Imports System.Collections.Concurrent
Imports System.Data.SqlClient
Imports DigitalData.Modules.Database
Imports DigitalData.Modules.EDMI.API
Imports DigitalData.Modules.EDMI.API.Constants
Imports DigitalData.Modules.EDMI.API.EDMIServiceReference
Imports DigitalData.Modules.Logging

Public Class DatabaseWithFallback
    Private ReadOnly _Logger As Logger
    Private ReadOnly _Client As Client
    Private ReadOnly _ClientConfig As GlobalStateClientConfiguration
    Private ReadOnly _DatabaseECM As MSSQLServer
    Private _DatabaseIDB As MSSQLServer
    ''' <summary>
    ''' Lokaler Override-Cache für ExecuteAppServiceWrite-Änderungen.
    ''' Schlüssel: "TABELLENNAME|FILTERAUSDRUCK" → geänderter DataTable-Snapshot.
    ''' Wird beim nächsten Server-Refresh (Client.UpdateTimer) automatisch obsolet.
    ''' </summary>
    Private ReadOnly _localOverrideCache As New ConcurrentDictionary(Of String, DataTable)()
    ''' <summary>Erstellt den Cache-Key aus Tabellenname und Filter.</summary>
    Private Shared Function GetOverrideCacheKey(pTable As String, pFilter As String) As String
        Return $"{pTable.ToUpper}|{pFilter}"
    End Function

    ''' <summary>Leert den lokalen Override-Cache (z.B. nach manuellem Refresh).</summary>
    Public Sub InvalidateLocalOverrideCache()
        _localOverrideCache.Clear()
        _Logger.Debug("InvalidateLocalOverrideCache: Lokaler Override-Cache geleert.")
    End Sub

    ''' <summary>Leert den Override-Cache für eine bestimmte Tabelle.</summary>
    Public Sub InvalidateLocalOverrideCache(pTableName As String)
        Dim oKeysToRemove = _localOverrideCache.Keys.
            Where(Function(k) k.StartsWith(pTableName.ToUpper & "|")).ToList()
        For Each oKey In oKeysToRemove
            Dim oRemoved As DataTable = Nothing
            _localOverrideCache.TryRemove(oKey, oRemoved)
        Next
        _Logger.Debug("InvalidateLocalOverrideCache: Override-Cache für Tabelle [{0}] geleert.", pTableName)
    End Sub
    ''' <summary>
    ''' Thread-sicherer Cache für Connection Strings, indexiert nach Connection-ID.
    ''' Verhindert wiederholte DB-Roundtrips für SELECT * FROM TBDD_CONNECTION.
    ''' </summary>
    Private ReadOnly _connectionStringCache As New ConcurrentDictionary(Of Integer, String)

    ''' <summary>
    ''' Liefert den Connection String für eine bekannte Connection-ID.
    ''' Beim ersten Aufruf wird der Wert aus der DB geladen und gecacht.
    ''' Hinweis: Bei parallelen Erstabrufen derselben ID kann die Factory mehrfach
    ''' aufgerufen werden – da der Wert idempotent ist, ist dies funktional korrekt.
    ''' </summary>
    Private Function GetCachedConnectionString(pConnectionId As Integer) As String
        Return _connectionStringCache.GetOrAdd(pConnectionId,
            Function(id)
                _Logger.Debug("GetCachedConnectionString: Cache miss für ConnectionId [{0}] - lade aus DB", id)
                Dim oConnectionString = _DatabaseECM.Get_ConnectionStringforID(id)
                _Logger.Debug("GetCachedConnectionString: ConnectionId [{0}] gecacht", id)
                Return oConnectionString
            End Function)
    End Function
    ''' <summary>
    ''' Leert den Connection-String-Cache, z.B. nach Konfigurationsänderungen.
    ''' </summary>
    Public Sub InvalidateConnectionCache()
        _connectionStringCache.Clear()
        _Logger.Debug("InvalidateConnectionCache: Connection-String-Cache geleert")
    End Sub
    ''' <summary>
    ''' Leert den Cache für eine bestimmte Connection-ID.
    ''' </summary>
    Public Sub InvalidateConnectionCache(pConnectionId As Integer)
        Dim removed As String = Nothing
        If _connectionStringCache.TryRemove(pConnectionId, removed) Then
            _Logger.Debug("InvalidateConnectionCache: ConnectionId [{0}] aus Cache entfernt", pConnectionId)
        End If
    End Sub
    ''' <summary>
    ''' Options for GetDatatable
    ''' </summary>
    Public Class GetDatatableOptions
        Public ReadOnly FallbackSQL
        Public ReadOnly FallbackType

