fix: subcategories are not properly handled for budget allocations

[pauleke65]

This PR ensures that subcategory budget allocations cannot exceed the total budget allocated to their parent category.

Changes:

• Updated the allocated_spending method to only sum parent category budgets.
• Added logic in the budget category form to enforce a max allocation based on the parent’s available budget.

Issue Fixed:
Fixes #1665

Testing:

• Tried allocating more to subcategories than the parent allows ✅
• Verified that subcategory allocations are correctly restricted ✅

Demo:

Screen.Recording.2025-02-10.at.11.25.58.AM.mov

[zachgoll]

I like this solution! I think we should rearrange a bit of the code though to fit the budget domain a bit closer. I've left some ideas on how we could do that.

Finally, I think in order for these client-side validations to properly work, we'll need to update the Turbo stream responses for the update action so that subcategory forms and their directly siblings are replaced each time a subcategory budget is updated. This will ensure that the max: validation value is directly updated to reflect the new "max" based on the other subcategory sibling budget amounts.

[pauleke65]

Finally, I think in order for these client-side validations to properly work, we'll need to update the Turbo stream responses for the update action so that subcategory forms and their directly siblings are replaced each time a subcategory budget is updated. This will ensure that the max: validation value is directly updated to reflect the new "max" based on the other subcategory sibling budget amounts.

I tried getting the forms to re-update on the new changes, but couldn't quite get it.
I'm still very new to rails, and not familiar with how turbo streams work but I'll give a second look

[zachgoll]

@pauleke65 yeah the streams take a bit of getting used to! I think it can all be achieved here in this file:

https://github.com/maybe-finance/maybe/blob/main/app/views/budget_categories/update.turbo_stream.erb

We'll likely need to add something along the lines of (untested code below):

<% if @budget_category.subcategory? %>
  <% @budget_category.siblings.each do |sibling| %>
    <%= turbo_stream.update dom_id(sibling, :form), partial: "budget_categories/budget_category_form", locals: { budget_category: sibling } %>
  <% end %>
<% end %>

And then over in _budget_category_form.html.erb, add the id so it can be referenced:

<div id=<%= dom_id(budget_category, :form) %> class="w-full flex gap-3">

And finally, add that siblings method to budget_category.rb:

def siblings
  budget.budget_categories.select { |bc| bc.category.parent_id == category.parent_id && bc.id != id }
end

[zachgoll]

Looks great! Just waiting for tests to pass and will get it merged.

[pauleke65]

resolved lint issues