StringSplitExtensions-VB

Friend NotInheritable Class StringSplitExtensions
    Private Sub New()
    End Sub
    <System.Runtime.CompilerServices.Extension> _
    Public Shared Function Split(this As [String], isSplitSymbol As Predicate(Of Char)) As String()
        Return Split(this, isSplitSymbol, Integer.MaxValue, StringSplitOptions.None)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Shared Function Split(this As [String], isSplitSymbol As Predicate(Of Char), options As StringSplitOptions) As String()
        Return Split(this, isSplitSymbol, Integer.MaxValue, options)
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Public Shared Function Split(this As [String], isSplitSymbol As Predicate(Of Char), count As Integer, options As StringSplitOptions) As String()
        If count < 0 Then
            Throw New ArgumentOutOfRangeException("count", "Count cannot be less than zero.")
        End If
        If (options < StringSplitOptions.None) OrElse (options > StringSplitOptions.RemoveEmptyEntries) Then
            Throw New ArgumentException([String].Format("Illegal enum value: {0}.", CInt(options)))
        End If

        Dim removeEmptyEntries As Boolean = options = StringSplitOptions.RemoveEmptyEntries
        If (count = 0) OrElse (removeEmptyEntries AndAlso (this.Length = 0)) Then
            Return New String(-1) {}
        End If

        Dim sepList As Integer() = New Integer(this.Length - 1) {}
        Dim numReplaces As Integer = this.MakeSeparatorList(isSplitSymbol, sepList)
        If (numReplaces = 0) OrElse (count = 1) Then
            Return New String() {this}
        End If

        If removeEmptyEntries Then
            Return this.InternalSplitOmitEmptyEntries(sepList, numReplaces, count)
        Else
            Return this.InternalSplitKeepEmptyEntries(sepList, numReplaces, count)
        End If

    End Function

    <System.Runtime.CompilerServices.Extension> _
    Private Shared Function MakeSeparatorList(this As [String], isSplitSymbol As Predicate(Of Char), ByRef sepList As Integer()) As Integer
        Dim numReplaces As Integer = 0

        Dim length As Integer = sepList.Length, j As Integer = 0
        While (j < this.Length) AndAlso (numReplaces < length)
            If isSplitSymbol(this(j)) Then
                sepList(System.Math.Max(System.Threading.Interlocked.Increment(numReplaces),numReplaces - 1)) = j
            End If
            j += 1
        End While

        Return numReplaces
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Private Shared Function InternalSplitKeepEmptyEntries(this As [String], sepList As Integer(), numReplaces As Integer, count As Integer) As String()
        Dim startIndex As Integer = 0
        Dim index As Integer = 0
        count -= 1
        Dim actualCount As Integer = If((numReplaces < count), numReplaces, count)
        Dim strArray As String() = New String(actualCount) {}
        Dim i As Integer = 0
        While (i < actualCount) AndAlso (startIndex < this.Length)
            strArray(System.Math.Max(System.Threading.Interlocked.Increment(index),index - 1)) = this.Substring(startIndex, sepList(i) - startIndex)
            startIndex = sepList(i) + 1
            i += 1
        End While
        If (startIndex < this.Length) AndAlso (actualCount >= 0) Then
            strArray(index) = this.Substring(startIndex)
            Return strArray
        End If
        If index = actualCount Then
            strArray(index) = [String].Empty
        End If
        Return strArray
    End Function

    <System.Runtime.CompilerServices.Extension> _
    Private Shared Function InternalSplitOmitEmptyEntries(this As [String], sepList As Integer(), numReplaces As Integer, count As Integer) As String()
        Dim actualCount As Integer = If((numReplaces < count), (numReplaces + 1), count)
        Dim strArray As String() = New String(actualCount - 1) {}
        Dim startIndex As Integer = 0
        Dim replaceIndex As Integer = 0
        Dim i As Integer = 0
        While (i < numReplaces) AndAlso (startIndex < this.Length)
            If (sepList(i) - startIndex) > 0 Then
                strArray(System.Math.Max(System.Threading.Interlocked.Increment(replaceIndex),replaceIndex - 1)) = this.Substring(startIndex, sepList(i) - startIndex)
            End If
            startIndex = sepList(i) + 1
            If replaceIndex = (count - 1) Then
                While (i < (numReplaces - 1)) AndAlso (startIndex = sepList(System.Threading.Interlocked.Increment(i)))
                    startIndex += 1
                End While
                Exit While
            End If
            i += 1
        End While
        If startIndex < this.Length Then
            strArray(System.Math.Max(System.Threading.Interlocked.Increment(replaceIndex),replaceIndex - 1)) = this.Substring(startIndex)
        End If
        Dim strArray2 As String() = strArray
        If replaceIndex <> actualCount Then
            strArray2 = New String(replaceIndex - 1) {}
            For j As Integer = 0 To replaceIndex - 1
                strArray2(j) = strArray(j)
            Next
        End If
        Return strArray2
    End Function
End Class