using System;
using System.Collections;
using System.ComponentModel;
using System.IO;
using System.Text;
using System.Xml;
using System.Web.UI;

namespace RSS
{
  #region RSSItem class
  /// <summary>
  /// An RSS feed item.
  /// </summary>
  public class RSSItem
  {
    private string title;
    /// <summary>
    /// Gets or sets the title for the item.
    /// </summary>
    public string Title
    {
      get { return title; }
      set { title = value; }
    }

    private string description;
    /// <summary>
    /// Gets or sets the description for the item.
    /// </summary>
    public string Description
    {
      get { return description; }
      set { description = value; }
    }

    private DateTime date;
    /// <summary>
    /// Gets or sets the date of the item.
    /// </summary>
    public DateTime Date
    {
      get { return date; }
      set { date = value; }
    }

    private string author;
    /// <summary>
    /// Gets or sets the author of the item.
    /// </summary>
    public string Author
    {
      get { return author; }
      set { author = value; }
    }

    private string link;
    /// <summary>
    /// Gets or sets the URL for the item.
    /// </summary>
    public string Link
    {
      get { return link; }
      set { link = value; }
    }
  }
  #endregion

  #region RSSItemComparer class

  internal class RSSItemComparer : IComparer
  {
    public int Compare(object x, object y)
    {
      RSSItem item1 = x as RSSItem;
      RSSItem item2 = y as RSSItem;
      return -(item1.Date.CompareTo(item2.Date));
    }
  }

  #endregion

  #region RSSGenerator class 
	/// <summary>
	/// Helper class to generate RSS feeds.
	/// </summary>
	public class RSSGenerator : Page
	{
    private ArrayList items = new ArrayList();
    /// <summary>
    /// Creates a new <see cref="RSSGenerator"/> instance.
    /// </summary>
		public RSSGenerator()
		{
		}

    /// <summary>Category for RSS properties</summary>
    protected const string RSSCategory = "RSS";

    /// <summary>
    /// Event triggered when the page is loaded.
    /// </summary>
    /// <param name="e">E.</param>
    protected override void OnLoad (EventArgs e)
    {
      Page.Response.Clear();
      Page.Response.ContentType = "text/xml";

      base.OnLoad(e);

      string rss = RSSFeedXml();
      Page.Response.Write(rss);
    }

    /// <summary>
    /// Adds an RSS item to the feed.
    /// </summary>
    public RSSItem AddItem()
    {
      RSSItem item = new RSSItem();
      items.Add(item);
      return item;
    }

    /// <summary>
    /// Clears the RSS items from the feed.
    /// </summary>
    public void ClearItems()
    {
      items.Clear();
    }

    #region properties
    
    private string title;
    /// <summary>
    /// Gets or sets the title of the feed.
    /// </summary>
    [Description("The title of the RSS feed")]
    [Category(RSSCategory)]
    public string Title
    {
      get { return title; }
      set { title = value; }
    }

    private string link;
    /// <summary>
    /// Gets or sets the URL for the website associated with this feed.
    /// </summary>
    [Description("The URL of the homepage for this feed")]
    [Category(RSSCategory)]
    public string Link
    {
      get { return link; }
      set { link = value; }
    }

    private string description;
    /// <summary>
    /// Gets or sets the description for this feed.
    /// </summary>
    [Description("Description of the feed")]
    [Category(RSSCategory)]
    public string Description
    {
      get { return description; }
      set { description = value; }
    }

    #endregion

    /// <summary>
    /// Returns the XML for the RSS feed.
    /// </summary>
    public string RSSFeedXml()
    {
      PopulateFeed();

      StringWriter stringWriter = new StringWriter(); 
      XmlTextWriter writer = new XmlTextWriter(stringWriter);

      // start document
      writer.WriteStartElement("rss");
      writer.WriteAttributeString("version","2.0");

      // channel
      writer.WriteStartElement("channel");

      writer.WriteElementString("title", title);
      writer.WriteElementString("link", link);
      writer.WriteElementString("description", description);

      items.Sort(new RSSItemComparer());
      foreach(RSSItem item in items)
      {
        writer.WriteStartElement("item");
        writer.WriteElementString("title", item.Title);
        writer.WriteElementString("description", item.Description);
        writer.WriteElementString("pubDate", item.Date.ToString("r"));
        writer.WriteElementString("author", item.Author);
        writer.WriteElementString("link", item.Link);
        writer.WriteEndElement(); // item
      }

      // end channel
      writer.WriteEndElement(); //channel

      // end document
      writer.WriteEndElement(); //rss

      writer.Flush();
      return stringWriter.ToString();
    }

    /// <summary>
    /// Populates the feed. Override to populate the feed
    /// </summary>
    protected virtual void PopulateFeed()
    {
    }
	}
  #endregion
}