmd">The command.</param>
            /// <param name="sql">The command text.</param>
            /// <param name="args">The command arguments.</param>
            /// <remarks>
            /// The command text must refer to arguments as @0, @1... each referring
            /// to the corresponding position in <paramref name="args"/>.
            /// </remarks>
            private static void SetCommand(SqlCommand cmd, string sql, params object[] args)
            {
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = sql;
                cmd.Parameters.Clear();
                for (var i = 0; i < args.Length; i++)
                    cmd.Parameters.AddWithValue("@" + i, args[i]);
            }

            /// <summary>
            /// Gets the file names of a database.
            /// </summary>
            /// <param name="cmd">The Sql command.</param>
            /// <param name="databaseName">The name of the database.</param>
            /// <param name="mdfName">The MDF logical name.</param>
            /// <param name="ldfName">The LDF logical name.</param>
            /// <param name="mdfFilename">The MDF filename.</param>
            /// <param name="ldfFilename">The LDF filename.</param>
            private void GetFilenames(SqlCommand cmd, string databaseName,
                out string mdfName, out string ldfName,
                out string mdfFilename, out string ldfFilename)
            {
                mdfName = ldfName = mdfFilename = ldfFilename = null;

                SetCommand(cmd, @"
                    SELECT DB_NAME(database_id), type_desc, name, physical_name
                    FROM master.sys.master_files
                    WHERE database_id=DB_ID(@0)",
                    databaseName);
                using (var reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        var type = reader.GetString(1);
                        if (type == "ROWS")
                        {
                            mdfName = reader.GetString(2);
                            ldfName = reader.GetString(3);
                        }
                        else if (type == "LOG")
                        {
                            ldfName = reader.GetString(2);
                            ldfFilename = reader.GetString(3);
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Copy database files.
        /// </summary>
        /// <param name="databaseName">The name of the source database.</param>
        /// <param name="filesPath">The directory containing source database files.</param>
        /// <param name="targetDatabaseName">The name of the target database.</param>
        /// <param name="targetFilesPath">The directory containing target database files.</param>
        /// <param name="sourceExtension">The source database files extension.</param>
        /// <param name="targetExtension">The target database files extension.</param>
        /// <param name="overwrite">A value indicating whether to overwrite the target files.</param>
        /// <param name="delete">A value indicating whether to delete the source files.</param>
        /// <remarks>
        /// The <paramref name="targetDatabaseName"/>, <paramref name="targetFilesPath"/>, <paramref name="sourceExtension"/>
        /// and <paramref name="targetExtension"/> parameters are optional. If they result in target being identical
        /// to source, no copy is performed. If <paramref name="delete"/> is false, nothing happens, otherwise the source
        /// files are deleted.
        /// If target is not identical to source, files are copied or moved, depending on the value of <paramref name="delete"/>.
        /// Extensions are used eg to copy MyDatabase.mdf to MyDatabase.mdf.temp.
        /// </remarks>
        public void CopyDatabaseFiles(string databaseName, string filesPath,
            string targetDatabaseName = null, string targetFilesPath = null,
            string sourceExtension = null, string targetExtension = null,
            bool overwrite = false, bool delete = false)
        {
            var nop = (targetFilesPath == null || targetFilesPath == filesPath)
                      && (targetDatabaseName == null || targetDatabaseName == databaseName)
                      && (sourceExtension == null && targetExtension == null || sourceExtension == targetExtension);
            if (nop && delete == false) return;

            GetDatabaseFiles(databaseName, filesPath,
                out _, out _, out _, out var mdfFilename, out var ldfFilename);

            if (sourceExtension != null)
            {
                mdfFilename += "." + sourceExtension;
                ldfFilename += "." + sourceExtension;
            }

            if (nop)
            {
                // delete
                if (File.Exists(mdfFilename)) File.Delete(mdfFilename);
                if (File.Exists(ldfFilename)) File.Delete(ldfFilename);
            }
            else
            {
                // copy or copy+delete ie move
                GetDatabaseFiles(targetDatabaseName ?? databaseName, targetFilesPath ?? filesPath,
                    out _, out _, out _, out var targetMdfFilename, out var targetLdfFilename);

                if (targetExtension != null)
                {
                    targetMdfFilename += "." + targetExtension;
                    targetLdfFilename += "." + targetExtension;
                }

                if (delete)
                {
                    if (overwrite && File.Exists(targetMdfFilename)) File.Delete(targetMdfFilename);
                    if (overwrite && File.Exists(targetLdfFilename)) File.Delete(targetLdfFilename);
                    File.Move(mdfFilename, targetMdfFilename);
                    File.Move(ldfFilename, targetLdfFilename);
                }
                else
                {
                    File.Copy(mdfFilename, targetMdfFilename, overwrite);
                    File.Copy(ldfFilename, targetLdfFilename, overwrite);
                }
            }
        }

