package planner

import (
	"encoding/json"
	"fmt"
	"oc-scheduler/infrastructure/utils"
	"slices"
	"sync"
	"time"

	oclib "cloud.o-forge.io/core/oc-lib"
	"cloud.o-forge.io/core/oc-lib/models/booking/planner"
	"cloud.o-forge.io/core/oc-lib/models/workflow"
	"cloud.o-forge.io/core/oc-lib/models/workflow/graph"
	"cloud.o-forge.io/core/oc-lib/tools"
)

const (
	checkWindowHours = 5
	checkStepMin     = 15 // time increment per scan step (minutes)
	plannerTTL       = 24 * time.Hour
)

// ---------------------------------------------------------------------------
// Planner cache — protected by plannerMu
// ---------------------------------------------------------------------------

// plannerEntry wraps a planner snapshot with refresh-ownership tracking.
// At most one check session may be the "refresh owner" of a given peer's
// planner at a time: it emits PB_PLANNER to request a fresh snapshot from
// oc-discovery and, on close (clean or forced), emits PB_CLOSE_PLANNER to
// release the stream. Any subsequent session that needs the same peer's
// planner will see Refreshing=true and skip the duplicate request.
type plannerEntry struct {
	Planner      *planner.Planner
	Refreshing   bool   // true while a PB_PLANNER request is in flight
	RefreshOwner string // session UUID that initiated the current refresh
}

type PlannerService struct {
	Mu            sync.RWMutex
	Cache         map[string]*plannerEntry
	SubMu         sync.RWMutex
	Subs          map[string][]chan string
	AddedAt       map[string]time.Time
	WorkflowSubMu sync.RWMutex
	WorkflowSubs  map[string][]chan struct{}
}

var singleton *PlannerService

// InitSelfPlanner bootstraps our own planner entry at startup.
// It waits (with 15-second retries) for our peer record to be present in the
// database before generating the first planner snapshot and broadcasting it
// on PB_PLANNER. This handles the race between oc-scheduler starting before
// oc-peer has fully registered our node.
func InitPlanner() {
	singleton = &PlannerService{
		AddedAt:      map[string]time.Time{},
		Subs:         map[string][]chan string{},
		Cache:        map[string]*plannerEntry{},
		WorkflowSubs: map[string][]chan struct{}{},
	}
	for {
		self, err := oclib.GetMySelf()
		if err != nil || self == nil {
			fmt.Println("InitPlanner: self peer not found yet, retrying in 15s...")
			time.Sleep(15 * time.Second)
			continue
		}
		singleton.RefreshSelf(self.PeerID, &tools.APIRequest{Admin: true})
		return
	}
}

func GetPlannerService() *PlannerService {
	return singleton
}

func (s *PlannerService) HandleStore(resp tools.NATSResponse) {
	m := map[string]interface{}{}
	p := planner.Planner{}
	if err := json.Unmarshal(resp.Payload, &m); err != nil {
		return
	}
	if err := json.Unmarshal(resp.Payload, &p); err != nil {
		return
	}
	s.Store(fmt.Sprintf("%v", m["peer_id"]), &p)
}

// missingPlannerPeers returns the peer IDs from res whose planner is absent
// or not yet populated in PlannerCache.
// func missingPlannerPeers(res map[string]bookingResource) []string {
func (s *PlannerService) MissingPeers(res map[string]utils.BookingResource) []string {
	var out []string
	for _, r := range res {
		s.Mu.RLock()
		entry := s.Cache[r.PeerPID]
		s.Mu.RUnlock()
		if entry == nil || entry.Planner == nil {
			out = append(out, r.PeerPID)
		}
	}
	return out
}

func (s *PlannerService) FindDate(wfID string, checkables map[string]utils.BookingResource, start time.Time, end *time.Time, preemption bool, asap bool) (time.Time, *time.Time, bool, bool, []string) {
	var unavailable, warnings []string
	// 4. Preemption: Planify ran (end is resolved), skip availability check.
	if preemption {
		return start, end, true, true, warnings
	}
	// 5b. For any peer whose planner is not yet cached, request it and wait
	// briefly so the decision is based on real data rather than a blind
	// "assume available". The wait is capped to avoid blocking the caller
	// when oc-discovery is unreachable.
	s.Fill(checkables, wfID)

	unavailable, warnings = s.checkResourceAvailability(checkables, start, end)

	if len(unavailable) == 0 {
		//result.Available = true
		return start, end, true, false, warnings
	}

