Convert from the (abandoned) footnotes plugin to WordPress core footnotes.

convert-footnotes.php

<?php
/**
 * A script to convert from the (abandoned) footnotes plugin to WP core footnotes.
 * This script is intended to be ran from wp-cli.
 * Requires WP 6.3. Does not require that the original footnotes plugin still be installed,
 * but does require that the options in `wp_options` are still in place.
 *
 * BACKUP YOUR DATABASE!
 * This script is not well-tested. It works for my (small) use-case. It should support
 * the original plugin's various short codes, but has only been tested with the
 * default `[ref]` and similar default settings.
 *
 * Proceed with caution!
 *
 * Usage:
 *  wp eval-file convert-footnotes.php
 *
 * @see https://wordpress.org/plugins/footnotes/
 */

// phpcs:set WordPress.NamingConventions.PrefixAllGlobals prefixes[] jdf


/**
 * Encapsulate in function to namespace variables.
 */
function jdf_run(): void {

	/**
	 * Ensure we have the footnotes block
	 */
	if ( ! WP_Block_Type_Registry::get_instance()->is_registered( 'core/footnotes' ) ) {
		echo 'Core footnotes block is not registered';
		die();
	}

	/**
	 * Get the plugin's settings.
	 */
	$footnotes_options = get_option( 'footnotes_storage' );

	if ( ! is_array( $footnotes_options ) ) {
		echo "Could not find 'footnotes' plugin options";
		die();
	}

	// Get the short code used by footnotes plugin.
	$start_tag         = $footnotes_options['footnote_inputfield_placeholder_start'];
	$end_tag           = $footnotes_options['footnote_inputfield_placeholder_end'];
	$escaped_start_tag = preg_quote( $start_tag );
	$escaped_end_tag   = preg_quote( $end_tag, '/' );

	// Get all posts to check.
	// Prior to 6.5, footnotes were only supported on core post types.
	$post_types = 'any';
	if ( ! is_wp_version_compatible( '6.5' ) ) {
		echo "Note: Prior to WP 6.5, footnotes were not supported on CPTs. Re-run the script after upgrading to convert footnotes on more post types.\n";
		$post_types = array( 'post', 'page' );
	}

	$args = array(
		'post_type'        => $post_types,
		'post_status'      => 'publish',
		'posts_per_page'   => '-1',
	);

	$all_posts = new WP_Query( $args );
	echo "Found {$all_posts->found_posts} posts\n";

	if ( $all_posts->have_posts() ) {
		while ( $all_posts->have_posts() ) {
			$all_posts->the_post();

			$content = get_the_content();

			$matches = array();
			$regex   = "/$escaped_start_tag(.*?)$escaped_end_tag/i";

			if ( preg_match_all( $regex, $content, $matches ) ) {
				$pid       = get_the_ID();
				$permalink = get_the_permalink();

				echo "Found plugin footnote on post ID: {$pid}, permalink: {$permalink}\n";

				/**
				 * In my case, there are duplicate matches because of the `source` block
				 * attribute from Jetpack's Markdown block.
				 * Deduping ensures no extra metadata is created.
				 * */
				$matches[0] = array_unique( $matches[0] );
				$matches[1] = array_unique( $matches[1] );

				// Get existing core footnotes.
				$footnotes = get_post_meta( $pid, 'footnotes', true );

				if ( empty( $footnotes ) ) {
					$footnotes = array();
				} else {
					$footnotes = json_decode( $footnotes );
				}

				foreach ( $matches[0] as $key => $match ) {
					$fn  = new stdClass();
					$uid = strtolower( jdf_GUID() );

					$fn->content = $matches[1][ $key ];
					$fn->id      = $uid;

					$footnotes[] = $fn;

					$fn_num = count( $footnotes );

					// Markup format is as of WP6.4.1.
					$content = str_replace(
						$matches[0][ $key ],
						sprintf( '<sup data-fn="%1$s" class="fn"><a href="#%1$s" id="%1$s-link">%2$d</a></sup>', $uid, $fn_num ),
						$content
					);
				}

				// Add the footnotes block, if it doesn't exist.
				if ( ! has_block( 'core/footnotes' ) ) {
					$content .= '<!-- wp:footnotes /-->';
				}

				// Confirm before updating.
				$prompt = readline( "Update post ID: {$pid}? (y) " );
				if ( $prompt === 'y' ) {
					echo "Updating $pid...\n";

					wp_update_post(
						array(
							'ID' => $pid,
							'post_content' => $content,
							'meta_input' => array(
								'footnotes' => wp_json_encode( $footnotes, JSON_UNESCAPED_UNICODE ),
							),
						)
					);
				} else {
					echo "Skipping $pid.\n";
				}
			}
		}
	}
}

jdf_run();


/**
 * Generates a GUID for use in linking footnotes.
 *
 * @link https://stackoverflow.com/a/26163679
 * @return string
 */
/* phpcs:disable */
function jdf_GUID()
{
    if (function_exists('com_create_guid') === true)
    {
        return trim(com_create_guid(), '{}');
    }

    return sprintf('%04X%04X-%04X-%04X-%04X-%04X%04X%04X', mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(16384, 20479), mt_rand(32768, 49151), mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535));
}
/* phpcs:enable */