Make an ACF repeater field downloadable as a CSV file (without titles)

cs-repeater-download.php

<?php
/**
 * Plugin Name: CS Repeater Download
 * Plugin URI: https://casperschultz.dk
 * Description: Plugin for downloading repeater field data.
 * Author: Casper Schultz
 * Author URI: https://casperschultz.dk
 * Text Domain: cs-repeater-download
 * Domain Path: /lang/
 * Version: 1.0
 */

namespace CasperSchultz\ACF\RepeaterDownload;

/**
 * Class CS_Repeater_Download
 * @package CasperSchultz\ACF\RepeaterDownload
 */
class CS_Repeater_Download {

	protected $repeater;

	public function __construct() {
    // @TODO add the repeater name that are to be downloadable.
		$this->repeater = 'team_attendants'; // Name of the repeater field that are to be downloadable.
    // @TODO add the post type that the download button should be displayed at.
		$this->post_types = 'hold'; // The post type that the download metabox is to be displayed at.
		$this->init();
	}

	public function init() {

		// Register meta box.
		add_action( 'add_meta_boxes', array( $this, 'register_meta_boxes' ) );

		// Add a new custom endpoint for the download rule.
		add_action( 'init', array( $this, 'add_rewrite_rule' ) );
		add_filter( 'query_vars', array( $this, 'add_query_vars' ) );

		// Generate the file.
		add_action( 'parse_request', array( $this, 'parse_request' ) );
	}

	/**
	 * Handle the custom endpoint we added.
	 */
	public function parse_request( $wp ) {

		// If the key does not exist, stop execution.
		if ( ! array_key_exists( 'cs-repeater-page-id', $wp->query_vars ) ) {
			return;
		}

		$page = absint( $wp->query_vars['cs-repeater-page-id'] );
		$output = '';

		if( have_rows( $this->repeater, $page ) ) {

			$rows = get_field( $this->repeater, $page );
			$field_count = count( $rows[0] );

			foreach ( $rows as $fields ) {

				$count = 1;

				foreach ( $fields as $value ) {
					$output .= $value;
					$count++;
					if ( $count < $field_count ) {
						$output .= ',';
					}
				}

				$output .= "\n";
			}
		}

		// Send the downloadable file.
		header("Content-type: text/plain");
		header("Content-Disposition: attachment; filename=attendants.txt");

		// Print the content.
		print $output;
		exit();
	}

	/**
	 * Add the needed query args.
	 */
	public function add_query_vars( $query_vars ) {
		$query_vars[] = 'cs-repeater-page-id';
		return $query_vars;
	}

	/**
	 * Adds a rewrite rule for our downloadable file.
	 */
	public function add_rewrite_rule() {
		add_rewrite_rule( '^cs-repeater-download/([0-9]+)/?', 'index.php?cs-repeater-page-id=$matches[1]', 'top' );
	}

	/**
	 * Register meta box(es).
	 */
	public function register_meta_boxes() {
		add_meta_box( 'meta-box-id', __( 'Download teams', 'cs-repeater-download' ), array( $this, 'meta_box_callback' ), $this->post_types, 'side' );
	}

	/**
	 * Meta box display callback.
	 *
	 * @param \WP_Post $post Current post object.
	 */
	public function meta_box_callback( $post ) {
		?>
			<p><?php _e( 'Download the teams as a comma seperated file (csv)', 'cs-repeater-download' ) ?></p>
			<a href="<?php get_site_url() ?>/cs-repeater-download/<?php echo $post->ID ?>" class="button button-primary button-large"><?php _e( 'Download', 'cs-repeater-download' ) ?></a>
		<?php
	}
}

/**
 * Run the plugin.
 */
function init() {
	new CS_Repeater_Download();
}
init();

/**
 * Need to flush rewrite rules on plugin activation.
 */
register_activation_hook( __FILE__, function() {
	add_rewrite_rule( '^cs-repeater-download/([0-9]+)/?', 'index.php?cs-repeater-page-id=$matches[1]', 'top' );
	flush_rewrite_rules();
} );