I'll try to better explain my thought process. I'll post the "libCommonInventoryFilters" later today.
Currently on the SELL tab we either have no filters (because the basic UI hides them), or custom AGS filters. AGS doesn't need to worry about conflicts, it just fills empty space. If another add-on wanted to put its own custom filters there, it would have to talk to AGS, or they would both need a toggle -- similar to how numerous combat add-ons have a toggle for every feature, and people mix them up in the most unimaginable ways. The idea of a centralized "pick one" setting is interesting, but it seems overkill for what we currently have. Perhaps if there were many contestants, but I doubt that will happen.
So, I wanted the default filters on the SELL tab, when AGS is not there. With AGS I don't really care, as long as there's exactly one set of filters
The library says:
"If you load me, I'm going to put filters on the SELL tab, unless you intend to put something better in there, in which case you need to explicitly tell me!" (does that make sense?)
You may have 3 add-ons wanting to put their controls in there, the library doesn't care how they get along, it just won't interfere if at least one of them tells it not to.
AF can include the library and do nothing else, it will just work.
FilterIt can include it and it will almost work (I just need to figure out why it's wrongly anchored).
AGS can include it, but must also call libCIF:disableGuildStoreSellFilters() in its EVENT_ADD_ON_LOADED, otherwise both sets would show up and overlap. It doesn't need to have a toggle, it can simply prefer its own filters.
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Now the difficult part: the search box. When filters are enabled on the SELL tab, there's no room for it.
AF moves the search box to the top, above filters. Which kinda makes sense, since the search persists as you switch filters. Btw, AF shows the search box on startup only, if you open/close the guild store, it won't appear in inventory/bank again. But don't worry, libCIF solves that, too.
AGS moves the search box below its filters on EVENT_OPEN_TRADING_HOUSE, and moves it back to the original location on EVENT_CLOSE_TRADING_HOUSE. This will probably need to be changed. I don't know when exactly these events occur, but if the CLOSE happens after SCENE_HIDING, I'd need to find a way to run another move function after that. But as with AF the search persists while switching filters, it'd probably be best to move it to the top.
FilterIt enables the search box, but uses it differently. It only works on the generic ALL filter, other top-level filters and sub-filters don't have a search box. Which means in the case of FilterIt, having the search box down there next to sub-filters actually makes sense. So I added libCIF:disableSearchBoxes(), which prevents the lib from showing search boxes and moving them to the top. Now I'm trying to figure out how to make FilterIt look nice on the SELL tab.
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And because adding filters forced me to play with the search box, the lib (by default) also moves search boxes to the AF location, and contains circonian's bug fixes as a bonus.