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+<?php
+/**
+ * A class for displaying various tree-like structures.
+ *
+ * Extend the Walker class to use it, see examples below. Child classes
+ * do not need to implement all of the abstract methods in the class. The child
+ * only needs to implement the methods that are needed.
+ *
+ * @since 2.1.0
+ *
+ * @package WordPress
+ * @abstract
+ */
+#[AllowDynamicProperties]
+class Walker {
+ /**
+ * What the class handles.
+ *
+ * @since 2.1.0
+ * @var string
+ */
+ public $tree_type;
+
+ /**
+ * DB fields to use.
+ *
+ * @since 2.1.0
+ * @var string[]
+ */
+ public $db_fields;
+
+ /**
+ * Max number of pages walked by the paged walker.
+ *
+ * @since 2.7.0
+ * @var int
+ */
+ public $max_pages = 1;
+
+ /**
+ * Whether the current element has children or not.
+ *
+ * To be used in start_el().
+ *
+ * @since 4.0.0
+ * @var bool
+ */
+ public $has_children;
+
+ /**
+ * Starts the list before the elements are added.
+ *
+ * The $args parameter holds additional values that may be used with the child
+ * class methods. This method is called at the start of the output list.
+ *
+ * @since 2.1.0
+ * @abstract
+ *
+ * @param string $output Used to append additional content (passed by reference).
+ * @param int $depth Depth of the item.
+ * @param array $args An array of additional arguments.
+ */
+ public function start_lvl( &$output, $depth = 0, $args = array() ) {}
+
+ /**
+ * Ends the list of after the elements are added.
+ *
+ * The $args parameter holds additional values that may be used with the child
+ * class methods. This method finishes the list at the end of output of the elements.
+ *
+ * @since 2.1.0
+ * @abstract
+ *
+ * @param string $output Used to append additional content (passed by reference).
+ * @param int $depth Depth of the item.
+ * @param array $args An array of additional arguments.
+ */
+ public function end_lvl( &$output, $depth = 0, $args = array() ) {}
+
+ /**
+ * Starts the element output.
+ *
+ * The $args parameter holds additional values that may be used with the child
+ * class methods. Also includes the element output.
+ *
+ * @since 2.1.0
+ * @since 5.9.0 Renamed `$object` (a PHP reserved keyword) to `$data_object` for PHP 8 named parameter support.
+ * @abstract
+ *
+ * @param string $output Used to append additional content (passed by reference).
+ * @param object $data_object The data object.
+ * @param int $depth Depth of the item.
+ * @param array $args An array of additional arguments.
+ * @param int $current_object_id Optional. ID of the current item. Default 0.
+ */
+ public function start_el( &$output, $data_object, $depth = 0, $args = array(), $current_object_id = 0 ) {}
+
+ /**
+ * Ends the element output, if needed.
+ *
+ * The $args parameter holds additional values that may be used with the child class methods.
+ *
+ * @since 2.1.0
+ * @since 5.9.0 Renamed `$object` (a PHP reserved keyword) to `$data_object` for PHP 8 named parameter support.
+ * @abstract
+ *
+ * @param string $output Used to append additional content (passed by reference).
+ * @param object $data_object The data object.
+ * @param int $depth Depth of the item.
+ * @param array $args An array of additional arguments.
+ */
+ public function end_el( &$output, $data_object, $depth = 0, $args = array() ) {}
+
+ /**
+ * Traverses elements to create list from elements.
+ *
+ * Display one element if the element doesn't have any children otherwise,
+ * display the element and its children. Will only traverse up to the max
+ * depth and no ignore elements under that depth. It is possible to set the
+ * max depth to include all depths, see walk() method.
+ *
+ * This method should not be called directly, use the walk() method instead.
+ *
+ * @since 2.5.0
+ *
+ * @param object $element Data object.
+ * @param array $children_elements List of elements to continue traversing (passed by reference).
+ * @param int $max_depth Max depth to traverse.
+ * @param int $depth Depth of current element.
+ * @param array $args An array of arguments.
+ * @param string $output Used to append additional content (passed by reference).
+ */
+ public function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) {
+ if ( ! $element ) {
+ return;
+ }
+
+ $id_field = $this->db_fields['id'];
+ $id = $element->$id_field;
+
+ // Display this element.
+ $this->has_children = ! empty( $children_elements[ $id ] );
+ if ( isset( $args[0] ) && is_array( $args[0] ) ) {
+ $args[0]['has_children'] = $this->has_children; // Back-compat.
+ }
+
+ $this->start_el( $output, $element, $depth, ...array_values( $args ) );
+
+ // Descend only when the depth is right and there are children for this element.
