using System;
using System.Collections.Generic;
using System.Configuration;
using System.Web;
using System.Web.Caching;
using System.Web.Configuration;

namespace VHelms.Web
{
   /// <summary>
   /// Can be used to open another web.config file with caching.
   /// </summary>
   public class MultiWebConfigManager
   {
      private static readonly Dictionary<string, Configuration> Configs = new Dictionary<string, Configuration>();

      #region Indexers
      /// <summary>           
      /// Gets the <see cref="System.Configuration.Configuration"/> from the specified path.           
      /// </summary>           
      /// <value></value>           
      public Configuration this[string configPath]
      {
         get { return GetConfig(configPath); }
      }

      /// <summary>           
      /// Gets the <see cref="System.String"/> from the specified configPath web.config's appSettings key.           
      /// </summary>           
      /// <value></value>           
      public string this[string configPath, string key]
      {
         get { return GetConfig(configPath).AppSettings.Settings[key].Value; }
      }
      #endregion Indexers

      #region Public methods

      /// <summary>           
      /// Gets the web.config file located at the specified path.           
      /// </summary>           
      /// <param name="configPath"></param>
      /// <returns></returns>           
      public static Configuration GetConfig(string configPath)
      {
         //attempt to load from dictionary                 
         if (Configs.ContainsKey(configPath))
            return Configs[configPath];

         //attempt to load from disk and add to dictionary                 
         Configuration config = LoadConfig(configPath);
         if (config != null)
         {
            Configs.Add(configPath, config);
            return config;
         }
         //doesn't exist, error out                 
         throw new ConfigurationErrorsException("A web configuration file could not be found at " + configPath);
      }
      #endregion Public methods

      #region Private methods
      /// <summary>           
      /// Loads the web.config from the given path.  If a web.config is found it is stored in cache and monitored for chagnes.           
      /// </summary>           
      /// <param name="configPath">The directory where the web.config is located.</param>           
      /// <returns></returns>           
      private static Configuration LoadConfig(string configPath)
      {
         Configuration config = WebConfigurationManager.OpenWebConfiguration(configPath);

         //If the config was loaded we want to monitor it for changes (use cache)                 
         //I decided to not store the config in the cache itself for performance (boxing/unboxing from cache)                  
         //  and complexity (dictionary in cache, only wanting to expire a single config vs.                  
         //  the entire dictionary on invalidation).                 
         string configFilePath = HttpContext.Current.Server.MapPath(configPath + "\\web.config");
         HttpContext.Current.Cache.Add("config_" + configPath, configPath, new CacheDependency(configFilePath), Cache.NoAbsoluteExpiration, new TimeSpan(0, 10, 0), CacheItemPriority.Normal, ConfigCacheRemoved);
         return config;
      }

      /// <summary>           
      /// Called when a configuration cache item is invalidated.           
      /// </summary>           
      /// <param name="name">The name of the cache item.</param>           
      /// <param name="value">The value of the cache item.</param>           
      /// <param name="reason">The reason the cache was invalidated.</param>           
      private static void ConfigCacheRemoved(string name, object value, CacheItemRemovedReason reason)
      {
         //if the item exists in the dictionary, remove it because it changed                 
         if (Configs.ContainsKey(value.ToString()))
            Configs.Remove(value.ToString());
      }
      #endregion Private methods
   }
}