package runtime

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"galaxy/backend/internal/dockerclient"
	"galaxy/model/rest"

	"github.com/google/uuid"
	"go.uber.org/zap"
)

// Service is the runtime-domain entry point. It owns the per-game
// lifecycle (start, stop, pause, resume, restart, patch,
// force-next-turn), the runtime cache, the player-mapping projection,
// and the operation log; it coordinates with the worker pool and the
// per-game scheduler goroutines.
type Service struct {
	deps Deps

	gameMu sync.Map // uuid.UUID -> *sync.Mutex

	scheduler *Scheduler
	workers   *WorkerPool
}

// NewService constructs a Service. Logger and Now default sensibly. The
// `Service` is `app.Component`-shaped through the embedded WorkerPool /
// Scheduler / Reconciler that callers register separately.
func NewService(deps Deps) (*Service, error) {
	if deps.Store == nil {
		return nil, errors.New("runtime: store must not be nil")
	}
	if deps.Cache == nil {
		return nil, errors.New("runtime: cache must not be nil")
	}
	if deps.EngineVersions == nil {
		return nil, errors.New("runtime: engine version service must not be nil")
	}
	if deps.Docker == nil {
		return nil, errors.New("runtime: docker client must not be nil")
	}
	if deps.Engine == nil {
		return nil, errors.New("runtime: engine client must not be nil")
	}
	if deps.Logger == nil {
		deps.Logger = zap.NewNop()
	}
	deps.Logger = deps.Logger.Named("runtime")
	if deps.Notification == nil {
		deps.Notification = NewNoopNotificationPublisher(deps.Logger)
	}
	if deps.Now == nil {
		deps.Now = time.Now
	}
	if deps.Config.WorkerPoolSize <= 0 {
		deps.Config.WorkerPoolSize = 1
	}
	if deps.Config.JobQueueSize <= 0 {
		deps.Config.JobQueueSize = 1
	}
	if deps.Config.StopGracePeriod <= 0 {
		deps.Config.StopGracePeriod = 10 * time.Second
	}
	if deps.Config.ReconcileInterval <= 0 {
		deps.Config.ReconcileInterval = 60 * time.Second
	}
	if strings.TrimSpace(deps.Config.ContainerStateMount) == "" {
		deps.Config.ContainerStateMount = "/var/lib/galaxy-game"
	}
	if !dockerclient.PullPolicy(deps.Config.ImagePullPolicy).IsKnown() {
		return nil, fmt.Errorf("runtime: invalid image pull policy %q", deps.Config.ImagePullPolicy)
	}
	svc := &Service{deps: deps}
	svc.scheduler = NewScheduler(svc)
	svc.workers = NewWorkerPool(svc)
	return svc, nil
}

// Logger exposes the named logger used by the service.
func (s *Service) Logger() *zap.Logger { return s.deps.Logger }

// Cache returns the in-memory projection.
func (s *Service) Cache() *Cache { return s.deps.Cache }

// EngineVersions returns the engine-version registry service.
func (s *Service) EngineVersions() *EngineVersionService { return s.deps.EngineVersions }

// Workers returns the runtime worker pool component.
func (s *Service) Workers() *WorkerPool { return s.workers }

// Reconciler builds an `app.Component` driving the periodic
// reconciliation loop documented in PLAN.md §5.5.
func (s *Service) Reconciler() *Reconciler { return NewReconciler(s) }

// SchedulerComponent returns the per-game scheduler bookkeeper. It
// implements `app.Component` so main.go can register it alongside the
// worker pool.
func (s *Service) SchedulerComponent() *Scheduler { return s.scheduler }

// gameLock returns a sync.Mutex unique to gameID. Used to serialise
// per-game runtime operations across goroutines.
func (s *Service) gameLock(gameID uuid.UUID) *sync.Mutex {
	if v, ok := s.gameMu.Load(gameID); ok {
		return v.(*sync.Mutex)
	}
	v, _ := s.gameMu.LoadOrStore(gameID, &sync.Mutex{})
	return v.(*sync.Mutex)
}

// =====================================================================
// Lifecycle entry points (consumed by lobby.RuntimeGateway adapter)
// =====================================================================

// StartGame queues a start job for gameID. Returns once the operation
// is durably recorded; the actual pull / create / start runs on a
// worker goroutine.
func (s *Service) StartGame(ctx context.Context, gameID uuid.UUID) error {
	op, err := s.beginOperation(ctx, gameID, OpStart, OpSourceLobby)
	if err != nil {
		return err
	}
	return s.enqueue(ctx, jobStart{operation: op})
}

