Imports System.IO
Imports System.Reflection
Imports System.Xml.Serialization
Imports DigitalData.Modules.Logging
Imports DigitalData.Modules.Config.ConfigAttributes

Public Class ConfigManager(Of T)
    Private Const USER_CONFIG_NAME As String = "UserConfig.xml"
    Private Const COMPUTER_CONFIG_NAME As String = "ComputerConfig.xml"

    Private ReadOnly _LogConfig As LogConfig
    Private ReadOnly _Logger As Logger
    Private ReadOnly _File As Filesystem.File
    Private ReadOnly _UserPath As String
    Private ReadOnly _ComputerPath As String

    Private _ForceUserConfig As Boolean = False
    Private _TestMode As Boolean = False

    ''' <summary>
    ''' The blueprint class from which the default config is created
    ''' </summary>
    Private ReadOnly _Blueprint As T
    Private ReadOnly _Serializer As XmlSerializer

    Public ReadOnly Property Config As T

    ''' <summary>
    ''' Creates a new instance of the ConfigManager
    ''' </summary>
    ''' <seealso cref="ConfigSample"/>
    ''' <param name="LogConfig">LogConfig instance</param>
    ''' <param name="UserConfigPath">The path to check for a user config file, eg. AppData</param>
    ''' <param name="ComputerConfigPath">The path to check for a computer config file, eg. ProgramData</param>
    ''' <param name="ForceUserConfig">Override values from ComputerConfig with UserConfig</param>
    Public Sub New(LogConfig As LogConfig, UserConfigPath As String, ComputerConfigPath As String, Optional ForceUserConfig As Boolean = False)
        _LogConfig = LogConfig
        _Logger = LogConfig.GetLogger()
        _File = New Filesystem.File(_LogConfig)

        _UserPath = Path.Combine(UserConfigPath, USER_CONFIG_NAME)
        _ComputerPath = Path.Combine(ComputerConfigPath, COMPUTER_CONFIG_NAME)
        _ForceUserConfig = ForceUserConfig

        _Blueprint = Activator.CreateInstance(Of T)
        _Serializer = New XmlSerializer(_Blueprint.GetType)

        If Not Directory.Exists(UserConfigPath) Then
            _Logger.Debug("UserConfigPath {0} did not exist and was created", UserConfigPath)
            Directory.CreateDirectory(UserConfigPath)
        End If

        If Not _File.TestPathIsDirectory(UserConfigPath) Then
            _Logger.Warn("UserConfigPath {0} is not a directory", UserConfigPath)
            Throw New ArgumentException($"Path {UserConfigPath} is not a directory!")
        End If

        If Not Directory.Exists(ComputerConfigPath) Then
            _Logger.Debug("ComputerConfigPath {0} did not exist and was created", ComputerConfigPath)
            Directory.CreateDirectory(ComputerConfigPath)
        End If

        If Not _File.TestPathIsDirectory(ComputerConfigPath) Then
            _Logger.Warn("ComputerConfigPath {0} is not a directory", ComputerConfigPath)
            Throw New ArgumentException($"Path {ComputerConfigPath} is not a directory!")
        End If

        _Config = LoadConfig()
    End Sub

    ''' <summary>
    ''' Creates a new ConfigManager with a single (user)config path
    ''' </summary>
    ''' <param name="LogConfig"></param>
    ''' <param name="ConfigPath"></param>
    Public Sub New(LogConfig As LogConfig, ConfigPath As String)
        MyClass.New(LogConfig, ConfigPath, ConfigPath, ForceUserConfig:=True)
    End Sub

    ''' <summary>
    ''' Save the current config object to `UserConfigPath`
    ''' </summary>
    ''' <returns>True if save was successful, False otherwise</returns>
    Public Function Save() As Boolean
        Try
            WriteToFile(_Config, _UserPath)
            Return True
        Catch ex As Exception
            _Logger.Error(ex)
            Return False
        End Try
    End Function

    ''' <summary>
    ''' Copies all properties from Source to Target, except those who have an attribute
    ''' listed in ExcludedAttributeTypes
    ''' </summary>
    ''' <typeparam name="T">Config Class</typeparam>
    ''' <param name="Source">Source config object</param>
    ''' <param name="Target">Target config object</param>
    ''' <param name="ExcludedAttributeTypes">List of Attribute type to exclude</param>
    Private Sub CopyValues(Of T)(Source As T, Target As T, Optional ExcludedAttributeTypes As List(Of Type) = Nothing)
        Dim oType As Type = GetType(T)
        Dim oExcludedAttributeTypes = IIf(IsNothing(ExcludedAttributeTypes), New List(Of Type), ExcludedAttributeTypes)
        Dim oProperties = oType.GetProperties().
            Where(Function(p) p.CanRead And p.CanWrite).
            Where(Function(p)
                      For Each oAttributeType As Type In oExcludedAttributeTypes
                          If Attribute.IsDefined(p, oAttributeType) Then
                              Return False
                          End If
                      Next
                      Return True
                  End Function)

