* @param WP_Block_Parser_Block $block A single parsed block object.
 * @return string String of rendered HTML.
 */
function serialize_block( $block ) {
	$block_content = '';

	$index = 0;
	foreach ( $block['innerContent'] as $chunk ) {
		$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index++ ] );
	}

	if ( ! is_array( $block['attrs'] ) ) {
		$block['attrs'] = array();
	}

	return get_comment_delimited_block_content(
		$block['blockName'],
		$block['attrs'],
		$block_content
	);
}

/**
 * Returns a joined string of the aggregate serialization of the given parsed
 * blocks.
 *
 * @since 5.3.1
 *
 * @param WP_Block_Parser_Block[] $blocks Parsed block objects.
 * @return string String of rendered HTML.
 */
function serialize_blocks( $blocks ) {
	return implode( '', array_map( 'serialize_block', $blocks ) );
}

/**
 * Filters and sanitizes block content to remove non-allowable HTML from
 * parsed block attribute values.
 *
 * @since 5.3.1
 *
 * @param string         $text              Text that may contain block content.
 * @param array[]|string $allowed_html      An array of allowed HTML elements
 *                                          and attributes, or a context name
 *                                          such as 'post'.
 * @param string[]       $allowed_protocols Array of allowed URL protocols.
 * @return string The filtered and sanitized content result.
 */
function filter_block_content( $text, $allowed_html = 'post', $allowed_protocols = array() ) {
	$result = '';

	if ( false !== strpos( $text, '<!--' ) && false !== strpos( $text, '--->' ) ) {
		$text = preg_replace_callback( '%<!--(.*?)--->%', '_filter_block_content_callback', $text );
	}

	$blocks = parse_blocks( $text );
	foreach ( $blocks as $block ) {
		$block   = filter_block_kses( $block, $allowed_html, $allowed_protocols );
		$result .= serialize_block( $block );
	}

	return $result;
}

/**
 * Callback used for regular expression replacement in filter_block_content().
 *
 * @private
 * @since 6.2.1
 *
 * @param array $matches Array of preg_replace_callback matches.
 * @return string Replacement string.
 */
function _filter_block_content_callback( $matches ) {
	return '<!--' . rtrim( $matches[1], '-' ) . '-->';
}

/**
 * Filters and sanitizes a parsed block to remove non-allowable HTML from block
 * attribute values.
 *
 * @since 5.3.1
 *
 * @param WP_Block_Parser_Block $block             The parsed block object.
 * @param array[]|string        $allowed_html      An array of allowed HTML
 *                                                 elements and attributes, or a
 *                                                 context name such as 'post'.
 * @param string[]              $allowed_protocols Allowed URL protocols.
 * @return array The filtered and sanitized block object result.
 */
function filter_block_kses( $block, $allowed_html, $allowed_protocols = array() ) {
	$block['attrs'] = filter_block_kses_value( $block['attrs'], $allowed_html, $allowed_protocols );

	if ( is_array( $block['innerBlocks'] ) ) {
		foreach ( $block['innerBlocks'] as $i => $inner_block ) {
			$block['innerBlocks'][ $i ] = filter_block_kses( $inner_block, $allowed_html, $allowed_protocols );
		}
	}

	return $block;
}

/**
 * Filters and sanitizes a parsed block attribute value to remove non-allowable
 * HTML.
 *
 * @since 5.3.1
 *
 * @param string[]|string $value             The attribute value to filter.
 * @param array[]|string  $allowed_html      An array of allowed HTML elements
 *                                           and attributes, or a context name
 *                                           such as 'post'.
 * @param string[]        $allowed_protocols Array of allowed URL protocols.
 * @return string[]|string The filtered and sanitized result.
 */
function filter_block_kses_value( $value, $allowed_html, $allowed_protocols = array() ) {
	if ( is_array( $value ) ) {
		foreach ( $value as $key => $inner_value ) {
			$filtered_key   = filter_block_kses_value( $key, $allowed_html, $allowed_protocols );
			$filtered_value = filter_block_kses_value( $inner_value, $allowed_html, $allowed_protocols );

			if ( $filtered_key !== $key ) {
				unset( $value[ $key ] );
			}

			$value[ $filtered_key ] = $filtered_value;
		}
	} elseif ( is_string( $value ) ) {
		return wp_kses( $value, $allowed_html, $allowed_protocols );
	}

