// A first-come-first-serve scheduler: acquires the first offer that can support the task
func FCFSScheduleFunc(r offers.Registry, unused SlaveIndex, task *podtask.T) (offers.Perishable, error) {
	podName := fmt.Sprintf("%s/%s", task.Pod.Namespace, task.Pod.Name)
	var acceptedOffer offers.Perishable
	err := r.Walk(func(p offers.Perishable) (bool, error) {
		offer := p.Details()
		if offer == nil {
			return false, fmt.Errorf("nil offer while scheduling task %v", task.ID)
		}
		if task.AcceptOffer(offer) {
			if p.Acquire() {
				acceptedOffer = p
				log.V(3).Infof("Pod %s accepted offer %v", podName, offer.Id.GetValue())
				return true, nil // stop, we found an offer
			}
		}
		return false, nil // continue
	})
	if acceptedOffer != nil {
		if err != nil {
			log.Warningf("problems walking the offer registry: %v, attempting to continue", err)
		}
		return acceptedOffer, nil
	}
	if err != nil {
		log.V(2).Infof("failed to find a fit for pod: %s, err = %v", podName, err)
		return nil, err
	}
	log.V(2).Infof("failed to find a fit for pod: %s", podName)
	return nil, noSuitableOffersErr
}

func (b *binder) rollback(task *podtask.T, err error) error {
	task.Offer.Release()
	task.Reset()
	if err2 := b.api.tasks().Update(task); err2 != nil {
		log.Errorf("failed to update pod task: %v", err2)
	}
	return err
}

func (k *k8smScheduler) launchTask(task *podtask.T) error {
	// assume caller is holding scheduler lock
	taskList := []*mesos.TaskInfo{task.BuildTaskInfo()}
	offerIds := []*mesos.OfferID{task.Offer.Details().Id}
	filters := &mesos.Filters{}
	_, err := k.internal.driver.LaunchTasks(offerIds, taskList, filters)
	return err
}

// filter func used for explicit task reconciliation, selects only non-terminal tasks which
// have been communicated to mesos (read: launched).
func explicitTaskFilter(t *podtask.T) bool {
	switch t.State {
	case podtask.StateRunning:
		return true
	case podtask.StatePending:
		return t.Has(podtask.Launched)
	default:
		return false
	}
}

// Call ScheduleFunc and subtract some resources, returning the name of the machine the task is scheduled on
func (k *kubeScheduler) doSchedule(task *podtask.T, err error) (string, error) {
	var offer offers.Perishable
	if task.HasAcceptedOffer() {
		// verify that the offer is still on the table
		offerId := task.GetOfferId()
		if offer, ok := k.api.offers().Get(offerId); ok && !offer.HasExpired() {
			// skip tasks that have already have assigned offers
			offer = task.Offer
		} else {
			task.Offer.Release()
			task.Reset()
			if err = k.api.tasks().Update(task); err != nil {
				return "", err
			}
		}
	}
	if err == nil && offer == nil {
		offer, err = k.api.algorithm()(k.api.offers(), k.api, task)
	}
	if err != nil {
		return "", err
	}
	details := offer.Details()
	if details == nil {
		return "", fmt.Errorf("offer already invalid/expired for task %v", task.ID)
	}
	slaveId := details.GetSlaveId().GetValue()
	if slave, ok := k.api.slaveFor(slaveId); !ok {
		// not much sense in Release()ing the offer here since its owner died
		offer.Release()
		k.api.offers().Invalidate(details.Id.GetValue())
		return "", fmt.Errorf("Slave disappeared (%v) while scheduling task %v", slaveId, task.ID)
	} else {
		if task.Offer != nil && task.Offer != offer {
			return "", fmt.Errorf("task.offer assignment must be idempotent, task %+v: offer %+v", task, offer)
		}

		// write resource limits into the pod spec which is transfered to the executor. From here
		// on we can expect that the pod spec of a task has proper limits for CPU and memory.
		// TODO(sttts): For a later separation of the kubelet and the executor also patch the pod on the apiserver
		if unlimitedCPU := mresource.LimitPodCPU(&task.Pod, k.defaultContainerCPULimit); unlimitedCPU {
			log.Warningf("Pod %s/%s without cpu limits is admitted %.2f cpu shares", task.Pod.Namespace, task.Pod.Name, mresource.PodCPULimit(&task.Pod))
		}
		if unlimitedMem := mresource.LimitPodMem(&task.Pod, k.defaultContainerMemLimit); unlimitedMem {
			log.Warningf("Pod %s/%s without memory limits is admitted %.2f MB", task.Pod.Namespace, task.Pod.Name, mresource.PodMemLimit(&task.Pod))
		}

		task.Offer = offer
		task.FillFromDetails(details)

		if err := k.api.tasks().Update(task); err != nil {
			offer.Release()
			return "", err
		}
		return slave.HostName, nil
	}
}

//TODO(jdef) unit test this, ensure that task's copy of api.Pod is not modified
func (b *binder) prepareTaskForLaunch(ctx api.Context, machine string, task *podtask.T, offerId string) error {
	pod := task.Pod

