package scheduler

import (
	"fmt"

	log "github.com/hashicorp/go-hclog"
	memdb "github.com/hashicorp/go-memdb"
	"github.com/hashicorp/nomad/helper/uuid"
	"github.com/hashicorp/nomad/nomad/structs"
)

const (
	// maxSystemScheduleAttempts is used to limit the number of times
	// we will attempt to schedule if we continue to hit conflicts for system
	// jobs.
	maxSystemScheduleAttempts = 5
)

// SystemScheduler is used for 'system' jobs. This scheduler is
// designed for services that should be run on every client.
type SystemScheduler struct {
	logger  log.Logger
	state   State
	planner Planner

	eval       *structs.Evaluation
	job        *structs.Job
	plan       *structs.Plan
	planResult *structs.PlanResult
	ctx        *EvalContext
	stack      *SystemStack
	nodes      []*structs.Node
	nodesByDC  map[string]int

	limitReached bool
	nextEval     *structs.Evaluation

	failedTGAllocs map[string]*structs.AllocMetric
	queuedAllocs   map[string]int
}

// NewSystemScheduler is a factory function to instantiate a new system
// scheduler.
func NewSystemScheduler(logger log.Logger, state State, planner Planner) Scheduler {
	return &SystemScheduler{
		logger:  logger.Named("system_sched"),
		state:   state,
		planner: planner,
	}
}

// Process is used to handle a single evaluation.
func (s *SystemScheduler) Process(eval *structs.Evaluation) error {
	// Store the evaluation
	s.eval = eval

	// Update our logger with the eval's information
	s.logger = s.logger.With("eval_id", eval.ID, "job_id", eval.JobID, "namespace", eval.Namespace)

	// Verify the evaluation trigger reason is understood
	switch eval.TriggeredBy {
	case structs.EvalTriggerJobRegister, structs.EvalTriggerNodeUpdate, structs.EvalTriggerFailedFollowUp,
		structs.EvalTriggerJobDeregister, structs.EvalTriggerRollingUpdate, structs.EvalTriggerPreemption,
		structs.EvalTriggerDeploymentWatcher, structs.EvalTriggerNodeDrain:
	default:
		desc := fmt.Sprintf("scheduler cannot handle '%s' evaluation reason",
			eval.TriggeredBy)
		return setStatus(s.logger, s.planner, s.eval, s.nextEval, nil, s.failedTGAllocs, structs.EvalStatusFailed, desc,
			s.queuedAllocs, "")
	}

	// Retry up to the maxSystemScheduleAttempts and reset if progress is made.
	progress := func() bool { return progressMade(s.planResult) }
	if err := retryMax(maxSystemScheduleAttempts, s.process, progress); err != nil {
		if statusErr, ok := err.(*SetStatusError); ok {
			return setStatus(s.logger, s.planner, s.eval, s.nextEval, nil, s.failedTGAllocs, statusErr.EvalStatus, err.Error(),
				s.queuedAllocs, "")
		}
		return err
	}

	// Update the status to complete
	return setStatus(s.logger, s.planner, s.eval, s.nextEval, nil, s.failedTGAllocs, structs.EvalStatusComplete, "",
		s.queuedAllocs, "")
}

// process is wrapped in retryMax to iteratively run the handler until we have no
// further work or we've made the maximum number of attempts.
func (s *SystemScheduler) process() (bool, error) {
	// Lookup the Job by ID
	var err error
	ws := memdb.NewWatchSet()
	s.job, err = s.state.JobByID(ws, s.eval.Namespace, s.eval.JobID)
	if err != nil {
		return false, fmt.Errorf("failed to get job '%s': %v",
			s.eval.JobID, err)
	}
	numTaskGroups := 0
	if !s.job.Stopped() {
		numTaskGroups = len(s.job.TaskGroups)
	}
	s.queuedAllocs = make(map[string]int, numTaskGroups)

	// Get the ready nodes in the required datacenters
	if !s.job.Stopped() {
		s.nodes, s.nodesByDC, err = readyNodesInDCs(s.state, s.job.Datacenters)
		if err != nil {
			return false, fmt.Errorf("failed to get ready nodes: %v", err)
		}
	}

	// Create a plan
	s.plan = s.eval.MakePlan(s.job)

	// Reset the failed allocations
	s.failedTGAllocs = nil

	// Create an evaluation context
	s.ctx = NewEvalContext(s.state, s.plan, s.logger)

	// Construct the placement stack
	s.stack = NewSystemStack(s.ctx)
	if !s.job.Stopped() {
		s.stack.SetJob(s.job)
	}

