Article: https://hwk.fr/blog/acf-creer-un-formulaire-de-connexion-inscription-en-ajax-grace-acf-form

wp-acf-form-ajax-frontend-form.php

<?php

/**
* ACF Form: Deregister ACF style
*/
add_action('wp_print_styles', 'hwk_acf_form_deregister_styles', 99);
function hwk_acf_form_deregister_styles(){
    wp_deregister_style('acf');
    wp_deregister_style('acf-field-group');
    wp_deregister_style('acf-global');
    wp_deregister_style('acf-input');
}

/**
* ACF Form: Elements Class
*/
add_filter('acf/load_field', 'hwk_acf_form_field_class');
function hwk_acf_form_field_class($field){
    if(is_admin() || wp_doing_ajax())
        return $field;
    
    $field['wrapper']['class'] .= ' col-12 form-group';
    
    if($field['type'] != 'checkbox')
        $field['class'] .= ' form-control';
    
    return $field;
}

/**
* ACF Form: Default form args
*/
add_filter('acf/validate_form', 'hwk_acf_form_args');
function hwk_acf_form_args($args){
    if(is_admin() || wp_doing_ajax())
        return $args;
    
    if(!$args['html_before_fields'])
        $args['html_before_fields'] = '<div class="row">';
    
    if(!$args['html_after_fields'])
        $args['html_after_fields'] = '</div>';
    
    if($args['html_updated_message'] == '<div id="message" class="updated"><p>%s</p></div>')
        $args['html_updated_message'] = '<div class="alert alert-success">%s</div>';
    
    if($args['html_submit_button'] == '<input type="submit" class="acf-button button button-primary button-large" value="%s" />')
        $args['html_submit_button'] = '<input type="submit" class="acf-button button btn btn-primary btn-lg" value="%s" />';
    
    // Set default Uploader to default
    $args['uploader'] = 'basic';
    
    return $args;
}

/**
* ACF Form: Elements Required Class
*/
add_filter('acf/get_field_label', 'hwk_acf_form_label', 10, 2);
function hwk_acf_form_label($label, $field){
    if(is_admin() || wp_doing_ajax())
        return $label;
    
    $label = str_replace('class="acf-required"', 'class="acf-required text-danger"', $label);
    return $label;
}

/**
* ACF Form: Allow Post ID to be null
*/
add_filter('acf/validate_post_id', 'hwk_acf_form_post_id_null', 10, 2);
function hwk_acf_form_post_id_null($post_id, $old_post_id){
    if($old_post_id === null)
        return false;
    
    return $post_id;
}

/**
* ACF Form: Set Screen
*/
add_action('acf/form_data', 'hwk_acf_form_screen');
function hwk_acf_form_screen($data){
    if(!isset($data['form']))
        return;
    
    $form = json_decode(acf_decrypt($data['form']), true);
    if(!isset($form['screen']))
        return;
    
    acf_hidden_input(array(
        'id'	=> 'screen',
        'name'	=> 'screen',
        'value'	=> $form['screen']
    ));
}

/**
* ACF Form: Helper – Get Screen
*/
function hwk_acf_form_get_screen(){
    if(isset($_POST['screen']) && !empty($_POST['screen']))
        return $_POST['screen'];
    
    return false;
}

/**
* ACF Form: Helper – Unset Screen
*/
function hwk_acf_form_unset_screen(){
    if(isset($_POST['screen']) && !empty($_POST['screen']))
        unset($_POST['screen']);
    
    return;
}

/**
* ACF Form: Helper – Get Form
*/
function hwk_acf_form_get_form($form = false){
    if(!$form)
        $form = $_POST['_acf_form'];
    
    if(!$form)
        return false;
    
    // AF Form
    if(function_exists('af_get_form') && isset($_POST['af_form']) && !empty($_POST['af_form']))
        return af_get_form($_POST['af_form']);
    
    // ACF Form
    $form = json_decode(acf_decrypt($form), true);
    if(!$form || empty($form) || !is_array($form))
        return false;
    
    return $form;
}

/**
* ACF Form: Helper – Get Data
*/
function hwk_acf_form_get_data($acf = false){
    if(!$acf)
        $acf = $_POST['acf'];
    
    if(!$acf)
        return false;
    
    $data = array();
    foreach($acf as $key => $value){
        $input = acf_get_field($key);
        
        if(!isset($input['name']))
            continue;

        if($input['type'] == 'group'){
            foreach($input['sub_fields'] as $sub_field){
                $data['input'][$input['name']][$sub_field['name']] = $value[$sub_field['key']];
                $data['key'][$input['name']][$sub_field['name']] = 'acf[' . $input['key'] . '][' . $sub_field['key'] .']';
            }
            
            continue;
        }

        $data['input'][$input['name']] = $value;
        $data['key'][$input['name']] = 'acf[' . $key .']';
    }

    if(empty($data))
        return false;

    return $data;
}

/**
* ACF Form: Helper – Get Return
*/
function hwk_acf_form_get_return($form = false){
    if(!$form)
        $form = hwk_acf_form_get_form();
    
    if(!$form)
        return false;
    
    $return = array();
    
    // ACF Form: Redirection
    if(isset($form['return']) && !empty($form['return']))
        $return['redirect'] = $form['return'];
    
    // ACF Form: Message
    if(isset($form['updated_message']) && !empty($form['updated_message']))
        $return['message'] = $form['updated_message'];
    
    // AF Form: Message
    if(isset($form['display']['success_message']) && !empty($form['display']['success_message']))
        $return['message'] = $form['display']['success_message'];
    
    return $return;
}

/**
* ACF Form: Helper - Get Error
*/
function hwk_acf_form_add_validation_error($key, $message){
    if(!acf()->validation->get_error($key)){
        acf_add_validation_error($key, $message);
        return;
    }
    
    foreach(acf()->validation->errors as &$value){
        if($value['input'] == $key)
            $value['message'] = $message;
    }
}