steps

type NewStepFunc[T any, U any] func() (Step[T, U], error)

type Step[T any, U any] interface {
	// Start gets called multiple times for the same Step, once per incoming value,
	// since StepResult is also the list monad (ie., supports multiple values)
	Start(ctx context.Context, input T) (StepResult[U], error)
	AddPublishedTopic(publisher message.Publisher, topic string) error
}

type StepFactory[T any, U any] interface {
	NewStep() (Step[T, U], error)
}

type StepMetadata struct {
	StepID     uuid.UUID `json:"step_id"`
	Type       string    `json:"type"`
	InputType  string    `json:"input_type"`
	OutputType string    `json:"output_type"`

	Metadata map[string]interface{} `json:"meta"`
}

type StepResult[T any] interface {
	Return() []helpers.Result[T]
	GetChannel() <-chan helpers.Result[T]
	// Cancel can't fail
	Cancel()
	GetMetadata() *StepMetadata
}

type StepResultImpl[T any] struct {
	// contains filtered or unexported fields
}

type StepResultOption[T any] func(*StepResultImpl[T])