Modify Contact form 7 plugin checkbox behavior

cf7_checkbox.php

<?php
// to drop in functions.php
// changes occur at line 120


add_action( 'wpcf7_init', 'wpcf7_add_shortcode_checkbox_alt' );

function wpcf7_add_shortcode_checkbox_alt() {
  wpcf7_add_shortcode( array( 'checkbox', 'checkbox*', 'radio' ),
    'my_checkbox', true );
}


function my_checkbox( $tag ) {
  $tag = new WPCF7_Shortcode( $tag );

  if ( empty( $tag->name ) )
    return '';

  $validation_error = wpcf7_get_validation_error( $tag->name );

  $class = wpcf7_form_controls_class( $tag->type );

  if ( $validation_error )
    $class .= ' wpcf7-not-valid';

  $label_first = $tag->has_option( 'label_first' );
  $use_label_element = $tag->has_option( 'use_label_element' );
  $exclusive = $tag->has_option( 'exclusive' );
  $free_text = $tag->has_option( 'free_text' );
  $multiple = false;

  if ( 'checkbox' == $tag->basetype )
    $multiple = ! $exclusive;
  else // radio
    $exclusive = false;

  if ( $exclusive )
    $class .= ' wpcf7-exclusive-checkbox';

  $atts = array();

  $atts['class'] = $tag->get_class_option( $class );
  // $atts['id'] = $tag->get_id_option();

  $tabindex = $tag->get_option( 'tabindex', 'int', true );

  if ( false !== $tabindex )
    $tabindex = absint( $tabindex );

  $html = '';
  $count = 0;

  $values = (array) $tag->values;
  $labels = (array) $tag->labels;

  if ( $data = (array) $tag->get_data_option() ) {
    if ( $free_text ) {
      $values = array_merge(
        array_slice( $values, 0, -1 ),
        array_values( $data ),
        array_slice( $values, -1 ) );
      $labels = array_merge(
        array_slice( $labels, 0, -1 ),
        array_values( $data ),
        array_slice( $labels, -1 ) );
    } else {
      $values = array_merge( $values, array_values( $data ) );
      $labels = array_merge( $labels, array_values( $data ) );
    }
  }

  $defaults = array();

  $default_choice = $tag->get_default_option( null, 'multiple=1' );

  foreach ( $default_choice as $value ) {
    $key = array_search( $value, $values, true );

    if ( false !== $key ) {
      $defaults[] = (int) $key + 1;
    }
  }

  if ( $matches = $tag->get_first_match_option( '/^default:([0-9_]+)$/' ) ) {
    $defaults = array_merge( $defaults, explode( '_', $matches[1] ) );
  }

  $defaults = array_unique( $defaults );

  $hangover = wpcf7_get_hangover( $tag->name, $multiple ? array() : '' );

  foreach ( $values as $key => $value ) {
    $class = 'wpcf7-list-item';

    $checked = false;

    if ( $hangover ) {
      if ( $multiple ) {
        $checked = in_array( esc_sql( $value ), (array) $hangover );
      } else {
        $checked = ( $hangover == esc_sql( $value ) );
      }
    } else {
      $checked = in_array( $key + 1, (array) $defaults );
    }

    if ( isset( $labels[$key] ) )
      $label = $labels[$key];
    else
      $label = $value;

    $item_atts = array(
      'type' => $tag->basetype,
      // 'name' => $tag->name . ( $multiple ? '[]' : '' ),
      'name' => $tag->name ,
      'value' => $value,
      'checked' => $checked ? 'checked' : '',
      'tabindex' => $tabindex ? $tabindex : '' ,
      'id' => $tag->get_id_option()
      );

    $item_atts = wpcf7_format_atts( $item_atts );

    if ( $label_first ) { // put label first, input last
      // $item = sprintf(
      //   '<label class="wpcf7-list-item-label">%1$s</label>&nbsp;<input %2$s />',
      //   esc_html( $label ), $item_atts );
      $item = '<label for="'. $tag->get_id_option() .'" class="wpcf7-list-item-label">'.esc_html( $label ).'</label><input '.$item_atts.' />';
      
    } else {
      // $item = sprintf(
      //   '<input %2$s /><label for="%1$s" class="wpcf7-list-item-label">%1$s</label>',
      //   esc_html( $label ), $item_atts );
      $item = '<input '.$item_atts.' /><label for="'. $tag->get_id_option() .'" class="wpcf7-list-item-label">'.esc_html( $label ).'</label>';

    }

    if ( $use_label_element )
      $item = '<label>' . $item . '</label>';

    if ( false !== $tabindex )
      $tabindex += 1;

    $count += 1;

    if ( 1 == $count ) {
      $class .= ' first';
    }

    if ( count( $values ) == $count ) { // last round
      $class .= ' last';

      if ( $free_text ) {
        $free_text_name = sprintf(
          '_wpcf7_%1$s_free_text_%2$s', $tag->basetype, $tag->name );

        $free_text_atts = array(
          'name' => $free_text_name,
          'class' => 'wpcf7-free-text',
          'tabindex' => $tabindex ? $tabindex : '' );

        if ( wpcf7_is_posted() && isset( $_POST[$free_text_name] ) ) {
          $free_text_atts['value'] = wp_unslash(
            $_POST[$free_text_name] );
        }

        $free_text_atts = wpcf7_format_atts( $free_text_atts );

        $item .= sprintf( ' <input type="text" %s />', $free_text_atts );

        $class .= ' has-free-text';
      }
    }

    $item = '<span class="' . esc_attr( $class ) . '">' . $item . '</span>';
    $html .= $item;
  }

  $atts = wpcf7_format_atts( $atts );

  $html = sprintf(
    '<span class="wpcf7-form-control-wrap %1$s"><span %2$s>%3$s</span>%4$s</span>',
    sanitize_html_class( $tag->name ), $atts, $html, $validation_error );

  return $html;
}


// END CF7 override
?>

Allows to create a markup like this :

<span class="wpcf7-list-item first last">
    <input type="checkbox" name="checkbox-terms" value="I agree to the Terms " id="checkbox-terms">
    <label for="checkbox-terms" class="wpcf7-list-item-label">I agree to the Terms </label>
</span>

so it's both semantic and accessible (and styleable)