	return $value;
}

/**
 * Parses blocks out of a content string, and renders those appropriate for the excerpt.
 *
 * As the excerpt should be a small string of text relevant to the full post content,
 * this function renders the blocks that are most likely to contain such text.
 *
 * @since 5.0.0
 *
 * @param string $content The content to parse.
 * @return string The parsed and filtered content.
 */
function excerpt_remove_blocks( $content ) {
	$allowed_inner_blocks = array(
		// Classic blocks have their blockName set to null.
		null,
		'core/freeform',
		'core/heading',
		'core/html',
		'core/list',
		'core/media-text',
		'core/paragraph',
		'core/preformatted',
		'core/pullquote',
		'core/quote',
		'core/table',
		'core/verse',
	);

	$allowed_blocks = array_merge( $allowed_inner_blocks, array( 'core/columns' ) );

	/**
	 * Filters the list of blocks that can contribute to the excerpt.
	 *
	 * If a dynamic block is added to this list, it must not generate another
	 * excerpt, as this will cause an infinite loop to occur.
	 *
	 * @since 5.0.0
	 *
	 * @param array $allowed_blocks The list of allowed blocks.
	 */
	$allowed_blocks = apply_filters( 'excerpt_allowed_blocks', $allowed_blocks );
	$blocks         = parse_blocks( $content );
	$output         = '';

	foreach ( $blocks as $block ) {
		if ( in_array( $block['blockName'], $allowed_blocks, true ) ) {
			if ( ! empty( $block['innerBlocks'] ) ) {
				if ( 'core/columns' === $block['blockName'] ) {
					$output .= _excerpt_render_inner_columns_blocks( $block, $allowed_inner_blocks );
					continue;
				}

				// Skip the block if it has disallowed or nested inner blocks.
				foreach ( $block['innerBlocks'] as $inner_block ) {
					if (
						! in_array( $inner_block['blockName'], $allowed_inner_blocks, true ) ||
						! empty( $inner_block['innerBlocks'] )
					) {
						continue 2;
					}
				}
			}

			$output .= render_block( $block );
		}
	}

	return $output;
}

/**
 * Render inner blocks from the `core/columns` block for generating an excerpt.
 *
 * @since 5.2.0
 * @access private
 *
 * @param array $columns        The parsed columns block.
 * @param array $allowed_blocks The list of allowed inner blocks.
 * @return string The rendered inner blocks.
 */
function _excerpt_render_inner_columns_blocks( $columns, $allowed_blocks ) {
	$output = '';

	foreach ( $columns['innerBlocks'] as $column ) {
		foreach ( $column['innerBlocks'] as $inner_block ) {
			if ( in_array( $inner_block['blockName'], $allowed_blocks, true ) && empty( $inner_block['innerBlocks'] ) ) {
				$output .= render_block( $inner_block );
			}
		}
	}

	return $output;
}

/**
 * Renders a single block into a HTML string.
 *
 * @since 5.0.0
 *
 * @global WP_Post  $post     The post to edit.
 * @global WP_Query $wp_query WordPress Query object.
 *
 * @param array $parsed_block A single parsed block object.
 * @return string String of rendered HTML.
 */
function render_block( $parsed_block ) {
	global $post, $wp_query;

	/**
	 * Allows render_block() to be short-circuited, by returning a non-null value.
	 *
	 * @since 5.1.0
	 *
	 * @param string|null $pre_render   The pre-rendered content. Default null.
	 * @param array       $parsed_block The block being rendered.
	 */
	$pre_render = apply_filters( 'pre_render_block', null, $parsed_block );
	if ( ! is_null( $pre_render ) ) {
		return $pre_render;
	}

	$source_block = $parsed_block;

	/**
	 * Filters the block being rendered in render_block(), before it's processed.
	 *
	 * @since 5.1.0
	 *
	 * @param array $parsed_block The block being rendered.
	 * @param array $source_block An un-modified copy of $parsed_block, as it appeared in the source content.
	 */
	$parsed_block = apply_filters( 'render_block_data', $parsed_block, $source_block );

	$context = array();

	if ( $post instanceof WP_Post ) {
		$context['postId'] = $post->ID;

