public function displayDepth(array $array)
    {
        $output = '';
        foreach ([
            'asks',
            'bids',
        ] as $type) {
            $entries = $array[$type];
            if ($type === 'asks') {
                $entries = array_reverse($entries);
            }

            $output .= "{$type}:" . PHP_EOL;
            foreach ($entries as $price => $quantity) {
                $total = number_format($price * $quantity, 8, '.', '');
                $quantity = str_pad(str_pad(number_format(rtrim($quantity, '.0')), 10, ' ', STR_PAD_LEFT), 15);
                $output .= "{$price} {$quantity} {$total}" . PHP_EOL;
            }
            // echo str_repeat('-', 32).PHP_EOL;
        }
        return $output;
    }