LRUCache.php

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<?php

class Elgg_Cache_LRUCache implements ArrayAccess {
    protected $maximumSize;

    protected $data = array();

    public function __construct($size) {
        if (!is_int($size) || $size <= 0) {
            throw new InvalidArgumentException();
        }
        $this->maximumSize = $size;
    }

    public function get($key, $default = null) {
        if (isset($this->data[$key])) {
            $this->recordAccess($key);
            return $this->data[$key];
        } else {
            return $default;
        }
    }

    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)]);
            }
        }
    }

    public function size() {
        return count($this->data);
    }

    public function containsKey($key) {
        return isset($this->data[$key]);
    }

    public function remove($key) {
        if (isset($this->data[$key])) {
            $value = $this->data[$key];
            unset($this->data[$key]);
            return $value;
        } else {
            return null;
        }
    }

    public function clear() {
        $this->data = array();
    }

    protected function recordAccess($key) {
        $value = $this->data[$key];
        unset($this->data[$key]);
        $this->data[$key] = $value;
    }

    public function offsetSet($key, $value) {
        $this->set($key, $value);
    }

    public function offsetGet($key) {
        return $this->get($key);
    }

    public function offsetUnset($key) {
        $this->remove($key);
    }

    public function offsetExists($key) {
        return $this->containsKey($key);
    }
}