package pi

import (
	"context"
	"crypto/sha256"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"sort"
	"strings"
	"time"

	"github.com/aritmolab/thothii/tools/tht/internal/compose"
	"github.com/distribution/reference"
)

var (
	ErrConfirmationRequired = errors.New("update requires --yes after reviewing the planned Pi version")
	ErrActiveSessions       = errors.New("active sessions must be drained before updating Pi; use --drain only after they are complete")
	ErrInterruptedUpdate    = errors.New("a previous Pi update is incomplete; run pi rollback --yes before starting another update")
	ErrInvalidRequest       = errors.New("invalid Pi lifecycle request")
	versionPattern          = regexp.MustCompile(`^[0-9]+(?:\.[0-9]+){1,3}(?:[-+][0-9A-Za-z.-]+)?$`)
)

// Source chooses whether the candidate is built from this checkout or pulled from an immutable image.
type Source string

const (
	BuildSource Source = "build"
	PullSource  Source = "pull"
)

// Request contains only non-secret operator inputs.
type Request struct {
	StatePath        string
	RestartStatePath string
	Version          string
	Source           Source
	Image            string
	Confirm          bool
	Drain            bool
}

// Result summarizes the completed, failed, or recovered transaction without command output.
type Result struct {
	Phase     Phase
	StatePath string
}

type lifecycleHooks struct {
	writeState func(string, State) error
	removeFile func(string) error
	sleep      func(time.Duration)
}

var defaultLifecycleHooks = lifecycleHooks{
	writeState: writeState,
	removeFile: durableRemove,
	sleep:      time.Sleep,
}

// Update performs a recoverable core-only Pi update using the default Compose command layout.
func Update(ctx context.Context, runner Runner, request Request) (result Result, retErr error) {
	return updateWithHooks(ctx, runner, request, defaultLifecycleHooks)
}

func updateWithHooks(ctx context.Context, runner Runner, request Request, hooks lifecycleHooks) (result Result, retErr error) {
	if request.StatePath == "" {
		return Result{}, errors.New("update state path is required")
	}
	if request.RestartStatePath == "" {
		request.RestartStatePath = pairedRestartStatePath(request.StatePath)
	}
	if err := validateRestartStatePaths(request.RestartStatePath, request.StatePath); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	lock, err := acquireLock(request.StatePath)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	defer lock.Release()
	if !request.Confirm {
		return Result{StatePath: request.StatePath}, ErrConfirmationRequired
	}
	if !versionPattern.MatchString(request.Version) {
		return Result{StatePath: request.StatePath}, fmt.Errorf("%w: Pi version must be an explicit pinned version", ErrInvalidRequest)
	}
	if request.Source == "" {
		return Result{StatePath: request.StatePath}, fmt.Errorf("%w: Pi update requires an explicit source: build or pull", ErrInvalidRequest)
	}
	if request.Source != BuildSource && request.Source != PullSource {
		return Result{StatePath: request.StatePath}, fmt.Errorf("%w: Pi update source must be build or pull", ErrInvalidRequest)
	}
	if request.Source == PullSource {
		canonical, err := canonicalDigestReference(request.Image)
		if err != nil {
			return Result{StatePath: request.StatePath}, fmt.Errorf("%w: %v", ErrInvalidRequest, err)
		}
		request.Image = canonical
	}
	if err := prepareLifecycleMutation(request.RestartStatePath, hooks.removeFile); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	if old, err := readState(request.StatePath); err == nil && stateNeedsRecovery(old) {
		return Result{StatePath: request.StatePath}, ErrInterruptedUpdate
	} else if err != nil && !errors.Is(err, os.ErrNotExist) {
		return Result{StatePath: request.StatePath}, err
	} else if err == nil && !old.MutationStarted {
		if cleanupErr := hooks.removeFile(lifecycleOverridePath(request.StatePath, old.Transaction)); cleanupErr != nil {
			return Result{StatePath: request.StatePath}, errors.New("safe prior preparation state could not be cleaned up")
		}
	}
	if err := setMaintenance(ctx, runner, true); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	clearMaintenance := true
	defer func() {
		if !clearMaintenance {
			return
		}
		if clearErr := setMaintenance(context.Background(), runner, false); clearErr != nil {
			result = Result{Phase: PhaseFailed, StatePath: request.StatePath}
			retErr = errors.Join(retErr, fmt.Errorf("maintenance admission gate could not be cleared: %w", clearErr))
		}
	}()

