source: branches/WebApplication/MVC2/HLWebPluginHost/PluginLib/PluginHelper.cs @ 4606

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.IO;
using System.Reflection;
using System.Web.Mvc;
using System.Diagnostics;

namespace HLWebPluginHost.PluginLib {

  /// <summary>
  /// Gathers all view locations and registers the plugins
  /// </summary>
  public class PluginHelper {

    /// <summary>
    /// Gathers all view locations and adds them to the custom view engine
    /// </summary>
    internal static void InitializePluginsAndLoadViewLocations() {
      Assembly[] pluginAssemblies = GetPluginAssemblies();

      List<string> viewLocations = new List<string>();

      foreach (Assembly plugin in pluginAssemblies) {
        var pluginAttribute = plugin.GetCustomAttributes(typeof(HLWebPluginViewLocations), false).FirstOrDefault() as HLWebPluginViewLocations;
        if (pluginAttribute != null)
          viewLocations.AddRange(pluginAttribute.viewLocations);
      }

      //The PluginViewEngine is used to locate views in the assemlbies 
      ViewEngines.Engines.Clear();
      ViewEngines.Engines.Add(new PluginViewEngine(viewLocations.ToArray()));
    }

    /// <summary>
    /// Builds dynamic links defined by the plugins
    /// </summary>
    /// <returns>List of plugin links</returns>
    public static List<PluginAction> GetPluginActions() {

      // todo: Load this links once on Application_Start() and cache them. 
      //       Currently the controller calls this everytime it renders the master page
      Assembly[] pluginAssemblies = GetPluginAssemblies();

      List<PluginAction> pluginLinks = new List<PluginAction>();

      foreach (Assembly plugin in pluginAssemblies) {
        var pluginAttribute = plugin.GetCustomAttributes(typeof(HLWebPluginViewLocations), false).FirstOrDefault() as HLWebPluginViewLocations;

        if (pluginAttribute.addLink) {
          pluginLinks.Add(new PluginAction() {
            Name = pluginAttribute.name,
            Action = pluginAttribute.action,
            Controller = pluginAttribute.controller
          });
        }
      }

      return pluginLinks;
    }

    private static Assembly[] GetPluginAssemblies() {
      IEnumerable<Assembly> loadedPluginAssemblies = AppDomain.CurrentDomain.GetAssemblies().Where(a => a.GetCustomAttributes(typeof(HLWebPluginViewLocations), false).Count() > 0).AsEnumerable();
      Assembly[] distinctLoadedPluginAssemblies = loadedPluginAssemblies.Distinct(new DLLComparer()).ToArray();
      
      return distinctLoadedPluginAssemblies;
    }

    public class PluginAction {
      public string Name { get; set; }
      public string Controller { get; set; }
      public string Action { get; set; }
    }

    private class DLLComparer : IEqualityComparer<Assembly> {
      #region IEqualityComparer<Assembly> Members

      public bool Equals(Assembly x, Assembly y) {
        return x.ManifestModule.ScopeName == y.ManifestModule.ScopeName;
      }

      public int GetHashCode(Assembly obj) {
        return obj.ManifestModule.ScopeName.GetHashCode();
      }

      #endregion
    }
  }
}