<?php

/**

 * HTML API: WP_HTML_Open_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 open elements.

 *

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

 *

 * > Initially, the stack of open elements is empty. The stack grows

 * > downwards; the topmost node on the stack is the first one added

 * > to the stack, and the bottommost node of the stack is the most

 * > recently added node in the stack (notwithstanding when the stack

 * > is manipulated in a random access fashion as part of the handling

 * > for misnested tags).

 *

 * @since 6.4.0

 *

 * @access private

 *

 * @see https://html.spec.whatwg.org/#stack-of-open-elements

 * @see WP_HTML_Processor

 */

class WP_HTML_Open_Elements {

	/**

	 * Holds the stack of open element references.

	 *

	 * @since 6.4.0

	 *

	 * @var WP_HTML_Token[]

	 */

	public $stack = array();

	/**

	 * Whether a P element is in button scope currently.

	 *

	 * This class optimizes scope lookup by pre-calculating

	 * this value when elements are added and removed to the

	 * stack of open elements which might change its value.

	 * This avoids frequent iteration over the stack.

	 *

	 * @since 6.4.0

	 *

	 * @var bool

	 */

	private $has_p_in_button_scope = false;

	/**

	 * A function that will be called when an item is popped off the stack of open elements.

	 *

	 * The function will be called with the popped item as its argument.

	 *

	 * @since 6.6.0

	 *

	 * @var Closure

	 */

	private $pop_handler = null;

	/**

	 * A function that will be called when an item is pushed onto the stack of open elements.

	 *

	 * The function will be called with the pushed item as its argument.

	 *

	 * @since 6.6.0

	 *

	 * @var Closure

	 */

	private $push_handler = null;

	/**

	 * Sets a pop handler that will be called when an item is popped off the stack of

	 * open elements.

	 *

	 * The function will be called with the pushed item as its argument.

	 *

	 * @since 6.6.0

	 *

	 * @param Closure $handler The handler function.

	 */

	public function set_pop_handler( Closure $handler ) {

		$this->pop_handler = $handler;

	}

	/**

	 * Sets a push handler that will be called when an item is pushed onto the stack of

	 * open elements.

	 *

	 * The function will be called with the pushed item as its argument.

	 *

	 * @since 6.6.0

	 *

	 * @param Closure $handler The handler function.

	 */

	public function set_push_handler( Closure $handler ) {

		$this->push_handler = $handler;

	}

	/**

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

	 */

	public function contains_node( $token ) {

		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 open elements.

	 *

	 * @since 6.4.0

	 *

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

	 */

	public function count() {

		return count( $this->stack );

	}

	/**

	 * Returns the node at the end of the stack of open 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 open elements, if one exists, otherwise null.

	 */

	public function current_node() {

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

		return $current_node ? $current_node : null;

	}

	/**

	 * Returns whether an element is in a specific scope.

	 *

	 * ## HTML Support

	 *

	 * This function skips checking for the termination list because there

	 * are no supported elements which appear in the termination list.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-the-specific-scope

	 *

	 * @param string   $tag_name         Name of tag check.

	 * @param string[] $termination_list List of elements that terminate the search.

	 * @return bool Whether the element was found in a specific scope.

	 */

	public function has_element_in_specific_scope( $tag_name, $termination_list ) {

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

			if ( $node->node_name === $tag_name ) {

				return true;

			}

			if (

				'(internal: H1 through H6 - do not use)' === $tag_name &&

				in_array( $node->node_name, array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' ), true )

			) {

				return true;

			}

			switch ( $node->node_name ) {

				case 'HTML':

					return false;

			}

			if ( in_array( $node->node_name, $termination_list, true ) ) {

				return false;

			}

		}

		return false;

	}

	/**

	 * Returns whether a particular element is in scope.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-scope

	 *

	 * @param string $tag_name Name of tag to check.

	 * @return bool Whether given element is in scope.

	 */

	public function has_element_in_scope( $tag_name ) {

		return $this->has_element_in_specific_scope(

			$tag_name,

			array(

				/*

				 * Because it's not currently possible to encounter

				 * one of the termination elements, they don't need

				 * to be listed here. If they were, they would be

				 * unreachable and only waste CPU cycles while

				 * scanning through HTML.

				 */

			)

		);

	}

	/**

	 * Returns whether a particular element is in list item scope.

	 *

	 * @since 6.4.0

	 * @since 6.5.0 Implemented: no longer throws on every invocation.

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-list-item-scope

	 *

	 * @param string $tag_name Name of tag to check.

	 * @return bool Whether given element is in scope.