	if err := waitForInactiveSessions(ctx, runner, request.Drain, hooks.sleep); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	if err := Doctor(ctx, runner); err != nil {
		return Result{StatePath: request.StatePath}, err
	}

	currentVersion, err := Status(ctx, runner)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	if currentVersion == request.Version {
		return Result{Phase: PhaseNoop, StatePath: request.StatePath}, nil
	}
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	previous, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	previous.ConfigurationSHA = configured.ConfigurationSHA
	transaction := lifecycleTransaction(request.StatePath)
	previous.Reference = lifecycleImageTag(transaction, "previous")
	candidateReference := lifecycleImageTag(transaction, "candidate")
	if err := tagImage(ctx, runner, previous.ID, previous.Reference, "previous Pi image pin"); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	state := State{
		Transaction: transaction,
		Phase:       PhasePreflight,
		Target:      Target{Version: request.Version, Source: sourceValue(request)},
		Previous:    previous,
		Candidate:   Image{Reference: candidateReference},
	}
	if err := hooks.writeState(request.StatePath, state); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	overridePath := lifecycleOverridePath(request.StatePath, transaction)
	if err := writeLifecycleOverride(overridePath, candidateReference); err != nil {
		return Result{StatePath: request.StatePath}, err
	}
	lifecycle := composeOverrideRunner{Runner: runner, path: overridePath}

	state.Phase = PhaseBuilding
	if err := hooks.writeState(request.StatePath, state); err != nil {
		result, retErr, clearMaintenance = failPreparation(request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	if err := prepareCandidate(ctx, lifecycle, request, candidateReference); err != nil {
		result, retErr, clearMaintenance = failPreparation(request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	running, err := activeSessions(ctx, runner)
	if err != nil {
		result, retErr, clearMaintenance = failPreparation(request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	if running {
		result, retErr, clearMaintenance = failPreparation(request.StatePath, overridePath, state, ErrActiveSessions, hooks)
		return result, retErr
	}
	state.MutationStarted = true
	if err := hooks.writeState(request.StatePath, state); err != nil {
		state.MutationStarted = false
		result, retErr, clearMaintenance = failPreparation(request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	clearMaintenance = false
	if err := recreateCore(ctx, lifecycle); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	if err := ensureMaintenance(ctx, lifecycle); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	state.Phase = PhaseRecreated
	state.Candidate, err = runningImage(ctx, lifecycle, candidateReference)
	if err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	if err := hooks.writeState(request.StatePath, state); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	if err := verifyCandidate(ctx, lifecycle, request.Version, previous); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	state.Phase, state.Error = PhasePromoting, ""
	if err := hooks.writeState(request.StatePath, state); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	if err := promoteLifecycleOverride(overridePath, currentImageOverridePath(request.StatePath), candidateReference); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	state.Phase = PhaseVerified
	if err := hooks.writeState(request.StatePath, state); err != nil {
		result, retErr, clearMaintenance = compensate(ctx, runner, request.StatePath, overridePath, state, err, hooks)
		return result, retErr
	}
	clearMaintenance = true
	return Result{Phase: PhaseVerified, StatePath: request.StatePath}, nil
}

func stateNeedsRecovery(state State) bool {
	switch state.Phase {
	case PhaseVerified, PhaseRolledBack, PhaseNoop:
		return false
	case PhaseFailed:
		return state.MutationStarted
	default:
		return state.MutationStarted
	}
}

func failPreparation(statePath, overridePath string, state State, cause error, hooks lifecycleHooks) (Result, error, bool) {
	state.Phase = PhaseFailed
	state.MutationStarted = false
	state.Error = "candidate preparation failed before core mutation"
	writeErr := hooks.writeState(statePath, state)
	removeErr := hooks.removeFile(overridePath)
	message := "candidate preparation failed before core mutation"
	if writeErr != nil || removeErr != nil {
		message += "; safe preparation cleanup was incomplete"
	}
	return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("%s: %w", message, cause), true
}

