Added drag functionality to update precendence for sort condition

[dikwickley]

Fixes #2349

Technical details

I have implemented the drag functionality from scratch without using any third party libraries.
It basically works by creating a ghost element that is draggable. While it is being dragged, it's position is used to calculate what index it is on and that updates the underlying list simultaneously.
When the pointer is released that list is updated to the original sort store.
The slide animation is achieved by https://svelte.dev/docs/svelte-animate#flip

@seancolsen please review.

Screenshots

Screen.Recording.2023-11-20.at.11.46.09.PM.mov

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[seancolsen]

I've given this a very quick, preliminary review. This is really impressive work, @dikwickley!

I've tested this locally. It works perfectly.

The code needs some clean up:

• Please fix the linting errors.
• Fix the icons so that they're cleaner. See the code in that same file that looks like <Icon {...iconAddNew} />. Make your icon code work like that one. We shouldn't see <svg> inside a component unless it's a very low-level component.
• 100 extra lines in this one component just to handle the dragging isn't great. I'm not opposed to merging it like this. But ideally, we'd abstract that code out into its own component so that the concerns are better separated and components can be more easily reused. See that comment you have, "Functionality for making sort entries draggable"... A comment like that is a good sign that the code needs to be pulled out into a new abstraction. The comment is useful, but this is the sort of code that can get real messy over time. The comment applies to the next 100 or so lines, but comments have no way to communicate that sort of scope. Other abstractions like functions, modules, components, and actions are better able to wrap up big chunks of code like this into nice tidy boxes so that they have descriptive names around all the code at once and clear interfaces with the world outside that code. If you want to take a crack at pulling this code out into some other abstraction, I think that would be cool. But it's not strictly necessary to merge this PR. I also wouldn't be opposed to using a 3rd party library for this, especially if there is one that plays well with Svelte. You might even be able to look at some of the drag and drop libraries to see how they structure their abstractions.

I'd like to review the code more thoroughly, but I'm heading off for a 1 week vacation soon so I'm short on time. I'll get back to this PR when I return. We'll definitely merge this. We just need to get it cleaned up a bit. Thanks for your hard work thus far!

[seancolsen]

@dikwickley

Thanks for fixing the linting errors and cleaning up the icons. Perfect!

I said:

ideally, we'd abstract that code out into its own component so that the concerns are better separated and components can be more easily reused

I see that you moved a bunch of code into a DraggableSortEntries.svelte component. That's not exactly what I had in mind. What I'm after here is a general-purpose abstraction that handles drag-and-drop sorting without concerning itself with any Mathesar-specific functionality. Your new component just moves code around with really separating the parts that I'd like to be separated.

I wanted to take a crack at this, because I imagine there being other areas of Mathesar that would benefit from this same sort of drag-and-drop sorting functionality. For example, with the proper abstraction, implementing the same precedence updating feature within the Grouping dialog would be trivially easy.

I thought I might be able to easily pull your code out into a new component, but I'm embarrassed to admit that I kind of got nerd sniped after getting my head into this problem! I ended up getting carried away and spending way too much time on this! But it was a fun problem. I've pushed my code up to your branch.

I've made the following changes to the drag-and-drop sorting functionality:

• I abstracted it all out into a set of three general-purpose Svelte actions. This means the changes within Mathesar-specific components are now very minimal.
• I changed the event handling logic to use pointerCapture, as I mentioned in the original ticket. This simplifies some of the code because you can listen to events on the trigger itself instead of the body.
• I changed the behavior when sorting so that no DOM mutations are made and all live sorting is done purely via CSS. This way we don't need to worry about creating and destroying the preview item and also hiding the grabbed item. This is a bit simpler and should be more robust in other cases where creating and destroying sort entry UI might have weird side effects.
• I made some changes to better support touch devices and tested them on Firefox and Chromium on a touch laptop.

Additionally, I fixed a bug introduced by allowing the user to edit the column within the sort entries. Prior to my fix, editing a column would bump that entry to have the lowest precedence.

Would you be up for reviewing my changes, testing them out, and making sure they make sense?

If this looks good to you, feel free to merge.

[seancolsen]

Oh wait: you won't be able to merge it yourself. You can submit a review or just post a comment, and I'll merge.

[dikwickley]

Thanks @seancolsen, i'll take a look.

[dikwickley]

@seancolsen this is really amazing. You have abstracted it out in a much functional way. I did try to abstract it out myself but failed as the code was quite coupled.
I have tested it out for all the use cases and it works flawlessly. I think it's good to go 🚀

[seancolsen]

Thanks!