// StopGame queues a stop job for gameID.
func (s *Service) StopGame(ctx context.Context, gameID uuid.UUID) error {
	op, err := s.beginOperation(ctx, gameID, OpStop, OpSourceLobby)
	if err != nil {
		return err
	}
	return s.enqueue(ctx, jobStop{operation: op})
}

// PauseGame flips the runtime row's `paused` flag. The container
// keeps running; the scheduler short-circuits ticks while paused.
// Synchronous because no Docker call is involved.
func (s *Service) PauseGame(ctx context.Context, gameID uuid.UUID) error {
	mu := s.gameLock(gameID)
	mu.Lock()
	defer mu.Unlock()
	now := s.deps.Now().UTC()
	paused := true
	pausedAtPtr := &now
	patch := runtimeRecordUpdate{Paused: &paused, PausedAt: &pausedAtPtr}
	rec, err := s.deps.Store.UpdateRuntimeRecord(ctx, gameID, patch, now)
	if err != nil {
		return err
	}
	s.deps.Cache.PutRuntime(rec)
	s.recordSyncOperation(ctx, gameID, OpPause, OpSourceLobby, rec.CurrentImageRef, rec.CurrentContainerID, nil)
	return nil
}

// ResumeGame clears the `paused` flag. Synchronous.
func (s *Service) ResumeGame(ctx context.Context, gameID uuid.UUID) error {
	mu := s.gameLock(gameID)
	mu.Lock()
	defer mu.Unlock()
	now := s.deps.Now().UTC()
	paused := false
	var nilTime *time.Time
	cleared := &nilTime
	patch := runtimeRecordUpdate{Paused: &paused, PausedAt: cleared}
	rec, err := s.deps.Store.UpdateRuntimeRecord(ctx, gameID, patch, now)
	if err != nil {
		return err
	}
	s.deps.Cache.PutRuntime(rec)
	s.recordSyncOperation(ctx, gameID, OpResume, OpSourceLobby, rec.CurrentImageRef, rec.CurrentContainerID, nil)
	return nil
}

// AdminRestart queues a restart job. Stop + remove + run with the
// same image_ref.
func (s *Service) AdminRestart(ctx context.Context, gameID uuid.UUID) (OperationLog, error) {
	op, err := s.beginOperation(ctx, gameID, OpRestart, OpSourceAdmin)
	if err != nil {
		return OperationLog{}, err
	}
	if err := s.enqueue(ctx, jobRestart{operation: op}); err != nil {
		return OperationLog{}, err
	}
	return op, nil
}

// AdminPatch validates the target version against the registry, then
// queues a stop + remove + run with the new image. Returns
// ErrPatchSemverIncompatible when the target crosses major/minor.
func (s *Service) AdminPatch(ctx context.Context, gameID uuid.UUID, targetVersion string) (OperationLog, error) {
	rec, err := s.GetRuntime(ctx, gameID)
	if err != nil {
		return OperationLog{}, err
	}
	if rec.CurrentEngineVersion == "" {
		return OperationLog{}, fmt.Errorf("%w: runtime has no current engine version", ErrConflict)
	}
	if err := CheckPatchCompatible(rec.CurrentEngineVersion, targetVersion); err != nil {
		return OperationLog{}, err
	}
	target, err := s.deps.EngineVersions.Resolve(ctx, targetVersion)
	if err != nil {
		return OperationLog{}, err
	}
	op, err := s.beginOperation(ctx, gameID, OpPatch, OpSourceAdmin)
	if err != nil {
		return OperationLog{}, err
	}
	if err := s.enqueue(ctx, jobPatch{operation: op, target: target}); err != nil {
		return OperationLog{}, err
	}
	return op, nil
}

// AdminForceNextTurn sets the skip_next_tick flag so the next
// scheduler tick fires immediately. Synchronous.
func (s *Service) AdminForceNextTurn(ctx context.Context, gameID uuid.UUID) (OperationLog, error) {
	mu := s.gameLock(gameID)
	mu.Lock()
	defer mu.Unlock()
	now := s.deps.Now().UTC()
	skip := true
	rec, err := s.deps.Store.UpdateRuntimeRecord(ctx, gameID, runtimeRecordUpdate{SkipNextTick: &skip}, now)
	if err != nil {
		return OperationLog{}, err
	}
	s.deps.Cache.PutRuntime(rec)
	op := s.recordSyncOperation(ctx, gameID, OpForceNextTurn, OpSourceAdmin, rec.CurrentImageRef, rec.CurrentContainerID, nil)
	return op, nil
}