// Rollback restores the image recorded in durable update state. It is safe for interrupted runs.
func Rollback(ctx context.Context, runner Runner, statePath, restartStatePath string, confirm bool) (result Result, retErr error) {
	return rollbackWithHooks(ctx, runner, statePath, restartStatePath, confirm, defaultLifecycleHooks)
}

func rollbackWithHooks(ctx context.Context, runner Runner, statePath, restartStatePath string, confirm bool, hooks lifecycleHooks) (result Result, retErr error) {
	if restartStatePath == "" {
		restartStatePath = pairedRestartStatePath(statePath)
	}
	if err := validateRestartStatePaths(restartStatePath, statePath); err != nil {
		return Result{StatePath: statePath}, err
	}
	lock, err := acquireLock(statePath)
	if err != nil {
		return Result{StatePath: statePath}, err
	}
	defer lock.Release()
	if !confirm {
		return Result{StatePath: statePath}, ErrConfirmationRequired
	}
	if err := prepareLifecycleMutation(restartStatePath, hooks.removeFile); err != nil {
		return Result{StatePath: statePath}, err
	}
	maintenanceErr := ensureMaintenance(ctx, runner)
	clearMaintenance := maintenanceErr == nil
	defer func() {
		if !clearMaintenance {
			return
		}
		if clearErr := setMaintenance(context.Background(), runner, false); clearErr != nil {
			result = Result{Phase: PhaseFailed, StatePath: statePath}
			retErr = errors.Join(retErr, fmt.Errorf("maintenance admission gate could not be cleared: %w", clearErr))
		}
	}()
	if maintenanceErr == nil {
		if active, err := activeSessions(ctx, runner); err != nil {
			return Result{StatePath: statePath}, err
		} else if active {
			return Result{StatePath: statePath}, ErrActiveSessions
		}
	}
	state, err := readState(statePath)
	if err != nil {
		if maintenanceErr == nil {
			clearMaintenance = false
		}
		return Result{StatePath: statePath}, err
	}
	overridePath := lifecycleOverridePath(statePath, state.Transaction)
	if err := writeLifecycleOverride(overridePath, state.Previous.Reference); err != nil {
		clearMaintenance = false
		return Result{StatePath: statePath}, err
	}
	lifecycle := composeOverrideRunner{Runner: runner, path: overridePath}
	if maintenanceErr != nil {
		stopped, stopErr := coreIsStopped(ctx, runner)
		if stopErr != nil || !stopped {
			return Result{StatePath: statePath}, maintenanceErr
		}
		if err := persistMaintenanceWithoutLiveCore(ctx, lifecycle); err != nil {
			return Result{Phase: PhaseFailed, StatePath: statePath}, err
		}
	}
	clearMaintenance = false
	if err := restore(ctx, lifecycle, state.Previous); err != nil {
		state.Phase, state.Error = PhaseFailed, "rollback failed"
		if writeErr := hooks.writeState(statePath, state); writeErr != nil {
			return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("rollback failed and recovery state could not be persisted")
		}
		return Result{Phase: PhaseFailed, StatePath: statePath}, err
	}
	if active, err := activeSessions(ctx, runner); err != nil {
		return Result{Phase: PhaseFailed, StatePath: statePath}, err
	} else if active {
		return Result{Phase: PhaseFailed, StatePath: statePath}, ErrActiveSessions
	}
	if err := promoteLifecycleOverride(overridePath, currentImageOverridePath(statePath), state.Previous.Reference); err != nil {
		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("rollback restored the core but durable current-image promotion failed: %w", err)
	}
	state.Phase, state.Error = PhaseRolledBack, ""
	if err := hooks.writeState(statePath, state); err != nil {
		return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("rollback restored the core but recovery state could not be persisted")
	}
	clearMaintenance = true
	return Result{Phase: PhaseRolledBack, StatePath: statePath}, nil
}

