Block.php

<?php

    namespace YourPlugin\Blocks;

    abstract class Block{

        /**
         * Block title
         *
         * @var string
         */
        protected $title = '';

        /**
         * Properties for this block
         *
         * @var array
         */
        protected $properties = [];

        /**
         * Constructor;
         */
        public function __construct( $props = [])
        {
            $this->properties = wp_parse_args( $props, $this->get_defaults() );
        }

        /**
         * Register this block:
         *
         * @return void
         */
        public function register()
        {
            
            add_action( 'acf/init', function(){

                if( function_exists( 'acf_register_block_type' ) ){
                    acf_register_block_type([
                        'name'              =>      $this->get_slug(),
                        'title'             =>      $this->title,
                        'description'       =>      $this->prop( 'description' ),
                        'render_template'   =>      $this->get_template(), 
                        'category'          =>      $this->prop( 'category' ),
                        'icon'              =>      $this->prop( 'icon' ),
                        'keywords'          =>      $this->prop( 'keywords' )
                    ]);
                }
            });

            if( function_exists( 'acf_add_local_field_group' ) ){
                acf_add_local_field_group([
                    'key' => 'block_fields_'.$this->get_slug(),
                    'title' => $this->title,
                    'fields' => $this->get_sanitized_fields(),
                    'location' => [[[
                        'param' => 'block',
                        'operator' => '==',
                        'value' => 'acf/'.$this->get_slug()
                    ]]],
                    'menu_order' => 0,
                    'position' => 'normal',
                    'style' => 'default',
                    'label_placement' => 'top',
                    'instruction_placement' => 'label',
                    'hide_on_screen' => '',
                    'active' => true,
                    'description' => '',
                ]);
            }
        }
        
        
        /**
         * Return the fields
         *
         * @return array
         */
        public function get_fields()
        {
            return [];
        }
    
        /**
         * Get all fields and add defaults to them
         * 
         * @return array
         */
        public function get_sanitized_fields( $fields = null )
        {
            if( is_null( $fields ) ){
                $fields = $this->get_fields();
            }

            foreach( $fields as $key => $field ){
                if( !isset( $field['key'] ) ){
                    $fields[$key]['key'] = $field['name'];
                }

                if( isset( $field['sub_fields'] ) && !empty( $field['sub_fields'] ) ){
                    $fields[$key]['sub_fields'] = $this->get_sanitized_fields( $field['sub_fields'] );
                }
            }
            
            return $fields;
        }


        /**
         * Return a property
         *
         * @return mixed
         */
        public function prop( $key, $default = null )
        {
            if( isset( $this->properties[ $key ] ) ){
                return $this->properties[ $key ];
            }

            return $default;
        }
            

        /**
         * Return the slug for this block
         *
         * @return string
         */
        public function get_slug()
        {
            return sanitize_title( $this->title );
        }


        /**
         * Return the template for this block:
         *
         * @return string
         */
        public function get_template()
        {
            return 'blocks/'.$this->get_slug().'.php';
        }


        /**
         * Return default properties
         *
         * @return array
         */
        public function get_defaults()
        {
            $defaults = [
                'description' => '',
                'category' => 'common',
                'icon' => 'admin-comments',
                'keywords' => []
            ];

            return apply_filters( 'my_plugin_custom_block_defaults', $defaults, $this );
        }
    }

example.php

<div class="example-block">
    <h3><?php echo get_field( 'example' );?></h3>

    <?php if( get_field('button') && is_array( get_field( 'button' ) ) ):
            $button = get_field( 'button' );    
    ?> 
        <a href="<?php echo esc_attr( $button['link'] );?>" class="button primary">
            <?php echo esc_html( $link['title'] );?>
        </a>
    <?php endif;?>
</div>

ExampleBlock.php

<?php

    namespace YourPlugin\Blocks;

    class ExampleBlock extends Block{

        /**
         * Title of this block
         * Determens how this block is added, saved and which template to use.
         * 
         * Block name: "Example"
         * Block slug/id: example
         * Template: /blocks/example.php
         *
         * @var string
         */
        protected $title = 'Example';


        /**
         * Return the fields
         *
         * @return Array
         */
        public function get_fields()
        {
            return [
                [
                    'label' => 'An example field',
                    'name' => 'example',    //field name for get_field()
                    'type' => 'text'        //type of field to show
                ],
                [
                    'label' => 'Button',
                    'name' => 'button',
                    'type' => 'link'
                ]
            ];
        }

    }

Block.php and ExampleBlock.php should be in the same folder. If you're not using autoloading in PHP, you need to require Block.php before ExampleBlock.php...

the template example.php should be in your active theme in the /blocks directory.

All blocks that you create (like ExampleBlock above) should be registered in a php-file:

( new ExampleBlock() )->register();

And by adding a get_defaults() function to your new blocks, you can control some of its settings:

  /**
    * Return default properties
    *
    * @return array
    */
    public function get_defaults()
    {
        return [
            'description' => 'This is a custom block description',
            'category' => 'common',
            'icon' => 'yes',
            'keywords' => [ 'myblock', 'testing' ]
        ];
    }