Attempt to reload current page in newly-selected version

[andrewandante]

Inspired by https://github.com/silverstripe/api.silverstripe.org/issues/106

Most of the time when I toggle the version switcher, I'm hoping to see the page I am currently on, but in a different version.

This PR attempts to do that, rather then defaulting to the homepage of the newly-selected version.

[williamdes]

That's a good idea ! What does it do when it does not exist on the target version ?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 63.92%. Comparing base (2ca5517) to head (0447854). Report is 23 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #60 +/- ## ============================================ - Coverage 64.31% 63.92% -0.39% - Complexity 1241 1254 +13 ============================================ Files 53 53 Lines 3584 3615 +31 ============================================ + Hits 2305 2311 +6 - Misses 1279 1304 +25 ```

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[andrewandante]

That's a good idea ! What does it do when it does not exist on the target version ?

It just 404s. Which is not-great, I think, but can be useful as "oh this class doesn't exist in version 4" or whatever, so I'm somewhat ok with it as a concept.

[williamdes]

That's a good idea ! What does it do when it does not exist on the target version ?

It just 404s. Which is not-great, I think, but can be useful as "oh this class doesn't exist in version 4" or whatever, so I'm somewhat ok with it as a concept.

Okay, well maybe we can find some middle ground with this Maybe asking the search bar to load the page that we where on before Like some return_to argument

[andrewandante]

We could sort of naively check for a 200-399 response before re-routing? Something like (pseudocode):

var headReq= new XMLHttpRequest();
headReq.open('HEAD', url, false);
headReq.send();
if (headReq.status < 200 || headReq.status > 399)
  return newVersionIndex;
else
  return url;

Or something like that. Essentially, the old behaviour unless the page exists

[williamdes]

I like this idea ! Not all servers support HEAD, but we can agree to say that they should and ignore this corner case. Or just try using GET if the first one fails

[andrewandante]

agree to say that they should

Yeah I think that's the approach - if it's unsupported it should return a 405 (I think) and the existing behaviour will resurface anyway. I've pushed an update to support this HEAD request

[williamdes]

Thank you for your work and patience, this is a great feature !

[andrewandante]

Thanks @williamdes - though I've just had a cursory glance at the code I wrote and think I might have the conditionals around the wrong way?