func compensate(ctx context.Context, runner Runner, statePath, overridePath string, state State, cause error, hooks lifecycleHooks) (Result, error, bool) {
	if err := writeLifecycleOverride(overridePath, state.Previous.Reference); err != nil {
		return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("update failed and rollback override could not be prepared: recovery required"), false
	}
	lifecycle := composeOverrideRunner{Runner: runner, path: overridePath}
	if err := ensureMaintenance(context.Background(), runner); err != nil {
		stopped, stopErr := coreIsStopped(context.Background(), runner)
		if stopErr != nil || !stopped {
			state.Phase, state.Error = PhaseFailed, "maintenance recovery failed"
			_ = hooks.writeState(statePath, state)
			return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("update failed and maintenance could not be reactivated: recovery required"), false
		}
		if markerErr := persistMaintenanceWithoutLiveCore(context.Background(), lifecycle); markerErr != nil {
			state.Phase, state.Error = PhaseFailed, "maintenance recovery failed"
			_ = hooks.writeState(statePath, state)
			return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("update failed and durable maintenance could not be established: recovery required"), false
		}
	} else if active, err := activeSessions(context.Background(), runner); err != nil || active {
		state.Phase, state.Error = PhaseFailed, "rollback inventory failed"
		_ = hooks.writeState(statePath, state)
		return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("update failed and rollback inventory is not quiescent: recovery required"), false
	}
	if restoreErr := restore(ctx, lifecycle, state.Previous); restoreErr != nil {
		state.Phase, state.Error = PhaseFailed, "candidate verification and automatic rollback failed"
		if writeErr := hooks.writeState(statePath, state); writeErr != nil {
			return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("update failed and rollback proof failed; recovery state could not be persisted"), false
		}
		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("update failed; automatic rollback also failed: recovery required"), false
	}
	if active, err := activeSessions(context.Background(), runner); err != nil || active {
		state.Phase, state.Error = PhaseFailed, "restored rollback inventory failed"
		_ = hooks.writeState(statePath, state)
		return Result{Phase: PhaseFailed, StatePath: statePath}, errors.New("previous core image was restored but rollback inventory is not quiescent: recovery required"), false
	}
	if err := promoteLifecycleOverride(overridePath, currentImageOverridePath(statePath), state.Previous.Reference); err != nil {
		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("previous core image was restored but durable selector promotion failed: %w", err), false
	}
	state.Phase, state.Error = PhaseRolledBack, ""
	if writeErr := hooks.writeState(statePath, state); writeErr != nil {
		return Result{Phase: PhaseFailed, StatePath: statePath}, fmt.Errorf("previous core image was restored but recovery state write failed: recovery required"), false
	}
	return Result{Phase: PhaseRolledBack, StatePath: statePath}, fmt.Errorf("update failed; previous core image was restored: %w", cause), true
}

func coreIsStopped(ctx context.Context, runner Runner) (bool, error) {
	result, err := runCompose(ctx, runner, "ps", "--status", "running", "-q", "core")
	if err != nil {
		return false, commandError("core running-state check", result, err)
	}
	return strings.TrimSpace(result.Stdout) == "", nil
}

const maintenanceMarkerScript = `
const fs = require("node:fs");
const path = require("node:path");
const marker = process.env.THT_MAINTENANCE_FILE;
if (!marker) throw new Error("THT_MAINTENANCE_FILE is required");
const directory = path.dirname(marker);
fs.mkdirSync(directory, { recursive: true });
const temporary = marker + ".rollback-" + process.pid + "-" + Date.now();
let file;
try {
  file = fs.openSync(temporary, "wx", 0o600);
  fs.writeFileSync(file, "{\"version\":1,\"active\":true}\n", "utf8");
  fs.fsyncSync(file);
  fs.closeSync(file);
  file = undefined;
  fs.renameSync(temporary, marker);
  const directoryFile = fs.openSync(directory, "r");
  try { fs.fsyncSync(directoryFile); } finally { fs.closeSync(directoryFile); }
} catch (error) {
  if (file !== undefined) try { fs.closeSync(file); } catch {}
  try { fs.unlinkSync(temporary); } catch {}
  throw error;
}
`

func persistMaintenanceWithoutLiveCore(ctx context.Context, runner Runner) error {
	result, err := runCompose(ctx, runner,
		"run", "--rm", "--no-deps", "--entrypoint", "node", "core", "-e", maintenanceMarkerScript,
	)
	if err != nil {
		return commandError("durable maintenance recovery", result, err)
	}
	return nil
}

func sourceValue(request Request) string {
	if request.Source == PullSource {
		return request.Image
	}
	return string(BuildSource)
}

func canonicalDigestReference(value string) (string, error) {
	if strings.Contains(value, "://") || strings.ContainsAny(value, "?#") || strings.Contains(value, "@") && strings.Contains(strings.Split(value, "@")[0], ":") && strings.Contains(strings.Split(value, "@")[0], "//") {
		return "", errors.New("pulled Pi image must be a credential-free canonical sha256 digest reference")
	}
	parsed, err := reference.ParseAnyReference(value)
	if err != nil {
		return "", errors.New("pulled Pi image must be a valid canonical sha256 digest reference")
	}
	canonical, ok := parsed.(reference.Canonical)
	if !ok || canonical.Digest().Algorithm().String() != "sha256" || len(canonical.Digest().Encoded()) != 64 {
		return "", errors.New("pulled Pi image must use an immutable sha256 digest")
	}
	return reference.FamiliarString(canonical), nil
}

