MapCacheLRU.php

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<?php
class MapCacheLRU {
    protected $cache = array(); // (key => value)

    protected $maxCacheKeys; // integer; max entries

    public function __construct( $maxKeys ) {
        if ( !is_int( $maxKeys ) || $maxKeys < 1 ) {
            throw new MWException( __METHOD__ . " must be given an integer and >= 1" );
        }
        $this->maxCacheKeys = $maxKeys;
    }

    public function set( $key, $value ) {
        if ( array_key_exists( $key, $this->cache ) ) {
            $this->ping( $key ); // push to top
        } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
            reset( $this->cache );
            $evictKey = key( $this->cache );
            unset( $this->cache[$evictKey] );
        }
        $this->cache[$key] = $value;
    }

    public function has( $key ) {
        return array_key_exists( $key, $this->cache );
    }

    public function get( $key ) {
        if ( array_key_exists( $key, $this->cache ) ) {
            $this->ping( $key ); // push to top
            return $this->cache[$key];
        } else {
            return null;
        }
    }

    public function clear( $keys = null ) {
        if ( $keys === null ) {
            $this->cache = array();
        } else {
            foreach ( (array)$keys as $key ) {
                unset( $this->cache[$key] );
            }
        }
    }

    protected function ping( $key ) {
        $item = $this->cache[$key];
        unset( $this->cache[$key] );
        $this->cache[$key] = $item;
    }
}