<?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;
}

$max_depth = (int) $max_depth;
$depth = (int) $depth;

$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 = '';

$max_depth = (int) $max_depth;

// 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 ) {
$output = '';

$max_depth = (int) $max_depth;

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 = (int) 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 = (int) 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 ] );
}
}