func setMaintenance(ctx context.Context, runner Runner, enabled bool) error {
	path := "deactivate"
	if enabled {
		path = "activate"
	}
	args := []string{"exec", "-T", "core", "curl", "-fsS", "-X", "POST", "http://127.0.0.1:8787/internal/maintenance/" + path}
	result, err := runCompose(ctx, runner, args...)
	status, valid := parseMaintenanceStatus(result.Stdout)
	if err == nil && valid && status.Active == enabled && status.Admissions == 0 && !status.RecoveryRequired {
		return nil
	}
	// Status identifies the safest immediate state after an ambiguous response. It cannot
	// acknowledge durability for an operation whose command returned an error.
	observed, statusErr := MaintenanceStatus(ctx, runner)
	if valid && status.RecoveryRequired {
		return recoveryRequired("maintenance durability was explicitly not acknowledged", err)
	}
	if statusErr == nil && observed.RecoveryRequired {
		return recoveryRequired("maintenance durability was explicitly not acknowledged", err)
	}
	if err != nil {
		if statusErr == nil && observed.Active == enabled && observed.Admissions == 0 {
			return recoveryRequired("maintenance durability was not acknowledged after a failed command", err)
		}
		return commandError("maintenance admission gate", result, err)
	}
	if statusErr == nil && observed.Active == enabled && observed.Admissions == 0 {
		return nil
	}
	return errors.New("maintenance admission gate did not acknowledge a quiescent state")
}

type MaintenanceState struct {
	Active           bool `json:"active"`
	Admissions       int  `json:"admissions"`
	RecoveryRequired bool `json:"recoveryRequired"`
}

func parseMaintenanceStatus(value string) (MaintenanceState, bool) {
	var status MaintenanceState
	err := json.Unmarshal([]byte(value), &status)
	return status, err == nil && status.Admissions >= 0
}

func MaintenanceStatus(ctx context.Context, runner Runner) (MaintenanceState, error) {
	result, err := runCompose(ctx, runner, "exec", "-T", "core", "curl", "-fsS", "http://127.0.0.1:8787/internal/maintenance/status")
	if err != nil {
		return MaintenanceState{}, commandError("maintenance status check", result, err)
	}
	status, valid := parseMaintenanceStatus(result.Stdout)
	if !valid {
		return MaintenanceState{}, errors.New("maintenance status check returned invalid data")
	}
	return status, nil
}

func ensureMaintenance(ctx context.Context, runner Runner) error {
	status, err := MaintenanceStatus(ctx, runner)
	if err == nil && status.Active && status.Admissions == 0 && !status.RecoveryRequired {
		return nil
	}
	if err == nil && status.RecoveryRequired {
		return recoveryRequired("maintenance durability was explicitly not acknowledged", nil)
	}
	return setMaintenance(ctx, runner, true)
}

func activeSessions(ctx context.Context, runner Runner) (bool, error) {
	scope := "all"
	if scoped, ok := runner.(interface{ SessionInventoryScope() string }); ok {
		if requested := scoped.SessionInventoryScope(); requested == "mine" || requested == "all" {
			scope = requested
		}
	}
	args := append([]string{"exec", "-T", "core", "curl", "-fsS"}, internalIdentityHeaders...)
	args = append(args, "http://127.0.0.1:8787/sessions?scope="+scope)
	result, err := runCompose(ctx, runner, args...)
	if err != nil {
		return false, commandError("active-session check", result, err)
	}
	var payload []struct {
		Status   string `json:"status"`
		Archived bool   `json:"archived"`
	}
	if err := json.Unmarshal([]byte(result.Stdout), &payload); err != nil {
		return false, errors.New("active-session check returned invalid session data")
	}
	for _, session := range payload {
		if !session.Archived && session.Status != "finalized" && session.Status != "closed" {
			return true, nil
		}
	}
	return false, nil
}

func waitForInactiveSessions(ctx context.Context, runner Runner, drain bool, sleep func(time.Duration)) error {
	running, err := activeSessions(ctx, runner)
	if err != nil {
		return err
	}
	if !running {
		return nil
	}
	if !drain {
		return ErrActiveSessions
	}
	for attempts := 0; attempts < 30; attempts++ {
		running, err = activeSessions(ctx, runner)
		if err != nil {
			return err
		}
		if !running {
			return nil
		}
		sleep(time.Second)
	}
	return ErrActiveSessions
}