// GetRuntime returns the runtime record for gameID, cache-first.
func (s *Service) GetRuntime(ctx context.Context, gameID uuid.UUID) (RuntimeRecord, error) {
	if rec, ok := s.deps.Cache.GetRuntime(gameID); ok {
		return rec, nil
	}
	rec, err := s.deps.Store.LoadRuntimeRecord(ctx, gameID)
	if err != nil {
		return RuntimeRecord{}, err
	}
	s.deps.Cache.PutRuntime(rec)
	return rec, nil
}

// ResolvePlayerMapping returns the (race_name, engine_player_uuid)
// projection for the supplied (game_id, user_id). Used by the user
// game-proxy handlers to populate the engine `actor` field.
func (s *Service) ResolvePlayerMapping(ctx context.Context, gameID, userID uuid.UUID) (PlayerMapping, error) {
	return s.deps.Store.LoadPlayerMapping(ctx, gameID, userID)
}

// EngineEndpoint returns the engine endpoint URL for gameID. Used by
// the user game-proxy handlers.
func (s *Service) EngineEndpoint(ctx context.Context, gameID uuid.UUID) (string, error) {
	rec, err := s.GetRuntime(ctx, gameID)
	if err != nil {
		return "", err
	}
	if rec.EngineEndpoint == "" {
		return "", fmt.Errorf("%w: runtime has no engine endpoint", ErrConflict)
	}
	return rec.EngineEndpoint, nil
}

// =====================================================================
// Worker / job execution
// =====================================================================

// job is the internal interface implemented by every long-running
// runtime task. The worker pool dispatches them in order.
type job interface {
	GameID() uuid.UUID
	Run(ctx context.Context, s *Service) error
	Operation() OperationLog
}

type jobStart struct{ operation OperationLog }
type jobStop struct{ operation OperationLog }
type jobRestart struct{ operation OperationLog }
type jobPatch struct {
	operation OperationLog
	target    EngineVersion
}

func (j jobStart) GameID() uuid.UUID       { return j.operation.GameID }
func (j jobStop) GameID() uuid.UUID        { return j.operation.GameID }
func (j jobRestart) GameID() uuid.UUID     { return j.operation.GameID }
func (j jobPatch) GameID() uuid.UUID       { return j.operation.GameID }
func (j jobStart) Operation() OperationLog { return j.operation }
func (j jobStop) Operation() OperationLog  { return j.operation }
func (j jobRestart) Operation() OperationLog { return j.operation }
func (j jobPatch) Operation() OperationLog { return j.operation }

func (j jobStart) Run(ctx context.Context, s *Service) error  { return s.runStart(ctx, j.operation) }
func (j jobStop) Run(ctx context.Context, s *Service) error   { return s.runStop(ctx, j.operation) }
func (j jobRestart) Run(ctx context.Context, s *Service) error {
	return s.runRestart(ctx, j.operation)
}
func (j jobPatch) Run(ctx context.Context, s *Service) error {
	return s.runPatch(ctx, j.operation, j.target)
}

// enqueue places job onto the worker channel. Returns ErrJobQueueFull
// when the channel is at capacity; ErrShutdown when the pool is
// stopped.
func (s *Service) enqueue(ctx context.Context, j job) error {
	if s.workers == nil {
		return ErrShutdown
	}
	return s.workers.submit(ctx, j)
}

// beginOperation persists a queued operation log row. Caller is
// responsible for transitioning it to running/succeeded/failed via
// completeOperation.
func (s *Service) beginOperation(ctx context.Context, gameID uuid.UUID, op, source string) (OperationLog, error) {
	in := operationLogInsert{
		OperationID: uuid.New(),
		GameID:      gameID,
		Op:          op,
		Source:      source,
		Status:      OpStatusQueued,
		StartedAt:   s.deps.Now().UTC(),
	}
	return s.deps.Store.InsertOperationLog(ctx, in)
}