	// 6. as_possible: find and commit to the next free slot.
	if asap {
		next := s.findNextSlot(checkables, start, end, checkWindowHours)
		if next != nil {
			start = *next
			if end != nil {
				shifted := next.Add(end.Sub(start))
				end = &shifted
			}
			return start, end, true, false, warnings
		} else {
			return start, end, false, false, warnings
		}
	}
	return start, end, false, false, warnings
}

func (s *PlannerService) Fill(checkables map[string]utils.BookingResource, wfID string) {
	if missing := s.MissingPeers(checkables); len(missing) > 0 {
		const plannerFetchTimeout = 2 * time.Second
		tmpSession := "check-oneshot-" + wfID
		ch, cancelSub := SubscribeUpdates(s.Subs, &s.SubMu, missing...)
		owned := s.Refresh(missing, tmpSession)
		select {
		case <-ch:
		case <-time.After(plannerFetchTimeout):
		}
		cancelSub()
		s.ReleaseRefreshOwnership(owned, tmpSession)
	}
}

// evictAfter waits ttl from first insertion then deletes the cache entry and
// emits PB_CLOSE_PLANNER so oc-discovery stops streaming for this peer.
// This is the only path that actually removes an entry from PlannerCache;
// session close (ReleaseRefreshOwnership) only resets ownership state.
func (s *PlannerService) EvictAfter(peerID string, ttl time.Duration) {
	time.Sleep(ttl)
	s.Mu.Lock()
	_, exists := s.Cache[peerID]
	if exists {
		delete(s.Cache, peerID)
		delete(s.AddedAt, peerID)
	}
	s.Mu.Unlock()
	if exists {
		utils.Notify(&s.SubMu, s.Subs, peerID, peerID)
		utils.Propalgate(peerID, tools.PropalgationMessage{Action: tools.PB_CLOSE_PLANNER})
	}
}

// SubscribePlannerUpdates registers interest in planner changes for the given
// peer IDs. The returned channel receives the peerID string (non-blocking) each
// time any of those planners is updated. Call cancel to unregister.
func SubscribeUpdates[T interface{}](subs map[string][]chan T, mu *sync.RWMutex, updates ...string) (<-chan T, func()) {
	ch := make(chan T, 1)
	mu.Lock()
	for _, k := range updates {
		subs[k] = append(subs[k], ch)
	}
	mu.Unlock()
	cancel := func() {
		mu.Lock()
		for _, k := range updates {
			subsk := subs[k]
			for i, s := range subsk {
				if s == ch {
					subs[k] = append(subsk[:i], subsk[i+1:]...)
					break
				}
			}
		}
		mu.Unlock()
	}
	return ch, cancel
}

// ---------------------------------------------------------------------------
// Cache helpers
// ---------------------------------------------------------------------------

func (s *PlannerService) Store(peerID string, p *planner.Planner) {
	s.Mu.Lock()
	entry := s.Cache[peerID]
	isNew := entry == nil
	if isNew {
		entry = &plannerEntry{}
		s.Cache[peerID] = entry
		s.AddedAt[peerID] = time.Now().UTC()
		go s.EvictAfter(peerID, plannerTTL)
	}
	entry.Planner = p
	s.Mu.Unlock()
	utils.Notify[string](&s.SubMu, s.Subs, peerID, peerID)
}

// ---------------------------------------------------------------------------
// Planner refresh / broadcast
// ---------------------------------------------------------------------------

// RequestPlannerRefresh asks oc-discovery for a fresh planner snapshot for
// each peer in peerIDs. Only the first session to request a given peer becomes
// its "refresh owner": subsequent sessions see Refreshing=true and skip the
// duplicate PB_PLANNER emission. Returns the subset of peerIDs for which this
// session claimed ownership (needed to release on close).