func runningImage(ctx context.Context, runner Runner, reference string) (Image, error) {
	container, err := runCompose(ctx, runner, "ps", "-q", "core")
	if err != nil || strings.TrimSpace(container.Stdout) == "" {
		return Image{}, commandError("running core image check", container, err)
	}
	id := strings.TrimSpace(container.Stdout)
	image, err := runner.Run(ctx, []string{"inspect", "--format", "{{.Image}}", id}, nil)
	if err != nil || strings.TrimSpace(image.Stdout) == "" {
		return Image{}, commandError("running core image check", image, err)
	}
	mounts, err := runner.Run(ctx, []string{"inspect", "--format", "{{json .Mounts}}", id}, nil)
	if err != nil {
		return Image{}, commandError("core volume check", mounts, err)
	}
	var raw []struct {
		Type        string `json:"Type"`
		Name        string `json:"Name"`
		Source      string `json:"Source"`
		Destination string `json:"Destination"`
		RW          bool   `json:"RW"`
		Mode        string `json:"Mode"`
		Propagation string `json:"Propagation"`
		Driver      string `json:"Driver"`
	}
	if err := json.Unmarshal([]byte(mounts.Stdout), &raw); err != nil {
		return Image{}, errors.New("core returned invalid persistence mount data")
	}
	if len(raw) == 0 {
		return Image{}, errors.New("core has no persistence mounts to preserve")
	}
	contract := make([]Mount, 0, len(raw))
	for _, mount := range raw {
		if mount.Type == "" || mount.Source == "" || mount.Destination == "" {
			return Image{}, errors.New("core returned incomplete persistence mount data")
		}
		contract = append(contract, Mount{Type: mount.Type, Name: mount.Name, SourceSHA256: mountSourceHash(mount.Source), SourceAliases: mountSourceAliases(mount.Type, mount.Source, runtime.GOOS), Destination: mount.Destination, RW: mount.RW, Options: strings.Join([]string{mount.Mode, mount.Propagation, mount.Driver}, "\x00")})
	}
	return Image{ID: strings.TrimSpace(image.Stdout), Reference: reference, Mounts: contract, MountFingerprint: mountFingerprint(contract)}, nil
}

func prepareCandidate(ctx context.Context, runner Runner, request Request, candidateReference string) error {
	if request.Source == BuildSource {
		result, err := runCompose(ctx, runner, "build", "--pull", "--build-arg", "PI_VERSION="+request.Version, "core")
		if err != nil {
			return commandError("Pi image build", result, err)
		}
		return nil
	}
	pull, err := runner.Run(ctx, []string{"pull", request.Image}, nil)
	if err != nil {
		return commandError("Pi image pull", pull, err)
	}
	return tagImage(ctx, runner, request.Image, candidateReference, "Pi image tag")
}

func recreateCore(ctx context.Context, runner Runner) error {
	result, err := runCompose(ctx, runner, "up", "--detach", "--wait", "--wait-timeout", "45", "--no-deps", "--force-recreate", "core")
	if err != nil {
		return commandError("core recreation", result, err)
	}
	return nil
}

func verifyCandidate(ctx context.Context, runner Runner, wanted string, previous Image) error {
	health, err := runCompose(ctx, runner, "exec", "-T", "core", "curl", "-fsS", "http://127.0.0.1:8787/health")
	if err != nil {
		return commandError("core health check", health, err)
	}
	if err := verifyCandidateVersionIdentity(ctx, runner, wanted); err != nil {
		return err
	}
	if err := Test(ctx, runner); err != nil {
		return err
	}
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return err
	}
	if configured.ConfigurationSHA != previous.ConfigurationSHA {
		return errors.New("external endpoint configuration changed during Pi update")
	}
	after, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return err
	}
	if !sameMounts(previous.Mounts, after.Mounts) {
		return errors.New("core persistence mount contract changed during Pi update")
	}
	return nil
}

func verifyCandidateVersionIdentity(ctx context.Context, runner Runner, wanted string) error {
	executable, err := Status(ctx, runner)
	if err != nil {
		return err
	}
	environment, label, err := expectedVersions(ctx, runner)
	if err != nil {
		return err
	}
	if executable != wanted || environment != wanted || label != wanted {
		return errors.New("candidate Pi executable, PI_VERSION, and image label do not all match the requested pinned version")
	}
	return nil
}