        ''' <summary>
        ''' Filter expression for the cached Datatable
        ''' </summary>
        Public Property FilterExpression As String = ""
        ''' <summary>
        ''' Columns to sort the cached Datatable by
        ''' </summary>
        Public Property SortByColumn As String = ""
        ''' <summary>
        ''' Force the fallback, skipping the service completely
        ''' </summary>
        Public Property ForceFallback As Boolean = False
        ''' <summary>
        ''' Connection Id to use, references TBDD_CONNECTION
        ''' </summary>
        Public Property ConnectionId As Integer = 0
        ''' <summary>
        ''' Erkennt URI-Cache-Syntax: "TABELLENNAME?FILTERAUSDRUCK"
        ''' Beispiel: "TBDD_USER?USER_ID=4524"
        ''' </summary>
        Public ReadOnly Property IsCacheQuery As Boolean
            Get
                If String.IsNullOrWhiteSpace(FallbackSQL) Then Return False
                Dim oTrimmed As String = FallbackSQL.TrimStart()
                ' Nur wenn kein SQL-Schlüsselwort vorhanden → Cache-Routing-Syntax
                Return FallbackSQL.Contains("?") AndAlso
                       Not oTrimmed.StartsWith("SELECT", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("INSERT", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("UPDATE", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("DELETE", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.Contains("DECLARE") AndAlso
                       Not oTrimmed.StartsWith("EXEC", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("DECLARE", StringComparison.OrdinalIgnoreCase)
            End Get
        End Property
        Public ReadOnly Property IsCacheWriteQuery As Boolean
            Get
                If String.IsNullOrWhiteSpace(FallbackSQL) Then Return False
                Dim oTrimmed As String = FallbackSQL.TrimStart()
                Return FallbackSQL.Contains("?") AndAlso
                       FallbackSQL.Contains("!") AndAlso
                       Not oTrimmed.StartsWith("SELECT", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("INSERT", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("UPDATE", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("DELETE", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("EXEC", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("DECLARE", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("--", StringComparison.OrdinalIgnoreCase) AndAlso
                       Not oTrimmed.StartsWith("/*", StringComparison.OrdinalIgnoreCase)
            End Get
        End Property
        ''' <summary>"TBDD_USER?USER_ID=4524" → "TBDD_USER"</summary>
        Public ReadOnly Property CacheQueryTable As String
            Get
                If Not IsCacheQuery Then Return String.Empty
                Return FallbackSQL.Substring(0, FallbackSQL.IndexOf("?")).Trim()
            End Get
        End Property

        ''' <summary>"TBDD_USER?USER_ID=4524" → "USER_ID=4524"</summary>
        Public ReadOnly Property CacheQueryFilter As String
            Get
                If Not IsCacheQuery Then Return String.Empty
                Return FallbackSQL.Substring(FallbackSQL.IndexOf("?") + 1).Trim()
            End Get
        End Property
        ''' <summary>"TBDD_USER?USER_ID=4524!STATUS=1" → "TBDD_USER"</summary>
        Public ReadOnly Property CacheWriteTable As String
            Get
                If Not IsCacheWriteQuery Then Return String.Empty
                Return FallbackSQL.Substring(0, FallbackSQL.IndexOf("?")).Trim()
            End Get
        End Property

        ''' <summary>"TBDD_USER?USER_ID=4524!STATUS=1" → "USER_ID=4524"</summary>
        Public ReadOnly Property CacheWriteFilter As String
            Get
                If Not IsCacheWriteQuery Then Return String.Empty
                Dim oStart As Integer = FallbackSQL.IndexOf("?") + 1
                Dim oLength As Integer = FallbackSQL.IndexOf("!") - oStart
                Return FallbackSQL.Substring(oStart, oLength).Trim()
            End Get
        End Property

        ''' <summary>"TBDD_USER?USER_ID=4524!STATUS=1" → "STATUS=1" | "DELETE"</summary>
        Public ReadOnly Property CacheWriteAction As String
            Get
                If Not IsCacheWriteQuery Then Return String.Empty
                Return FallbackSQL.Substring(FallbackSQL.IndexOf("!") + 1).Trim()
            End Get
        End Property

        ''' <summary>True wenn die Aktion ein DELETE ist</summary>
        Public ReadOnly Property CacheWriteIsDelete As Boolean
            Get
                Return IsCacheWriteQuery AndAlso
                       CacheWriteAction.Equals("DELETE", StringComparison.OrdinalIgnoreCase)
            End Get
        End Property

        ''' <summary>
        ''' Generiert das SQL aus der URI-Write-Syntax.
        ''' UPDATE: "TBDD_USER?USER_ID=4524!STATUS=1"  → "UPDATE TBDD_USER SET STATUS=1 WHERE USER_ID=4524"
        ''' DELETE: "TBDD_USER?USER_ID=4524!DELETE"    → "DELETE FROM TBDD_USER WHERE USER_ID=4524"
        ''' </summary>
        Public ReadOnly Property CacheWriteToSql As String
            Get
                If Not IsCacheWriteQuery Then Return String.Empty
                If CacheWriteIsDelete Then
                    Return $"DELETE FROM {CacheWriteTable} WHERE {CacheWriteFilter}"
                Else
                    Return $"UPDATE {CacheWriteTable} SET {CacheWriteAction} WHERE {CacheWriteFilter}"
                End If
            End Get
        End Property
        ''' <summary>
        ''' Creates a new options object for GetDatatable options
        ''' </summary>
        ''' <param name="pFallbackSQL">SQL Command to execute as fallback</param>
        ''' <param name="pFallbackType">Named Database to use for the fallback SQL Command</param>
        Public Sub New(pFallbackSQL As String, pFallbackType As Constants.DatabaseType)
            FallbackSQL = pFallbackSQL
            FallbackType = pFallbackType
        End Sub
        ''' <summary>
        ''' Creates a new options object using URI-Syntax (Cache-Query or URI-Write-Query).
        ''' FallbackType defaults to ECM – only relevant if URI detection fails and falls back to SQL.
        ''' Beispiel Read:  "TBDD_USER?USER_ID=4524"
        ''' Beispiel Write: "TBDD_USER?USER_ID=4524!STATUS=1"
        ''' Beispiel Write: "TBDD_USER?USER_ID=4524!DELETE"
        ''' </summary>
        ''' <param name="pURISyntax">URI-Syntax string</param>
        Public Sub New(pURISyntax As String)
            FallbackSQL = pURISyntax
            FallbackType = Constants.DatabaseType.ECM
        End Sub
    End Class
    Public Sub New(LogConfig As LogConfig, Client As Client, DatabaseECM As MSSQLServer, DatabaseIDB As MSSQLServer)
        _Logger = LogConfig.GetLogger()
        _Client = Client
        _DatabaseECM = DatabaseECM
        _DatabaseIDB = DatabaseIDB

