Option Explicit On
Option Strict On

Public Class Form1

    Private Function PullInfo(ByVal fileContents As String, ByRef line As String, ByRef startPos As Integer) As Boolean

        Dim position As Integer
        position = fileContents.IndexOf(ControlChars.NewLine, startPos)
        If position = -1 Then
            ' wasn't found
            Return False
        Else
            ' was found - fill current line and update start position
            line = fileContents.Substring(startPos, position - startPos)
            startPos = position + 2
            Return True
        End If
    End Function


    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ' declare variables
        Dim allText As String
        Dim current As String
        Dim lineExists As Boolean
        Dim start As Integer

        If My.Computer.FileSystem.FileExists("DVDs.txt") Then

            allText = My.Computer.FileSystem.ReadAllText("DVDs.txt")
            Do
                lineExists = PullInfo(allText, current, start)
                If lineExists Then
                    lstChoice.Items.Add(current)
                End If

            Loop Until Not lineExists
        Else
            MsgBox("Please ensure that DVDs.txt file is in the debug folder under the project")
        End If

    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("purchases.txt", _
                txtTitle.Text & _
                "," & txtPrice.Text & "," & txtTax.Text _
                & "," & txtTotal.Text & ControlChars.NewLine, True)

        Else
            MsgBox("Please select a movie before paying")
        End If

    End Sub

    Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
        txtTitle.Clear()
        txtPrice.Clear()
        txtTax.Clear()
        txtTotal.Clear()

    End Sub

    Private Sub btnQuit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnQuit.Click
        Me.Close()

    End Sub

    Private Sub lstChoice_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lstChoice.SelectedIndexChanged
        Dim choice As String
        Dim title As String
        Dim priceStr As String
        Dim price As Double
        Dim commaPos As Integer
        Dim isConverted As Boolean
        Dim tax As Double
        Dim total As Double
        Const taxRate As Double = 0.07

        choice = lstChoice.SelectedItem.ToString
        commaPos = choice.IndexOf(",")
        title = choice.Substring(0, commaPos)
        txtTitle.Text = title
        priceStr = choice.Substring(commaPos + 1)
        isConverted = Double.TryParse(priceStr, price)
        If isConverted Then
            txtPrice.Text = priceStr
            tax = price * taxRate
            total = price + tax
            txtTax.Text = tax.ToString("c2")
            txtTotal.Text = total.ToString("c2")

        Else
            MsgBox("Movie info is incorrect, please call for help")
        End If
    End Sub
End Class