	// Compute the target job allocations
	if err := s.computeJobAllocs(); err != nil {
		s.logger.Error("failed to compute job allocations", "error", err)
		return false, err
	}

	// If the plan is a no-op, we can bail. If AnnotatePlan is set submit the plan
	// anyways to get the annotations.
	if s.plan.IsNoOp() && !s.eval.AnnotatePlan {
		return true, nil
	}

	// If the limit of placements was reached we need to create an evaluation
	// to pickup from here after the stagger period.
	if s.limitReached && s.nextEval == nil {
		s.nextEval = s.eval.NextRollingEval(s.job.Update.Stagger)
		if err := s.planner.CreateEval(s.nextEval); err != nil {
			s.logger.Error("failed to make next eval for rolling update", "error", err)
			return false, err
		}
		s.logger.Debug("rolling update limit reached, next eval created", "next_eval_id", s.nextEval.ID)
	}

	// Submit the plan
	result, newState, err := s.planner.SubmitPlan(s.plan)
	s.planResult = result
	if err != nil {
		return false, err
	}

	// Decrement the number of allocations pending per task group based on the
	// number of allocations successfully placed
	adjustQueuedAllocations(s.logger, result, s.queuedAllocs)

	// If we got a state refresh, try again since we have stale data
	if newState != nil {
		s.logger.Debug("refresh forced")
		s.state = newState
		return false, nil
	}

	// Try again if the plan was not fully committed, potential conflict
	fullCommit, expected, actual := result.FullCommit(s.plan)
	if !fullCommit {
		s.logger.Debug("plan didn't fully commit", "attempted", expected, "placed", actual)
		return false, nil
	}

	// Success!
	return true, nil
}

// computeJobAllocs is used to reconcile differences between the job,
// existing allocations and node status to update the allocations.
func (s *SystemScheduler) computeJobAllocs() error {
	// Lookup the allocations by JobID
	ws := memdb.NewWatchSet()
	allocs, err := s.state.AllocsByJob(ws, s.eval.Namespace, s.eval.JobID, true)
	if err != nil {
		return fmt.Errorf("failed to get allocs for job '%s': %v",
			s.eval.JobID, err)
	}

	// Determine the tainted nodes containing job allocs
	tainted, err := taintedNodes(s.state, allocs)
	if err != nil {
		return fmt.Errorf("failed to get tainted nodes for job '%s': %v",
			s.eval.JobID, err)
	}

	// Update the allocations which are in pending/running state on tainted
	// nodes to lost
	updateNonTerminalAllocsToLost(s.plan, tainted, allocs)

	// Filter out the allocations in a terminal state
	allocs, terminalAllocs := structs.FilterTerminalAllocs(allocs)

	// Diff the required and existing allocations
	diff := diffSystemAllocs(s.job, s.nodes, tainted, allocs, terminalAllocs)
	s.logger.Debug("reconciled current state with desired state",
		"place", len(diff.place), "update", len(diff.update),
		"migrate", len(diff.migrate), "stop", len(diff.stop),
		"ignore", len(diff.ignore), "lost", len(diff.lost))

	// Add all the allocs to stop
	for _, e := range diff.stop {
		s.plan.AppendUpdate(e.Alloc, structs.AllocDesiredStatusStop, allocNotNeeded, "")
	}

	// Add all the allocs to migrate
	for _, e := range diff.migrate {
		s.plan.AppendUpdate(e.Alloc, structs.AllocDesiredStatusStop, allocNodeTainted, "")
	}

	// Lost allocations should be transitioned to desired status stop and client
	// status lost.
	for _, e := range diff.lost {
		s.plan.AppendUpdate(e.Alloc, structs.AllocDesiredStatusStop, allocLost, structs.AllocClientStatusLost)
	}

	// Attempt to do the upgrades in place
	destructiveUpdates, inplaceUpdates := inplaceUpdate(s.ctx, s.eval, s.job, s.stack, diff.update)
	diff.update = destructiveUpdates

	if s.eval.AnnotatePlan {
		s.plan.Annotations = &structs.PlanAnnotations{
			DesiredTGUpdates: desiredUpdates(diff, inplaceUpdates, destructiveUpdates),
		}
	}

	// Check if a rolling upgrade strategy is being used
	limit := len(diff.update)
	if !s.job.Stopped() && s.job.Update.Rolling() {
		limit = s.job.Update.MaxParallel
	}

	// Treat non in-place updates as an eviction and new placement.
	s.limitReached = evictAndPlace(s.ctx, diff, diff.update, allocUpdating, &limit)

	// Nothing remaining to do if placement is not required
	if len(diff.place) == 0 {
		if !s.job.Stopped() {
			for _, tg := range s.job.TaskGroups {
				s.queuedAllocs[tg.Name] = 0
			}
		}
		return nil
	}

