Imports System.Data.SqlClient
Imports System.Data.SQLite

Public Class cSQL2SQLLite


    Function Main(tableName As String)

        Dim sqlServerConString = Class1.DBDoku
        Dim sqliteFile As String = "C:\verag\offline_db.sqlite"
        Dim sqliteConnString As String = $"Data Source={sqliteFile};Version=3;"



        UpdateOrCreateTable(sqlServerConString, sqliteConnString, tableName)
        CopyDataIncrementally(sqlServerConString, sqliteConnString, tableName)

    End Function


    Sub UpdateOrCreateTable(sqlServerConnectionString As String, localSqlServerConnectionString As String, tableName As String)
        ' SQL Server-Abfrage für die Spalteninformationen
        Dim query As String = $"SELECT COLUMN_NAME, DATA_TYPE, CHARACTER_MAXIMUM_LENGTH, IS_NULLABLE FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = '{tableName}'"
        Dim columnDefinitions As New List(Of String)

        ' Abfrage für die Spaltenstruktur der Remote-Tabelle
        Using con As New SqlConnection(sqlServerConnectionString)
            con.Open()
            Using cmd As New SqlCommand(query, con)
                Using reader As SqlDataReader = cmd.ExecuteReader()
                    While reader.Read()
                        Dim columnName As String = reader("COLUMN_NAME").ToString()
                        Dim dataType As String = reader("DATA_TYPE").ToString()
                        If reader("CHARACTER_MAXIMUM_LENGTH") IsNot DBNull.Value Then
                            dataType &= $"({reader("CHARACTER_MAXIMUM_LENGTH").ToString()})"
                        End If
                        Dim isNullable As String = If(reader("IS_NULLABLE").ToString() = "YES", "NULL", "NOT NULL")
                        columnDefinitions.Add($"{columnName} {dataType} {isNullable}")
                    End While
                End Using
            End Using
        End Using

        ' Die lokale SQL Server-Datenbank, in der die Tabelle erstellt wird
        Using localSqlCon As New SqlConnection(localSqlServerConnectionString)
            localSqlCon.Open()

            ' Prüfen, ob die Tabelle bereits existiert
            Dim tableExistsQuery As String = $"SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = '{tableName}'"
            Using cmd As New SqlCommand(tableExistsQuery, localSqlCon)
                Dim exists As Object = cmd.ExecuteScalar()
                If exists Is Nothing Then
                    ' Erstelle die Tabelle, wenn sie nicht existiert
                    Dim createTableSQL As String = $"CREATE TABLE {tableName} ({String.Join(", ", columnDefinitions)});"
                    Using createCmd As New SqlCommand(createTableSQL, localSqlCon)
                        createCmd.ExecuteNonQuery()
                    End Using
                Else
                    ' Falls die Tabelle bereits existiert, überprüfe und füge neue Spalten hinzu
                    For Each columnDef In columnDefinitions
                        Dim columnName As String = columnDef.Split(" ")(0)
                        Dim addColumnSQL As String = $"ALTER TABLE {tableName} ADD COLUMN {columnDef};"
                        Try
                            Using alterCmd As New SqlCommand(addColumnSQL, localSqlCon)
                                alterCmd.ExecuteNonQuery()
                            End Using
                        Catch ex As Exception
                            ' Falls die Spalte bereits existiert, wird die Exception ignoriert
                        End Try
                    Next
                End If
            End Using
        End Using
    End Sub


    Sub CopyDataIncrementally(sqlServerConnectionString As String, sqliteConnectionString As String, tableName As String)
        Dim query As String = $"SELECT * FROM {tableName}"

        Using sqlCon As New SqlConnection(sqlServerConnectionString)
            sqlCon.Open()
            Using cmd As New SqlCommand(query, sqlCon)
                Using reader As SqlDataReader = cmd.ExecuteReader()
                    Using sqliteCon As New SQLiteConnection(sqliteConnectionString)
                        sqliteCon.Open()

                        While reader.Read()
                            Dim columns As New List(Of String)
                            Dim values As New List(Of String)
                            Dim parameters As New List(Of SQLiteParameter)

                            For i As Integer = 0 To reader.FieldCount - 1
                                Dim columnName As String = reader.GetName(i)
                                columns.Add(columnName)
                                values.Add($"@{columnName}")
                                parameters.Add(New SQLiteParameter($"@{columnName}", reader.GetValue(i)))
                            Next

                            Dim insertSQL As String = $"INSERT OR IGNORE INTO {tableName} ({String.Join(", ", columns)}) VALUES ({String.Join(", ", values)})"
                            Using insertCmd As New SQLiteCommand(insertSQL, sqliteCon)
                                insertCmd.Parameters.AddRange(parameters.ToArray())
                                insertCmd.ExecuteNonQuery()
                            End Using
                        End While
                    End Using
                End Using
            End Using
        End Using
    End Sub

    Function MapSQLServerToSQLiteType(sqlType As String, length As Object) As String
        Select Case sqlType.ToLower()
            Case "int", "bigint", "smallint", "tinyint"
                Return "INTEGER"
            Case "bit"
                Return "BOOLEAN"
            Case "decimal", "numeric", "money", "smallmoney", "float", "real"
                Return "REAL"
            Case "char", "nchar", "varchar", "nvarchar", "text", "ntext"
                Return "TEXT"
            Case "datetime", "smalldatetime", "date", "time", "datetime2"
                Return "TEXT"
            Case Else
                Return "TEXT"
        End Select
    End Function

End Class