adds LRU cache

diff --git a/engine/classes/ElggLRUCache.php b/engine/classes/ElggLRUCache.php
new file mode 100644 (file)
index 0000000..add78ec
--- /dev/null
+++ b/engine/classes/ElggLRUCache.php
@@ -0,0 +1,132 @@
+<?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 {
+       /** @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;
+               }
+       }
+
+       /**
+        * Put something in the cache
+        *
+        * @param int|string $key   The key. Strings that are ints are cast to ints.
+        * @param mixed      $value The value to cache
+        * @return void
+        */
+       public function put($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;
+       }
+}