// RequestPlannerRefresh
func (s *PlannerService) Refresh(peerIDs []string, executionsID string) []string {
	var owned []string
	for _, peerID := range peerIDs {
		s.Mu.Lock()
		entry := s.Cache[peerID]
		if entry == nil {
			entry = &plannerEntry{}
			s.Cache[peerID] = entry
			s.AddedAt[peerID] = time.Now().UTC()
			go s.EvictAfter(peerID, plannerTTL)
		}
		shouldRequest := !entry.Refreshing
		if shouldRequest {
			entry.Refreshing = true
			entry.RefreshOwner = executionsID
		}
		s.Mu.Unlock()
		if shouldRequest {
			owned = append(owned, peerID)
			if p, err := oclib.GetMySelf(); err == nil && p != nil && p.PeerID == peerID {
				go s.RefreshSelf(peerID, &tools.APIRequest{Admin: true})
			} else {
				payload, _ := json.Marshal(map[string]any{"peer_id": peerID})
				utils.Propalgate(peerID, tools.PropalgationMessage{
					Action:  tools.PB_PLANNER,
					Payload: payload,
				})
			}
		}
	}
	return owned
}

// ReleaseRefreshOwnership is called when a check session closes (clean or
// forced). For each peer this session owns, it resets the refresh state and
// emits PB_CLOSE_PLANNER so oc-discovery stops the planner stream.
// The planner data itself stays in the cache until TTL eviction.
func (s *PlannerService) ReleaseRefreshOwnership(peerIDs []string, executionsID string) {
	for _, peerID := range peerIDs {
		s.Mu.Lock()
		if entry := s.Cache[peerID]; entry != nil && entry.RefreshOwner == executionsID {
			entry.Refreshing = false
			entry.RefreshOwner = ""
		}
		s.Mu.Unlock()
		utils.Notify(&s.SubMu, s.Subs, peerID, peerID)
		payload, _ := json.Marshal(map[string]any{"peer_id": peerID})
		utils.Propalgate(peerID, tools.PropalgationMessage{
			Action:  tools.PB_CLOSE_PLANNER,
			Payload: payload,
		})
	}
}

// broadcastPlanner iterates the storage and compute peers of the given workflow
// and, for each peer not yet in the cache, emits a PB_PLANNER propagation so
// downstream consumers (oc-discovery, other schedulers) refresh their state.
func (s *PlannerService) Broadcast(wf *workflow.Workflow) {
	if wf.Graph == nil {
		return
	}
	items := []graph.GraphItem{}
	items = append(items, wf.GetGraphItems(wf.Graph.IsStorage)...)
	items = append(items, wf.GetGraphItems(wf.Graph.IsCompute)...)

	seen := []string{}
	for _, item := range items {
		_, res := item.GetResource()
		if res == nil {
			continue
		}
		creatorID := res.GetCreatorID()
		if slices.Contains(seen, creatorID) {
			continue
		}

		data := oclib.NewRequestAdmin(oclib.LibDataEnum(oclib.PEER), nil).LoadOne(creatorID)
		p := data.ToPeer()
		if p == nil {
			continue
		}

		s.Mu.RLock()
		cached := s.Cache[p.PeerID]
		s.Mu.RUnlock()

		// Only request if no snapshot and no refresh already in flight.
		if cached == nil || (cached.Planner == nil && !cached.Refreshing) {
			payload, err := json.Marshal(map[string]interface{}{"peer_id": p.PeerID})
			if err != nil {
				continue
			}
			seen = append(seen, creatorID)
			utils.Propalgate(p.PeerID, tools.PropalgationMessage{
				Action:  tools.PB_PLANNER,
				Payload: payload,
			})
		}
	}
}

// ---------------------------------------------------------------------------
// Self-planner refresh
// ---------------------------------------------------------------------------

func (s *PlannerService) RefreshSelf(peerID string, request *tools.APIRequest) {
	p, err := planner.GenerateShallow(request)
	if err != nil {
		fmt.Println("refreshSelfPlanner: could not generate planner:", err)
		return
	}
	// Update the local cache and notify any waiting CheckStream goroutines.
	s.Store(peerID, p)
	// Broadcast the updated planner so remote peers (and oc-discovery) can
	// refresh their view of our availability.
	type plannerWithPeer struct {
		PeerID string `json:"peer_id"`
		*planner.Planner
	}
	plannerPayload, err := json.Marshal(plannerWithPeer{PeerID: peerID, Planner: p})
	if err != nil {
		return
	}
	utils.Propalgate(peerID, tools.PropalgationMessage{
		Action:  tools.PB_PLANNER,
		Payload: plannerPayload,
	})
}

