package runtime

import (
	"archive/tar"
	"archive/zip"
	"compress/gzip"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"
	"time"

	"browser.local/run/protocol"
)

const (
	selfUpdateManifestVersion = 1
	maxSelfUpdateBytes        = int64(512 * 1024 * 1024)
	maxSelfUpdateEntries      = 8
	defaultUpdateHealthWait   = 30 * time.Second
)

var ErrSelfUpdateRestartRequested = errors.New("Run self-update restart requested")

type SelfUpdateManifest struct {
	Version           int       `json:"version"`
	JobID             string    `json:"jobId"`
	Attempt           int       `json:"attempt"`
	LeaseToken        string    `json:"leaseToken"`
	ArtifactID        string    `json:"artifactId"`
	ArtifactChecksum  string    `json:"artifactChecksum"`
	ArtifactSizeBytes int64     `json:"artifactSizeBytes"`
	TargetOS          string    `json:"targetOs"`
	TargetArch        string    `json:"targetArch"`
	TargetRelease     string    `json:"targetRelease"`
	CurrentExecutable string    `json:"currentExecutable"`
	StagedExecutable  string    `json:"stagedExecutable"`
	BackupExecutable  string    `json:"backupExecutable"`
	HealthFile        string    `json:"healthFile"`
	WorkingDirectory  string    `json:"workingDirectory"`
	Phase             string    `json:"phase"`
	DownloadedBytes   int64     `json:"downloadedBytes"`
	BinaryChecksum    string    `json:"binaryChecksum,omitempty"`
	CreatedAt         time.Time `json:"createdAt"`
	UpdatedAt         time.Time `json:"updatedAt"`
}

type SelfUpdateActivator interface {
	Activate(string) error
}

type ProcessSelfUpdateActivator struct{}

func (ProcessSelfUpdateActivator) Activate(manifestPath string) error {
	manifest, err := loadSelfUpdateManifest(manifestPath)
	if err != nil {
		return err
	}
	command := exec.Command(manifest.StagedExecutable)
	command.Dir = manifest.WorkingDirectory
	command.Env = append(cleanUpdateEnvironment(os.Environ()), "RUN_MODE=self-update-helper", "RUN_UPDATE_MANIFEST="+manifestPath)
	command.Stdout = io.Discard
	command.Stderr = io.Discard
	return command.Start()
}

func (worker *Worker) executeRunSelfUpdate(ctx context.Context, assignment protocol.RunJobAssignment) LifecycleExecutionResult {
	if err := protocol.ValidateRunJobAssignment(assignment); err != nil {
		return lifecycleFailure("unsafe_self_update_job", err.Error())
	}
	state, err := worker.registeredState()
	if err != nil {
		return lifecycleFailure("self_update_unregistered", "Run worker is not registered")
	}
	input, err := worker.client.GetRunUpdateInput(ctx, protocol.RunUpdateInputRequest{RunEndpointID: state.RunEndpointID, SessionToken: state.SessionToken, JobID: assignment.JobID, LeaseToken: assignment.LeaseToken, Attempt: assignment.Attempt})
	if err != nil {
		return lifecycleFailure("self_update_input_failed", "could not load fenced Run update input")
	}
	if err := validateRunUpdateInput(assignment, input); err != nil {
		return lifecycleFailure("unsafe_self_update_input", err.Error())
	}
	transactionRoot := filepath.Join(worker.cfg.WorkspaceRoot, "self-updates", safeWorkspaceName(assignment.JobID))
	if err := os.MkdirAll(transactionRoot, 0o700); err != nil {
		return lifecycleFailure("self_update_workspace_failed", "could not create update transaction workspace")
	}
	manifestPath := filepath.Join(transactionRoot, "manifest.json")
	archivePath := filepath.Join(transactionRoot, "update.archive")
	manifest, err := prepareSelfUpdateManifest(manifestPath, assignment, input, transactionRoot)
	if err != nil {
		return lifecycleFailure("self_update_manifest_failed", err.Error())
	}
	if manifest.Phase != "staged" {
		manifest.Phase = "downloading"
		if err := persistSelfUpdateManifest(manifestPath, manifest); err != nil {
			return lifecycleFailure("self_update_manifest_failed", err.Error())
		}
		if err := worker.downloadRunUpdate(ctx, assignment, input, archivePath, manifestPath, &manifest); err != nil {
			if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
				return LifecycleExecutionResult{State: lifecycleResultStateCancelled, Progress: protocol.RunJobProgressReport{Percent: 100, Message: "Run update download cancelled"}, Message: "Run update download cancelled", ErrorCode: "run_self_update_cancelled"}
			}
			return lifecycleFailure("self_update_download_failed", err.Error())
		}
		stagedPath := filepath.Join(transactionRoot, input.ExecutableName+".staged")
		binaryChecksum, err := stageRunUpdateBinary(archivePath, input.PackageFormat, input.ExecutableName, stagedPath)
		if err != nil {
			return lifecycleFailure("self_update_extract_failed", err.Error())
		}
		manifest.StagedExecutable = stagedPath
		manifest.BinaryChecksum = binaryChecksum
		manifest.Phase = "staged"
		manifest.UpdatedAt = time.Now().UTC()
		if err := persistSelfUpdateManifest(manifestPath, manifest); err != nil {
			return lifecycleFailure("self_update_manifest_failed", err.Error())
		}
	}
	evidence, _ := json.Marshal(protocol.RunUpdateExecutionEvidence{TargetRelease: input.TargetRelease, Phase: "staged"})
	return LifecycleExecutionResult{State: lifecycleResultStateSucceeded, Progress: protocol.RunJobProgressReport{Percent: 100, Message: "Run update verified and staged"}, ResultRef: fmt.Sprintf("artifact://jobs/%s/run-update-staged", safeWorkspaceName(assignment.JobID)), Message: "Run update verified and staged", ExecutionResult: protocol.RunJobExecutionResult{Kind: "run.update.staged", Checksum: input.Checksum, SizeBytes: input.SizeBytes, Summary: "verified update staged", Content: string(evidence)}, ActivationManifest: manifestPath}
}

