namespace YAF.Modules
{
   using System;
   using System.Web.UI.HtmlControls;

   using YAF.Types;
   using YAF.Types.Attributes;
   using YAF.Types.Constants;
   using YAF.Utils.Helpers;
   /// <summary>
   /// Generates a canonical meta tag to fight the dreaded duplicate content SEO warning
   /// </summary>
   [YafModule( "Canonical Meta Tag Module", "BonzoFestoon", 1 )]
   public class CanonicalMetaTagModule : SimpleBaseForumModule
   {
      public override void InitAfterPage()
      {
         this.CurrentForumPage.PreRender += this.CurrentForumPage_PreRender;
      }
      
      /// <summary>
      /// Handles the PreRender event of the ForumPage control.
      /// </summary>
      /// <param name="sender">The source of the event.</param>
      /// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
      private void CurrentForumPage_PreRender( [NotNull] object sender, [NotNull] EventArgs e )
      {
         const string topicLinkParams = "t={0}";
         HtmlHead head = this.ForumControl.Page.Header
                         ?? this.CurrentForumPage.FindControlRecursiveBothAs<HtmlHead>( "YafHead" );

         if ( head != null )
         {
            // in cases where we are not going to index, but follow, we will not add a canonical tag.
            string tag = null;
            switch ( this.ForumPageType ) // Just in case there are other types I am not thinking of.
            {
               case ForumPages.posts:
                  int topicId = this.PageContext.PageTopicID;
                  string topicUrl = YAF.Utils.YafBuildLink.GetLink( ForumPages.posts, true, topicLinkParams, topicId );
                  tag = string.Format( "<link rel=\"canonical\" href=\"{0}\" />", topicUrl );
                  break;
               default:
                  // there is not much SEO value to having lists indexed 
                  // because they change as soon as some adds a new topic 
                  // or post so don't index them, but follow the links
                  tag = "<meta name=\"robots\" content=\"noindex,follow\" />";
                  break;
            }
            if ( !string.IsNullOrWhiteSpace( tag ) )
            {
               head.Controls.Add( new System.Web.UI.LiteralControl( tag ) );
            }
         }
         else
         {
            // Ichabod Crane is running scared!
         }
      }
   }
}