	// Record the number of allocations that needs to be placed per Task Group
	for _, allocTuple := range diff.place {
		s.queuedAllocs[allocTuple.TaskGroup.Name] += 1
	}

	// Compute the placements
	return s.computePlacements(diff.place)
}

// computePlacements computes placements for allocations
func (s *SystemScheduler) computePlacements(place []allocTuple) error {
	nodeByID := make(map[string]*structs.Node, len(s.nodes))
	for _, node := range s.nodes {
		nodeByID[node.ID] = node
	}

	nodes := make([]*structs.Node, 1)
	for _, missing := range place {
		node, ok := nodeByID[missing.Alloc.NodeID]
		if !ok {
			return fmt.Errorf("could not find node %q", missing.Alloc.NodeID)
		}

		// Update the set of placement nodes
		nodes[0] = node
		s.stack.SetNodes(nodes)

		// Attempt to match the task group
		option := s.stack.Select(missing.TaskGroup, nil)

		if option == nil {
			// If nodes were filtered because of constraint mismatches and we
			// couldn't create an allocation then decrementing queued for that
			// task group
			if s.ctx.metrics.NodesFiltered > 0 {
				s.queuedAllocs[missing.TaskGroup.Name] -= 1

				// If we are annotating the plan, then decrement the desired
				// placements based on whether the node meets the constraints
				if s.eval.AnnotatePlan && s.plan.Annotations != nil &&
					s.plan.Annotations.DesiredTGUpdates != nil {
					desired := s.plan.Annotations.DesiredTGUpdates[missing.TaskGroup.Name]
					desired.Place -= 1
				}
			}

			// Check if this task group has already failed
			if metric, ok := s.failedTGAllocs[missing.TaskGroup.Name]; ok {
				metric.CoalescedFailures += 1
				continue
			}
		}

		// Store the available nodes by datacenter
		s.ctx.Metrics().NodesAvailable = s.nodesByDC

		// Compute top K scoring node metadata
		s.ctx.Metrics().PopulateScoreMetaData()

		// Set fields based on if we found an allocation option
		if option != nil {
			resources := &structs.AllocatedResources{
				Tasks: option.TaskResources,
				Shared: structs.AllocatedSharedResources{
					DiskMB: int64(missing.TaskGroup.EphemeralDisk.SizeMB),
				},
			}

			// Create an allocation for this
			alloc := &structs.Allocation{
				ID:                 uuid.Generate(),
				Namespace:          s.job.Namespace,
				EvalID:             s.eval.ID,
				Name:               missing.Name,
				JobID:              s.job.ID,
				TaskGroup:          missing.TaskGroup.Name,
				Metrics:            s.ctx.Metrics(),
				NodeID:             option.Node.ID,
				TaskResources:      resources.OldTaskResources(),
				AllocatedResources: resources,
				DesiredStatus:      structs.AllocDesiredStatusRun,
				ClientStatus:       structs.AllocClientStatusPending,

				SharedResources: &structs.Resources{
					DiskMB: missing.TaskGroup.EphemeralDisk.SizeMB,
				},
			}

			// If the new allocation is replacing an older allocation then we
			// set the record the older allocation id so that they are chained
			if missing.Alloc != nil {
				alloc.PreviousAllocation = missing.Alloc.ID
			}

			// If this placement involves preemption, set DesiredState to evict for those allocations
			if option.PreemptedAllocs != nil {
				var preemptedAllocIDs []string
				for _, stop := range option.PreemptedAllocs {
					s.plan.AppendPreemptedAlloc(stop, structs.AllocDesiredStatusEvict, alloc.ID)

					preemptedAllocIDs = append(preemptedAllocIDs, stop.ID)
					if s.eval.AnnotatePlan && s.plan.Annotations != nil {
						s.plan.Annotations.PreemptedAllocs = append(s.plan.Annotations.PreemptedAllocs, stop.Stub())
						if s.plan.Annotations.DesiredTGUpdates != nil {
							desired := s.plan.Annotations.DesiredTGUpdates[missing.TaskGroup.Name]
							desired.Preemptions += 1
						}
					}
				}
				alloc.PreemptedAllocations = preemptedAllocIDs
			}

			s.plan.AppendAlloc(alloc)
		} else {
			// Lazy initialize the failed map
			if s.failedTGAllocs == nil {
				s.failedTGAllocs = make(map[string]*structs.AllocMetric)
			}

			s.failedTGAllocs[missing.TaskGroup.Name] = s.ctx.Metrics()
		}
	}

	return nil
}