	// we make an effort here to avoid making changes to the task's copy of the pod, since
	// we want that to reflect the initial user spec, and not the modified spec that we
	// build for the executor to consume.
	oemCt := pod.Spec.Containers
	pod.Spec.Containers = append([]api.Container{}, oemCt...) // (shallow) clone before mod

	if pod.Annotations == nil {
		pod.Annotations = make(map[string]string)
	} else {
		oemAnn := pod.Annotations
		pod.Annotations = make(map[string]string)
		for k, v := range oemAnn {
			pod.Annotations[k] = v
		}
	}
	pod.Annotations[annotation.BindingHostKey] = machine
	task.SaveRecoveryInfo(pod.Annotations)

	for _, entry := range task.Spec.PortMap {
		oemPorts := pod.Spec.Containers[entry.ContainerIdx].Ports
		ports := append([]api.ContainerPort{}, oemPorts...)
		p := &ports[entry.PortIdx]
		p.HostPort = int(entry.OfferPort)
		op := strconv.FormatUint(entry.OfferPort, 10)
		pod.Annotations[fmt.Sprintf(annotation.PortMappingKeyFormat, p.Protocol, p.ContainerPort)] = op
		if p.Name != "" {
			pod.Annotations[fmt.Sprintf(annotation.PortNameMappingKeyFormat, p.Protocol, p.Name)] = op
		}
		pod.Spec.Containers[entry.ContainerIdx].Ports = ports
	}

	// the kubelet-executor uses this to instantiate the pod
	log.V(3).Infof("prepared pod spec: %+v", pod)

	data, err := api.Codec.Encode(&pod)
	if err != nil {
		log.V(2).Infof("Failed to marshal the pod spec: %v", err)
		return err
	}
	task.Spec.Data = data
	return nil
}

// Call ScheduleFunc and subtract some resources, returning the name of the machine the task is scheduled on
func (k *kubeScheduler) doSchedule(task *podtask.T, err error) (string, error) {
	var offer offers.Perishable
	if task.HasAcceptedOffer() {
		// verify that the offer is still on the table
		offerId := task.GetOfferId()
		if offer, ok := k.api.offers().Get(offerId); ok && !offer.HasExpired() {
			// skip tasks that have already have assigned offers
			offer = task.Offer
		} else {
			task.Offer.Release()
			task.Reset()
			if err = k.api.tasks().Update(task); err != nil {
				return "", err
			}
		}
	}
	if err == nil && offer == nil {
		offer, err = k.api.algorithm()(k.api.offers(), k.api, task)
	}
	if err != nil {
		return "", err
	}
	details := offer.Details()
	if details == nil {
		return "", fmt.Errorf("offer already invalid/expired for task %v", task.ID)
	}
	slaveId := details.GetSlaveId().GetValue()
	if slave, ok := k.api.slaveFor(slaveId); !ok {
		// not much sense in Release()ing the offer here since its owner died
		offer.Release()
		k.api.offers().Invalidate(details.Id.GetValue())
		return "", fmt.Errorf("Slave disappeared (%v) while scheduling task %v", slaveId, task.ID)
	} else {
		if task.Offer != nil && task.Offer != offer {
			return "", fmt.Errorf("task.offer assignment must be idempotent, task %+v: offer %+v", task, offer)
		}
		task.Offer = offer
		//TODO(jdef) FillFromDetails currently allocates fixed (hardwired) cpu and memory resources for all
		//tasks. This will be fixed once we properly integrate parent-cgroup support into the kublet-executor.
		//For now we are completely ignoring the resources specified in the pod.
		//see: https://github.com/mesosphere/kubernetes-mesos/issues/68
		task.FillFromDetails(details)
		if err := k.api.tasks().Update(task); err != nil {
			offer.Release()
			return "", err
		}
		return slave.HostName, nil
	}
}

// assumes that: caller has acquired scheduler lock and that the task is still pending
func (b *binder) bind(ctx api.Context, binding *api.Binding, task *podtask.T) (err error) {
	// sanity check: ensure that the task hasAcceptedOffer(), it's possible that between
	// Schedule() and now that the offer for this task was rescinded or invalidated.
	// ((we should never see this here))
	if !task.HasAcceptedOffer() {
		return fmt.Errorf("task has not accepted a valid offer %v", task.ID)
	}

	// By this time, there is a chance that the slave is disconnected.
	offerId := task.GetOfferId()
	if offer, ok := b.api.offers().Get(offerId); !ok || offer.HasExpired() {
		// already rescinded or timed out or otherwise invalidated
		return b.rollback(task, fmt.Errorf("failed prior to launchTask due to expired offer for task %v", task.ID))
	}

	if err = b.prepareTaskForLaunch(ctx, binding.Target.Name, task, offerId); err == nil {
		log.V(2).Infof("launching task: %q on target %q slave %q for pod \"%v/%v\"",
			task.ID, binding.Target.Name, task.Spec.SlaveID, task.Pod.Namespace, task.Pod.Name)
		if err = b.api.launchTask(task); err == nil {
			b.api.offers().Invalidate(offerId)
			task.Set(podtask.Launched)
			if err = b.api.tasks().Update(task); err != nil {
				// this should only happen if the task has been removed or has changed status,
				// which SHOULD NOT HAPPEN as long as we're synchronizing correctly
				log.Errorf("failed to update task w/ Launched status: %v", err)
			}
			return
		}
	}
	return b.rollback(task, fmt.Errorf("Failed to launch task %v: %v", task.ID, err))
}