        _Logger.Debug("Client exists: [{0}]", Not IsNothing(Client))
        _Logger.Debug("DatabaseECM exists: [{0}]", Not IsNothing(DatabaseECM))
        _Logger.Debug("DatabaseIDB exists: [{0}]", Not IsNothing(DatabaseIDB))

        ' Load client config, will throw if client is not yet connected to service
        _ClientConfig = Client?.ClientConfig
    End Sub

    ''' <summary>
    ''' Set the IDB Database class after initializing the class. 
    ''' It is now your responsibility to make sure to not use any IDB calls before calling this method.
    ''' </summary>
    Public Sub InitializeIDB(pDatabaseIDB As MSSQLServer)
        _DatabaseIDB = pDatabaseIDB
    End Sub

    Public Function GetConnectionString(pConnectionId As Integer) As String
        Return _DatabaseECM.GetConnectionStringForId(pConnectionId)
    End Function


#Region "GetDatatable"
    ''' <summary>URI-Cache-Syntax wird über GetDatatable(pOptions) ausgewertet.</summary>
    Public Function GetDatatableECM(pSQL As String) As DataTable
        Return GetDatatable(New GetDatatableOptions(pSQL, Constants.DatabaseType.ECM))
    End Function

    Public Async Function GetDatatableECMAsync(pSQL As String) As Task(Of DataTable)
        Return Await GetDatatableFromServiceAsync(pSQL, Constants.DatabaseType.ECM, 0)
    End Function

    ''' <summary>URI-Cache-Syntax wird über GetDatatable(pOptions) ausgewertet.</summary>
    Public Function GetDatatableIDB(pSQL As String) As DataTable
        Return GetDatatable(New GetDatatableOptions(pSQL, Constants.DatabaseType.IDB))
    End Function

    Public Async Function GetDatatableIDBAsync(pSQL As String) As Task(Of DataTable)
        Return Await GetDatatableFromServiceAsync(pSQL, Constants.DatabaseType.IDB, 0)
    End Function

    Public Function GetDatatableWithConnection(pSQL As String, pConnectionId As Integer) As DataTable
        ' ===== URI-CACHE-SYNTAX: "TABELLENNAME?FILTERAUSDRUCK" =====
        Dim oOptions As New GetDatatableOptions(pSQL, Constants.DatabaseType.None) With {.ConnectionId = pConnectionId}
        If oOptions.IsCacheQuery Then
            Return GetDatatable(oOptions.CacheQueryTable, oOptions)
        End If
        Return GetDatatable(oOptions)
    End Function

    Public Async Function GetDatatableWithConnectionAsync(pSQL As String, pConnectionId As Integer) As Task(Of DataTable)
        Return Await GetDatatableFromServiceAsync(pSQL, Constants.DatabaseType.None, pConnectionId)
    End Function
#End Region

#Region "GetScalarValue"
    Public Function GetScalarValueECM(pSQL As String) As Object
        Return GetScalarValue(pSQL, Constants.DatabaseType.ECM)
    End Function

    Public Async Function GetScalarValueECMAsync(pSQL As String) As Task(Of Object)
        Return Await GetScalarValueFromServiceAsync(pSQL, Constants.DatabaseType.ECM, 0)
    End Function

    Public Function GetScalarValueIDB(pSQL As String) As Object
        Return GetScalarValue(pSQL, Constants.DatabaseType.IDB)
    End Function

    Public Async Function GetScalarValueIDBAsync(pSQL As String) As Task(Of Object)
        Return Await GetScalarValueFromServiceAsync(pSQL, Constants.DatabaseType.IDB, 0)
    End Function

    Public Function GetScalarValueWithConnection(pSQL As String, pConnectionId As Integer) As Object
        Return GetScalarValue(pSQL, Constants.DatabaseType.None, pConnectionId:=pConnectionId)
    End Function

    Public Async Function GetScalarValueWithConnectionAsync(pSQL As String, pConnectionId As Integer) As Task(Of Object)
        Return Await GetScalarValueFromServiceAsync(pSQL, Constants.DatabaseType.None, pConnectionId)
    End Function
#End Region

#Region "ExecuteNonQuery"
    ' URI-Cache-Syntax ("TABELLE?FILTER") ist hier nicht anwendbar:
    ' ExecuteNonQuery führt schreibende Operationen aus (INSERT/UPDATE/DELETE)
    ' und liefert kein Ergebnis, das aus dem AppServer-Cache gelesen werden könnte.
    Public Function ExecuteNonQueryECM(pSQL As String) As Boolean
        Return ExecuteNonQuery(pSQL, Constants.DatabaseType.ECM)
    End Function

    Public Async Function ExecuteNonQueryECMAsync(pSQL As String) As Task(Of Boolean)
        Return Await ExecuteNonQueryFromServiceAsync(pSQL, Constants.DatabaseType.ECM, 0)
    End Function

    Public Function ExecuteNonQueryIDB(pSQL As String) As Boolean
        Return ExecuteNonQuery(pSQL, Constants.DatabaseType.IDB)
    End Function

    Public Async Function ExecuteNonQueryIDBAsync(pSQL As String) As Task(Of Boolean)
        Return Await ExecuteNonQueryFromServiceAsync(pSQL, Constants.DatabaseType.IDB, 0)
    End Function

    Public Function ExecuteNonQueryWithConnection(pSQL As String, pConnectionId As Integer) As Boolean
        Return ExecuteNonQuery(pSQL, Constants.DatabaseType.None, pConnectionId:=pConnectionId)
    End Function

    Public Async Function ExecuteNonQueryWithConnectionAsync(pSQL As String, pConnectionId As Integer) As Task(Of Boolean)
        Return Await ExecuteNonQueryFromServiceAsync(pSQL, Constants.DatabaseType.None, pConnectionId)
    End Function
#End Region


