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app/views/questionnaires/_form.html.erb

<%= form_with(model: questionnaire) do |form| %>
  <div class="field">
    <%= form.label :name %>
    <%= form.text_field :name %>
  </div>

  <div data-controller="nested-form">
    <template data-nested-form-target='template'>
      <%= form.fields_for :questions, Question.new, child_index: 'TEMPLATE_RECORD' do |question| %>
        <%= render 'question_fields', form: question %>
      <% end %>
    </template>

    <%= form.fields_for :questions do |question| %>
      <%= render 'question_fields', form: question %>
    <% end %>

    <div data-nested-form-target="add_item">
      <%= link_to "Add Question", "#", data: { action: "nested-form#add_association" } %>
    </div>
  </div>


  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  static targets = ["select", "choice", "long"]

  connect() {
    this.selected()
  }

  selected() {
    this.hideFields()
    switch (this.selectTarget.value) {
      case 'single_choice':
        this.choiceTarget.classList.remove('hidden')
        break;
      case 'multiple_choice':
        this.choiceTarget.classList.remove('hidden')
        break;
      case 'long_answer':
        this.longTarget.classList.remove('hidden')
        break;
    }
  }

  hideFields() {
    this.choiceTarget.classList.add('hidden')
    this.longTarget.classList.add('hidden')
  }
}

import { Controller } from "@hotwired/stimulus"

export default class extends Controller {
  static targets = ["add_item", "template"]

  add_association(event) {
    event.preventDefault()
    var content = this.templateTarget.innerHTML.replace(/TEMPLATE_RECORD/g, new Date().valueOf())
    this.add_itemTarget.insertAdjacentHTML('beforebegin', content)
  }

  remove_association(event) {
    event.preventDefault()
    let item = event.target.closest(".nested-fields")
    item.querySelector("input[name*='_destroy']").value = 1
    item.style.display = 'none'
  }
}