1 files changed, 157 insertions, 0 deletions
diff --git a/library/HTMLPurifier/Zipper.php b/library/HTMLPurifier/Zipper.php
new file mode 100644
index 000000000..6e21ea070
--- /dev/null
+++ b/library/HTMLPurifier/Zipper.php
@@ -0,0 +1,157 @@
+<?php
+
+/**
+ * A zipper is a purely-functional data structure which contains
+ * a focus that can be efficiently manipulated.  It is known as
+ * a "one-hole context".  This mutable variant implements a zipper
+ * for a list as a pair of two arrays, laid out as follows:
+ *
+ *      Base list: 1 2 3 4 [ ] 6 7 8 9
+ *      Front list: 1 2 3 4
+ *      Back list: 9 8 7 6
+ *
+ * User is expected to keep track of the "current element" and properly
+ * fill it back in as necessary.  (ToDo: Maybe it's more user friendly
+ * to implicitly track the current element?)
+ *
+ * Nota bene: the current class gets confused if you try to store NULLs
+ * in the list.
+ */
+
+class HTMLPurifier_Zipper
+{
+    public $front, $back;
+
+    public function __construct($front, $back) {
+        $this->front = $front;
+        $this->back = $back;
+    }
+
+    /**
+     * Creates a zipper from an array, with a hole in the
+     * 0-index position.
+     * @param Array to zipper-ify.
+     * @return Tuple of zipper and element of first position.
+     */
+    static public function fromArray($array) {
+        $z = new self(array(), array_reverse($array));
+        $t = $z->delete(); // delete the "dummy hole"
+        return array($z, $t);
+    }
+
+    /**
+     * Convert zipper back into a normal array, optionally filling in
+     * the hole with a value. (Usually you should supply a $t, unless you
+     * are at the end of the array.)
+     */
+    public function toArray($t = NULL) {
+        $a = $this->front;
+        if ($t !== NULL) $a[] = $t;
+        for ($i = count($this->back)-1; $i >= 0; $i--) {
+            $a[] = $this->back[$i];
+        }
+        return $a;
+    }
+
+    /**
+     * Move hole to the next element.
+     * @param $t Element to fill hole with
+     * @return Original contents of new hole.
+     */
+    public function next($t) {
+        if ($t !== NULL) array_push($this->front, $t);
+        return empty($this->back) ? NULL : array_pop($this->back);
+    }
+
+    /**
+     * Iterated hole advancement.
+     * @param $t Element to fill hole with
+     * @param $i How many forward to advance hole
+     * @return Original contents of new hole, i away
+     */
+    public function advance($t, $n) {
+        for ($i = 0; $i < $n; $i++) {
+            $t = $this->next($t);
+        }
+        return $t;
+    }
+
+    /**
+     * Move hole to the previous element
+     * @param $t Element to fill hole with
+     * @return Original contents of new hole.
+     */
+    public function prev($t) {
+        if ($t !== NULL) array_push($this->back, $t);
+        return empty($this->front) ? NULL : array_pop($this->front);
+    }
+
+    /**
+     * Delete contents of current hole, shifting hole to
+     * next element.
+     * @return Original contents of new hole.
+     */
+    public function delete() {
+        return empty($this->back) ? NULL : array_pop($this->back);
+    }
+
+    /**
+     * Returns true if we are at the end of the list.
+     * @return bool
+     */
+    public function done() {
+        return empty($this->back);
+    }
+
+    /**
+     * Insert element before hole.
+     * @param Element to insert
+     */
+    public function insertBefore($t) {
+        if ($t !== NULL) array_push($this->front, $t);
+    }
+
+    /**
+     * Insert element after hole.
+     * @param Element to insert
+     */
+    public function insertAfter($t) {
+        if ($t !== NULL) array_push($this->back, $t);
+    }
+
+    /**
+     * Splice in multiple elements at hole.  Functional specification
+     * in terms of array_splice:
+     *
+     *      $arr1 = $arr;
+     *      $old1 = array_splice($arr1, $i, $delete, $replacement);
+     *
+     *      list($z, $t) = HTMLPurifier_Zipper::fromArray($arr);
+     *      $t = $z->advance($t, $i);
+     *      list($old2, $t) = $z->splice($t, $delete, $replacement);
+     *      $arr2 = $z->toArray($t);
+     *
+     *      assert($old1 === $old2);
+     *      assert($arr1 === $arr2);
+     *
+     * NB: the absolute index location after this operation is
+     * *unchanged!*
+     *
+     * @param Current contents of hole.
+     */
+    public function splice($t, $delete, $replacement) {
+        // delete
+        $old = array();
+        $r = $t;
+        for ($i = $delete; $i > 0; $i--) {
+            $old[] = $r;
+            $r = $this->delete();
+        }
+        // insert
+        for ($i = count($replacement)-1; $i >= 0; $i--) {
+            $this->insertAfter($r);
+            $r = $replacement[$i];
+        }
+        return array($old, $r);
+    }
+}