using System;
using System.Web;

namespace EnVisage.Code.Session
{
    /// <summary>
    /// Utility class for interacting with and managing Session objects.
    /// </summary>
    public static class SessionManager
    {
        #region Methods

        /// <summary>
        /// Retrieves an object stored in the current user session associated with the specified session key.
        /// </summary>
        /// <typeparam name="T">The expected type of the stored object</typeparam>
        /// <param name="key">The key which indexes the object within the current session</param>
        /// <returns>An object of type T if found; otherwise the default of T</returns>
        /// <exception cref="Exception">thrown if the value could not be cast to the specified type or an unknown error occured</exception>
        public static T GetValue<T>(string key)
        {
            object sessionObject = null;
            string errorMessage;
            try
            {
                sessionObject = HttpContext.Current.Session[key];
                if (sessionObject != null)
                    return ((T)sessionObject);
                return default(T);
            }
            catch (InvalidCastException invalidCastException)
            {
                string sessionObjectType = sessionObject == null ? "null" : sessionObject.GetType().ToString();

                errorMessage = string.Format("SessionManager.GetValueWithDefault failed to cast Session['{0}'] to {1}.  Object found is of type {2}.", key, typeof(T), sessionObjectType);
                var wrappedException = new Exception(errorMessage, invalidCastException);
                throw wrappedException;
            }
            catch (Exception exception)
            {
                errorMessage = string.Format("SessionManager.GetValueWithDefault failed to return Session['{0}'].", key);
                var wrappedException = new Exception(errorMessage, exception);
                throw wrappedException;
            }
        }

        /// <summary>
        /// Stores the specified object into the user's current session indexed with the specified key.
        /// </summary>
        /// <typeparam name="T">The type of object to be stored in session</typeparam>
        /// <param name="key">The key which indexes the the object within session</param>
        /// <param name="value">The object to be stored in session</param>
        public static void SetValue<T>(string key, T value)
        {
            HttpContext.Current.Session[key] = value;
        }

        /// <summary>
        /// Determines if an object indexed by the specified key exists with the current session.
        /// </summary>
        /// <param name="key">The index key of the object whose existence is to be checked</param>
        /// <returns>True if an object exists; otherwise false</returns>
        public static bool Exists(string key)
        {
            return HttpContext.Current.Session[key] != null;
        }

        /// <summary>
        /// Removes the object associated with the specified key from the user's current session.
        /// </summary>
        /// <param name="key">The key which indexes the object to be removed.</param>
        public static void Remove(string key)
        {
            if (HttpContext.Current.Session[key] != null)
                HttpContext.Current.Session.Remove(key);

        }

        #endregion
    }
}