class SandboxSimulation
{
    const GET_CHECKOUT_SESSION_SIMCODE = 'WCEXAAPGetCheckoutSessionSimCode';
    const UPDATE_CHECKOUT_SESSION_SIMCODE = 'WCEXAAPUpdateCheckoutSessionSimCode';
    const CREATE_CHARGE_SIMCODE = 'WCEXAAPCreateChargeSimCode';
    const CAPTURE_CHARGE_SIMCODE = 'WCEXAAPCaptureChargeSimCode';
    const CREATE_REFUND_SIMCODE = 'WCEXAAPCreateRefundSimCode';

    /**
     * AmazonPay module object
     *
     * @var AmazonPay
     */
    private $module;

    /**
     * Sets `$module` member var with dependency injection.
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param AmazonPay $module
     * @return void
     */
    public function __construct(AmazonPay $module) {
        $this->module = $module;
    }

    /**
     * Appends sim code to `GetCheckoutSession` request headers if applicable
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param array|null $requestheaders Default: `null`
     * @return array|null
     */
    public function getCheckoutSessionSetSimCodeIfSandbox($requestheaders = null) {
        return $this->setSimCode($requestheaders, self::GET_CHECKOUT_SESSION_SIMCODE);
    }

    /**
     * Appends sim code to `UpdateCheckoutSession` request headers if applicable
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param array|null $requestheaders Default: `null`
     * @return array|null
     */
    public function updateCheckoutSessionSetSimCodeIfSandbox($requestheaders = null) {
        return $this->setSimCode($requestheaders, self::UPDATE_CHECKOUT_SESSION_SIMCODE);
    }

    /**
     * Appends sim code to `CreateCharge` request headers if applicable
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param array|null $requestheaders Default: `null`
     * @return array|null
     */
    public function createChargeSetSimCodeIfSandbox($requestheaders = null) {
        return $this->setSimCode($requestheaders, self::CREATE_CHARGE_SIMCODE);
    }

    /**
     * Appends sim code to `CaptureCharge` request headers if applicable
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param array|null $requestheaders Default: `null`
     * @return array|null
     */
    public function captureChargeSetSimCodeIfSandbox($requestheaders = null) {
        return $this->setSimCode($requestheaders, self::CAPTURE_CHARGE_SIMCODE);
    }

    /**
     * Appends sim code to `CreateRefund` request headers if applicable
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param array|null $requestheaders Default: `null`
     * @return array|null
     */
    public function createRefundSetSimCodeIfSandbox($requestheaders = null) {
        return $this->setSimCode($requestheaders, self::CREATE_REFUND_SIMCODE);
    }

    /**
     * Appends simulation code key value pair to `$requestheaders` if in sandbox mode
     * and the given `$_ENV` key is set.
     *
     * @author Evan D Shaw <evandanielshaw@gmail.com>
     * @param array|null $requestheaders Default: `null`
     * @param string     $envkey
     * @return array|null
     */
    private function setSimCode($requestheaders, $envkey) {
        if ($this->module->isSandboxMode() && isset($_ENV[$envkey])) {
            if ($requestheaders === null) {
                $requestheaders = [];
            }
            $requestheaders['x-amz-pay-simulation-code'] = $_ENV[$envkey];
        }

        return $requestheaders;
    }
}