+ if ( ( 0 == $max_depth || $max_depth > $depth + 1 ) && isset( $children_elements[ $id ] ) ) {
+
+ foreach ( $children_elements[ $id ] as $child ) {
+
+ if ( ! isset( $newlevel ) ) {
+ $newlevel = true;
+ // Start the child delimiter.
+ $this->start_lvl( $output, $depth, ...array_values( $args ) );
+ }
+ $this->display_element( $child, $children_elements, $max_depth, $depth + 1, $args, $output );
+ }
+ unset( $children_elements[ $id ] );
+ }
+
+ if ( isset( $newlevel ) && $newlevel ) {
+ // End the child delimiter.
+ $this->end_lvl( $output, $depth, ...array_values( $args ) );
+ }
+
+ // End this element.
+ $this->end_el( $output, $element, $depth, ...array_values( $args ) );
+ }
+
+ /**
+ * Displays array of elements hierarchically.
+ *
+ * Does not assume any existing order of elements.
+ *
+ * $max_depth = -1 means flatly display every element.
+ * $max_depth = 0 means display all levels.
+ * $max_depth > 0 specifies the number of display levels.
+ *
+ * @since 2.1.0
+ * @since 5.3.0 Formalized the existing `...$args` parameter by adding it
+ * to the function signature.
+ *
+ * @param array $elements An array of elements.
+ * @param int $max_depth The maximum hierarchical depth.
+ * @param mixed ...$args Optional additional arguments.
+ * @return string The hierarchical item output.
+ */
+ public function walk( $elements, $max_depth, ...$args ) {
+ $output = '';
+
+ // Invalid parameter or nothing to walk.
+ if ( $max_depth < -1 || empty( $elements ) ) {
+ return $output;
+ }
+
+ $parent_field = $this->db_fields['parent'];
+
+ // Flat display.
+ if ( -1 == $max_depth ) {
+ $empty_array = array();
+ foreach ( $elements as $e ) {
+ $this->display_element( $e, $empty_array, 1, 0, $args, $output );
+ }
+ return $output;
+ }
+
+ /*
+ * Need to display in hierarchical order.
+ * Separate elements into two buckets: top level and children elements.
+ * Children_elements is two dimensional array. Example:
+ * Children_elements[10][] contains all sub-elements whose parent is 10.
+ */
+ $top_level_elements = array();
+ $children_elements = array();
+ foreach ( $elements as $e ) {
+ if ( empty( $e->$parent_field ) ) {
+ $top_level_elements[] = $e;
+ } else {
+ $children_elements[ $e->$parent_field ][] = $e;
+ }
+ }
+
+ /*
+ * When none of the elements is top level.
+ * Assume the first one must be root of the sub elements.
+ */
+ if ( empty( $top_level_elements ) ) {
+
+ $first = array_slice( $elements, 0, 1 );
+ $root = $first[0];
+
+ $top_level_elements = array();
+ $children_elements = array();
+ foreach ( $elements as $e ) {
+ if ( $root->$parent_field == $e->$parent_field ) {
+ $top_level_elements[] = $e;
+ } else {
+ $children_elements[ $e->$parent_field ][] = $e;
+ }
+ }
+ }
+
+ foreach ( $top_level_elements as $e ) {
+ $this->display_element( $e, $children_elements, $max_depth, 0, $args, $output );
+ }
+
+ /*
+ * If we are displaying all levels, and remaining children_elements is not empty,
+ * then we got orphans, which should be displayed regardless.
+ */
+ if ( ( 0 == $max_depth ) && count( $children_elements ) > 0 ) {
+ $empty_array = array();
+ foreach ( $children_elements as $orphans ) {
+ foreach ( $orphans as $op ) {
+ $this->display_element( $op, $empty_array, 1, 0, $args, $output );
+ }
+ }
+ }
+
+ return $output;
+ }
+
+ /**
+ * Produces a page of nested elements.
+ *
+ * Given an array of hierarchical elements, the maximum depth, a specific page number,
+ * and number of elements per page, this function first determines all top level root elements
+ * belonging to that page, then lists them and all of their children in hierarchical order.
+ *
+ * $max_depth = 0 means display all levels.
+ * $max_depth > 0 specifies the number of display levels.
+ *
+ * @since 2.7.0
+ * @since 5.3.0 Formalized the existing `...$args` parameter by adding it
+ * to the function signature.
+ *
+ * @param array $elements An array of elements.
+ * @param int $max_depth The maximum hierarchical depth.
+ * @param int $page_num The specific page number, beginning with 1.
+ * @param int $per_page Number of elements per page.
+ * @param mixed ...$args Optional additional arguments.
+ * @return string XHTML of the specified page of elements.
