// ProcessEvent executes the state function and stores
// the returned new state.
func (b *fsmBehavior) ProcessEvent(event cells.Event) error {
	switch event.Topic() {
	case cells.StatusTopic:
		status := FSMStatus{
			Done:  b.done,
			Error: b.err,
		}
		if err := event.Respond(status); err != nil {
			return err
		}
	default:
		if b.done {
			return nil
		}
		state, err := b.state(b.cell, event)
		if err != nil {
			b.done = true
			b.err = err
		} else if state == nil {
			b.done = true
		}
		b.state = state
	}
	return nil
}

// newEventData returns the passed event as event data to collect.
func newEventData(event cells.Event) EventData {
	data := EventData{
		Topic:   event.Topic(),
		Payload: event.Payload(),
	}
	return data
}

// Locked represents the locked state receiving coins.
func (m *lockMachine) Locked(ctx cells.Cell, event cells.Event) (behaviors.FSMState, error) {
	switch event.Topic() {
	case "cents?":
		return m.Locked, event.Respond(m.cents)
	case "info?":
		info := fmt.Sprintf("state 'locked' with %d cents", m.cents)
		return m.Locked, event.Respond(info)
	case "coin!":
		cents := payloadCents(event)
		if cents < 1 {
			return nil, fmt.Errorf("do not insert buttons")
		}
		m.cents += cents
		if m.cents > 100 {
			m.cents -= 100
			return m.Unlocked, nil
		}
		return m.Locked, nil
	case "button-press!":
		if m.cents > 0 {
			ctx.Environment().EmitNewContext("restorer", "drop!", m.cents, event.Context())
			m.cents = 0
		}
		return m.Locked, nil
	case "screwdriver!":
		// Allow a screwdriver to bring the lock into an undefined state.
		return nil, nil
	}
	return m.Locked, fmt.Errorf("illegal topic in state 'locked': %s", event.Topic())
}

// cents retrieves the cents out of the payload of an event.
func payloadCents(event cells.Event) int {
	cents, ok := event.Payload().Get(cells.DefaultPayload)
	if !ok {
		return -1
	}
	return cents.(int)
}

// ProcessEvent calls a callback functions with the event data.
func (b *callbackBehavior) ProcessEvent(event cells.Event) error {
	for _, callbackFunc := range b.callbackFuncs {
		if err := callbackFunc(event.Topic(), event.Payload()); err != nil {
			return err
		}
	}
	return nil
}

// PrecessEvent emits a ticker event each time the
// defined duration elapsed.
func (b *tickerBehavior) ProcessEvent(event cells.Event) error {
	if event.Topic() == TickerTopic {
		pvs := cells.PayloadValues{
			TickerIDPayload:   b.cell.ID(),
			TickerTimePayload: time.Now(),
		}
		b.cell.EmitNew(TickerTopic, pvs)
	}
	return nil
}

func (b *restorerBehavior) ProcessEvent(event cells.Event) error {
	switch event.Topic() {
	case "grab!":
		cents := b.cents
		b.cents = 0
		return event.Respond(cents)
	case "drop!":
		b.cents += payloadCents(event)
	}
	return nil
}

// Configuration returns the configuration payload
// of the passed event or an empty configuration.
func Configuration(event cells.Event) etc.Etc {
	payload, ok := event.Payload().Get(ConfigurationPayload)
	if !ok {
		logger.Warningf("event does not contain configuration payload")
		cfg, _ := etc.ReadString("{etc}")
		return cfg
	}
	cfg, ok := payload.(etc.Etc)
	if !ok {
		logger.Warningf("configuration payload has illegal type")
		cfg, _ := etc.ReadString("{etc}")
		return cfg
	}
	return cfg
}

