adding

type Planet struct {
	Name        string `json:"name" valid:"length(2|128)"`
	Climate     string `json:"climate" valid:"length(2|128)"`
	Terrain     string `json:"terrain" valid:"length(2|128)"`
	Appearances int    `json:"appearances" valid:"optional"`
}

type PlanetsClient interface {
	GetPlanetAppearances(context.Context, string) (int, error)
}

type Repository interface {
	// AddPlanet saves a given planet to the repository.
	AddPlanet(context.Context, Planet) (string, error)
}

type Service interface {
	// AddPlanet invokes the operations needed to save a planet
	AddPlanet(context.Context, Planet) (string, error)
}

type ValidationError struct {
	Err    error
	Fields map[string]string
}