    ''' <summary>
    ''' Returns a Datatable by trying to fetch a cached version from the service, then querying the database through the service and querying the database directly as fallback. 
    ''' </summary>
    ''' <param name="pDataTableName">Name of the Cached Datatable</param>
    ''' <param name="pOptions">Options object</param>
    Public Function GetDatatable(pDataTableName As String, pOptions As GetDatatableOptions) As DataTable
        ' ===== URI-CACHE-SYNTAX: "TABELLENNAME?FILTERAUSDRUCK" =====
        If pOptions.IsCacheQuery AndAlso Not pOptions.ForceFallback AndAlso
           Not (_ClientConfig IsNot Nothing AndAlso _ClientConfig.ForceDirectDatabaseAccess) Then
            Dim oTable As String = pOptions.CacheQueryTable
            Dim oFilter As String = pOptions.CacheQueryFilter

            ' ===== LOKALER OVERRIDE-CACHE – vorrangig prüfen =====
            Dim oCacheKey As String = GetOverrideCacheKey(oTable, oFilter)
            Dim oOverride As DataTable = Nothing
            If _localOverrideCache.TryGetValue(oCacheKey, oOverride) Then
                _Logger.Debug("✔ GetDatatable: Lokaler Override-Cache trifft für [{0}] Filter [{1}]", oTable, oFilter)
                Return oOverride
            End If

            _Logger.Debug("GetDatatable: URI-Cache-Query erkannt – Tabelle [{0}] Filter [{1}]", oTable, oFilter)

            If _Client IsNot Nothing AndAlso IsTableCached(oTable) Then
                Try
                    Dim oResult As TableResult = _Client.GetDatatableByName(oTable, oFilter, pOptions.SortByColumn)
                    If oResult IsNot Nothing AndAlso oResult.OK Then
                        _Logger.Debug("✔ GetDatatable: URI-Cache-Query [{0}] – {1} Zeilen", oTable, oResult.Table?.Rows.Count)
                        Return oResult.Table
                    End If
                Catch ex As Exception
                    _Logger.Error(ex)
                End Try
                _Logger.Warn("⚠ GetDatatable: URI-Cache-Query [{0}] fehlgeschlagen – kein SQL-Fallback verfügbar", oTable)
                Return Nothing
            End If

            _Logger.Warn("⚠ GetDatatable: URI-Cache-Query – Tabelle [{0}] nicht im AppServer-Cache", oTable)
            Return Nothing
        End If
        Return GetDatatable(pDataTableName, pOptions.FallbackSQL, pOptions.FallbackType, pOptions.FilterExpression, pOptions.SortByColumn, pOptions.ForceFallback, pOptions.ConnectionId)
    End Function

    Public Function GetDatatable(pSQL As String, pConnectionId As Integer) As DataTable
        ' ===== URI-CACHE-SYNTAX: "TABELLENNAME?FILTERAUSDRUCK" =====
        Dim oOptions As New GetDatatableOptions(pSQL, Constants.DatabaseType.ECM) With {.ConnectionId = pConnectionId}
        If oOptions.IsCacheQuery Then
            Return GetDatatable(oOptions.CacheQueryTable, oOptions)
        End If
        Return GetDatatable("FORCE_FALLBACK", pSQL, Constants.DatabaseType.ECM, pSortByColumn:=Nothing, pForceFallback:=False, pConnectionId:=pConnectionId)

    End Function

    ''' <summary>
    ''' Returns a datatable directly from the database – or from AppServer cache if URI-Cache-Syntax is detected.
    ''' </summary>
    ''' <param name="pOptions">Options object</param>
    Public Function GetDatatable(pOptions As GetDatatableOptions) As DataTable
        ' ===== URI-CACHE-SYNTAX: "TABELLENNAME?FILTERAUSDRUCK" =====
        If pOptions.IsCacheQuery Then
            Return GetDatatable(pOptions.CacheQueryTable, pOptions)
        End If
        Dim oForceFallback = True
        Return GetDatatable("FORCE_FALLBACK", pOptions.FallbackSQL, pOptions.FallbackType, pOptions.FilterExpression, pOptions.SortByColumn, oForceFallback, pOptions.ConnectionId)
    End Function

    ''' <summary>
    ''' Returns a Datatable by trying to fetch a cached version from the service, then querying the database through the service and querying the database directly as fallback.
    ''' </summary>
    ''' <param name="pDataTableName">Name of the Cached Datatable</param>
    ''' <param name="pFallbackSQL">SQL Command to execute as fallback</param>
    ''' <param name="pFallbackType">Named Database to use for the fallback SQL Command</param>
    ''' <param name="pFilterExpression">Filter expression for the cached Datatable</param>
    ''' <param name="pSortByColumn">Columns to sort the cached Datatable by</param>
    ''' <param name="pForceFallback">Force the fallback, skipping the service completely</param>
    ''' <param name="pConnectionId">Connection Id to use, references TBDD_CONNECTION</param>
    Public Function GetDatatable(pDataTableName As String, pFallbackSQL As String, pFallbackType As Constants.DatabaseType, Optional pFilterExpression As String = "", Optional pSortByColumn As String = "", Optional pForceFallback As Boolean = False, Optional pConnectionId As Integer = 0) As DataTable
        Try
            Dim oTableResult As TableResult = Nothing
            _Logger.Debug("GetDatatable: Fetching datatable [{0}] , Filter Expression [{1}], Sort By Column [{2}], Force Fallback [{3}]",
                          pDataTableName, pFilterExpression, pSortByColumn, pForceFallback)
            ' If there is no client, we assume there is no service (configured)
            If _Client Is Nothing Then
                _Logger.Debug("GetDatatable: Client is empty, falling back to direct database access.")
                Return GetDatatableFromDatabase(pFallbackSQL, pFallbackType, pConnectionId)
            End If