func restore(ctx context.Context, runner Runner, previous Image) error {
	if err := tagImage(ctx, runner, previous.ID, previous.Reference, "rollback image restore"); err != nil {
		return err
	}
	if err := recreateCore(ctx, runner); err != nil {
		return err
	}
	if err := ensureMaintenance(ctx, runner); err != nil {
		return err
	}
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return err
	}
	after, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return err
	}
	if after.ID != previous.ID {
		return errors.New("rollback core image does not match recorded previous image")
	}
	if configured.ConfigurationSHA != previous.ConfigurationSHA {
		return errors.New("external endpoint configuration drift prevents rollback proof")
	}
	if !sameMounts(previous.Mounts, after.Mounts) {
		return errors.New("core persistence mount contract changed during rollback")
	}
	if err := Doctor(ctx, runner); err != nil {
		return err
	}
	if err := Test(ctx, runner); err != nil {
		return err
	}
	return nil
}

func tagImage(ctx context.Context, runner Runner, source, target, label string) error {
	result, err := runner.Run(ctx, []string{"image", "tag", source, target}, nil)
	if err != nil {
		return commandError(label, result, err)
	}
	return nil
}

type composeOverrideRunner struct {
	Runner
	path string
}

func (r composeOverrideRunner) Run(ctx context.Context, args []string, stdin io.Reader) (compose.Result, error) {
	if len(args) > 0 && args[0] == "compose" {
		withOverride := append([]string{"compose", "-f", r.path}, args[1:]...)
		return r.Runner.Run(ctx, withOverride, stdin)
	}
	return r.Runner.Run(ctx, args, stdin)
}

func lifecycleTransaction(statePath string) string {
	value := fmt.Sprintf("%s\x00%d\x00%d", filepath.Clean(statePath), os.Getpid(), time.Now().UnixNano())
	sum := sha256.Sum256([]byte(value))
	return fmt.Sprintf("%x", sum[:8])
}

func lifecycleImageTag(transaction, role string) string {
	return "thothii-core:tht-" + transaction + "-" + role
}

func lifecycleOverridePath(statePath, transaction string) string {
	if transaction == "" {
		transaction = "recovery"
	}
	return filepath.Join(filepath.Dir(statePath), "pi-lifecycle-"+transaction+".yaml")
}

func currentImageOverridePath(statePath string) string {
	return filepath.Join(filepath.Dir(statePath), "current-image.yaml")
}

func writeLifecycleOverride(path, image string) error {
	quoted, err := json.Marshal(image)
	if err != nil {
		return errors.New("lifecycle image override could not be encoded")
	}
	contents := []byte(`services:
  core:
    image: ` + string(quoted) + `
  workspace-maintenance:
    image: ` + string(quoted) + `
`)
	if err := writeFileDurably(path, ".pi-lifecycle-", contents); err != nil {
		return errors.New("lifecycle image override could not be written durably")
	}
	return nil
}

func promoteLifecycleOverride(source, destination, expectedImage string) error {
	return promoteLifecycleOverrideWith(source, destination, expectedImage, durableReplace)
}

func promoteLifecycleOverrideWith(
	source, destination, expectedImage string,
	replace func(string, string, string) error,
) error {
	if err := replace(source, destination, filepath.Dir(destination)); err != nil {
		selected, readErr := readLifecycleOverride(destination)
		if readErr == nil && selected == expectedImage {
			return recoveryRequired("lifecycle image override changed but durability was not acknowledged", err)
		}
		return recoveryRequired("lifecycle image override could not be promoted durably", err)
	}
	selected, err := readLifecycleOverride(destination)
	if err != nil || selected != expectedImage {
		return errors.New("promoted lifecycle image override could not be verified")
	}
	return nil
}

func readLifecycleOverride(path string) (string, error) {
	contents, err := os.ReadFile(path)
	if err != nil {
		return "", err
	}
	for _, line := range strings.Split(string(contents), "\n") {
		line = strings.TrimSpace(line)
		if !strings.HasPrefix(line, "image:") {
			continue
		}
		encoded := strings.TrimSpace(strings.TrimPrefix(line, "image:"))
		var image string
		if json.Unmarshal([]byte(encoded), &image) != nil || image == "" || strings.ContainsAny(image, "\r\n") {
			return "", errors.New("lifecycle image override is invalid")
		}
		return image, nil
	}
	return "", errors.New("lifecycle image override has no core image")
}

