Public Class Form1

    Private Function ExtractLine(ByVal text As String, ByRef line As String, ByRef startPos As Integer, ByRef foundPos As Integer) As Boolean
        ' find the next occurrence of the new line char
        foundPos = text.IndexOf(ControlChars.NewLine, startPos)
        ' check if it was found
        If foundPos = -1 Then
            Return False
        Else
            ' pull out the current line of the file
            line = text.Substring(startPos, foundPos - startPos)
            ' update the starting point for search
            startPos = foundPos + 2
            Return True
        End If
    End Function
    
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim allText As String
        Dim lineExists As Boolean
        Dim currentDVD As String
        Dim start As Integer = 0
        Dim foundPos As Integer

        ' check if file exists
        If My.Computer.FileSystem.FileExists("DVDs.txt") Then

            ' read the file contents
            allText = My.Computer.FileSystem.ReadAllText("DVDs.txt")

            ' while not at end, extract line
            Do
                lineExists = ExtractLine(allText, currentDVD, start, foundPos)
                If lineExists Then
                    ' stick the line in the list box
                    lstChoice.Items.Add(currentDVD)
                End If
            Loop While lineExists
        Else
            MsgBox("Please put the DVDs.txt file in the bin folder for the project")
        End If
    End Sub

    Private Sub lstChoice_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lstChoice.SelectedIndexChanged

        Dim choice As String
        choice = lstChoice.SelectedItem().ToString()
        Dim movie As String
        Dim priceStr As String
        Dim commaPos As Integer
        commaPos = choice.IndexOf(",")
        movie = choice.Substring(0, commaPos)
        txtTitle.Text = movie
        priceStr = choice.Substring(commaPos + 2)
        txtPrice.Text = priceStr

        Dim tax As Double
        Dim price As Double
        Dim total As Double
        Dim isConverted As Boolean
        isConverted = Double.TryParse(priceStr, price)
        tax = price * 0.07
        total = price + tax
        txtTax.Text = tax.ToString("c")
        txtTotal.Text = total.ToString("c")




    End Sub

    Private Sub btnPay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPay.Click
        If txtTitle.Text <> "" Then
            My.Computer.FileSystem.WriteAllText("sales.txt", txtTitle.Text & _
               "," & txtPrice.Text & "," & txtTax.Text & "," & _
                txtTotal.Text & ControlChars.NewLine, True)
        End If
    End Sub
End Class