            ' If ForceFallback flag is set, we go to database immediately
            If pForceFallback Or _ClientConfig.ForceDirectDatabaseAccess Then
                _Logger.Debug("GetDatatable: ForceFallback is True, falling back to direct database access.")
                Return GetDatatableFromDatabase(pFallbackSQL, pFallbackType, pConnectionId)
            End If

            ' If the table is not cached, we try going through the service
            If Not IsTableCached(pDataTableName) Then
                _Logger.Debug("GetDatatable: Datatable [{0}] is not chached, fetching data from service.", pDataTableName)
                Return GetDatatableFromService(pFallbackSQL, pFallbackType, pConnectionId)
            End If

            ' If there is a proper ConnectionId, we try going through the service
            If pConnectionId > 0 Then
                _Logger.Debug("GetDatatable: ConnectionId is set, fetching data from service.")
                Return GetDatatableFromService(pFallbackSQL, pFallbackType, pConnectionId)
            End If

            Try
                _Logger.Debug("GetDatatable: Datatable is chached, fetching data from cache.")
                oTableResult = _Client.GetDatatableByName(pDataTableName, pFilterExpression, pSortByColumn)
            Catch ex As Exception
                _Logger.Error(ex)
                oTableResult = Nothing
            End Try

            If oTableResult Is Nothing OrElse oTableResult.OK = False Then
                _Logger.Warn("⚠ GetDatatable: Datatable [{0}] could not be fetched from AppServer Cache. Falling back to direct Database Access.", pDataTableName)
                Return GetDatatableFromDatabase(pFallbackSQL, pFallbackType, pConnectionId)
            Else
                _Logger.Debug("✔ GetDatatable: Datatable [{0}] fetched from AppServer Cache.", pDataTableName)
                Return oTableResult.Table
            End If

        Catch ex As Exception
            _Logger.Error(ex)
            Return Nothing

        End Try
    End Function

    ''' <summary>
    ''' Returns a Scalar Value by querying the database through the service and querying the database directly as fallback.
    ''' URI-Cache-Syntax wird unterstützt: "TABELLENNAME?FILTERAUSDRUCK" – liefert Wert der ersten Spalte der ersten Zeile aus dem AppServer-Cache.
    ''' </summary>
    ''' <param name="pSQL">SQL Command to execute as fallback – oder URI-Cache-Syntax "TABELLENNAME?FILTERAUSDRUCK"</param>
    ''' <param name="pDatabaseType">Named Database to use for the fallback SQL Command</param>
    ''' <param name="pForceFallback">Force the fallback, skipping the service completely</param>
    ''' <param name="pConnectionId">Connection Id to use, references TBDD_CONNECTION</param>
    Public Function GetScalarValue(pSQL As String, pDatabaseType As Constants.DatabaseType, Optional pForceFallback As Boolean = False, Optional pConnectionId As Integer = 0) As Object
        Try
            ' ===== URI-CACHE-SYNTAX: "TABELLENNAME?FILTERAUSDRUCK" =====
            ' ForceFallback übersteuert auch die URI-Cache-Syntax
            Dim oOptions As New GetDatatableOptions(pSQL, pDatabaseType)
            If oOptions.IsCacheQuery AndAlso Not pForceFallback AndAlso
               Not (_ClientConfig IsNot Nothing AndAlso _ClientConfig.ForceDirectDatabaseAccess) Then
                Dim oTable As String = oOptions.CacheQueryTable
                Dim oFilter As String = oOptions.CacheQueryFilter
                _Logger.Debug("GetScalarValue: URI-Cache-Query erkannt – Tabelle [{0}] Filter [{1}]", oTable, oFilter)

                If _Client IsNot Nothing AndAlso IsTableCached(oTable) Then
                    Try
                        Dim oResult As TableResult = _Client.GetDatatableByName(oTable, oFilter, "")
                        If oResult IsNot Nothing AndAlso oResult.OK AndAlso
                           oResult.Table IsNot Nothing AndAlso oResult.Table.Rows.Count > 0 Then
                            Dim oScalar As Object = oResult.Table.Rows(0)(0)
                            _Logger.Debug("✔ GetScalarValue: URI-Cache-Query [{0}] – Scalar [{1}]", oTable, oScalar)
                            Return oScalar
                        End If
                    Catch ex As Exception
                        _Logger.Error(ex)
                    End Try
                    _Logger.Warn("⚠ GetScalarValue: URI-Cache-Query [{0}] fehlgeschlagen – kein SQL-Fallback verfügbar", oTable)
                    Return Nothing
                End If

                _Logger.Warn("⚠ GetScalarValue: URI-Cache-Query – Tabelle [{0}] nicht im AppServer-Cache", oTable)
                Return Nothing
            End If

            If _Client Is Nothing Then
                Return GetScalarValueFromDatabase(pSQL, pDatabaseType, pConnectionId)
            End If
            If pForceFallback Or _ClientConfig.ForceDirectDatabaseAccess Then
                Return GetScalarValueFromDatabase(pSQL, pDatabaseType, pConnectionId)
            End If
            Return GetScalarValueFromService(pSQL, pDatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Error(ex)
            Return Nothing
        End Try
    End Function