+ */
+ public function paged_walk( $elements, $max_depth, $page_num, $per_page, ...$args ) {
+ if ( empty( $elements ) || $max_depth < -1 ) {
+ return '';
+ }
+
+ $output = '';
+
+ $parent_field = $this->db_fields['parent'];
+
+ $count = -1;
+ if ( -1 == $max_depth ) {
+ $total_top = count( $elements );
+ }
+ if ( $page_num < 1 || $per_page < 0 ) {
+ // No paging.
+ $paging = false;
+ $start = 0;
+ if ( -1 == $max_depth ) {
+ $end = $total_top;
+ }
+ $this->max_pages = 1;
+ } else {
+ $paging = true;
+ $start = ( (int) $page_num - 1 ) * (int) $per_page;
+ $end = $start + $per_page;
+ if ( -1 == $max_depth ) {
+ $this->max_pages = ceil( $total_top / $per_page );
+ }
+ }
+
+ // Flat display.
+ if ( -1 == $max_depth ) {
+ if ( ! empty( $args[0]['reverse_top_level'] ) ) {
+ $elements = array_reverse( $elements );
+ $oldstart = $start;
+ $start = $total_top - $end;
+ $end = $total_top - $oldstart;
+ }
+
+ $empty_array = array();
+ foreach ( $elements as $e ) {
+ ++$count;
+ if ( $count < $start ) {
+ continue;
+ }
+ if ( $count >= $end ) {
+ break;
+ }
+ $this->display_element( $e, $empty_array, 1, 0, $args, $output );
+ }
+ return $output;
+ }
+
+ /*
+ * Separate elements into two buckets: top level and children elements.
+ * Children_elements is two dimensional array, e.g.
+ * $children_elements[10][] contains all sub-elements whose parent is 10.
+ */
+ $top_level_elements = array();
+ $children_elements = array();
+ foreach ( $elements as $e ) {
+ if ( empty( $e->$parent_field ) ) {
+ $top_level_elements[] = $e;
+ } else {
+ $children_elements[ $e->$parent_field ][] = $e;
+ }
+ }
+
+ $total_top = count( $top_level_elements );
+ if ( $paging ) {
+ $this->max_pages = ceil( $total_top / $per_page );
+ } else {
+ $end = $total_top;
+ }
+
+ if ( ! empty( $args[0]['reverse_top_level'] ) ) {
+ $top_level_elements = array_reverse( $top_level_elements );
+ $oldstart = $start;
+ $start = $total_top - $end;
+ $end = $total_top - $oldstart;
+ }
+ if ( ! empty( $args[0]['reverse_children'] ) ) {
+ foreach ( $children_elements as $parent => $children ) {
+ $children_elements[ $parent ] = array_reverse( $children );
+ }
+ }
+
+ foreach ( $top_level_elements as $e ) {
+ ++$count;
+
+ // For the last page, need to unset earlier children in order to keep track of orphans.
+ if ( $end >= $total_top && $count < $start ) {
+ $this->unset_children( $e, $children_elements );
+ }
+
+ if ( $count < $start ) {
+ continue;
+ }
+
+ if ( $count >= $end ) {
+ break;
+ }
+
+ $this->display_element( $e, $children_elements, $max_depth, 0, $args, $output );
+ }
+
+ if ( $end >= $total_top && count( $children_elements ) > 0 ) {
+ $empty_array = array();
+ foreach ( $children_elements as $orphans ) {
+ foreach ( $orphans as $op ) {
+ $this->display_element( $op, $empty_array, 1, 0, $args, $output );
+ }
+ }
+ }
+
+ return $output;
+ }
+
+ /**
+ * Calculates the total number of root elements.
+ *
+ * @since 2.7.0
+ *
+ * @param array $elements Elements to list.
+ * @return int Number of root elements.
+ */
+ public function get_number_of_root_elements( $elements ) {
+ $num = 0;
+ $parent_field = $this->db_fields['parent'];
+
+ foreach ( $elements as $e ) {
+ if ( empty( $e->$parent_field ) ) {
+ ++$num;
+ }
+ }
+ return $num;
+ }
+
+ /**
+ * Unsets all the children for a given top level element.
+ *
+ * @since 2.7.0
+ *
+ * @param object $element The top level element.
+ * @param array $children_elements The children elements.
+ */
+ public function unset_children( $element, &$children_elements ) {
+ if ( ! $element || ! $children_elements ) {
+ return;
+ }
+
+ $id_field = $this->db_fields['id'];
+ $id = $element->$id_field;
+
+ if ( ! empty( $children_elements[ $id ] ) && is_array( $children_elements[ $id ] ) ) {
+ foreach ( (array) $children_elements[ $id ] as $child ) {
+ $this->unset_children( $child, $children_elements );
+ }
+ }
+
+ unset( $children_elements[ $id ] );
+ }
+}