function bbp_admin_upgrade_user_topic_subscriptions() {

	// Define variables
	$bbp_db    = bbp_db();
	$statement = esc_html__( 'Upgrading user topic subscriptions… %s', 'bbpress' );
	$result    = esc_html__( 'No topic subscriptions to upgrade.',            'bbpress' );
	$total     = 0;
	$old_key   = $bbp_db->prefix . '_bbp_subscriptions';
	$new_key   = '_bbp_subscription';

	// Results
	$query     = "SELECT * FROM {$bbp_db->usermeta} WHERE meta_key = %s ORDER BY user_id";
	$prepare   = $bbp_db->prepare( $query, $old_key );
	$subs      = $bbp_db->get_results( $prepare );

	// Bail if no topic subscriptions found
	if ( empty( $subs ) || is_wp_error( $subs ) ) {
		return array( 1, sprintf( $statement, $result ) );
	}

	// Loop through each user's topic subscriptions
	foreach ( $subs as $meta ) {

		// Get post IDs
		$post_ids = explode( ',', $meta->meta_value );

		// Add user ID to all subscribed topics
		foreach ( $post_ids as $post_id ) {

			// Skip if already exists
			if ( $bbp_db->get_var( $bbp_db->prepare( "SELECT COUNT(*) FROM {$bbp_db->postmeta} WHERE post_id = %d AND meta_key = %s AND meta_value = %d", $post_id, $new_key, $meta->user_id ) ) ) {
				continue;
			}

			// Add the post meta
			$added = add_post_meta( $post_id, $new_key, $meta->user_id, false );

			// Bump counts if successfully added
			if ( ! empty( $added ) ) {
				++$total;
			}
		}
	}

	// Cleanup
	unset( $subs, $added, $post_ids );

	// Complete results
	$result = sprintf( _n( 'Complete! %d topic subscription upgraded.', 'Complete! %d topic subscriptions upgraded.', $total, 'bbpress' ), bbp_number_format( $total ) );

	return array( 0, sprintf( $statement, $result ) );
}