var (
    // ErrBusy is returned by Start while the Lamp is on.
    ErrBusy = errors.New("machine: busy")
    // ErrOff is returned by Stop while the Lamp is off.
    ErrOff = errors.New("machine: off")
)

// NewLamp returns a Lamp. It returns a *docgen.ConfigError for a Tries
// above MaxTries.
func NewLamp(cfg Config) (*Lamp, error) {
    if cfg.Tries > MaxTries {
        return nil, &docgen.ConfigError{Field: "Tries"}
    }
    l := &Lamp{wait: cfg.Wait, tries: cfg.Tries}
    if l.wait == 0 {
        l.wait = DefaultWait
    }
    if cfg.Tries == 0 {
        l.tries = 1
    }
    return l, nil
}

// Start turns the Lamp on. It returns ErrBusy while the Lamp is on.
func (l *Lamp) Start(now time.Duration) error {
    if l.state == LampOn {
        return ErrBusy
    }
    if l.state == LampOff {
        l.state, l.until = LampOn, now+l.wait
    }
    return nil
}

// Stop turns the Lamp off. It returns ErrOff while the Lamp is off.
func (l *Lamp) Stop() error {
    if l.state != LampOn {
        return ErrOff
    }
    l.off()
    return nil
}

// Package docgen is the fixture root package of the docgen tests.
package docgen

// ConfigError is the error of a constructor for a field with a value out
// of range.
type ConfigError struct{ Field string }

func (e *ConfigError) Error() string { return "bad " + e.Field }