Simple bin packing

Bin.php

<?php

class Bin
{
	private $capacity;
	private $content;

	/**
	 * @param integer $capacity
	 * @param array $content
	 */
	public function __construct($capacity, array $content = [])
	{
		$this->capacity = $capacity;
		$this->content = $content;
	}


	/**
	 * @param integer $item
	 *
	 * @return bool
	 */
	public function add($item)
	{
		if($this->addable($item))
		{
			array_push($this->content, $item);
			return true;
		}

		return false;
	}


	/**
	 * @param integer $item
	 *
	 * @return bool
	 */
	public function addable($item)
	{
		return array_sum($this->content) + $item <= $this->capacity && $item > 0;
	}
}

BinPool.php

<?php

/**
 * Class BinPool
 * simple implementation of bin packing
 *
 * Given a pool of item sizes/weights, a bin capacity and a quantity of bins, can the pool be fully allocated
 * to the bins and have room to add another item
 */
class BinPool
{
	/**
	 * @var integer
	 */
	private $bin_capacity;

	/**
	 * @var integer
	 */
	private $bin_quantity;

	/**
	 * @var array
	 */
	private $pool;

	/**
	 * @var Bin[]
	 */
	private $bins = [];

	/**
	 * @param integer $bin_capacity     the capacity of each bin
	 * @param integer $bin_quantity     how many bins
	 * @param array $pool               an array of numeric sizes/weights
	 */
	public function __construct($bin_capacity, $bin_quantity, array $pool = [])
	{
		$this->bin_capacity = $bin_capacity;
		$this->bin_quantity = $bin_quantity;
		$this->pool = $pool;

		$this->bins = array_map(function() use ($bin_capacity, $bin_quantity) {
			return new Bin($bin_capacity);}, array_pad([], $bin_quantity, null));
	}

	/**
	 * @param $item
	 *
	 * @return bool
	 */
	public function addable($item)
	{
		$this->validatePool();
		$this->buildBins();

		foreach($this->bins as $bin)
		{
			if($bin->addable($item))
			{
				return true;
			}
		}

		return false;
	}

	private function validatePool()
	{
		if (!empty($this->pool))
		{
			if (max($this->pool) > $this->bin_capacity)
			{
				throw new RuntimeException("An item in the pool exceeds the max size of {$this->bin_capacity}");
			}
		}
	}

	private function buildBins()
	{
		while(!empty($this->pool))
		{
			$item = array_pop($this->pool);

			foreach($this->bins as $bin)
			{
				if($bin->add($item))
				{
					break;
				}
			}
		}
	}
}

usage.php

<?php

// autolader, incudes, etc...

$pool = [1,1,1,2,2];
$bp = new BinPool(4, 2, $pool);
$bp->isAddable(1); //true

$pool = [1,1,2,2,2];
$bp = new BinPool(4, 2, $pool);
$bp->isAddable(1); //false