<?php

/**

 * HTML API: WP_HTML_Active_Formatting_Elements class

 *

 * @package WordPress

 * @subpackage HTML-API

 * @since 6.4.0

 */

/**

 * Core class used by the HTML processor during HTML parsing

 * for managing the stack of active formatting elements.

 *

 * This class is designed for internal use by the HTML processor.

 *

 * > Initially, the list of active formatting elements is empty.

 * > It is used to handle mis-nested formatting element tags.

 * >

 * > The list contains elements in the formatting category, and markers.

 * > The markers are inserted when entering applet, object, marquee,

 * > template, td, th, and caption elements, and are used to prevent

 * > formatting from "leaking" into applet, object, marquee, template,

 * > td, th, and caption elements.

 * >

 * > In addition, each element in the list of active formatting elements

 * > is associated with the token for which it was created, so that

 * > further elements can be created for that token if necessary.

 *

 * @since 6.4.0

 *

 * @access private

 *

 * @see https://html.spec.whatwg.org/#list-of-active-formatting-elements

 * @see WP_HTML_Processor

 */

class WP_HTML_Active_Formatting_Elements {

	/**

	 * Holds the stack of active formatting element references.

	 *

	 * @since 6.4.0

	 *

	 * @var WP_HTML_Token[]

	 */

	private $stack = array();

	/**

	 * Reports if a specific node is in the stack of active formatting elements.

	 *

	 * @since 6.4.0

	 *

	 * @param WP_HTML_Token $token Look for this node in the stack.

	 * @return bool Whether the referenced node is in the stack of active formatting elements.

	 */

		foreach ( $this->walk_up() as $item ) {

			if ( $token->bookmark_name === $item->bookmark_name ) {

				return true;

			}

		}

		return false;

	}

	/**

	 * Returns how many nodes are currently in the stack of active formatting elements.

	 *

	 * @since 6.4.0

	 *

	 * @return int How many node are in the stack of active formatting elements.

	 */

	public function count() {

		return count( $this->stack );

	}

	/**

	 * Returns the node at the end of the stack of active formatting elements,

	 * if one exists. If the stack is empty, returns null.

	 *

	 * @since 6.4.0

	 *

	 * @return WP_HTML_Token|null Last node in the stack of active formatting elements, if one exists, otherwise null.

	 */

	public function current_node() {

		$current_node = end( $this->stack );

		return $current_node ? $current_node : null;

	}

	/**

	 * Pushes a node onto the stack of active formatting elements.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#push-onto-the-list-of-active-formatting-elements

	 *

	 * @param WP_HTML_Token $token Push this node onto the stack.

	 */

		/*

		 * > 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;

	}

	/**

	 * Removes a node from the stack of active formatting elements.

	 *

	 * @since 6.4.0

	 *

	 * @param WP_HTML_Token $token Remove this node from the stack, if it's there already.

	 * @return bool Whether the node was found and removed from the stack of active formatting elements.

	 */

		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;

	}

	/**

	 * Steps through the stack of active formatting elements, starting with the

	 * top element (added first) and walking downwards to the one added last.

	 *

	 * This generator function is designed to be used inside a "foreach" loop.

	 *

	 * Example:

	 *

	 *     $html = '<em><strong><a>We are here';

	 *     foreach ( $stack->walk_down() as $node ) {

	 *         echo "{$node->node_name} -> ";

	 *     }

	 *     > EM -> STRONG -> A ->

	 *

	 * To start with the most-recently added element and walk towards the top,

	 * see WP_HTML_Active_Formatting_Elements::walk_up().

	 *

	 * @since 6.4.0

	 */

	public function walk_down() {

		$count = count( $this->stack );

		for ( $i = 0; $i < $count; $i++ ) {

			yield $this->stack[ $i ];

		}

	}

	/**

	 * Steps through the stack of active formatting elements, starting with the

	 * bottom element (added last) and walking upwards to the one added first.

	 *

	 * This generator function is designed to be used inside a "foreach" loop.

	 *

	 * Example:

	 *

	 *     $html = '<em><strong><a>We are here';

	 *     foreach ( $stack->walk_up() as $node ) {

	 *         echo "{$node->node_name} -> ";

	 *     }

	 *     > A -> STRONG -> EM ->

	 *

	 * To start with the first added element and walk towards the bottom,

	 * see WP_HTML_Active_Formatting_Elements::walk_down().

	 *

	 * @since 6.4.0

	 */

	public function walk_up() {

		for ( $i = count( $this->stack ) - 1; $i >= 0; $i-- ) {

			yield $this->stack[ $i ];

		}

	}

}