<?php



class WP_HTML_Active_Formatting_Elements {
	
	private $stack = array();

	
	public function contains_node( WP_HTML_Token $token ) {
		foreach ( $this->walk_up() as $item ) {
			if ( $token->bookmark_name === $item->bookmark_name ) {
				return true;
			}
		}

		return false;
	}

	
	public function count() {
		return count( $this->stack );
	}

	
	public function current_node() {
		$current_node = end( $this->stack );

		return $current_node ? $current_node : null;
	}

	
	public function insert_marker(): void {
		$this->push( new WP_HTML_Token( null, 'marker', false ) );
	}

	
	public function push( WP_HTML_Token $token ) {
		/*
		 * > If there are already three elements in the list of active formatting elements after the last marker,
		 * > if any, or anywhere in the list if there are no markers, that have the same tag name, namespace, and
		 * > attributes as element, then remove the earliest such element from the list of active formatting
		 * > elements. For these purposes, the attributes must be compared as they were when the elements were
		 * > created by the parser; two elements have the same attributes if all their parsed attributes can be
		 * > paired such that the two attributes in each pair have identical names, namespaces, and values
		 * > (the order of the attributes does not matter).
		 *
		 * @todo Implement the "Noah's Ark clause" to only add up to three of any given kind of formatting elements to the stack.
		 */
		// > Add element to the list of active formatting elements.
		$this->stack[] = $token;
	}

	
	public function remove_node( WP_HTML_Token $token ) {
		foreach ( $this->walk_up() as $position_from_end => $item ) {
			if ( $token->bookmark_name !== $item->bookmark_name ) {
				continue;
			}

			$position_from_start = $this->count() - $position_from_end - 1;
			array_splice( $this->stack, $position_from_start, 1 );
			return true;
		}

		return false;
	}

	
	public function walk_down() {
		$count = count( $this->stack );

		for ( $i = 0; $i < $count; $i++ ) {
			yield $this->stack[ $i ];
		}
	}

	
	public function walk_up() {
		for ( $i = count( $this->stack ) - 1; $i >= 0; $i-- ) {
			yield $this->stack[ $i ];
		}
	}

	
	public function clear_up_to_last_marker(): void {
		foreach ( $this->walk_up() as $item ) {
			array_pop( $this->stack );
			if ( 'marker' === $item->node_name ) {
				break;
			}
		}
	}
}