--- /dev/null
+<?php
+/**
+ * A class for displaying various tree-like structures.
+ *
+ * Extend the Walker class to use it, see examples at the 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. Also, the methods are
+ * not strictly abstract in that the parameter definition needs to be followed.
+ * The child classes can have additional parameters.
+ *
+ * @package WordPress
+ * @since 2.1.0
+ * @abstract
+ */
+class Walker {
+ /**
+ * What the class handles.
+ *
+ * @since 2.1.0
+ * @var string
+ * @access public
+ */
+ var $tree_type;
+
+ /**
+ * DB fields to use.
+ *
+ * @since 2.1.0
+ * @var array
+ * @access protected
+ */
+ var $db_fields;
+
+ /**
+ * Max number of pages walked by the paged walker
+ *
+ * @since 2.7.0
+ * @var int
+ * @access protected
+ */
+ var $max_pages = 1;
+
+ /**
+ * Starts the list before the elements are added.
+ *
+ * Additional parameters are used in child classes. 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 $output Passed by reference. Used to append additional content.
+ */
+ function start_lvl(&$output) {}
+
+ /**
+ * Ends the list of after the elements are added.
+ *
+ * Additional parameters are used in child classes. 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 $output Passed by reference. Used to append additional content.
+ */
+ function end_lvl(&$output) {}
+
+ /**
+ * Start the element output.
+ *
+ * Additional parameters are used in child classes. The args parameter holds
+ * additional values that may be used with the child class methods. Includes
+ * the element output also.
+ *
+ * @since 2.1.0
+ * @abstract
+ *
+ * @param string $output Passed by reference. Used to append additional content.
+ */
+ function start_el(&$output) {}
+
+ /**
+ * Ends the element output, if needed.
+ *
+ * Additional parameters are used in child classes. The args parameter holds
+ * additional values that may be used with the child class methods.
+ *
+ * @since 2.1.0
+ * @abstract
+ *
+ * @param string $output Passed by reference. Used to append additional content.
+ */
+ function end_el(&$output) {}
+
+ /**
+ * Traverse 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 shouldn't 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.
+ * @param int $max_depth Max depth to traverse.
+ * @param int $depth Depth of current element.
+ * @param array $args
+ * @param string $output Passed by reference. Used to append additional content.
+ * @return null Null on failure with no changes to parameters.
+ */
+ function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ) {
+
+ if ( !$element )
+ return;
+
+ $id_field = $this->db_fields['id'];
+
+ //display this element
+ if ( is_array( $args[0] ) )
+ $args[0]['has_children'] = ! empty( $children_elements[$element->$id_field] );
+ $cb_args = array_merge( array(&$output, $element, $depth), $args);
+ call_user_func_array(array(&$this, 'start_el'), $cb_args);
+
+ $id = $element->$id_field;
+
+ // descend only when the depth is right and there are childrens for this element
+ if ( ($max_depth == 0 || $max_depth > $depth+1 ) && isset( $children_elements[$id]) ) {
+
+ foreach( $children_elements[ $id ] as $child ){
+
+ if ( !isset($newlevel) ) {
+ $newlevel = true;
+ //start the child delimiter
+ $cb_args = array_merge( array(&$output, $depth), $args);
+ call_user_func_array(array(&$this, 'start_lvl'), $cb_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
+ $cb_args = array_merge( array(&$output, $depth), $args);
+ call_user_func_array(array(&$this, 'end_lvl'), $cb_args);
+ }
+
+ //end this element
+ $cb_args = array_merge( array(&$output, $element, $depth), $args);
+ call_user_func_array(array(&$this, 'end_el'), $cb_args);
+ }
+
+ /**
+ * Display array of elements hierarchically.
+ *
+ * It is a generic function which 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
+ *
+ * @param array $elements
+ * @param int $max_depth
+ * @return string
+ */
+ function walk( $elements, $max_depth) {
+
+ $args = array_slice(func_get_args(), 2);
+ $output = '';
+
+ if ($max_depth < -1) //invalid parameter
+ return $output;
+
+ if (empty($elements)) //nothing to walk
+ return $output;
+
+ $id_field = $this->db_fields['id'];
+ $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, eg.
+ * children_elements[10][] contains all sub-elements whose parent is 10.
+ */
+ $top_level_elements = array();
+ $children_elements = array();
+ foreach ( $elements as $e) {
+ if ( 0 == $e->$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 ( ( $max_depth == 0 ) && 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;
+ }
+
+ /**
+ * paged_walk() - produce 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.
+ *
+ * @package WordPress
+ * @since 2.7
+ * @param int $max_depth = 0 means display all levels; $max_depth > 0 specifies the number of display levels.
+ * @param int $page_num the specific page number, beginning with 1.
+ * @return XHTML of the specified page of elements
+ */
+ function paged_walk( $elements, $max_depth, $page_num, $per_page ) {
+
+ /* sanity check */
+ if ( empty($elements) || $max_depth < -1 )
+ return '';
+
+ $args = array_slice( func_get_args(), 4 );
+ $output = '';
+
+ $id_field = $this->db_fields['id'];
+ $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, eg.
+ * children_elements[10][] contains all sub-elements whose parent is 10.
+ */
+ $top_level_elements = array();
+ $children_elements = array();
+ foreach ( $elements as $e) {
+ if ( 0 == $e->$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;
+ }
+
+ function get_number_of_root_elements( $elements ){
+
+ $num = 0;
+ $parent_field = $this->db_fields['parent'];
+
+ foreach ( $elements as $e) {
+ if ( 0 == $e->$parent_field )
+ $num++;
+ }
+ return $num;
+ }
+
+ // unset all the children for a given top level element
+ function unset_children( $e, &$children_elements ){
+
+ if ( !$e || !$children_elements )
+ return;
+
+ $id_field = $this->db_fields['id'];
+ $id = $e->$id_field;
+
+ if ( !empty($children_elements[$id]) && is_array($children_elements[$id]) )
+ foreach ( (array) $children_elements[$id] as $child )
+ $this->unset_children( $child, $children_elements );
+
+ if ( isset($children_elements[$id]) )
+ unset( $children_elements[$id] );
+
+ }
+}
+
+?>
\ No newline at end of file
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