	 */

	public function has_element_in_list_item_scope( $tag_name ) {

		return $this->has_element_in_specific_scope(

			$tag_name,

			array(

				// There are more elements that belong here which aren't currently supported.

				'OL',

				'UL',

			)

		);

	}

	/**

	 * Returns whether a particular element is in button scope.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-button-scope

	 *

	 * @param string $tag_name Name of tag to check.

	 * @return bool Whether given element is in scope.

	 */

	public function has_element_in_button_scope( $tag_name ) {

		return $this->has_element_in_specific_scope( $tag_name, array( 'BUTTON' ) );

	}

	/**

	 * Returns whether a particular element is in table scope.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-table-scope

	 *

	 * @throws WP_HTML_Unsupported_Exception Always until this function is implemented.

	 *

	 * @param string $tag_name Name of tag to check.

	 * @return bool Whether given element is in scope.

	 */

	public function has_element_in_table_scope( $tag_name ) {

		throw new WP_HTML_Unsupported_Exception( 'Cannot process elements depending on table scope.' );

		return false; // The linter requires this unreachable code until the function is implemented and can return.

	}

	/**

	 * Returns whether a particular element is in select scope.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-select-scope

	 *

	 * @throws WP_HTML_Unsupported_Exception Always until this function is implemented.

	 *

	 * @param string $tag_name Name of tag to check.

	 * @return bool Whether given element is in scope.

	 */

	public function has_element_in_select_scope( $tag_name ) {

		throw new WP_HTML_Unsupported_Exception( 'Cannot process elements depending on select scope.' );

		return false; // The linter requires this unreachable code until the function is implemented and can return.

	}

	/**

	 * Returns whether a P is in BUTTON scope.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#has-an-element-in-button-scope

	 *

	 * @return bool Whether a P is in BUTTON scope.

	 */

	public function has_p_in_button_scope() {

		return $this->has_p_in_button_scope;

	}

	/**

	 * Pops a node off of the stack of open elements.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#stack-of-open-elements

	 *

	 * @return bool Whether a node was popped off of the stack.

	 */

	public function pop() {

		$item = array_pop( $this->stack );

		if ( null === $item ) {

			return false;

		}

		if ( 'context-node' === $item->bookmark_name ) {

			$this->stack[] = $item;

			return false;

		}

		$this->after_element_pop( $item );

		return true;

	}

	/**

	 * Pops nodes off of the stack of open elements until one with the given tag name has been popped.

	 *

	 * @since 6.4.0

	 *

	 * @see WP_HTML_Open_Elements::pop

	 *

	 * @param string $tag_name Name of tag that needs to be popped off of the stack of open elements.

	 * @return bool Whether a tag of the given name was found and popped off of the stack of open elements.

	 */

	public function pop_until( $tag_name ) {

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

			if ( 'context-node' === $item->bookmark_name ) {

				return true;

			}

			$this->pop();

			if (

				'(internal: H1 through H6 - do not use)' === $tag_name &&

				in_array( $item->node_name, array( 'H1', 'H2', 'H3', 'H4', 'H5', 'H6' ), true )

			) {

				return true;

			}

			if ( $tag_name === $item->node_name ) {

				return true;

			}

		}

		return false;

	}

	/**

	 * Pushes a node onto the stack of open elements.

	 *

	 * @since 6.4.0

	 *

	 * @see https://html.spec.whatwg.org/#stack-of-open-elements

	 *

	 * @param WP_HTML_Token $stack_item Item to add onto stack.

	 */

	public function push( $stack_item ) {

		$this->stack[] = $stack_item;

		$this->after_element_push( $stack_item );

	}

	/**

	 * Removes a specific node from the stack of open elements.

	 *

	 * @since 6.4.0

	 *

	 * @param WP_HTML_Token $token The node to remove from the stack of open elements.

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

	 */

	public function remove_node( $token ) {

		if ( 'context-node' === $token->bookmark_name ) {

			return false;

		}

		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 );

			$this->after_element_pop( $item );

			return true;

		}

		return false;

	}

	/**

	 * Steps through the stack of open 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_Open_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 open 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_Open_Elements::walk_down().

	 *

	 * @since 6.4.0

	 * @since 6.5.0 Accepts $above_this_node to start traversal above a given node, if it exists.

	 *

	 * @param ?WP_HTML_Token $above_this_node Start traversing above this node, if provided and if the node exists.

	 */

	public function walk_up( $above_this_node = null ) {

		$has_found_node = null === $above_this_node;

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

			$node = $this->stack[ $i ];

			if ( ! $has_found_node ) {

				$has_found_node = $node === $above_this_node;

				continue;

			}

			yield $node;

		}

	}

	/*

	 * Internal helpers.

	 */