publish (only flash-messages)

Author: vindarel

docs/building-blocks/flash-messages.lisp

@@ -0,0 +1,68 @@
+
+;;;
+;;; Demo of flash messages:
+;;; anywhere in a route, easily add flash messages to the session.
+;;; They are rendered at the next rendering of a template.
+;;; They are removed from the session once rendered.
+;;;
+
+;; inspired by https://github.com/rudolfochrist/booker/blob/main/app/controllers.lisp
+
+(uiop:add-package-local-nickname :ht :hunchentoot)
+
+(djula:add-template-directory ".")
+
+(defparameter *flash-template* (djula:compile-template* "flash-template.html"))
+
+(defparameter *port* 9876)
+
+(defvar *server* nil "Our Hunchentoot acceptor")
+
+(defun flash (type message)
+  "Add a flash message in the session.
+
+  TYPE: can be anything as you do what you want with it in the template.
+     Here, it is a string that represents the Bulma CSS class for notifications: is-primary, is-warning etc.
+  MESSAGE: string"
+  (let* ((session (ht:start-session))
+         (flash (ht:session-value :flash session)))
+    (setf (ht:session-value :flash session)
+          ;; With a cons, REST returns 1 element
+          ;; (when with a list, REST returns a list)
+          (cons (cons type message) flash))))
+
+;;; delete flash after it is used.
+(defmethod ht:handle-request :after (acceptor request)
+  (ht:delete-session-value :flash))
+
+#+another-solution
+(defun render (template &rest args)
+  (apply
+   #'djula:render-template* template nil
+   (list*
+    :flashes (or (ht:session-value :flash)
+               (list (cons "is-primary" "No more flash messages were found in the session. This is a default notification.")))
+    args)))
+
+
+(easy-routes:defroute flash-route ("/flash/" :method :get) ()
+  #-another-solution
+  (djula:render-template*  *flash-template* nil
+                           :flashes (or (ht:session-value :flash)
+                                        (list (cons "is-primary" "No more flash messages were found in the session. This is a default notification."))))
+  #+another-solution
+  (render *flash-template*)
+  )
+
+(easy-routes:defroute flash-redirect-route ("/tryflash/") ()
+  (flash "is-warning" "This is a warning message held in the session. It should appear only once: reload this page and you won't see the flash message again.")
+  (ht:redirect "/flash/"))
+
+(defun start (&key (port *port*))
+  (format t "~&Starting the web server on port ~a~&" port)
+  (force-output)
+  (setf *server* (make-instance 'easy-routes:easy-routes-acceptor :port port))
+  (ht:start *server*))
+
+(defun stop ()
+  (ht:stop *server*))