Fix behavior with large undo lists

[SerCeMan]

Hello!

It seems like undo doesn't work with large undo lists, because you always grab first 50 elements of a vector. I have tried "undo" in my application and have got wrong results.

Please, fix me if I didn't understand the idea correctly.

[SerCeMan]

Fix works for me

[SerCeMan]

And also, the possibility to inject middleware to every handler without encapsulating register-handler will be a great feature. (I need possibility to inject my undo middleware to every handler in dev mode)

[danielcompton]

Hi @SerCeMan, thanks for this! re-frame isn't big on tests in general, but this strikes me as a case where some tests could be helpful. Could you add some that fail on the old behaviour and pass on the new?

As far as injecting handlers into lots of middleware goes, you could make a (def dev-middleware [...] to use. Would that work?

[mike-thompson-day8]

@SerCeMan We started off thinking we needed undoable on all events, and then we realised having undo on everything was a problem.

We have this sort of a case: the user clicks on a button, generating a dispatch, and the event handler initiates a server connection, whose on-success handler initiates a further dispatch, and the associated event hander processes that response. And ... you don't want undoable on all those event handlers. Just the first, user initiated one (clicking on the button), not the intermediate ones. Otherwise your users can undo back into intermediate states, like twirly-thing-showing-while-waiting-for-server-response.

Your millage may vary, of course. Perhaps your app has no intermediate states (generally caused by event handlers doing further dispatches).

BUT, if you do decide you want undoable on all event handlers, then just write/use your own version of re-frame.core/register-handler https://github.com/Day8/re-frame/blob/master/src/re_frame/core.cljs#L46-L50

;; untested
(defn register-undoable-handler         ;; my version which always has undo middleware
  ([id handler]
    (re-frame.core/register-handler id [(undoable)] handler)
  ([id middleware handler]
     (re-frame.core/register-handler id [(undoable) middleware] handler)))   

Then, in your app, use reigster-undoable-handler instead of re-frame.core/register-handler

Thinks for the bug fix!!

[danielcompton]

Don't worry about the tests @SerCeMan, I'm working on them now.

[danielcompton]

Thanks for this! I've merged your changes in bb78981.

[SerCeMan]

Thanks! About undoable, I use it not only for undo/redo behaviour but also for showing the difference between versions in dev mode, it very convenient for me.

[danielcompton]

You might also find https://github.com/Day8/re-frame/wiki/Debugging convenient for that, it lets you trace individual function calls