    ''' <summary>
    ''' Executes a non-query SQL command through the service and falls back to direct database access.
    ''' </summary>
    ''' <param name="pSQL">SQL Command to execute</param>
    ''' <param name="pDatabaseType">Named Database to use for the SQL Command</param>
    ''' <param name="pForceFallback">Force the fallback, skipping the service completely</param>
    ''' <param name="pConnectionId">Connection Id to use, references TBDD_CONNECTION</param>
    Public Function ExecuteNonQuery(pSQL As String, pDatabaseType As Constants.DatabaseType, Optional pForceFallback As Boolean = False, Optional pConnectionId As Integer = 0) As Boolean
        Try
            ' If there is no client, we assume there is no service (configured)
            If _Client Is Nothing Then
                _Logger.Debug("ExecuteNonQuery - Client is empty, falling back to direct database access.")
                Return ExecuteNonQueryFromDatabase(pSQL, pDatabaseType, pConnectionId)
            End If

            ' If ForceFallback flag is set, we go to database immediately
            If pForceFallback Or _ClientConfig.ForceDirectDatabaseAccess Then
                _Logger.Debug("ExecuteNonQuery - ForceFallback is set, falling back to direct database access.")
                Return ExecuteNonQueryFromDatabase(pSQL, pDatabaseType, pConnectionId)
            End If

            Return ExecuteNonQueryFromService(pSQL, pDatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Error(ex)
            Return False

        End Try
    End Function
    ''' <summary>
    ''' Führt ein UPDATE oder DELETE über URI-Write-Syntax aus.
    ''' Der geänderte Snapshot wird lokal gecacht und bei GetDatatable/GetScalarValue
    ''' vorrangig ausgewertet – bis der Server-Refresh den Cache neu befüllt.
    ''' UPDATE: "TBDD_USER?USER_ID=4524!STATUS=1"
    ''' DELETE: "TBDD_USER?USER_ID=4524!DELETE"
    ''' </summary>
    Public Function ExecuteAppServiceWrite(pOptions As GetDatatableOptions) As Boolean
        If Not pOptions.IsCacheWriteQuery Then
            _Logger.Warn("⚠ ExecuteAppServiceWrite: Keine gültige URI-Write-Syntax – [{0}] – Abbruch.", pOptions.FallbackSQL)
            Return False
        End If

        If _Client Is Nothing OrElse Not IsTableCached(pOptions.CacheWriteTable) Then
            _Logger.Warn("⚠ ExecuteAppServiceWrite: Tabelle [{0}] nicht im AppServer-Cache – Abbruch.", pOptions.CacheWriteTable)
            Return False
        End If

        _Logger.Debug("ExecuteAppServiceWrite: Tabelle [{0}] | Filter [{1}] | Aktion [{2}] | IsDelete [{3}]",
                      pOptions.CacheWriteTable, pOptions.CacheWriteFilter, pOptions.CacheWriteAction, pOptions.CacheWriteIsDelete)
        Try
            ' Aktuellen Snapshot aus Cache laden
            Dim oResult As TableResult = _Client.GetDatatableByName(pOptions.CacheWriteTable, pOptions.CacheWriteFilter, "")
            If oResult Is Nothing OrElse Not oResult.OK OrElse oResult.Table Is Nothing Then
                _Logger.Warn("⚠ ExecuteAppServiceWrite: Cache-Abfrage für [{0}] fehlgeschlagen.", pOptions.CacheWriteTable)
                Return False
            End If

            Dim oMatchingRows As DataRow() = oResult.Table.Select(pOptions.CacheWriteFilter)
            If oMatchingRows.Length = 0 Then
                _Logger.Debug("ExecuteAppServiceWrite: Keine Zeilen für Filter [{0}] gefunden.", pOptions.CacheWriteFilter)
                Return True
            End If

            If pOptions.CacheWriteIsDelete Then
                For Each oRow As DataRow In oMatchingRows
                    oRow.Delete()
                Next
                oResult.Table.AcceptChanges()
                _Logger.Debug("✔ ExecuteAppServiceWrite: DELETE – [{0}] Zeilen entfernt.", oMatchingRows.Length)
            Else
                For Each oPair As String In pOptions.CacheWriteAction.Split(","c)
                    Dim oParts = oPair.Split("="c)
                    If oParts.Length <> 2 Then Continue For
                    Dim oCol As String = oParts(0).Trim()
                    Dim oVal As String = oParts(1).Trim().Trim("'"c)
                    For Each oRow As DataRow In oMatchingRows
                        If oResult.Table.Columns.Contains(oCol) Then
                            oRow(oCol) = oVal
                        End If
                    Next
                Next
                oResult.Table.AcceptChanges()
                _Logger.Debug("✔ ExecuteAppServiceWrite: UPDATE – [{0}] Zeilen aktualisiert.", oMatchingRows.Length)
            End If

            ' ===== OVERRIDE-CACHE BEFÜLLEN =====
            Dim oCacheKey As String = GetOverrideCacheKey(pOptions.CacheWriteTable, pOptions.CacheWriteFilter)
            _localOverrideCache(oCacheKey) = oResult.Table
            _Logger.Debug("✔ ExecuteAppServiceWrite: Override-Cache gesetzt für [{0}]", oCacheKey)

            Return True

        Catch ex As Exception
            _Logger.Error(ex)
            Return False
        End Try
    End Function
    Private Function IsTableCached(pName As String) As Boolean
        _Logger.Debug("IsTableCached: Checking if table [{0}] is cached.", pName)
        If _Client Is Nothing Then
            _Logger.Warn("⚠ IsTableCached: Client is nothing, cannot check if table is cached.")
            Return False
        End If

        Return _Client.CachedTables.Contains(pName.ToUpper)
    End Function

    Private Function GetDatatableFromService(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As DataTable
        Try
            _Logger.Debug("GetDatatableFromService: Fetching data from service [{0}] with Connection Id [{1}] and Command [{2}]", DatabaseType.ToString, pConnectionId, pSQLCommand)
            Dim oResult As GetDatatableResponse = Nothing

