Worked Example

Validate the request payload.

final class ValidatePromotionInput implements FlowStepHandler
{
    public function handle(FlowContext $context): FlowStepResult
    {
        $input = $context->input();

        if (($input['discount_pct'] ?? 0) <= 0) {
            return FlowStepResult::failure('discount_pct must be positive');
        }

        return FlowStepResult::success();
    }
}

Simulate impact.

final class SimulatePromotionImpact implements FlowStepHandler
{
    public function handle(FlowContext $context): FlowStepResult
    {
        return FlowStepResult::success(
            output: ['eligible_customers' => 1200],
            businessImpact: ['margin_risk_eur' => 4200],
        );
    }
}

Persist and compensate.

Flow::define('promotion.create')
    ->withInput(['brand', 'discount_pct', 'starts_at', 'ends_at'])
    ->step('validate', ValidatePromotionInput::class)
    ->step('simulate', SimulatePromotionImpact::class)
        ->withDryRun(true)
    ->step('persist', PersistPromotion::class)
        ->compensateWith(ReversePromotion::class)
    ->register();