// ProcessEvent collects and re-emits events.
func (b *collectorBehavior) ProcessEvent(event cells.Event) error {
	switch event.Topic() {
	case cells.CollectedTopic:
		response := make([]EventData, len(b.collected))
		copy(response, b.collected)
		if err := event.Respond(response); err != nil {
			return err
		}
	case cells.ResetTopic:
		b.collected = []EventData{}
	default:
		b.collected = append(b.collected, newEventData(event))
		if len(b.collected) > b.max {
			b.collected = b.collected[1:]
		}
		b.cell.Emit(event)
	}
	return nil
}

func (b *collectBehavior) ProcessEvent(event cells.Event) error {
	switch event.Topic() {
	case cells.ProcessedTopic:
		processed := make([]string, len(b.processed))
		copy(processed, b.processed)
		err := event.Respond(processed)
		if err != nil {
			return err
		}
	case cells.ResetTopic:
		b.processed = []string{}
	case cells.PingTopic:
		err := event.Respond(cells.PongResponse)
		if err != nil {
			return err
		}
	case iterateTopic:
		err := b.c.SubscribersDo(func(s cells.Subscriber) error {
			return s.ProcessNewEvent("love", b.c.ID()+" loves "+s.ID(), event.Context())
		})
		if err != nil {
			return err
		}
	case panicTopic:
		panic("Ouch!")
	case subscribersTopic:
		var ids []string
		b.c.SubscribersDo(func(s cells.Subscriber) error {
			ids = append(ids, s.ID())
			return nil
		})
		err := event.Respond(ids)
		if err != nil {
			return err
		}
	default:
		b.processed = append(b.processed, fmt.Sprintf("%v", event))
		return b.c.Emit(event)
	}
	return nil
}

// ProcessEvent reads, validates and emits a configuration.
func (b *configuratorBehavior) ProcessEvent(event cells.Event) error {
	switch event.Topic() {
	case ReadConfigurationTopic:
		// Read configuration
		filename, ok := event.Payload().GetString(ConfigurationFilenamePayload)
		if !ok {
			logger.Errorf("cannot read configuration without filename payload")
			return nil
		}
		logger.Infof("reading configuration from %q", filename)
		cfg, err := etc.ReadFile(filename)
		if err != nil {
			return errors.Annotate(err, ErrCannotReadConfiguration, errorMessages)
		}
		// If wanted then validate it.
		if b.validate != nil {
			err = b.validate(cfg)
			if err != nil {
				return errors.Annotate(err, ErrCannotValidateConfiguration, errorMessages)
			}
		}
		// All done, emit it.
		pvs := cells.PayloadValues{
			ConfigurationPayload: cfg,
		}
		b.cell.EmitNewContext(ConfigurationTopic, pvs, event.Context())
	}
	return nil
}

// ProcessEvent counts the event for the return value of the counter func
// and emits this value.
func (b *counterBehavior) ProcessEvent(event cells.Event) error {
	switch event.Topic() {
	case cells.CountersTopic:
		response := b.copyCounters()
		if err := event.Respond(response); err != nil {
			return err
		}
	case cells.ResetTopic:
		b.counters = make(map[string]int64)
	default:
		cids := b.counterFunc(b.cell.ID(), event)
		if cids != nil {
			for _, cid := range cids {
				v, ok := b.counters[cid]
				if ok {
					b.counters[cid] = v + 1
				} else {
					b.counters[cid] = 1
				}
				topic := "counter:" + cid
				b.cell.EmitNewContext(topic, b.counters[cid], event.Context())
			}
		}
	}
	return nil
}

// Unlocked represents the unlocked state receiving coins.
func (m *lockMachine) Unlocked(ctx cells.Cell, event cells.Event) (behaviors.FSMState, error) {
	switch event.Topic() {
	case "cents?":
		return m.Unlocked, event.Respond(m.cents)
	case "info?":
		info := fmt.Sprintf("state 'unlocked' with %d cents", m.cents)
		return m.Unlocked, event.Respond(info)
	case "coin!":
		cents := payloadCents(event)
		ctx.EmitNewContext("return", cents, event.Context())
		return m.Unlocked, nil
	case "button-press!":
		ctx.Environment().EmitNewContext("restorer", "drop!", m.cents, event.Context())
		m.cents = 0
		return m.Locked, nil
	}
	return m.Unlocked, fmt.Errorf("illegal topic in state 'unlocked': %s", event.Topic())
}