add index to nested forms

Hi guys.

currently struggling to retrieve child index reference in nested forms.
I have my main form:

<%= form_for(resource, as: resource_name, url: registration_path(resource_name), html: { method: :put, class: 'form-horizontal' }) do |f| %>
<%= render 'shared/devise_errors' %>
<div id="profiles">
            <%= f.fields_for :profiles do |profile_form| %>
                <%= render 'profile_fields', f: profile_form%>
            <%end%>
    </div>
    <div class="actions">
  <%= f.submit "Enregistrer", class: "btn btn-primary float-right" %>
</div>
<% end %>

and sub form _profile_fields.html.erb:

<div class="card text-justify" >

  <div class="card-header">
    <h4 class="card-title">
      <%indexi = f.options[:child_index].to_i+1 %>
      <%index= indexi.to_s %>
      <div class="form-group row">
        <%= f.label :label, class:'info col-md-4 col-form-label'%>
        <div class="input-group col-md-8">
          <%= f.text_field :label, class: "form-control", placeholder: "Profile #{index}",:value:(f.object.label || "Profile #{index}") %>

thks Jack.

I changed it for:

  <%= render partial:'profile_fields', locals: {f: profile_form, i: profile_form.index}%>

but receiving a

undefined local variable or method `i' for #<#Class:0x,...
for my subform line:

    <%= f.text_field :label, class: "form-control", placeholder: "Profile #{i}" %>

presumably profile_form.index is not defined ?

Seems strange to me. In the meantime, I found a workaround using CSS.

this is the top of my sub-form:
<section><%= f.label :label, class:'info col-md-4 col-form-label'%></section>

and this is the CSS added:

body {
  counter-reset: section;
}
section {
  counter-increment: section;
  white-space: nowrap;
  overflow: hidden;
}
section label:after {
  content: ' ' counter(section);
}