start implementing /danger/restore-snapshot defroute (web.lisp).

The server needs to be restarted after restoring the website from a
Snapshot. This commit has code which establishes if the website is running on
localhost and informs the user to restart the server (most likely in SLIME)
manaully. If the website is running in prod. and using Systemd, the service will
need to be restarted that way (user doesn't have access to SBCL or SLIME in that
context). So, a Bash script will need to be written and that script will need
to be called using (most likely) utils:run-bash-command.

At the moment, I haven't got far enough into developing this website to have
established a Systemd service or running outside my local dev. machine. So, I
have left a TODO comment here stating the prod. side of the defroute is not
implemented yet.

src/web.lisp

@@ -1758,6 +1758,44 @@
                       "You are not authorised to delete page." "error")
 		     (redirect "/login")))))))
 
+(defroute ("/danger/restore-snapshot" :method :POST) ()
+  (destructuring-bind
+      (&key snapshot-name authenticity-token &allow-other-keys)
+      (utils:request-params (lack.request:request-body-parameters ningle:*request*))
+    (cond ((not (string= authenticity-token (auth:csrf-token)))
+	   `(,+forbidden+ (:content-type "text/plain") ("Denied")))
+	  (t (hermetic:auth
+	      (:administrator)
+	      ;; Authorised
+              (cond ((validation::string-is-nil-or-empty? snapshot-name)
+                     (utils:set-alert "No Snapshot Name provided."
+                                      "missing-data")
+                     (redirect "/danger/manage-snapshots"))
+                    ((not (storage:raw-directory-exists?
+                           (format nil "snapshots/~a/" snapshot-name)))
+                     (utils:set-alert "Cannot find selected Snapshot."
+                                      "invalid-data")
+                     (redirect "/danger/manage-snapshots"))
+                    (t (snapshot:restore-from-snapshot snapshot-name)
+                       (if (str:contains?
+                            "://localhost:" (utils:build-url-root ningle:*request*))
+                           (utils:set-alert
+                            "Snapshot restored. Restart local server for changes to take effect."
+                            "success")
+                           (progn
+                             (utils:set-alert
+                              "Snapshot restored restarting server. Please wait..."
+                              "success")
+                             ;; TODO: WRITE SCRIPT TO RESTART SYSTEMD SERVICE.
+                             ;; utils:run-bash-command "Restart Systemd Service"
+                             (format
+                              t "[INFO] Restarting Systemd service is not yet implemented.")))
+                           (redirect "/danger/manage-snapshots")))
+	            ;; Not Authorised
+	            (progn (utils:set-alert
+                            "You are not authorised to delete page." "error")
+		           (redirect "/login")))))))
+
 ;;
 ;; Error pages