// recordSyncOperation logs an operation that completed synchronously
// (pause / resume / force-next-turn). It writes both the queued and
// the terminal row to keep the audit trail consistent with worker
// jobs.
func (s *Service) recordSyncOperation(ctx context.Context, gameID uuid.UUID, op, source, imageRef, containerID string, runErr error) OperationLog {
	in := operationLogInsert{
		OperationID: uuid.New(),
		GameID:      gameID,
		Op:          op,
		Source:      source,
		Status:      OpStatusRunning,
		ImageRef:    imageRef,
		ContainerID: containerID,
		StartedAt:   s.deps.Now().UTC(),
	}
	rec, err := s.deps.Store.InsertOperationLog(ctx, in)
	if err != nil {
		s.deps.Logger.Warn("operation log insert failed",
			zap.String("game_id", gameID.String()),
			zap.String("op", op),
			zap.Error(err))
		return OperationLog{}
	}
	status := OpStatusSucceeded
	errCode := ""
	errMsg := ""
	if runErr != nil {
		status = OpStatusFailed
		errCode = "internal_error"
		errMsg = runErr.Error()
	}
	completed, err := s.deps.Store.CompleteOperationLog(ctx, rec.OperationID, status, errCode, errMsg, s.deps.Now().UTC())
	if err != nil {
		s.deps.Logger.Warn("operation log complete failed",
			zap.String("game_id", gameID.String()),
			zap.String("op", op),
			zap.Error(err))
		return rec
	}
	return completed
}

// completeOperation flips the row to a terminal status. runErr is nil
// on success.
func (s *Service) completeOperation(ctx context.Context, op OperationLog, runErr error) {
	status := OpStatusSucceeded
	errCode := ""
	errMsg := ""
	if runErr != nil {
		status = OpStatusFailed
		errCode = "internal_error"
		errMsg = runErr.Error()
	}
	if _, err := s.deps.Store.CompleteOperationLog(ctx, op.OperationID, status, errCode, errMsg, s.deps.Now().UTC()); err != nil {
		s.deps.Logger.Warn("operation log complete failed",
			zap.String("game_id", op.GameID.String()),
			zap.String("op", op.Op),
			zap.String("operation_id", op.OperationID.String()),
			zap.Error(err))
	}
}

// =====================================================================
// runStart — the heart of the package
// =====================================================================

func (s *Service) runStart(ctx context.Context, op OperationLog) error {
	gameID := op.GameID
	mu := s.gameLock(gameID)
	mu.Lock()
	defer mu.Unlock()

	game, err := s.deps.Store.LoadGameProjection(ctx, gameID)
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	if strings.TrimSpace(game.TargetEngineVersion) == "" {
		err := fmt.Errorf("%w: game has no target_engine_version", ErrInvalidInput)
		s.publishStartConfigInvalid(ctx, op, "target_engine_version is empty")
		s.completeOperation(ctx, op, err)
		return err
	}
	memberships, err := s.deps.Store.ListActiveMemberships(ctx, gameID)
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	if len(memberships) == 0 {
		err := fmt.Errorf("%w: game has no active memberships", ErrConflict)
		s.publishStartConfigInvalid(ctx, op, "no active memberships")
		s.completeOperation(ctx, op, err)
		return err
	}

	version, err := s.deps.EngineVersions.Resolve(ctx, game.TargetEngineVersion)
	if err != nil {
		s.publishStartConfigInvalid(ctx, op, fmt.Sprintf("engine version %q: %v", game.TargetEngineVersion, err))
		s.completeOperation(ctx, op, err)
		return err
	}

	mappings := make([]PlayerMapping, 0, len(memberships))
	races := make([]rest.InitRace, 0, len(memberships))
	for _, m := range memberships {
		mappings = append(mappings, PlayerMapping{
			GameID:           gameID,
			UserID:           m.UserID,
			RaceName:         m.RaceName,
			EnginePlayerUUID: uuid.New(),
		})
		races = append(races, rest.InitRace{RaceName: m.RaceName})
	}
	if err := s.deps.Store.InsertPlayerMappings(ctx, mappings); err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}

	statePath := filepath.Join(filepath.Clean(s.deps.Config.ContainerStateMount), gameID.String())
	hostStatePath := filepath.Join(filepath.Clean(s.hostStateRoot()), gameID.String())

