filter_tree_controller.js

import { Controller } from '@hotwired/stimulus'

export default class extends Controller {
  connect () {
    this.element.addEventListener('change', this.handleChange.bind(this))
  }

  handleChange (event) {
    this.traverseDown(event.target, event.target.checked)

    this.dispatch('change', {
      detail: { element: event.target }
    })
  }

  traverseDown (element, checked) {
    let rootElement

    // if a <summary> is closer than a <details>, we're in a category summary and need to toggle all children
    if (element.closest('details').contains(element.closest('summary'))) {
      rootElement = element.closest('details')
    }

    if (rootElement) {
      for (const checkbox of rootElement.querySelectorAll(
        ':scope > :not(summary) input[type=checkbox]'
      )) {
        checkbox.checked = checked
        checkbox.indeterminate = false
      }
    }
    // else we're in a leaf

    this.traverseUp(element)
  }

  traverseUp (element) {
    const closestDetails = element.closest('details')
    const childCheckboxes = [
      ...closestDetails.querySelectorAll(
        ':scope > :not(summary) input[type=checkbox]'
      )
    ]

    const rootCheckbox = closestDetails.querySelector(
      ':scope > summary input[type=checkbox]'
    )

    if (childCheckboxes.every(element => element.checked)) {
      rootCheckbox.checked = true
      rootCheckbox.indeterminate = false
    } else if (childCheckboxes.every(element => !element.checked)) {
      rootCheckbox.checked = false
      rootCheckbox.indeterminate = false
    } else {
      rootCheckbox.checked = false
      rootCheckbox.indeterminate = true
    }

    const rootDetails =
      element.tagName === 'DETAILS'
        ? element.parentElement.closest('details')
        : element.closest('details')

    if (rootDetails && rootDetails != element) this.traverseUp(rootDetails)
  }
}