<?php
//Created by Nurcahyo al Hidayah <2light.hidayah@gmail.com>
// Free to use,,

function hitung_fifo(&$beli, &$query){
$return = 0;
$txt='';
foreach ($query as $key => $value){
		$jbeli=0;
		if ($query[$key]['stock'] !== 0){

				if ($query[$key]['stock'] >= $beli){  /// kalo stoknya > dari jumlah beli, maka beli=$beli

					$query[$key]['stock']-=$beli;
					$return += $beli * $query[$key]['h'];
					$jbeli=$beli;
					$harga=$query[$key]['h'];
					$pembelian=$beli * $query[$key]['h'];


				}else{ // kalo stoknya < dari jumlah beli, maka beli=$beli-stok yang ada
					$return+=$query[$key]['stock'] * $query[$key]['h'];
					$pembelian=$query[$key]['stock'] * $query[$key]['h'];
					$jbeli=$beli;
					$harga=$query[$key]['h'];

					$beli = $beli - $query[$key]['stock'];
					$query[$key]['stock'] = 0;
				}
	     }
		$txt.=$jbeli-$beli.'*'.$harga.'='.$pembelian.'<br>';
		$pembelian=0;
	}
return $txt.' <br>TOtal : '.$return;
}




$query = array(
			array('id' => 1, 'code' => 'a', 'stock' => 8, 'h' => 100),
		    array('id' => 2, 'code' => 'a', 'stock' => 4, 'h' => 110),
		    array('id' => 3, 'code' => 'a', 'stock' => 15, 'h' => 120));
$beli = 10;
$code = 'a';
$bayar = hitung_fifo($beli, $query);
echo $bayar;
echo '<br><br>';
print_r($query);



=========================
hasilnya:
8*100=800
0*110=220
0*120=240

TOtal : 1260

Array ( [0] => Array ( [id] => 1 [code] => a [stock] => 0 [h] => 100 ) [1] => Array ( [id] => 2 [code] => a [stock] => 2 [h] => 110 ) [2] => Array ( [id] => 3 [code] => a [stock] => 13 [h] => 120 ) )