// findNextSlot scans forward from 'from' in checkStepMin increments for up to
// windowH hours and returns the first candidate start time at which all
// resources are simultaneously free.
func (s *PlannerService) findNextSlot(resources map[string]utils.BookingResource, from time.Time, originalEnd *time.Time, windowH int) *time.Time {
	duration := 5 * time.Minute
	if originalEnd != nil {
		if d := originalEnd.Sub(from); d > 0 {
			duration = d
		}
	}
	step := time.Duration(checkStepMin) * time.Minute
	limit := from.Add(time.Duration(windowH) * time.Hour)
	for t := from.Add(step); t.Before(limit); t = t.Add(step) {
		e := t.Add(duration)
		if unavail, _ := s.checkResourceAvailability(resources, t, &e); len(unavail) == 0 {
			return &t
		}
	}
	return nil
}

// checkResourceAvailability returns the IDs of unavailable resources and
// human-readable warning messages.
func (s *PlannerService) checkResourceAvailability(res map[string]utils.BookingResource, start time.Time, end *time.Time) (unavailable []string, warnings []string) {
	for _, r := range res {
		s.Mu.RLock()
		entry := s.Cache[r.PeerPID]
		s.Mu.RUnlock()
		if entry == nil || entry.Planner == nil {
			warnings = append(warnings, fmt.Sprintf(
				"peer %s planner not in cache for resource %s – assuming available", r.PeerPID, r.ID))
			continue
		}
		if !s.checkInstance(entry.Planner, r.ID, r.InstanceID, start, end) {
			unavailable = append(unavailable, r.ID)
			warnings = append(warnings, fmt.Sprintf(
				"resource %s is not available in [%s – %s]",
				r.ID, start.Format(time.RFC3339), utils.FormatOptTime(end)))
		}
	}
	return
}

// CheckResourceInstance checks whether a resource/instance is available on the
// local planner cache for the given peer. Called by scheduling_resources when
// validating an incoming booking creation.
func (s *PlannerService) CheckResourceInstance(peerID, resourceID, instanceID string, start time.Time, end *time.Time) bool {
	s.Mu.RLock()
	entry := s.Cache[peerID]
	s.Mu.RUnlock()
	if entry == nil || entry.Planner == nil {
		return true // no planner cached → assume available
	}
	return s.checkInstance(entry.Planner, resourceID, instanceID, start, end)
}

// SubscribePlannerUpdates returns a channel that receives a peerID each time
// one of the given peers' planners is updated.
func (s *PlannerService) SubscribePlannerUpdates(peerIDs ...string) (<-chan string, func()) {
	return SubscribeUpdates[string](s.Subs, &s.SubMu, peerIDs...)
}

// SubscribeWorkflowUpdates returns a channel signalled when the workflow changes.
func (s *PlannerService) SubscribeWorkflowUpdates(wfID string) (<-chan struct{}, func()) {
	return SubscribeUpdates[struct{}](s.WorkflowSubs, &s.WorkflowSubMu, wfID)
}

// NotifyWorkflow signals all subscribers watching wfID.
func (s *PlannerService) NotifyWorkflow(wfID string) {
	utils.Notify[struct{}](&s.WorkflowSubMu, s.WorkflowSubs, wfID, struct{}{})
}

// checkInstance checks availability for the specific instance resolved by the
// scheduler. When instanceID is empty (no instance selected / none resolvable),
// it falls back to checking all instances known in the planner and returns true
// if any one has remaining capacity. Returns true when no capacity is recorded.
func (s *PlannerService) checkInstance(p *planner.Planner, resourceID string, instanceID string, start time.Time, end *time.Time) bool {
	if instanceID != "" {
		return p.Check(resourceID, instanceID, nil, start, end)
	}
	caps, ok := p.Capacities[resourceID]
	if !ok || len(caps) == 0 {
		return true
	}
	for id := range caps {
		if p.Check(resourceID, id, nil, start, end) {
			return true
		}
	}
	return false
}