        /// <summary>
        /// Gets a value indicating whether database files exist.
        /// </summary>
        /// <param name="databaseName">The name of the source database.</param>
        /// <param name="filesPath">The directory containing source database files.</param>
        /// <param name="extension">The database files extension.</param>
        /// <returns>A value indicating whether the database files exist.</returns>
        /// <remarks>
        /// Extensions are used eg to copy MyDatabase.mdf to MyDatabase.mdf.temp.
        /// </remarks>
        public bool DatabaseFilesExist(string databaseName, string filesPath, string extension = null)
        {
            GetDatabaseFiles(databaseName, filesPath,
                out _, out _, out _, out var mdfFilename, out var ldfFilename);

            if (extension != null)
            {
                mdfFilename += "." + extension;
                ldfFilename += "." + extension;
            }

            return File.Exists(mdfFilename) && File.Exists(ldfFilename);
        }

        /// <summary>
        /// Gets the name of the database files.
        /// </summary>
        /// <param name="databaseName">The name of the database.</param>
        /// <param name="filesPath">The directory containing database files.</param>
        /// <param name="logName">The name of the log.</param>
        /// <param name="baseFilename">The base filename (the MDF filename without the .mdf extension).</param>
        /// <param name="baseLogFilename">The base log filename (the LDF filename without the .ldf extension).</param>
        /// <param name="mdfFilename">The MDF filename.</param>
        /// <param name="ldfFilename">The LDF filename.</param>
        private static void GetDatabaseFiles(string databaseName, string filesPath,
            out string logName,
            out string baseFilename, out string baseLogFilename,
            out string mdfFilename, out string ldfFilename)
        {
            logName = databaseName + "_log";
            baseFilename = Path.Combine(filesPath, databaseName);
            baseLogFilename = Path.Combine(filesPath, logName);
            mdfFilename = baseFilename + ".mdf";
            ldfFilename = baseFilename + "_log.ldf";
        }

        #endregion

        #region SqlLocalDB

        /// <summary>
        /// Executes the SqlLocalDB command.
        /// </summary>
        /// <param name="args">The arguments.</param>
        /// <param name="output">The command standard output.</param>
        /// <param name="error">The command error output.</param>
        /// <returns>The process exit code.</returns>
        /// <remarks>
        /// Execution is successful if the exit code is zero, and error is empty.
        /// </remarks>
        private int ExecuteSqlLocalDb(string args, out string output, out string error)
        {
            if (_exe == null) // should never happen - we should not execute if not available
            {
                output = string.Empty;
                error = "SqlLocalDB.exe not found";
                return -1;
            }

            var p = new Process
            {
                StartInfo =
                {
                    UseShellExecute = false,
                    RedirectStandardOutput = true,
                    RedirectStandardError = true,
                    FileName = _exe,
                    Arguments = args,
                    CreateNoWindow = true,
                    WindowStyle = ProcessWindowStyle.Hidden
                }
            };
            p.Start();
            output = p.StandardOutput.ReadToEnd();
            error = p.StandardError.ReadToEnd();
            p.WaitForExit();

            return p.ExitCode;
        }

        /// <summary>
        /// Returns a Unicode string with the delimiters added to make the input string a valid SQL Server delimited identifier.
        /// </summary>
        /// <param name="name">The name to quote.</param>
        /// <param name="quote">A quote character.</param>
        /// <returns></returns>
        /// <remarks>
        /// This is a C# implementation of T-SQL QUOTEDNAME.
        /// <paramref name="quote"/> is optional, it can be '[' (default), ']', '\'' or '"'.
        /// </remarks>
        private static string QuotedName(string name, char quote = '[')
        {
            switch (quote)
            {
                case '[':
                case ']':
                    return "[" + name.Replace("]", "]]") + "]";
                case '\'':
                    return "'" + name.Replace("'", "''") + "'";
                case '"':
                    return "\"" + name.Replace("\"", "\"\"") + "\"";
                default:
                    throw new NotSupportedException("Not a valid quote character.");
            }
        }

        #endregion
    }
}