module AuthenticatedSystem
  protected
    # Returns true or false if the user is logged in.
    # Preloads @current_user with the user model if they're logged in.
    def logged_in?
      !!current_user
    end

    # Accesses the current user from the session.
    # Future calls avoid the database because nil is not equal to false.
    def current_user
      @current_user ||= login_from_session unless @current_user == false
    end

    # Store the given user id in the session.
    def current_user=(new_user)
      session[:user_id] = new_user ? new_user.id : nil
      @current_user = new_user || false
    end

    # Check if the user is authorized
    #
    # Override this method in your controllers if you want to restrict access
    # to only a few actions or if you want to check if the user
    # has the correct rights.
    #
    # Example:
    #
    #  # only allow nonbobs
    #  def authorized?
    #    current_user.login != "bob"
    #  end
    #
    def authorized?(action = action_name, resource = nil)
      logged_in?
    end

    # Filter method to enforce a login requirement.
    #
    # To require logins for all actions, use this in your controllers:
    #
    #   before_filter :login_required
    #
    # To require logins for specific actions, use this in your controllers:
    #
    #   before_filter :login_required, :only => [ :edit, :update ]
    #
    # To skip this in a subclassed controller:
    #
    #   skip_before_filter :login_required
    #
    def login_required
      authorized? || access_denied
    end

    # Redirect as appropriate when an access request fails.
    #
    # The default action is to redirect to the login screen.
    #
    # Override this method in your controllers if you want to have special
    # behavior in case the user is not authorized
    # to access the requested action.  For example, a popup window might
    # simply close itself.
    def access_denied
      respond_to do |format|
        format.html do
          store_location
          redirect_to new_session_path
        end
      end
    end

    # Store the URI of the current request in the session.
    #
    # We can return to this location by calling #redirect_back_or_default.
    def store_location
      session[:return_to] = request.fullpath
    end

    # Redirect to the URI stored by the most recent store_location call or
    # to the passed default.  Set an appropriately modified
    #   after_filter :store_location, :only => [:index, :new, :show, :edit]
    # for any controller you want to be bounce-backable.
    def redirect_back_or_default(default)
      redirect_to(session[:return_to] || default)
      session[:return_to] = nil
    end

    # Inclusion hook to make #current_user and #logged_in?
    # available as ActionView helper methods.
    def self.included(base)
      base.send :helper_method, :current_user, :logged_in?, :authorized? if base.respond_to? :helper_method
    end

    #
    # Login
    #

    # Called from #current_user.  First attempt to login by the user id stored in the session.
    def login_from_session
      self.current_user = User.find_by_id(session[:user_id]) if session[:user_id]
    end
    
    #
    # Logout
    #

    # This is ususally what you want; resetting the session willy-nilly wreaks
    # havoc with forgery protection, and is only strictly necessary on login.
    # However, **all session state variables should be unset here**.
    def logout_keeping_session!
      # Kill server-side auth cookie
      @current_user.forget_me if @current_user.is_a? User
      @current_user = false     # not logged in, and don't do it for me
      session[:user_id] = nil   # keeps the session but kill our variable
      # explicitly kill any other session variables you set
    end

    # The session should only be reset at the tail end of a form POST --
    # otherwise the request forgery protection fails. It's only really necessary
    # when you cross quarantine (logged-out to logged-in).
    def logout_killing_session!
      logout_keeping_session!
      reset_session
    end
end