Option Explicit On
Option Strict On
Public Class Permutation
    Private _Charset As String = vbNullString
    Private _IndexArray(_Max) As Integer
    Private _Max As Short = &H1
    Private _Min As Short = &H0
    Private _TimePerCalculation As Double = &H0
    Private _Estimater As UInt16 = &H0
    Private _Watch As New Stopwatch
    Public Sub New(ByVal Charset As String, ByVal Max As Short, _
                   ByVal Min As Short)
        _Charset = Charset
        _Max = Max
        _Min = Min
        ReDim _IndexArray(_Max)
        For Nullifier As Integer = &H0 To (_Min - &H1)
            _IndexArray(Nullifier) = &H1
        Next
        _Watch.Start()
    End Sub
    Public Sub Add()
        _IndexArray(&H0) = _IndexArray(&H0) + &H1
        For Index As Short = &H0 To CShort(_Max - &H1)
            If (_IndexArray(Index) > &H0) And _
               (_IndexArray(Index) > Len(_Charset)) Then
                _IndexArray(Index) = &H1
                _IndexArray(Index + &H1) = _IndexArray(Index + &H1) + &H1
            End If
        Next Index
    End Sub
    Public Function GenerateString(Optional ByVal AddToNextTurn As Boolean = True) As String
        _Estimater = CUShort(_Estimater + &H1)
        If _Estimater Mod UInt16.MaxValue = &H0 Then
            _TimePerCalculation = (_Watch.ElapsedMilliseconds / UInt16.MaxValue)
            _Watch.Reset()
            _Watch.Start()
            _Estimater = &H0
        End If
        Dim Result As String = vbNullString
        For Index As Short = &H0 To _Max
            If _IndexArray(Index) <> &H0 Then
                Result = Result & Mid(_Charset, _IndexArray(Index), &H1)
            End If
        Next
        If AddToNextTurn = True Then Add()
        Return Result
    End Function
    Public ReadOnly Property GetExitValue() As Double
        Get
            Dim Result As Double = &H0
            For Index As Integer = _Min To _Max
                Result += (Len(_Charset) ^ Index)
            Next
            Return Result
        End Get
    End Property
    Public ReadOnly Property GetExitString() As String
        Get
            Return New String(CChar(_Charset.Substring(_Charset.Length - &H1, &H1)), _Max)
        End Get
    End Property
    Public ReadOnly Property TimePerCalculation() As Double
        Get
            Return _TimePerCalculation
        End Get
    End Property
    Public Function MakeMD5(ByVal Word As String) As String
        Dim MD5 As New System.Security.Cryptography.MD5CryptoServiceProvider
        Dim ByteHash() As Byte
        Dim Result As String = vbNullString
        ByteHash = MD5.ComputeHash(System.Text.Encoding.ASCII.GetBytes(Word))
        For Index As Integer = &H0 To &HF
            Result &= ByteHash(Index).ToString("x").PadLeft(&H2, CChar("0"))
        Next
        Return Result
    End Function
End Class