            Select Case DatabaseType
                Case Constants.DatabaseType.ECM
                    oResult = _Client.GetDatatableFromECM(pSQLCommand)
                Case Constants.DatabaseType.IDB
                    oResult = _Client.GetDatatableFromIDB(pSQLCommand)
                Case Else
                    Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End Select

            If oResult Is Nothing OrElse oResult.OK = False Then
                _Logger.Warn("⚠ GetDatatableFromService: Service returned invalid response [{0}]. Falling back to direct database access.", If(oResult Is Nothing, "null", oResult.ErrorMessage))
                Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End If

            Return oResult.Table

        Catch ex As InvalidOperationException
            _Logger.Warn("⚠ GetDatatableFromService skipped: [{0}] Falling back to direct database access.", ex.Message)
            Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Warn("⚠ GetDatatableFromService failed. Falling back to direct database access.")
            _Logger.Error(ex)
            Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        End Try
    End Function

    Private Async Function GetDatatableFromServiceAsync(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Task(Of DataTable)
        _Logger.Debug("GetDatatableFromServiceAsync called | SQL=[{0}] | DB=[{1}] | ConnId=[{2}]",
                      pSQLCommand, DatabaseType.ToString, pConnectionId)

        If _Client Is Nothing OrElse _ClientConfig?.ForceDirectDatabaseAccess Then
            ' ← Kein Task.Run: direkt synchron, Thread ist ohnehin frei
            Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
        End If

        Try
            Dim oResult As GetDatatableResponse = Nothing

            Select Case DatabaseType
                Case Constants.DatabaseType.ECM
                    oResult = Await _Client.GetDatatableFromECMAsync(pSQLCommand)
                Case Constants.DatabaseType.IDB
                    oResult = Await _Client.GetDatatableFromIDBAsync(pSQLCommand)
                Case Else
                    oResult = Await _Client.GetDatatableFromConnectionAsync(pSQLCommand, pConnectionId)
            End Select

            If oResult Is Nothing OrElse oResult.OK = False Then
                _Logger.Warn("⚠ GetDatatableFromServiceAsync failed | Fallback to DB | Error=[{0}]",
                             If(oResult Is Nothing, "null", oResult.ErrorMessage))
                Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End If

            Return oResult.Table

        Catch ex As InvalidOperationException
            _Logger.Warn("⚠ GetDatatableFromServiceAsync offline: [{0}] | Fallback to DB", ex.Message)
            Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Warn("⚠ GetDatatableFromServiceAsync failed | Fallback to DB")
            _Logger.Error(ex)
            Return GetDatatableFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
        End Try
    End Function
    Private Function GetDatatableFromDatabase(pSQLCommand As String, pDatabaseType As Constants.DatabaseType, pConnectionId As Integer) As DataTable
        Try
            _Logger.Debug("GetDatatableFromDatabase: Fetching data from database [{0}] with Connection Id [{1}] and Command [{2}]", pDatabaseType.ToString, pConnectionId, pSQLCommand)

            Select Case pDatabaseType
                Case Constants.DatabaseType.IDB
                    Return _DatabaseIDB.GetDatatable(pSQLCommand)

                Case Else
                    If pConnectionId > 0 Then
                        _Logger.Debug("Retrieving Connection String from Connection Id [{0}]", pConnectionId)
                        Dim oConnectionString = GetCachedConnectionString(pConnectionId)  ' ← NEU: Cache statt direkter DB-Abfrage
                        Return _DatabaseECM.GetDatatableWithConnection(pSQLCommand, oConnectionString)
                    Else
                        Return _DatabaseECM.GetDatatable(pSQLCommand)
                    End If

            End Select

        Catch ex As Exception
            _Logger.Error(ex)
            Return Nothing

        End Try
    End Function
    Private Async Function GetScalarValueFromServiceAsync(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Task(Of Object)
        _Logger.Debug("GetScalarValueFromServiceAsync called | SQL=[{0}] | DB=[{1}] | ConnId=[{2}]",
                      pSQLCommand, DatabaseType.ToString, pConnectionId)

        If _Client Is Nothing OrElse _ClientConfig?.ForceDirectDatabaseAccess Then
            Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId) ' ← kein Task.Run
        End If

        Try
            Dim oResult As GetScalarValueResponse = Nothing

            Select Case DatabaseType
                Case Constants.DatabaseType.ECM
                    oResult = Await _Client.GetScalarValueFromECMAsync(pSQLCommand)
                Case Constants.DatabaseType.IDB
                    oResult = Await _Client.GetScalarValueFromIDBAsync(pSQLCommand)
                Case Else
                    oResult = Await _Client.GetScalarValueFromConnectionAsync(pSQLCommand, pConnectionId)
            End Select

            If oResult Is Nothing OrElse oResult.OK = False Then
                _Logger.Warn("⚠ GetScalarValueFromServiceAsync failed | Fallback to DB")
                Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End If

            Return oResult.Scalar

        Catch ex As InvalidOperationException
            _Logger.Warn("⚠ GetScalarValueFromServiceAsync offline: [{0}] | Fallback to DB", ex.Message)
            Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Warn("⚠ GetScalarValueFromServiceAsync failed | Fallback to DB")
            _Logger.Error(ex)
            Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
        End Try
    End Function
    Private Function GetScalarValueFromService(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Object
        Try
            Dim oResult As GetScalarValueResponse = Nothing
            _Logger.Debug("GetScalarValueFromService [{0}] with Connection Id [{1}] and Command [{2}]", DatabaseType.ToString, pConnectionId, pSQLCommand)
            Select Case DatabaseType
                Case Constants.DatabaseType.ECM
                    oResult = _Client.GetScalarValueFromECM(pSQLCommand)
                Case Constants.DatabaseType.IDB
                    oResult = _Client.GetScalarValueFromIDB(pSQLCommand)
                Case Else
                    Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End Select