		/*
		 * The `postType` context is largely unnecessary server-side, since the ID
		 * is usually sufficient on its own. That being said, since a block's
		 * manifest is expected to be shared between the server and the client,
		 * it should be included to consistently fulfill the expectation.
		 */
		$context['postType'] = $post->post_type;
	}

	if ( $wp_query instanceof WP_Query && isset( $wp_query->tax_query->queried_terms['category'] ) ) {
		$context['query'] = array( 'categoryIds' => array() );
		foreach ( $wp_query->tax_query->queried_terms['category']['terms'] as $category_slug_or_id ) {
			$context['query']['categoryIds'][] = 'slug' === $wp_query->tax_query->queried_terms['category']['field'] ? get_cat_ID( $category_slug_or_id ) : $category_slug_or_id;
		}
	}

	/**
	 * Filters the default context provided to a rendered block.
	 *
	 * @since 5.5.0
	 *
	 * @param array $context      Default context.
	 * @param array $parsed_block Block being rendered, filtered by `render_block_data`.
	 */
	$context = apply_filters( 'render_block_context', $context, $parsed_block );

	$block = new WP_Block( $parsed_block, $context );

	return $block->render();
}

/**
 * Parses blocks out of a content string.
 *
 * @since 5.0.0
 *
 * @param string $content Post content.
 * @return array[] Array of parsed block objects.
 */
function parse_blocks( $content ) {
	/**
	 * Filter to allow plugins to replace the server-side block parser
	 *
	 * @since 5.0.0
	 *
	 * @param string $parser_class Name of block parser class.
	 */
	$parser_class = apply_filters( 'block_parser_class', 'WP_Block_Parser' );

	$parser = new $parser_class();
	return $parser->parse( $content );
}

/**
 * Parses dynamic blocks out of `post_content` and re-renders them.
 *
 * @since 5.0.0
 *
 * @param string $content Post content.
 * @return string Updated post content.
 */
function do_blocks( $content ) {
	$blocks = parse_blocks( $content );
	$output = '';

	foreach ( $blocks as $block ) {
		$output .= render_block( $block );
	}

	// If there are blocks in this content, we shouldn't run wpautop() on it later.
	$priority = has_filter( 'the_content', 'wpautop' );
	if ( false !== $priority && doing_filter( 'the_content' ) && has_blocks( $content ) ) {
		remove_filter( 'the_content', 'wpautop', $priority );
		add_filter( 'the_content', '_restore_wpautop_hook', $priority + 1 );
	}

	return $output;
}

/**
 * If do_blocks() needs to remove wpautop() from the `the_content` filter, this re-adds it afterwards,
 * for subsequent `the_content` usage.
 *
 * @access private
 *
 * @since 5.0.0
 *
 * @param string $content The post content running through this filter.
 * @return string The unmodified content.
 */
function _restore_wpautop_hook( $content ) {
	$current_priority = has_filter( 'the_content', '_restore_wpautop_hook' );

	add_filter( 'the_content', 'wpautop', $current_priority - 1 );
	remove_filter( 'the_content', '_restore_wpautop_hook', $current_priority );

	return $content;
}

/**
 * Returns the current version of the block format that the content string is using.
 *
 * If the string doesn't contain blocks, it returns 0.
 *
 * @since 5.0.0
 *
 * @param string $content Content to test.
 * @return int The block format version is 1 if the content contains one or more blocks, 0 otherwise.
 */
function block_version( $content ) {
	return has_blocks( $content ) ? 1 : 0;
}

/**
 * Registers a new block style.
 *
 * @since 5.3.0
 *
 * @param string $block_name       Block type name including namespace.
 * @param array  $style_properties Array containing the properties of the style name,
 *                                 label, style (name of the stylesheet to be enqueued),
 *                                 inline_style (string containing the CSS to be added).
 * @return bool True if the block style was registered with success and false otherwise.
 */
function register_block_style( $block_name, $style_properties ) {
	return WP_Block_Styles_Registry::get_instance()->register( $block_name, $style_properties );
}

/**
 * Unregisters a block style.
 *
 * @since 5.3.0
 *
 * @param string $block_name       Block type name including namespace.
 * @param array  $block_style_name Block style name.
 * @return bool True if the block style was unregistered with success and false otherwise.
 */
function unregister_block_style( $block_name, $block_style_name ) {
	return WP_Block_Styles_Registry::get_instance()->unregister( $block_name, $block_style_name );
}