	// Bind-mount sources are resolved by the Docker daemon against
	// the host filesystem, not against the backend process namespace.
	// Production deploys mount the same `BACKEND_GAME_STATE_ROOT`
	// path into the backend container at the same path, so creating
	// the per-game subdirectory inside backend makes it visible to
	// the daemon at the same absolute path.
	//
	// The directory is created with mode 0o777 (and explicitly
	// chmod-ed to override umask) because the engine container may
	// run as a different uid than backend. Both processes need
	// read-write access to the bind-mounted state path; backend has
	// no way to know the engine container's uid ahead of time, so
	// world-writable is the conservative default. Production
	// deployments that pin both containers to the same user can
	// tighten the mode through a future configuration knob.
	if err := os.MkdirAll(hostStatePath, 0o777); err != nil {
		s.completeOperation(ctx, op, fmt.Errorf("create host state path %q: %w", hostStatePath, err))
		return err
	}
	if err := os.Chmod(hostStatePath, 0o777); err != nil {
		s.completeOperation(ctx, op, fmt.Errorf("chmod host state path %q: %w", hostStatePath, err))
		return err
	}

	spec := dockerclient.RunSpec{
		Name:     ContainerName(gameID.String()),
		Image:    version.ImageRef,
		Hostname: HostName(gameID.String()),
		Network:  s.dockerNetwork(),
		Env: map[string]string{
			"GAME_STATE_PATH": statePath,
		},
		Labels: map[string]string{
			"galaxy.game_id":        gameID.String(),
			"galaxy.engine_version": version.Version,
		},
		BindMounts: []dockerclient.BindMount{
			{
				HostPath:  hostStatePath,
				MountPath: s.deps.Config.ContainerStateMount,
				ReadOnly:  false,
			},
		},
		LogDriver:  s.deps.Config.ContainerLogDriver,
		LogOpts:    s.deps.Config.ContainerLogOpts,
		CPUQuota:   s.deps.Config.ContainerCPUQuota,
		Memory:     s.deps.Config.ContainerMemory,
		PIDsLimit:  s.deps.Config.ContainerPIDsLimit,
		PullPolicy: dockerclient.PullPolicy(s.deps.Config.ImagePullPolicy),
	}

	runResult, err := s.deps.Docker.Run(ctx, spec)
	if err != nil {
		s.publishStartFailure(ctx, op, version.ImageRef, err)
		s.completeOperation(ctx, op, err)
		return err
	}

	now := s.deps.Now().UTC()
	startedAt := runResult.StartedAt
	if startedAt.IsZero() {
		startedAt = now
	}
	startedAtPtr := &startedAt
	rec, err := s.upsertRuntimeRecord(ctx, runtimeRecordInsert{
		GameID:               gameID,
		Status:               RuntimeStatusStarting,
		CurrentContainerID:   runResult.ContainerID,
		CurrentImageRef:      version.ImageRef,
		CurrentEngineVersion: version.Version,
		EngineEndpoint:       runResult.EngineEndpoint,
		StatePath:            statePath,
		DockerNetwork:        s.dockerNetwork(),
		TurnSchedule:         game.TurnSchedule,
		StartedAt:            &startedAt,
	}, runtimeRecordUpdate{
		Status:               strPtr(RuntimeStatusStarting),
		CurrentContainerID:   strPtr(runResult.ContainerID),
		CurrentImageRef:      strPtr(version.ImageRef),
		CurrentEngineVersion: strPtr(version.Version),
		EngineEndpoint:       strPtr(runResult.EngineEndpoint),
		StatePath:            strPtr(statePath),
		DockerNetwork:        strPtr(s.dockerNetwork()),
		TurnSchedule:         strPtr(game.TurnSchedule),
		StartedAt:            &startedAtPtr,
	})
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}

	// Wait for the engine HTTP listener before issuing init. Docker
	// reports the container as running as soon as the entrypoint
	// starts, but the Go binary inside may take a moment to bind
	// the port; without this loop, Init races the listener and
	// fails with `connection refused`.
	if err := s.waitForEngineHealthz(ctx, runResult.EngineEndpoint, 30*time.Second); err != nil {
		s.deps.Logger.Warn("engine healthz never succeeded",
			zap.String("game_id", gameID.String()),
			zap.Error(err))
		s.transitionRuntimeStatus(ctx, gameID, RuntimeStatusEngineUnreachable, "")
		s.completeOperation(ctx, op, err)
		return err
	}

	initResp, err := s.deps.Engine.Init(ctx, runResult.EngineEndpoint, rest.InitRequest{Races: races})
	if err != nil {
		s.deps.Logger.Warn("engine init failed",
			zap.String("game_id", gameID.String()),
			zap.Error(err))
		s.transitionRuntimeStatus(ctx, gameID, RuntimeStatusEngineUnreachable, "")
		s.completeOperation(ctx, op, err)
		return err
	}

