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+<?php
+
+/**
+ * Least Recently Used Cache
+ *
+ * A fixed sized cache that removes the element used last when it reaches its
+ * size limit.
+ *
+ * Based on https://github.com/cash/LRUCache
+ *
+ * @access private
+ *
+ * @package Elgg.Core
+ * @subpackage Cache
+ */
+class ElggLRUCache implements ArrayAccess {
+ /** @var int */
+ protected $maximumSize;
+
+ /**
+ * The front of the array contains the LRU element
+ *
+ * @var array
+ */
+ protected $data = array();
+
+ /**
+ * Create a LRU Cache
+ *
+ * @param int $size The size of the cache
+ * @throws InvalidArgumentException
+ */
+ public function __construct($size) {
+ if (!is_int($size) || $size <= 0) {
+ throw new InvalidArgumentException();
+ }
+ $this->maximumSize = $size;
+ }
+
+ /**
+ * Get the value cached with this key
+ *
+ * @param int|string $key The key. Strings that are ints are cast to ints.
+ * @param mixed $default The value to be returned if key not found. (Optional)
+ * @return mixed
+ */
+ public function get($key, $default = null) {
+ if (isset($this->data[$key])) {
+ $this->recordAccess($key);
+ return $this->data[$key];
+ } else {
+ return $default;
+ }
+ }
+
+ /**
+ * Add something to the cache
+ *
+ * @param int|string $key The key. Strings that are ints are cast to ints.
+ * @param mixed $value The value to cache
+ * @return void
+ */
+ public function set($key, $value) {
+ if (isset($this->data[$key])) {
+ $this->data[$key] = $value;
+ $this->recordAccess($key);
+ } else {
+ $this->data[$key] = $value;
+ if ($this->size() > $this->maximumSize) {
+ // remove least recently used element (front of array)
+ reset($this->data);
+ unset($this->data[key($this->data)]);
+ }
+ }
+ }
+
+ /**
+ * Get the number of elements in the cache
+ *
+ * @return int
+ */
+ public function size() {
+ return count($this->data);
+ }
+
+ /**
+ * Does the cache contain an element with this key
+ *
+ * @param int|string $key The key
+ * @return boolean
+ */
+ public function containsKey($key) {
+ return isset($this->data[$key]);
+ }
+
+ /**
+ * Remove the element with this key.
+ *
+ * @param int|string $key The key
+ * @return mixed Value or null if not set
+ */
+ public function remove($key) {
+ if (isset($this->data[$key])) {
+ $value = $this->data[$key];
+ unset($this->data[$key]);
+ return $value;
+ } else {
+ return null;
+ }
+ }
+
+ /**
+ * Clear the cache
+ *
+ * @return void
+ */
+ public function clear() {
+ $this->data = array();
+ }
+
+ /**
+ * Moves the element from current position to end of array
+ *
+ * @param int|string $key The key
+ * @return void
+ */
+ protected function recordAccess($key) {
+ $value = $this->data[$key];
+ unset($this->data[$key]);
+ $this->data[$key] = $value;
+ }
+
+ /**
+ * Assigns a value for the specified key
+ *
+ * @see ArrayAccess::offsetSet()
+ *
+ * @param int|string $key The key to assign the value to.
+ * @param mixed $value The value to set.
+ * @return void
+ */
+ public function offsetSet($key, $value) {
+ $this->set($key, $value);
+ }
+
+ /**
+ * Get the value for specified key
+ *
+ * @see ArrayAccess::offsetGet()
+ *
+ * @param int|string $key The key to retrieve.
+ * @return mixed
+ */
+ public function offsetGet($key) {
+ return $this->get($key);
+ }
+
+ /**
+ * Unsets a key.
+ *
+ * @see ArrayAccess::offsetUnset()
+ *
+ * @param int|string $key The key to unset.
+ * @return void
+ */
+ public function offsetUnset($key) {
+ $this->remove($key);
+ }
+
+ /**
+ * Does key exist?
+ *
+ * @see ArrayAccess::offsetExists()
+ *
+ * @param int|string $key A key to check for.
+ * @return boolean
+ */
+ public function offsetExists($key) {
+ return $this->containsKey($key);
+ }
+}