            If oResult Is Nothing OrElse oResult.OK = False Then
                _Logger.Warn("⚠ GetScalarValueFromService: Service returned invalid response [{0}]. Falling back to direct database access.", If(oResult Is Nothing, "null", oResult.ErrorMessage))
                Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End If

            Return oResult.Scalar

        Catch ex As InvalidOperationException
            _Logger.Warn("⚠ GetScalarValueFromService skipped: [{0}] Falling back to direct database access.", ex.Message)
            Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Warn("⚠ GetScalarValueFromService failed. Falling back to direct database access.")
            _Logger.Error(ex)
            Return GetScalarValueFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        End Try
    End Function


    Private Function GetScalarValueFromDatabase(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Object
        Try
            _Logger.Debug("DBwFF GetScalarValueFromDatabase [{0}] with Connection Id [{1}] and Command [{2}]", DatabaseType.ToString, pConnectionId, pSQLCommand)
            Select Case DatabaseType
                Case Constants.DatabaseType.IDB
                    Return _DatabaseIDB.GetScalarValue(pSQLCommand)

                Case Else
                    If pConnectionId > 0 Then
                        Dim oConnectionString = GetCachedConnectionString(pConnectionId)  ' ← NEU: Cache statt direkter DB-Abfrage
                        Return _DatabaseECM.GetScalarValueWithConnection(pSQLCommand, oConnectionString)
                    Else
                        Return _DatabaseECM.GetScalarValue(pSQLCommand)
                    End If

            End Select

        Catch ex As Exception
            _Logger.Error(ex)
            Return Nothing

        End Try
    End Function
    Private Async Function ExecuteNonQueryFromServiceAsync(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Task(Of Boolean)
        _Logger.Debug("ExecuteNonQueryFromServiceAsync called | SQL=[{0}] | DB=[{1}] | ConnId=[{2}]",
                      pSQLCommand, DatabaseType.ToString, pConnectionId)

        If _Client Is Nothing OrElse _ClientConfig?.ForceDirectDatabaseAccess Then
            Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId) ' ← kein Task.Run
        End If

        Try
            Dim oResult As ExecuteNonQueryResponse = Nothing

            Select Case DatabaseType
                Case Constants.DatabaseType.ECM
                    oResult = Await _Client.ExecuteNonQueryFromECMAsync(pSQLCommand)
                Case Constants.DatabaseType.IDB
                    oResult = Await _Client.ExecuteNonQueryFromIDBAsync(pSQLCommand)
                Case Else
                    oResult = Await _Client.ExecuteNonQueryFromConnectionAsync(pSQLCommand, pConnectionId)
            End Select

            If oResult Is Nothing OrElse oResult.OK = False Then
                _Logger.Warn("⚠ ExecuteNonQueryFromServiceAsync failed | Fallback to DB")
                Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End If

            Return oResult.Result

        Catch ex As InvalidOperationException
            _Logger.Warn("⚠ ExecuteNonQueryFromServiceAsync offline: [{0}] | Fallback to DB", ex.Message)
            Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Warn("⚠ ExecuteNonQueryFromServiceAsync failed | Fallback to DB")
            _Logger.Error(ex)
            Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
        End Try
    End Function
    Private Function ExecuteNonQueryFromService(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Boolean
        Try
            Dim oResult As ExecuteNonQueryResponse = Nothing
            _Logger.Debug("ExecuteNonQueryFromService [{0}] with Connection Id [{1}] and Command [{2}]", DatabaseType.ToString, pConnectionId, pSQLCommand)
            Select Case DatabaseType
                Case Constants.DatabaseType.ECM
                    oResult = _Client.ExecuteNonQueryFromECM(pSQLCommand)
                Case Constants.DatabaseType.IDB
                    oResult = _Client.ExecuteNonQueryFromIDB(pSQLCommand)
                Case Else
                    Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End Select

            If oResult Is Nothing OrElse oResult.OK = False Then
                _Logger.Warn("⚠ ExecuteNonQueryFromService: Service returned invalid response [{0}]. Falling back to direct database access.", If(oResult Is Nothing, "null", oResult.ErrorMessage))
                Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)
            End If

            Return oResult.Result

        Catch ex As InvalidOperationException
            _Logger.Warn("⚠ ExecuteNonQueryFromService skipped: [{0}] Falling back to direct database access.", ex.Message)
            Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        Catch ex As Exception
            _Logger.Warn("⚠ ExecuteNonQueryFromService failed. Falling back to direct database access.")
            _Logger.Error(ex)
            Return ExecuteNonQueryFromDatabase(pSQLCommand, DatabaseType, pConnectionId)

        End Try
    End Function

    Private Function ExecuteNonQueryFromDatabase(pSQLCommand As String, DatabaseType As Constants.DatabaseType, pConnectionId As Integer) As Boolean
        Try
            _Logger.Debug("ExecuteNonQueryFromDatabase [{0}] with Connection Id [{1}] and Command [{2}]", DatabaseType.ToString, pConnectionId, pSQLCommand)

            Select Case DatabaseType
                Case Constants.DatabaseType.IDB
                    Return _DatabaseIDB.ExecuteNonQuery(pSQLCommand)

                Case Else
                    If pConnectionId > 0 Then
                        Dim oConnectionString = GetCachedConnectionString(pConnectionId)  ' ← NEU: Cache statt direkter DB-Abfrage
                        Return _DatabaseECM.ExecuteNonQueryWithConnection(pSQLCommand, oConnectionString)
                    Else
                        Return _DatabaseECM.ExecuteNonQuery(pSQLCommand)
                    End If

            End Select

        Catch ex As Exception
            _Logger.Error(ex)
            Return False

        End Try
    End Function
End Class