Uploading files within a foreach loop

Question

How can I access and upload an image file within a foreach loop, given that I'm currently unable to access the file even though the array from the POST request is working?

function Products($data)
{
    foreach ($data as $row) {
        $product_id = $row['product_id'];

        $file_name = $_FILES['file']['name'];
        $file_size = $_FILES['file']['size'];
        $file_tmp = $_FILES['file']['tmp_name'];
        $file_type = $_FILES['file']['type'];
        $file_ext = pathinfo($file_name, PATHINFO_EXTENSION);
        $expensions = array("jpeg", "jpg", "png", "JPEG", "JPG", "PNG");

        $fileName = date('Ymdhis').".".$file_ext;

        // Insert Sample Function
        InsertFunction($fileName, $product_id);
    }
}

$array = array(
    array('product_id' => 1, 'file' => /*$_FILES 1*/),
    array('product_id' => 2, 'file' => /*$_FILES 2*/),
);

echo json_encode(Products($array));

I tried to pass the file variable on the $_FILES but it was not working.