Imports System.IO
Imports Microsoft.VisualBasic.MIME.application.json
Imports Microsoft.VisualBasic.MIME.application.json.BSON
Imports Microsoft.VisualBasic.Scripting.MetaData

Public Class StreamEmit

    ReadOnly toBuffers As New Dictionary(Of Type, toBuffer)
    ReadOnly loadBuffers As New Dictionary(Of Type, loadBuffer)

    Sub New()
        For Each [handle] In EmitHandler.PopulatePrimitiveHandles
            toBuffers(handle.target) = handle.emit
        Next
        For Each [handle] In EmitHandler.PopulatePrimitiveParsers
            loadBuffers(handle.target) = handle.emit
        Next
    End Sub

    Public Function Emit(Of T)(streamAs As Func(Of T, Stream)) As StreamEmit
        toBuffers(GetType(T)) = Function(obj) streamAs(obj)
        Return Me
    End Function

    Public Function Emit(Of T)(fromStream As Func(Of Stream, T)) As StreamEmit
        loadBuffers(GetType(T)) = Function(buf) fromStream(buf)
        Return Me
    End Function

    Public Function handleCreate(buf As Stream, type As Type, emit As StreamMethods) As Object
        If emit = StreamMethods.Auto Then
            If loadBuffers.ContainsKey(type) Then
                Return loadBuffers(type)(buf)
            Else
                Return BSONFormat.Load(buf).CreateObject(type)
            End If
        ElseIf emit = StreamMethods.BSON Then
            Return BSONFormat.Load(buf).CreateObject(type)
        ElseIf loadBuffers.ContainsKey(type) Then
            Return loadBuffers(type)(buf)
        Else
            Throw New NotImplementedException
        End If
    End Function

    Public Function handleSerialize(param As Object) As ObjectStream
        Dim type As Type = param.GetType

        If toBuffers.ContainsKey(type) Then
            Return New ObjectStream(New TypeInfo(type, fullpath:=True), StreamMethods.Emit, toBuffers(type)(param))
        Else
            Dim element = type.GetJsonElement(param, New JSONSerializerOptions)
            Dim buf As Stream = BSONFormat.SafeGetBuffer(element)

            Return New ObjectStream(New TypeInfo(type, fullpath:=True), StreamMethods.BSON, buf)
        End If
    End Function
End Class