How to transform PrestaShop 1.7 checkout accordion steps into steps progress bar?

I'm pretty new to PrestaShop and PHP, I was asked to transform the current accordion checkout steps of PrestaShop 1.7 (classic theme) into a steps progress bar. I've got some good enough notions of CSS and a bit of JavaScript but I'm totally at lost when I look at the PrestaShop files. :(

Here some code (what's in comment is what I tried to add to create the steps progress bar). The checkout-process.tpl is a mystery:

{foreach from=$steps item="step" key="index"}
  {render identifier  =  $step.identifier
          position    =  ($index + 1)
          ui          =  $step.ui
          {* steps       =  $steps *}
  }
{/foreach}

Then I've got the checkout-step.tpl:

{block name='step'}
{* <div id="checkout-steps">
  <ul id="checkout-steps__bar">
    {foreach from=$steps item="step" key="index"}
    <li id="{$step.identifier}" class="step-title h3">{$step.title}</li>
    {/foreach}
  </ul>
</div> *}

<section id="{$identifier}" class="{[
                              'checkout-step'   => true,
                              '-current'        => $step_is_current,
                              '-reachable'      => $step_is_reachable,
                              '-complete'       => $step_is_complete,
                              'js-current-step' => $step_is_current
                          ]|classnames}">
  <h1 class="step-title h3">
    <i class="material-icons rtl-no-flip done">&#xE876;</i>
    <span class="step-number">{$position}</span>
    {$title}
    <span class="step-edit text-muted">
      <img src="{$urls.img_url}/icn/edit.png" alt="{l s='Update' d='Shop.Theme.Actions'}" class="icn-16" />
      {l s='Edit' d='Shop.Theme.Actions'}</span>
  </h1>

  <div class="content">
    {block name='step_content'}DUMMY STEP CONTENT{/block}
  </div>
</section>
{/block}

I managed to got the title by editing CheckoutProcess.php:

public function render(array $extraParams = array())
    {
        $scope = $this->smarty->createData(
            $this->smarty
        );

        $params = array(
            'steps' => array_map(function (CheckoutStepInterface $step) {
                return array(
                    'identifier' => $step->getIdentifier(),
                    'ui' => new RenderableProxy($step),
                    // Add title to steps array
                    'title' => $step->getTitle(),
                );
            }, $this->getSteps()),
        );

        $scope->assign(array_merge($extraParams, $params));

        $tpl = $this->smarty->createTemplate(
            $this->template,
            $scope
        );

        return $tpl->fetch();
    }

I don't think I'm doing the right thing but if I almost understood what's happening there, I've got no clue where to begin. -_-" If anybody got some advices or even better (one can always dream) already attempt this kind of modification, I'll be glad for any information, help, code example!! Thanks in advance.

It took me a while and it's probably not the best way to go, but I managed the transformation by adding my progress bar then overriding the default behaviour with custom CSS and JavaScript.

It's a lot of code, I'm not sure it's useful I post it there but if anyone want some information or the code, I will share it gladly!