Walker::paged_walk( array $elements, int $max_depth, int $page_num, int $per_page, mixed $args ): string

Source

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;
}

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