bp_document_rename_file( int $document_id, int $attachment_document_id, string $title = '',  $backend = false )

function bp_document_rename_file( $document_id = 0, $attachment_document_id = 0, $title = '', $backend = false ) {

	global $wpdb, $bp;

	if ( 0 === $document_id && '' === $title ) {
		return false;
	}

	if ( (int) $document_id > 0 ) {
		$has_access = bp_document_user_can_edit( $document_id );
		if ( ! $has_access ) {
			return false;
		}
	}

	$file_name    = $title;
	$new_filename = $title;

	// Variables.
	$post                     = get_post( $attachment_document_id );
	$file_parts               = bp_document_get_file_parts( $attachment_document_id );
	$old_filename             = $file_parts['filename'];
	$new_filename_unsanitized = $new_filename;

	// sanitizing file name (using sanitize_title because sanitize_file_name doesn't remove accents).
	$new_filename = sanitize_file_name( $new_filename );

	$file_abs_path     = get_attached_file( $post->ID );
	$file_abs_dir      = dirname( $file_abs_path );
	$new_file_abs_path = preg_replace( '~[^/]+$~', $new_filename . '.' . $file_parts['extension'], $file_abs_path );

	$file_abs_path     = get_attached_file( $post->ID );
	$file_abs_dir      = dirname( $file_abs_path );
	$new_file_abs_path = preg_replace( '~[^/]+$~', $new_filename . '.' . $file_parts['extension'], $file_abs_path );

	$file_rel_path     = get_post_meta( $post->ID, '_wp_attached_file', 1 );
	$new_file_rel_path = preg_replace( '~[^/]+$~', $new_filename . '.' . $file_parts['extension'], $file_rel_path );

	$uploads_path = wp_upload_dir();
	$uploads_path = $uploads_path['basedir'];

	// attachment miniatures.
	$searches = bp_document_get_attachment_urls( $attachment_document_id );

	// Validations.
	if ( ! $post ) {
		return __( 'Post with ID ' . $attachment_document_id . ' does not exist!', 'buddyboss' );
	}
	if ( $post && $post->post_type != 'attachment' ) {
		return __( 'Post with ID ' . $attachment_document_id . ' is not an attachment!', 'buddyboss' );
	}
	if ( ! $new_filename ) {
		return __( 'The document name is empty!', 'buddyboss' );
	}
	if ( $new_filename != sanitize_file_name( $new_filename ) ) {
		return __( 'Bad characters or invalid document name!', 'buddyboss' );
	}
	if ( file_exists( $new_file_abs_path ) ) {
		return __( 'A file with that name already exists in the containing folder!', 'buddyboss' );
	}
	if ( ! is_writable( $file_abs_dir ) ) {
		return __( 'The document containing directory is not writable!', 'buddyboss' );
	}

	// Change the attachment post.
//	$post_changes = array();
//	$post_changes['ID']         = $post->ID;
//	$post_changes['guid']       = preg_replace( '~[^/]+$~', $new_filename . '.' . $file_parts['extension'], $post->guid );
//	$post_changes['post_title'] = ( true ) ? bp_document_filename_to_title( $new_filename_unsanitized ) : $post->post_title;
//	$post_changes['post_name']  = wp_unique_post_slug( $new_filename, $post->ID, $post->post_status, $post->post_type, $post->post_parent );
//	wp_update_post( $post_changes );
//	unset( $post_changes );


	$my_post = array(
		'ID'         => $post->ID,
		'post_title' => bp_document_filename_to_title( $new_filename_unsanitized ),
//		'post_name'  => $new_filename,
		'guid'       => preg_replace( '~[^/]+$~', $new_filename . '.' . $file_parts['extension'], $post->guid ),
	);

	$post_id = wp_update_post( $my_post );

	// Change attachment post metas & rename files.
	foreach ( get_intermediate_image_sizes() as $size ) {
		$size_data = image_get_intermediate_size( $attachment_document_id, $size );

		@unlink( $uploads_path . DIRECTORY_SEPARATOR . $size_data['path'] );
	}

	if ( ! @rename( $file_abs_path, $new_file_abs_path ) ) {
		return __( 'File renaming error!', 'buddyboss' );
	}

	if ( ! function_exists( 'wp_generate_attachment_metadata' ) ) {
		require_once ABSPATH . 'wp-admin' . '/includes/image.php';
		require_once ABSPATH . 'wp-admin' . '/includes/file.php';
		require_once ABSPATH . 'wp-admin' . '/includes/media.php';
	}
	update_post_meta( $attachment_document_id, '_wp_attached_file', $new_file_rel_path );
	wp_update_attachment_metadata( $attachment_document_id, wp_generate_attachment_metadata( $attachment_document_id, $new_file_abs_path ) );

	// Replace the old with the new media link in the content of all posts and metas.
	$replaces = bp_document_get_attachment_urls( $attachment_document_id );

	$i          = 0;
	$post_types = get_post_types();
	unset( $post_types['attachment'] );

	while ( $posts = get_posts(
		array(
			'post_type'   => $post_types,
			'post_status' => 'any',
			'numberposts' => 100,
			'offset'      => $i * 100,
		)
	) ) {
		foreach ( $posts as $post ) {
			// Updating post content if necessary.
			$new_post                 = array( 'ID' => $post->ID );
			$new_post['post_content'] = str_replace( '\\', '\\\\', $post->post_content );
			$new_post['post_content'] = str_replace( $searches, $replaces, $new_post['post_content'] );
			if ( $new_post['post_content'] != $post->post_content ) {
				wp_update_post( $new_post );
			}

			// Updating post metas if necessary.
			$metas = get_post_meta( $post->ID );
			foreach ( $metas as $key => $meta ) {
				$meta[0]  = bp_document_unserialize_deep( $meta[0] );
				$new_meta = bp_document_replace_media_urls( $meta[0], $searches, $replaces );
				if ( $new_meta != $meta[0] ) {
					update_post_meta( $post->ID, $key, $new_meta, $meta[0] );
				}
			}
		}

		$i++;
	}

	// Updating options if necessary.
	$options = bp_document_get_all_options();
	foreach ( $options as $option ) {
		$option['value'] = bp_document_unserialize_deep( $option['value'] );
		$new_option      = bp_document_replace_media_urls( $option['value'], $searches, $replaces );
		if ( $new_option != $option['value'] ) {
			update_option( $option['name'], $new_option );
		}
	}

	$query = $wpdb->prepare( "UPDATE {$bp->document->table_name} SET title = %s, date_modified = %s WHERE id = %d AND attachment_id = %d", $new_filename, bp_core_current_time(), $document_id, $attachment_document_id );
	$query = $wpdb->query( $query ); // db call ok; no-cache ok;

	bp_document_update_meta( $document_id, 'file_name', $new_filename );

	if ( false === $query ) {
		return false;
	}

	$response = apply_filters(
		'bp_document_rename_file',
		array(
			'document_id'            => $document_id,
			'attachment_document_id' => $attachment_document_id,
			'title'                  => $new_filename,
		)
	);

	@unlink( $file_abs_path );

	return $response;
}