// RecoverMaintenance clears a stale durable gate only after the running core and terminal
// recovery metadata prove that no rollback is still required.
func RecoverMaintenance(ctx context.Context, runner Runner, statePath string, confirm bool) error {
	if !confirm {
		return ErrConfirmationRequired
	}
	lock, err := acquireLock(statePath)
	if err != nil {
		return err
	}
	defer lock.Release()
	return recoverMaintenanceLocked(ctx, runner, statePath)
}

func recoverMaintenanceLocked(ctx context.Context, runner Runner, statePath string) error {
	state, stateErr := readState(statePath)
	if stateErr == nil {
		transactionOverride := lifecycleOverridePath(statePath, state.Transaction)
		switch {
		case state.Phase == PhasePromoting:
			if err := recoverPromotion(ctx, runner, statePath, transactionOverride, &state); err != nil {
				return err
			}
		case !state.MutationStarted && state.Phase != PhaseVerified && state.Phase != PhaseRolledBack && state.Phase != PhaseNoop:
			state.Phase, state.Error = PhaseFailed, "candidate preparation interrupted before core mutation"
			if err := writeState(statePath, state); err != nil {
				return errors.New("maintenance recovery could not finalize safe preparation state")
			}
			if err := durableRemove(transactionOverride); err != nil {
				return errors.New("maintenance recovery could not remove the safe preparation override")
			}
		case stateNeedsRecovery(state):
			return ErrInterruptedUpdate
		default:
			if err := durableRemove(transactionOverride); err != nil {
				return errors.New("maintenance recovery could not remove the lifecycle override")
			}
		}
	} else if !errors.Is(stateErr, os.ErrNotExist) {
		return stateErr
	}
	status, err := MaintenanceStatus(ctx, runner)
	if err != nil {
		return err
	}
	if !status.Active {
		return nil
	}
	if err := Doctor(ctx, runner); err != nil {
		return err
	}
	return setMaintenance(ctx, runner, false)
}

func recoverPromotion(ctx context.Context, runner Runner, statePath, transactionOverride string, state *State) error {
	currentOverride := currentImageOverridePath(statePath)
	selected, currentErr := readLifecycleOverride(currentOverride)
	if currentErr != nil || selected != state.Candidate.Reference {
		pending, pendingErr := readLifecycleOverride(transactionOverride)
		if pendingErr != nil || pending != state.Candidate.Reference {
			if currentErr == nil && selected == state.Previous.Reference {
				if err := verifyRestoredCurrent(ctx, runner, state.Previous); err != nil {
					return ErrInterruptedUpdate
				}
				state.Phase, state.Error = PhaseRolledBack, ""
				return writeState(statePath, *state)
			}
			return ErrInterruptedUpdate
		}
		if err := promoteLifecycleOverride(transactionOverride, currentOverride, state.Candidate.Reference); err != nil {
			return err
		}
	}
	if err := verifyCandidate(ctx, runner, state.Target.Version, state.Previous); err != nil {
		return err
	}
	state.Phase, state.Error = PhaseVerified, ""
	return writeState(statePath, *state)
}

func verifyRestoredCurrent(ctx context.Context, runner Runner, previous Image) error {
	configured, err := renderedCore(ctx, runner)
	if err != nil {
		return err
	}
	after, err := runningImage(ctx, runner, configured.Reference)
	if err != nil {
		return err
	}
	if after.ID != previous.ID || configured.ConfigurationSHA != previous.ConfigurationSHA || !sameMounts(previous.Mounts, after.Mounts) {
		return errors.New("running core does not match the durable previous-image selector")
	}
	if err := Doctor(ctx, runner); err != nil {
		return err
	}
	return Test(ctx, runner)
}

func sameStrings(left, right []string) bool {
	left, right = append([]string(nil), left...), append([]string(nil), right...)
	sort.Strings(left)
	sort.Strings(right)
	return strings.Join(left, "\x00") == strings.Join(right, "\x00")
}

func sameMounts(left, right []Mount) bool {
	if len(left) != len(right) {
		return false
	}
	identityWithoutSource := func(m Mount) string {
		return m.Type + "\x00" + m.Name + "\x00" + m.Destination + "\x00" + fmt.Sprint(m.RW) + "\x00" + m.Options
	}
	sourceMatches := func(a, b Mount) bool {
		if a.SourceSHA256 == b.SourceSHA256 {
			return true
		}
		for _, alias := range a.SourceAliases {
			if alias == b.SourceSHA256 {
				return true
			}
		}
		for _, alias := range b.SourceAliases {
			if alias == a.SourceSHA256 {
				return true
			}
		}
		return false
	}
	matched := make([]bool, len(right))
	for _, candidate := range left {
		found := false
		for index, observed := range right {
			if matched[index] || identityWithoutSource(candidate) != identityWithoutSource(observed) || !sourceMatches(candidate, observed) {
				continue
			}
			matched[index], found = true, true
			break
		}
		if !found {
			return false
		}
	}
	return true
}