lru-impl.php

<?php

declare(strict_types=1);

namespace App\Cache;

/**
 * @template TCacheItem
 * @template-implements LRUCacheInterface<TCacheItem>
 */
final class LRUCache implements LRUCacheInterface
{
    /**
     * @var array<string, TCacheItem>
     */
    private array $items = [];
    private int $size;
    
    public function __construct(int $size)
    {
        if ($size <= 0) {
            throw new InvalidArgumentException('Cache size must be greater than 0');
        }
        
        $this->size = $size;
    }
    
    /** {@inheritDoc} */
    public function add(string $key, $item): void
    {
        // already on the list
        if (isset($this->items[$key])) {
            $this->items[$key] = $item;
            $this->moveToFront($key);
            
            return;
        }
        
        $this->items[$key] = $item;
        
        // there's still room for new items
        if (\count($this->items) <= $this->size) {
            return;
        }
        
        // no room for new items
        // remove the least used element
        \reset($this->items);
        unset($this->items[\key($this->items)]);
    }
    
    /** {@inheritDoc} */
    public function get(string $key)
    {        
        if (false === isset($this->items[$key])) {
            return null;
        }
        
        $this->moveToFront($key);
        
        return $this->items[$key];
    }
    
    private function moveToFront(string $key): void
    {
        $cachedItem = $this->items[$key];
        
        unset($this->items[$key]);
        
        $this->items[$key] = $cachedItem;
    }
}