	// Engine is up. Transition the runtime row to running and publish
	// the snapshot into lobby.
	rec, err = s.transitionRuntimeStatus(ctx, gameID, RuntimeStatusRunning, "ok")
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	s.scheduler.startGame(rec)
	if err := s.publishSnapshot(ctx, gameID, initResp); err != nil {
		s.deps.Logger.Warn("publish init snapshot failed",
			zap.String("game_id", gameID.String()),
			zap.Error(err))
	}
	s.completeOperation(ctx, op, nil)
	return nil
}

// runStop stops + removes the engine container and transitions the
// runtime row to `stopped`.
func (s *Service) runStop(ctx context.Context, op OperationLog) error {
	gameID := op.GameID
	mu := s.gameLock(gameID)
	mu.Lock()
	defer mu.Unlock()

	rec, err := s.GetRuntime(ctx, gameID)
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	s.scheduler.stopGame(gameID)
	if rec.CurrentContainerID != "" {
		if err := s.deps.Docker.Stop(ctx, rec.CurrentContainerID, int(s.deps.Config.StopGracePeriod/time.Second)); err != nil && !errors.Is(err, dockerclient.ErrContainerNotFound) {
			s.completeOperation(ctx, op, err)
			return err
		}
		if err := s.deps.Docker.Remove(ctx, rec.CurrentContainerID); err != nil {
			s.completeOperation(ctx, op, err)
			return err
		}
	}
	now := s.deps.Now().UTC()
	stoppedAtPtr := &now
	updated, err := s.deps.Store.UpdateRuntimeRecord(ctx, gameID, runtimeRecordUpdate{
		Status:    strPtr(RuntimeStatusStopped),
		StoppedAt: &stoppedAtPtr,
	}, now)
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	s.deps.Cache.PutRuntime(updated)
	if err := s.deps.Store.DeletePlayerMappingsForGame(ctx, gameID); err != nil {
		s.deps.Logger.Warn("delete player_mappings on stop failed",
			zap.String("game_id", gameID.String()),
			zap.Error(err))
	}
	s.completeOperation(ctx, op, nil)
	return nil
}

// runRestart stops + removes + runs a fresh container with the same
// image_ref. Reuses runStart's logic via re-loading the lobby
// projection.
func (s *Service) runRestart(ctx context.Context, op OperationLog) error {
	if err := s.runStop(ctx, op); err != nil {
		return err
	}
	// Reuse runStart with a freshly minted operation row so the audit
	// trail remains consistent.
	startOp, err := s.beginOperation(ctx, op.GameID, OpStart, op.Source)
	if err != nil {
		return err
	}
	return s.runStart(ctx, startOp)
}

// runPatch stops + removes the current container, updates the engine
// version reference, and starts a fresh container.
func (s *Service) runPatch(ctx context.Context, op OperationLog, target EngineVersion) error {
	mu := s.gameLock(op.GameID)
	mu.Lock()
	defer mu.Unlock()

	rec, err := s.GetRuntime(ctx, op.GameID)
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	s.scheduler.stopGame(op.GameID)
	if rec.CurrentContainerID != "" {
		if err := s.deps.Docker.Stop(ctx, rec.CurrentContainerID, int(s.deps.Config.StopGracePeriod/time.Second)); err != nil && !errors.Is(err, dockerclient.ErrContainerNotFound) {
			s.completeOperation(ctx, op, err)
			return err
		}
		if err := s.deps.Docker.Remove(ctx, rec.CurrentContainerID); err != nil {
			s.completeOperation(ctx, op, err)
			return err
		}
	}

	statePath := rec.StatePath
	if statePath == "" {
		statePath = filepath.Join(filepath.Clean(s.deps.Config.ContainerStateMount), op.GameID.String())
	}
	hostStatePath := filepath.Join(filepath.Clean(s.hostStateRoot()), op.GameID.String())

