package companion

import "sync"

type RunKey struct {
	Instance          string
	SessionGeneration uint64
	OwnerCharacterID  string
	LifecycleToken    uint64
	SpawnSequence     uint64
	Nonce             string
}

func (k RunKey) valid() bool {
	return validIdentity(k.Instance) && k.SessionGeneration > 0 && validCharacterID(k.OwnerCharacterID) &&
		k.LifecycleToken > 0 && k.SpawnSequence > 0 && validHash(k.Nonce)
}

type Phase string

const (
	Prepared      Phase = "prepared"
	Ready         Phase = "room_ready"
	Created       Phase = "spawned_inactive"
	Bound         Phase = "owner_bound"
	Active        Phase = "active"
	Transitioning Phase = "transitioning"
	Dead          Phase = "dead"
	Retiring      Phase = "retiring"
	Disposed      Phase = "disposed"
	Skipped       Phase = "skipped"
)

type Event struct {
	Run              RunKey
	Sequence         uint64
	Kind             string
	RoomGeneration   uint64
	ObjectKey        uint16
	ObjectGeneration uint64
}

type Status struct {
	Run              RunKey
	Phase            Phase
	ConfigRevision   uint64
	SnapshotHash     string
	LastSequence     uint64
	RoomGeneration   uint64
	ObjectKey        uint16
	ObjectGeneration uint64
	OwnerBound       bool
}

// Instance is an isolated coordinator, not a client message handler.
// Callers must authenticate events and hold the real runtime/object admission
// boundary. An object-confirmation event is never proof of native creation by
// itself. No network endpoint or game callback currently invokes this type.
type Instance struct {
	mu              sync.Mutex
	status          Status
	snapshot        Snapshot
	last            Event
	playerObjectKey uint16
}

func NewInstance(key RunKey, snapshot Snapshot, configRevision uint64, playerObjectKey uint16) (*Instance, error) {
	if !key.valid() || playerObjectKey == 0 || playerObjectKey == 65535 {
		return nil, ErrStaleRun
	}
	if snapshot.SchemaVersion != 1 || snapshot.OwnerCharacterID != key.OwnerCharacterID ||
		!validCharacterID(snapshot.SourceCharacterID) || snapshot.SourceCharacterID == key.OwnerCharacterID ||
		snapshot.ProfileID == "" || !validHash(snapshot.ClientSHA256) || !validHash(snapshot.PVFSHA256) {
		return nil, ErrSnapshot
	}
	frozen := snapshot.Clone()
	return &Instance{status: Status{Run: key, Phase: Prepared, ConfigRevision: configRevision,
		SnapshotHash: frozen.Fingerprint()}, snapshot: frozen, playerObjectKey: playerObjectKey}, nil
}

func (i *Instance) Status() Status     { i.mu.Lock(); defer i.mu.Unlock(); return i.status }
func (i *Instance) Snapshot() Snapshot { i.mu.Lock(); defer i.mu.Unlock(); return i.snapshot.Clone() }

// occupied contains other actors only, freshly inspected by the future bridge.
// nil means collision evidence missing and rejects a first native creation.
// Successful repeated messages are no-ops; a reused sequence with new content
// is an error. No transition can create another APC or respawn a dead one.
func (i *Instance) Apply(e Event, occupied map[uint16]bool) error {
	i.mu.Lock()
	defer i.mu.Unlock()
	s := i.status
	if e.Run != s.Run {
		return ErrStaleRun
	}
	if e.Sequence == 0 {
		return ErrTransition
	}
	if e.Sequence == s.LastSequence && e == i.last {
		return nil
	}
	if e.Sequence <= s.LastSequence {
		return ErrTransition
	}
	switch e.Kind {
	case "room_ready":
		if s.Phase != Prepared && s.Phase != Transitioning {
			return ErrTransition
		}
		if e.RoomGeneration <= s.RoomGeneration {
			return ErrRoom
		}
		s.RoomGeneration = e.RoomGeneration
		if s.Phase == Prepared {
			s.Phase = Ready
		} else {
			s.Phase = Active
		}
	case "native_created":
		if (s.Phase != Ready && s.Phase != Retiring) || e.RoomGeneration != s.RoomGeneration {
			return ErrRoom
		}
		// A native create may finish after cancellation. Track it for exact
		// cleanup, but never authorize it or replace an existing actor.
		if s.Phase == Retiring && s.ObjectKey != 0 {
			return ErrCollision
		}
		if occupied == nil || e.ObjectKey == 0 || e.ObjectKey == 65535 || e.ObjectKey == i.playerObjectKey || occupied[e.ObjectKey] || e.ObjectGeneration == 0 {
			return ErrCollision
		}
		s.ObjectKey = e.ObjectKey
		s.ObjectGeneration = e.ObjectGeneration
		if s.Phase == Ready {
			s.Phase = Created
		}
	case "owner_bound", "activate":
		if e.ObjectKey != s.ObjectKey || e.ObjectGeneration != s.ObjectGeneration || e.RoomGeneration != s.RoomGeneration {
			return ErrCollision
		}
		if e.Kind == "owner_bound" {
			if s.Phase != Created {
				return ErrTransition
			}
			s.Phase = Bound
			s.OwnerBound = true
		} else {
			if s.Phase != Bound {
				return ErrTransition
			}
			s.Phase = Active
		}
	case "room_leaving":
		if s.Phase != Active || e.RoomGeneration != s.RoomGeneration {
			return ErrTransition
		}
		s.Phase = Transitioning
	case "dead":
		if s.Phase != Active && s.Phase != Transitioning {
			return ErrTransition
		}
		if e.ObjectKey != s.ObjectKey || e.ObjectGeneration != s.ObjectGeneration {
			return ErrCollision
		}
		s.Phase = Dead
	case "retire":
		if s.Phase == Disposed || s.Phase == Skipped {
			return ErrTransition
		}
		s.Phase = Retiring
	case "disposed":
		if s.Phase != Retiring {
			return ErrTransition
		}
		// The bridge must also prove the native operation/callbacks drained;
		// a missing room manager is not proof that the actor was destroyed.
		if e.ObjectKey != s.ObjectKey || e.ObjectGeneration != s.ObjectGeneration {
			return ErrCollision
		}
		if e.RoomGeneration != s.RoomGeneration {
			return ErrRoom
		}
		s.Phase = Disposed
		s.OwnerBound = false
	case "skip":
		if s.Phase != Prepared && s.Phase != Ready {
			return ErrTransition
		}
		s.Phase = Skipped
	default:
		return ErrTransition
	}
	s.LastSequence = e.Sequence
	i.status = s
	i.last = e
	return nil
}

// Retiring/dead owners remain valid for already-in-flight combat. The bridge
// must validate targets and safely drain reports before reporting disposed.
// Object generation is internal evidence; no existing game wire is changed.
func (i *Instance) Owns(run RunKey, objectKey uint16, generation uint64) bool {
	i.mu.Lock()
	defer i.mu.Unlock()
	s := i.status
	return run == s.Run && s.OwnerBound && objectKey != 0 && objectKey == s.ObjectKey && generation == s.ObjectGeneration
}