        For Each oProperty As PropertyInfo In oProperties
            Dim oValue = oProperty.GetValue(Source, Nothing)
            If Not IsNothing(oValue) Then
                oProperty.SetValue(Target, oValue, Nothing)
            End If
        Next
    End Sub

    Private Function LoadConfig() As T
        ' first create an empty/default config object
        Dim oConfig = Activator.CreateInstance(_Blueprint.GetType)
        ' then Try to load computer config
        oConfig = LoadComputerConfig(oConfig)
        ' now try to load userconfig
        oConfig = LoadUserConfig(oConfig)
        Return oConfig
    End Function

    Private Function LoadComputerConfig(ByVal Config As T) As T
        If File.Exists(_ComputerPath) Then
            Try
                Dim oComputerConfig = ReadFromFile(_ComputerPath)
                CopyValues(oComputerConfig, Config)
            Catch ex As Exception
                _Logger.Error(ex)
                _Logger.Warn("Computer config could not be loaded!")
            End Try
        Else
            _ForceUserConfig = True
        End If

        Return Config
    End Function

    Private Function LoadUserConfig(ByVal Config As T) As T
        If File.Exists(_UserPath) Then
            Try
                Dim oUserConfig = ReadFromFile(_UserPath)

                ' if user config exists
                If Not IsNothing(oUserConfig) Then
                    Dim oExcludedAttributes As New List(Of Type)

                    ' Copy values from user config to final config
                    If _ForceUserConfig Then
                        CopyValues(oUserConfig, Config, New List(Of Type))
                    Else
                        CopyValues(oUserConfig, Config, New List(Of Type) From {
                            GetType(ConnectionStringAttribute),
                            GetType(ConnectionStringTestAttribute)
                        })
                    End If
                End If

                'Dim oConnectionProperty = TestHasAttribute(oConfig, GetType(ConnectionStringAttribute))
            Catch ex As Exception
                _Logger.Error(ex)
                _Logger.Warn("User config could not be loaded!")
            End Try
        End If

        Return Config
    End Function

    Private Function LoadDefaultConfig() As T
        _Logger.Debug("Creating default config in UserPath: {0}", _UserPath)
        Dim oConfig = Activator.CreateInstance(_Blueprint.GetType)

        Try
            WriteToFile(oConfig, _UserPath)
        Catch ex As Exception
            _Logger.Warn("Could not create default config in UserPath: {0}", _UserPath)
        End Try

        Return oConfig
    End Function

    Private Function TestHasAttribute(Config As T, AttributeType As Type) As Boolean
        For Each oProperty As PropertyInfo In Config.GetType.GetProperties()
            If Attribute.IsDefined(oProperty, GetType(ConnectionStringAttribute)) Then
                Return True
            End If
        Next

        Return False
    End Function

    ''' <summary>
    ''' Serialize a config object to byte array
    ''' </summary>
    ''' <param name="Data"></param>
    ''' <returns></returns>
    Private Function Serialize(Data As T) As Byte()
        Try
            _Logger.Debug("Serializing config object")

            Using oStream = New MemoryStream()
                _Serializer.Serialize(oStream, Data)
                Return oStream.ToArray()
            End Using
        Catch ex As Exception
            _Logger.Error(ex)
            Throw ex
        End Try
    End Function

    ''' <summary>
    ''' Write an object to disk as xml
    ''' </summary>
    ''' <param name="Data">The object to write</param>
    ''' <param name="Path">The file name to write to</param>
    Private Sub WriteToFile(Data As T, Path As String)
        Try
            _Logger.Debug("Saving config to: {0}", Path)
            Dim oBytes = Serialize(Data)

            Using oFileStream = New FileStream(Path, FileMode.Create, FileAccess.Write)
                oFileStream.Write(oBytes, 0, oBytes.Length)
                oFileStream.Flush()
            End Using
        Catch ex As Exception
            _Logger.Error(ex)
            Throw ex
        End Try
    End Sub

    ''' <summary>
    ''' Reads an xml from disk and deserializes to object
    ''' </summary>
    ''' <returns></returns>
    Private Function ReadFromFile(Path As String) As T
        Try
            _Logger.Debug("Loading config from: {0}", Path)
            Dim oConfig As T

            Using oReader As New StreamReader(Path)
                oConfig = _Serializer.Deserialize(oReader)
            End Using

            ' If oConfig is Nothing, a config file was created but nothing was written to it.
            ' In this case we need to create oConfig from defaults so we have at least some config object
            If oConfig Is Nothing Then
                _Logger.Debug("Config file is valid but empty. Loading default values")
                oConfig = Activator.CreateInstance(_Blueprint.GetType)
            End If

            Return oConfig
        Catch ex As Exception
            _Logger.Error(ex)
            Throw ex
        End Try
    End Function
End Class