	spec := dockerclient.RunSpec{
		Name:     ContainerName(op.GameID.String()),
		Image:    target.ImageRef,
		Hostname: HostName(op.GameID.String()),
		Network:  s.dockerNetwork(),
		Env: map[string]string{
			"GAME_STATE_PATH": statePath,
		},
		Labels: map[string]string{
			"galaxy.game_id":        op.GameID.String(),
			"galaxy.engine_version": target.Version,
		},
		BindMounts: []dockerclient.BindMount{
			{HostPath: hostStatePath, MountPath: s.deps.Config.ContainerStateMount},
		},
		LogDriver:  s.deps.Config.ContainerLogDriver,
		LogOpts:    s.deps.Config.ContainerLogOpts,
		CPUQuota:   s.deps.Config.ContainerCPUQuota,
		Memory:     s.deps.Config.ContainerMemory,
		PIDsLimit:  s.deps.Config.ContainerPIDsLimit,
		PullPolicy: dockerclient.PullPolicy(s.deps.Config.ImagePullPolicy),
	}
	runResult, err := s.deps.Docker.Run(ctx, spec)
	if err != nil {
		s.publishStartFailure(ctx, op, target.ImageRef, err)
		s.completeOperation(ctx, op, err)
		return err
	}
	now := s.deps.Now().UTC()
	startedAt := runResult.StartedAt
	if startedAt.IsZero() {
		startedAt = now
	}
	startedAtPtr := &startedAt
	updated, err := s.deps.Store.UpdateRuntimeRecord(ctx, op.GameID, runtimeRecordUpdate{
		Status:               strPtr(RuntimeStatusRunning),
		CurrentContainerID:   strPtr(runResult.ContainerID),
		CurrentImageRef:      strPtr(target.ImageRef),
		CurrentEngineVersion: strPtr(target.Version),
		EngineEndpoint:       strPtr(runResult.EngineEndpoint),
		StartedAt:            &startedAtPtr,
		EngineHealth:         strPtr("ok"),
	}, now)
	if err != nil {
		s.completeOperation(ctx, op, err)
		return err
	}
	s.deps.Cache.PutRuntime(updated)
	s.scheduler.startGame(updated)
	s.completeOperation(ctx, op, nil)
	return nil
}

// =====================================================================
// Snapshot / status helpers
// =====================================================================

// publishSnapshot writes a runtime_health_snapshots row, refreshes the
// runtime cache from `current_turn` / `engine_health`, and forwards
// the snapshot to lobby.
func (s *Service) publishSnapshot(ctx context.Context, gameID uuid.UUID, state rest.StateResponse) error {
	now := s.deps.Now().UTC()
	payload, err := json.Marshal(state)
	if err != nil {
		return fmt.Errorf("marshal snapshot: %w", err)
	}
	if err := s.deps.Store.InsertHealthSnapshot(ctx, uuid.New(), gameID, now, payload); err != nil {
		return err
	}
	currentTurn := int32(state.Turn)
	patch := runtimeRecordUpdate{
		CurrentTurn:    &currentTurn,
		EngineHealth:   strPtr("ok"),
		LastObservedAt: dblTime(now),
	}
	if state.Finished {
		patch.Status = strPtr(RuntimeStatusFinished)
		finishedAtPtr := &now
		patch.FinishedAt = &finishedAtPtr
	}
	rec, err := s.deps.Store.UpdateRuntimeRecord(ctx, gameID, patch, now)
	if err != nil {
		return err
	}
	s.deps.Cache.PutRuntime(rec)

	if s.deps.Lobby != nil {
		mappings, err := s.deps.Store.ListPlayerMappingsForGame(ctx, gameID)
		if err != nil {
			s.deps.Logger.Warn("list player_mappings on snapshot failed",
				zap.String("game_id", gameID.String()),
				zap.Error(err))
		}
		userByEngine := make(map[uuid.UUID]uuid.UUID, len(mappings))
		userByRace := make(map[string]uuid.UUID, len(mappings))
		for _, m := range mappings {
			userByEngine[m.EnginePlayerUUID] = m.UserID
			userByRace[m.RaceName] = m.UserID
		}
		stats := make([]LobbyPlayerStats, 0, len(state.Players))
		for _, p := range state.Players {
			userID, ok := userByEngine[p.ID]
			if !ok {
				userID = userByRace[p.RaceName]
			}
			if userID == uuid.Nil {
				continue
			}
			stats = append(stats, LobbyPlayerStats{
				UserID:            userID,
				CurrentPlanets:    int32(p.Planets),
				CurrentPopulation: int32(p.Population),
				MaxPlanets:        int32(p.Planets),
				MaxPopulation:     int32(p.Population),
			})
		}
		runtimeStatus := RuntimeStatusRunning
		if state.Finished {
			runtimeStatus = RuntimeStatusFinished
		}
		err = s.deps.Lobby.OnRuntimeSnapshot(ctx, gameID, LobbySnapshot{
			CurrentTurn:   currentTurn,
			RuntimeStatus: runtimeStatus,
			EngineHealth:  "ok",
			ObservedAt:    now,
			PlayerStats:   stats,
		})
		if err != nil {
			s.deps.Logger.Warn("lobby snapshot consumer failed",
				zap.String("game_id", gameID.String()),
				zap.Error(err))
		}
	}
	return nil
}

