Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    ' This page never posts back
    If Not Page.IsPostBack Then

        Dim bOrderValid As Boolean = False
        Dim sLogError As String = ""

        ' Validate payment
        Dim orderId As String
        Dim processorOrderId As String
        Dim strPostedVariables As String
        Dim arrPostedVariables As New System.Collections.Specialized.NameValueCollection
        Try
            ' Get the posted variables. Exclude the signature (it must be excluded when we hash and also when we validate)
            Dim req As System.Collections.Specialized.NameValueCollection = Request.Form
            Dim key, value As String
            Dim i As Integer
            For i = 0 To req.Count - 1
                key = req.Keys(i)
                value = req(i)
                If key <> "signature" Then
                    strPostedVariables = strPostedVariables & key & "=" & HttpUtility.UrlEncode(value) & "&"
                    arrPostedVariables.Add(key, value)
                End If
            Next
            ' Remove the last &
            strPostedVariables = strPostedVariables.TrimEnd("&"c)

            orderId = Request.Form("m_payment_id")
            processorOrderId = Request.Form("pf_payment_id")

            ' Are we testing or making live payments
            Dim query As System.Collections.Specialized.NameValueCollection = Me.Request.QueryString

            Dim site, merchant_id, paymentMode As String
            Dim arrStr() As String

            If System.Configuration.ConfigurationSettings.AppSettings.Get("OpMode") = "Test" Then
                paymentMode = "Test"
                site = System.Configuration.ConfigurationSettings.AppSettings.Get("PayFast_Test_Validations")
                merchant_id = System.Configuration.ConfigurationSettings.AppSettings.Get("PayFast_Test_MerchantId")
                arrStr = Split(System.Configuration.ConfigurationSettings.AppSettings.Get("PayFast_Test_Servers"), ",")
            Else
                paymentMode = "Live"
                site = System.Configuration.ConfigurationSettings.AppSettings.Get("PayFast_Live_Validations")
                merchant_id = System.Configuration.ConfigurationSettings.AppSettings.Get("PayFast_Live_MerchantId")
                arrStr = Split(System.Configuration.ConfigurationSettings.AppSettings.Get("PayFast_Live_Servers"), ",")
            End If

            ' Get the posted signature from the form
            Dim postedSignature As String = Request.Form("signature")
            If postedSignature = "" Then
                sLogError = "Warning: " & orderId & " :: " & processorOrderId & " :: " & "Missing Signature."
                GoTo Bail
            End If

            ' Verify that we are the intended merchant
            If arrPostedVariables("merchant_id") <> merchant_id Then
                sLogError = "Warning: " & orderId & " :: " & processorOrderId & " :: " & "Invalid merchantId."
                GoTo Bail
            End If


            ' Check if this is a legitimate request from the payment processor
            Dim sServer As String = CStr(Request.UserHostAddress)
            Dim bIp As Boolean = False
            For i = LBound(arrStr) To UBound(arrStr)
                If sServer = arrStr(i) Then
                    bIp = True
                    Exit For
                End If
            Next
            If Not bIp Then
                sLogError = "Warning: " & orderId & " :: " & processorOrderId & " :: " & "Invalid notification source."
                GoTo Bail
            End If


            ' Check if order already processed
            If CheckOrderStatus(orderId) <> "PROVISIONAL" Then
                sLogError = "Warning: " & orderId & " :: " & processorOrderId & " :: " & "Order already processed."
                GoTo Bail
            End If


            ' The request is legitimate. Post back to payment processor to validate the data received
            Dim wc As System.Net.WebClient
            Try
                wc = New System.Net.WebClient

                Dim arrResponse As Byte() = wc.UploadValues(site, "POST", arrPostedVariables)
                Dim result As String = System.Text.Encoding.ASCII.GetString(arrResponse)

                ' Get the response and replace the line breaks with spaces
                result = result.Replace(vbCrLf, " ").Replace(vbCr, " ").Replace(vbLf, " ")

                ' Was the data valid?
                If Not result.StartsWith("VALID") Then
                    sLogError = "Warning: " & orderId & " :: " & processorOrderId & " :: " & "Validation failed."
                    GoTo Bail
                End If

            Catch ex As Exception
                sLogError = "Error (PayFastNotify_Page_Load): " & ex.Source & "  ::  " & ex.Message & vbCrLf & ex.StackTrace
            Finally
                wc.Dispose()
                If sLogError <> "" Then
                    GoTo Bail
                End If
            End Try

        Catch ex As Exception
            sLogError = "Error (PayFastNotify_Page_Load): " & ex.Source & "  ::  " & ex.Message & vbCrLf & ex.StackTrace
            GoTo Bail
        End Try

        ' Confirm order
        ' Add some parameters to the arrPostedVariables collection to pass to the ConfirmOrder Sub
        arrPostedVariables.Add("signature", Request.Form("signature").ToString)
        arrPostedVariables.Add("pf_server_ip", CStr(Request.UserHostAddress))
        ConfirmOrder(orderId, arrPostedVariables)

        Exit Sub
Bail:
        ' Log any errors or warnings to the database
        UpdateLog(sErrorLog)
    End If
End Sub