(defclass buffer ()
  ((name :accessor name :initarg :name)
   (mode :accessor mode :initarg :mode)
   (view :accessor view :initarg :view)
   (modes :accessor modes :initarg :modes)))

(defmethod print-object ((self buffer) stream)
  (format stream "~s" (name self)))

(defmethod add-mode ((self buffer) mode &optional (overwrite nil))
  (let ((found-mode (find mode (modes self)
			  :test #'(lambda (class mode) (typep mode class)))))
    (unless found-mode
      (push mode (modes self)))
    (when (and found-mode overwrite)
      (setf (modes self)
	    (remove-if #'(lambda (item) (typep item 'mode)) (modes self)))
      (push mode (modes self)))))

(defmethod switch-mode ((self buffer) mode-class)
  (let ((found-mode
	 (find mode-class (modes self)
	       :test #'(lambda (class mode) (typep mode class)))))
    (if found-mode
	(setf (mode self) found-mode)
	nil)))

(defmethod add-or-switch-to-mode ((self buffer) mode)
  (add-mode self mode)
  (switch-mode self (class-of mode)))