// transitionRuntimeStatus updates the status / engine_health columns
// and refreshes the cache.
func (s *Service) transitionRuntimeStatus(ctx context.Context, gameID uuid.UUID, status, health string) (RuntimeRecord, error) {
	now := s.deps.Now().UTC()
	patch := runtimeRecordUpdate{Status: &status}
	if health != "" {
		patch.EngineHealth = &health
	}
	if status == RuntimeStatusFinished {
		finishedAtPtr := &now
		patch.FinishedAt = &finishedAtPtr
	}
	if status == RuntimeStatusStopped {
		stoppedAtPtr := &now
		patch.StoppedAt = &stoppedAtPtr
	}
	rec, err := s.deps.Store.UpdateRuntimeRecord(ctx, gameID, patch, now)
	if err != nil {
		return RuntimeRecord{}, err
	}
	s.deps.Cache.PutRuntime(rec)
	return rec, nil
}

// upsertRuntimeRecord inserts the record when no row exists; updates
// it otherwise. Used by runStart so a re-attempt after a worker crash
// stays idempotent.
func (s *Service) upsertRuntimeRecord(ctx context.Context, in runtimeRecordInsert, patch runtimeRecordUpdate) (RuntimeRecord, error) {
	rec, err := s.deps.Store.InsertRuntimeRecord(ctx, in)
	if err == nil {
		s.deps.Cache.PutRuntime(rec)
		return rec, nil
	}
	if !errors.Is(err, ErrConflict) {
		return RuntimeRecord{}, err
	}
	updated, err := s.deps.Store.UpdateRuntimeRecord(ctx, in.GameID, patch, s.deps.Now().UTC())
	if err != nil {
		return RuntimeRecord{}, err
	}
	s.deps.Cache.PutRuntime(updated)
	return updated, nil
}

// dockerNetwork returns the user-defined Docker network name engine
// containers attach to. Wired from cfg.Docker.Network through Deps.
func (s *Service) dockerNetwork() string { return s.deps.DockerNetwork }

// waitForEngineHealthz polls the engine `/healthz` endpoint until it
// responds 2xx or until the timeout elapses. The Docker daemon
// reports a container as `running` as soon as the entrypoint starts,
// but the engine binary may need a moment to bind its TCP port; the
// retry loop bridges that gap so the immediately-following Init call
// does not race the listener.
func (s *Service) waitForEngineHealthz(ctx context.Context, baseURL string, timeout time.Duration) error {
	deadline := time.Now().Add(timeout)
	var lastErr error
	for {
		probeCtx, cancel := context.WithTimeout(ctx, time.Second)
		err := s.deps.Engine.Healthz(probeCtx, baseURL)
		cancel()
		if err == nil {
			return nil
		}
		lastErr = err
		if time.Now().After(deadline) {
			return fmt.Errorf("engine healthz never succeeded within %s: %w", timeout, lastErr)
		}
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-time.After(200 * time.Millisecond):
		}
	}
}

// hostStateRoot returns the host-side root directory under which the
// per-game state directory is created. Wired from cfg.Game.StateRoot
// through Deps.
func (s *Service) hostStateRoot() string {
	if s.deps.HostStateRoot != "" {
		return s.deps.HostStateRoot
	}
	return s.deps.Config.ContainerStateMount
}

// strPtr returns a pointer to s. Helps assemble runtimeRecordUpdate
// values inline.
func strPtr(s string) *string { return &s }

// dblTime returns a `**time.Time` set to t. Used to clear / set the
// nullable timestamp columns of `runtime_records` through
// runtimeRecordUpdate.
func dblTime(t time.Time) **time.Time { p := &t; return &p }