158 lines
4.3 KiB
PHP
158 lines
4.3 KiB
PHP
<?php
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/**
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* A zipper is a purely-functional data structure which contains
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* a focus that can be efficiently manipulated. It is known as
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* a "one-hole context". This mutable variant implements a zipper
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* for a list as a pair of two arrays, laid out as follows:
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*
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* Base list: 1 2 3 4 [ ] 6 7 8 9
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* Front list: 1 2 3 4
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* Back list: 9 8 7 6
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*
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* User is expected to keep track of the "current element" and properly
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* fill it back in as necessary. (ToDo: Maybe it's more user friendly
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* to implicitly track the current element?)
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*
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* Nota bene: the current class gets confused if you try to store NULLs
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* in the list.
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*/
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class HTMLPurifier_Zipper
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{
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public $front, $back;
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public function __construct($front, $back) {
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$this->front = $front;
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$this->back = $back;
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}
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/**
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* Creates a zipper from an array, with a hole in the
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* 0-index position.
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* @param Array to zipper-ify.
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* @return Tuple of zipper and element of first position.
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*/
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static public function fromArray($array) {
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$z = new self(array(), array_reverse($array));
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$t = $z->delete(); // delete the "dummy hole"
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return array($z, $t);
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}
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/**
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* Convert zipper back into a normal array, optionally filling in
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* the hole with a value. (Usually you should supply a $t, unless you
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* are at the end of the array.)
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*/
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public function toArray($t = NULL) {
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$a = $this->front;
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if ($t !== NULL) $a[] = $t;
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for ($i = count($this->back)-1; $i >= 0; $i--) {
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$a[] = $this->back[$i];
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}
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return $a;
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}
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/**
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* Move hole to the next element.
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* @param $t Element to fill hole with
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* @return Original contents of new hole.
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*/
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public function next($t) {
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if ($t !== NULL) array_push($this->front, $t);
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return empty($this->back) ? NULL : array_pop($this->back);
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}
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/**
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* Iterated hole advancement.
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* @param $t Element to fill hole with
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* @param $i How many forward to advance hole
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* @return Original contents of new hole, i away
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*/
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public function advance($t, $n) {
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for ($i = 0; $i < $n; $i++) {
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$t = $this->next($t);
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}
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return $t;
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}
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/**
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* Move hole to the previous element
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* @param $t Element to fill hole with
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* @return Original contents of new hole.
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*/
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public function prev($t) {
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if ($t !== NULL) array_push($this->back, $t);
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return empty($this->front) ? NULL : array_pop($this->front);
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}
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/**
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* Delete contents of current hole, shifting hole to
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* next element.
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* @return Original contents of new hole.
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*/
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public function delete() {
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return empty($this->back) ? NULL : array_pop($this->back);
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}
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/**
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* Returns true if we are at the end of the list.
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* @return bool
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*/
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public function done() {
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return empty($this->back);
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}
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/**
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* Insert element before hole.
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* @param Element to insert
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*/
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public function insertBefore($t) {
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if ($t !== NULL) array_push($this->front, $t);
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}
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/**
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* Insert element after hole.
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* @param Element to insert
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*/
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public function insertAfter($t) {
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if ($t !== NULL) array_push($this->back, $t);
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}
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/**
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* Splice in multiple elements at hole. Functional specification
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* in terms of array_splice:
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*
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* $arr1 = $arr;
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* $old1 = array_splice($arr1, $i, $delete, $replacement);
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*
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* list($z, $t) = HTMLPurifier_Zipper::fromArray($arr);
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* $t = $z->advance($t, $i);
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* list($old2, $t) = $z->splice($t, $delete, $replacement);
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* $arr2 = $z->toArray($t);
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*
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* assert($old1 === $old2);
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* assert($arr1 === $arr2);
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*
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* NB: the absolute index location after this operation is
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* *unchanged!*
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*
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* @param Current contents of hole.
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*/
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public function splice($t, $delete, $replacement) {
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// delete
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$old = array();
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$r = $t;
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for ($i = $delete; $i > 0; $i--) {
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$old[] = $r;
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$r = $this->delete();
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}
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// insert
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for ($i = count($replacement)-1; $i >= 0; $i--) {
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$this->insertAfter($r);
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$r = $replacement[$i];
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}
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return array($old, $r);
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}
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}
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