Inject item into product category

<?php
/*
Plugin Name: Inject into Product archive
Plugin URI: https://www.facebook.com/groups/advanced.woocommerce/permalink/2119468894734185/
Description: Inject a div after every fourth product in product archive.
Author: Damien Carbery
Author URI: https://www.damiencarbery.com
Version: 0.1
*/

add_action( 'wp_head', 'dcwd_override_columns_setting' );
function dcwd_override_columns_setting() {
    wc_set_loop_prop( 'columns', 300 );
}


static $i = 0;
global $i;
static $inject_counter = 1;
global $inject_counter;


// This is where you write the code to put information into the new space.
// The counter tells you which space it is.
function inject_item( $counter ) {
    switch ( $counter ) {
        case 1:
?>
<div class="informationfirst">
    <h2 class="information"> INFORMATION </h2>
        <p class="text"> Lorem ipsum dolor sit amet, consectetur adipiscing elit.
        Aliquam elementum iaculis velit, vel maximus ante finibus vitae.
        Nam venenatis ultrices tempus. Morbi ornare nisl ac vulputate elementum.</p>
            <a class="button" href="http://google.com"> Click! </a>
</div>
<?php
            break;
        case 2:
?>
<div class="informationsecond">
    <h3 class="information"> INFORMATION SECOND GO GO</h2>
        <p class="text"> Elementum iaculis velit, vel maximus ante finibus vitae.
        Nam venenatis ultrices tempus. Morbi ornare nisl ac vulputate elementum.</p>
            <a class="button" href="http://google.com"> Click! </a>
</div>
<?php
            break;
        case 3:
?>
<div class="informationTHIRD">
    <h4 class="information"> INFORMATION THIRD</h2>
        <p class="text"> Morbi ornare nisl ac vulputate elementum.</p>
            <a class="button" href="http://google.com"> Click! </a>
</div>
<?php
            break;
    }
}


// Add a new item to the list after every fourth product.
add_action( 'woocommerce_shop_loop', 'inject_into_product_archive' );
function inject_into_product_archive() {
    global $i, $inject_counter;


    // This additional counter variable is a hack. The first space was being added after the
    // 4th product but when it was after every 3rd product.
    $current_position = $i - $inject_counter;
    if ( $current_position < 0 ) $current_position = 0;
    //error_log( "Inject: $i - $inject_counter = $current_position" );
    if ( ( $current_position > 0 ) && ( $current_position % 4 == 3 ) ) {
        $i++;
        $classes = array();
        $classes[] = 'product';
        $classes = dcwd_add_post_class_in_archive( $classes, '', '' );
        echo '<li class="'. join( ' ', $classes ).'">';
        inject_item( $inject_counter );
        echo '</li>';
        $inject_counter++;
        //error_log( "Inject div: $i" );
        //$i++;
    }
    $i++;
}


// Manually add the 'first' and 'last' classes to the li elements to force them onto the different rows.
add_filter( 'post_class', 'dcwd_add_post_class_in_archive', 30, 3 );
function dcwd_add_post_class_in_archive( $classes, $class, $post_id ) {
    if ( ! is_product_category() ) {
        return $classes;
    }
    global $i;

    //error_log( "Add first/last post class: $i (post $post_id)" );
    if ( $i % 3 == 0 ) {
        $classes[] = 'last';
        //error_log( "Add LAST post class: $i (post $post_id)" );
    }
    else if ( $i % 3 == 1 ) {
        $classes[] = 'first';
        //error_log( "Add FIRST post class: $i (post $post_id)" );
    }

    return $classes;
}