Last Five Pages Visited Cookie - asp.net

Question

So, I have a series of product pages and all I'd like to do is store the last 5 products viewed in a cookie so it can be displayed as a site-history. The problem I have isn't adding the five initial items to the cookie, its when they view 6, 7 or 10 items. Does anyone have any really decent suggestions on how to tackle this?
Currently I have this flawed logic (i have replaced the cookie name (xxx) for brevity);
Dim i As Integer = 0
Dim productcount As Integer = 0
If HttpContext.Current.Request.Cookies("xxx") Is Nothing Then
Dim gingernuts As New HttpCookie("xxx")
gingernuts.Values("productcount") = 0
gingernuts.Expires = DateTime.Now.AddDays(365)
HttpContext.Current.Response.Cookies.Add(gingernuts)
End If
productcount = HttpContext.Current.Request.Cookies("xxx")("productcount")
For i = 0 To productcount
If HttpContext.Current.Request.Cookies("xxx")("product" & i & "") = "" Then
HttpContext.Current.Response.Cookies("xxx")("product" & i & "") = Request.QueryString("id")
Else
HttpContext.Current.Response.Cookies("xxx")("product" & i & "") = HttpContext.Current.Request.Cookies("xxx")("product" & i & "")
End If
Next
If productcount = 5 Then
HttpContext.Current.Response.Cookies("xxx")("productcount") = 5
HttpContext.Current.Response.Cookies("xxx")("product0") = ""
Else
HttpContext.Current.Response.Cookies("xxx")("productcount") = productcount + 1
End If
Suggestions and critisism welcomed and appreciated.
Chris

Answer 1

Just use a simple cookie value which is a comma delimited list of the most recently viewed product IDs. (Note my VB.NET is that strong).
MostRecentIDs as String() '' // Instance level variables
Const ListSize = 5
'' // in a method somewhere
context As HttpContext = HttpContext.Current
cookie As HttpCookie = context.Request.Cookies("mri")
mri As Queue(Of String)
If cookie Is Nothing Then
mri = New Queue(Of String)(cookie.Value.Split(",".ToCharArray())
Else
mri = New Queue(Of String)
cookie = New HttpCookie("mri")
End If
If mri.Contains(Request.QueryString("id")) Then
If mri.Count >= ListSize Then mri.Dequeue()
mri.Enqueue(Request.QueryString("id"))
End If
MostRecentIDs = mri.ToArray();
cookie.Value = String.Join(",", MostRecentIDs)
cookie.Expires = DateTime.Now.AddDays(365)
context.Response.Add(cookie)
Now you have access to the most recent product IDs as a simple string array.
This code handles the case where the cookie has not yet been created.
The cookie itself is much smaller.
Managing the size of the list can easily be paramaterised.
Code above based on the tested C# code below that I dropped into an empty ASPX file:-
const int listSize = 8;
string[] _mru;
protected void Page_Load(object sender, EventArgs e)
{
HttpCookie cookie = Request.Cookies["mru"];
Queue<string> mru;
if (cookie != null)
{
mru = new Queue<string>(cookie.Value.Split(','));
}
else
{
mru = new Queue<string>();
cookie = new HttpCookie("mru");
}
if (!mru.Contains(Request.QueryString["id"]))
{
if (mru.Count >= listSize) mru.Dequeue();
mru.Enqueue(Request.QueryString["id"]);
}
_mru = mru.ToArray();
cookie.Value = String.Join(",", _mru);
cookie.Expires = DateTime.Now.AddDays(365);
Response.Cookies.Add(cookie);
}

Answer 2

This is how i will do it, if I am understanding your question right :)
If product count is less than 5 just append the new product. Else replace product0 with product1 till 4 and then add new product at 4
If productcount < 5 Then 'Do the null value check before this
HttpContext.Current.Response.Cookies("xxx")("productcount") = productCount + 1
HttpContext.Current.Response.Cookies("xxx")("product" & productCount + 1) = ""
Else
For i = 0 To productcount - 1
'Replace product 0 with 1, 1 with 2...till 3 with 4
HttpContext.Current.Response.Cookies("xxx")("product" & i & "") = HttpContext.Current.Response.Cookies("xxx")("product" & i + 1& "")
Next
HttpContext.Current.Response.Cookies("xxx")("product" & 4 & "") = Request.QueryString("id")
End If

Answer 3

Anthony answered this question perfectly, but for future reference and for those using VB, this is the code:
Imports System.Collections.Generic
Const listSize As Integer = 5
Private _mru As String()
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Dim cookie As HttpCookie = Request.Cookies("mru")
Dim mru As Queue(Of String)
If cookie IsNot Nothing Then
mru = New Queue(Of String)(cookie.Value.Split(","c))
Else
mru = New Queue(Of String)()
cookie = New HttpCookie("mru")
End If
If mru.Count >= listSize Then
mru.Dequeue()
End If
mru.Enqueue(Request.QueryString("id"))
_mru = mru.ToArray()
cookie.Value = [String].Join(",", _mru)
cookie.Expires = DateTime.Now.AddDays(365)
Response.Cookies.Add(cookie)
End Sub
Many thanks to all the contributors here also.