Blocksy 2 Add Custom Hook to Single Posts Before Last 3rd Block

blc-2-add-custom-hook-before-last-3rd-block.php

<?php
add_filter( 'the_content', function ( $content ) {
    if ( is_single() ) {
        $blocks = parse_blocks( $content );
        $block_count = count( $blocks );

        $insert_before_block = 3;
        $custom_hook_content = apply_filters( 'blocksy:before:certain:last:block', '' );

        if ( $block_count >= $insert_before_block ) {
            array_splice( $blocks, $block_count - $insert_before_block, 0, $custom_hook_content );
        } else {
            $blocks[] = $custom_hook_content;
        }

        $content = '';
        foreach ( $blocks as $block ) {
            $content .= render_block( $block );
        }
    }

    return $content;
});