func validateRunUpdateInput(assignment protocol.RunJobAssignment, input protocol.RunUpdateInputResponse) error {
	if input.JobID != assignment.JobID || input.ServerInstanceID != assignment.ServerInstanceID || input.RunEndpointID != assignment.RunEndpointID || assignment.InputRef != "artifact://"+input.ArtifactID {
		return fmt.Errorf("Run update input scope does not match job")
	}
	if input.TargetOS != runtime.GOOS || input.TargetArch != runtime.GOARCH {
		return fmt.Errorf("Run update target does not match this executable")
	}
	if input.PackageFormat != "zip" && input.PackageFormat != "tar.gz" && input.PackageFormat != "raw-executable" {
		return fmt.Errorf("Run update package format is unsupported")
	}
	if input.SizeBytes <= 0 || input.SizeBytes > maxSelfUpdateBytes || input.ChunkSizeBytes <= 0 || input.ChunkSizeBytes > 1024*1024 || !validSHA256(input.Checksum) {
		return fmt.Errorf("Run update artifact bounds are invalid")
	}
	expectedName := "run"
	if runtime.GOOS == "windows" {
		expectedName = "run.exe"
	}
	if input.ExecutableName != expectedName || !protocol.ValidLogicalFileKey(input.TargetRelease) {
		return fmt.Errorf("Run update executable or release identity is unsafe")
	}
	return nil
}

func prepareSelfUpdateManifest(path string, assignment protocol.RunJobAssignment, input protocol.RunUpdateInputResponse, root string) (SelfUpdateManifest, error) {
	if existing, err := loadSelfUpdateManifest(path); err == nil {
		if existing.JobID != assignment.JobID || existing.ArtifactID != input.ArtifactID || existing.ArtifactChecksum != input.Checksum || existing.TargetRelease != input.TargetRelease || existing.Attempt > assignment.Attempt {
			return SelfUpdateManifest{}, fmt.Errorf("existing update transaction does not match active attempt")
		}
		if existing.Phase == "staged" {
			if existing.StagedExecutable == "" || !pathWithinRoot(root, existing.StagedExecutable) || existing.BinaryChecksum == "" {
				return SelfUpdateManifest{}, fmt.Errorf("staged update manifest is outside the transaction workspace")
			}
			checksum, _, checksumErr := checksumFile(existing.StagedExecutable)
			if checksumErr != nil || checksum != existing.BinaryChecksum {
				return SelfUpdateManifest{}, fmt.Errorf("staged Run binary checksum changed")
			}
		}
		existing.Attempt = assignment.Attempt
		existing.LeaseToken = assignment.LeaseToken
		return existing, nil
	} else if !errors.Is(err, os.ErrNotExist) {
		return SelfUpdateManifest{}, err
	}
	current, err := os.Executable()
	if err != nil {
		return SelfUpdateManifest{}, err
	}
	current, err = filepath.Abs(current)
	if err != nil {
		return SelfUpdateManifest{}, err
	}
	info, err := os.Lstat(current)
	if err != nil || info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
		return SelfUpdateManifest{}, fmt.Errorf("current Run executable is not a regular file")
	}
	workingDirectory, err := os.Getwd()
	if err != nil {
		return SelfUpdateManifest{}, err
	}
	now := time.Now().UTC()
	manifest := SelfUpdateManifest{Version: selfUpdateManifestVersion, JobID: assignment.JobID, Attempt: assignment.Attempt, LeaseToken: assignment.LeaseToken, ArtifactID: input.ArtifactID, ArtifactChecksum: input.Checksum, ArtifactSizeBytes: input.SizeBytes, TargetOS: input.TargetOS, TargetArch: input.TargetArch, TargetRelease: input.TargetRelease, CurrentExecutable: current, BackupExecutable: filepath.Join(root, "previous-run.backup"), HealthFile: filepath.Join(root, "healthy"), WorkingDirectory: workingDirectory, Phase: "downloading", CreatedAt: now, UpdatedAt: now}
	return manifest, nil
}

func pathWithinRoot(root, path string) bool {
	rootAbs, rootErr := filepath.Abs(root)
	pathAbs, pathErr := filepath.Abs(path)
	if rootErr != nil || pathErr != nil {
		return false
	}
	relative, err := filepath.Rel(rootAbs, pathAbs)
	return err == nil && relative != ".." && !strings.HasPrefix(relative, ".."+string(os.PathSeparator)) && relative != "."
}

func (worker *Worker) downloadRunUpdate(ctx context.Context, assignment protocol.RunJobAssignment, input protocol.RunUpdateInputResponse, archivePath, manifestPath string, manifest *SelfUpdateManifest) error {
	file, err := os.OpenFile(archivePath, os.O_CREATE|os.O_RDWR, 0o600)
	if err != nil {
		return err
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil {
		return err
	}
	offset := info.Size()
	if offset < 0 || offset > input.SizeBytes {
		return fmt.Errorf("partial update artifact has invalid size")
	}
	if _, err := file.Seek(offset, io.SeekStart); err != nil {
		return err
	}
	for offset < input.SizeBytes {
		if ctx.Err() != nil {
			return ctx.Err()
		}
		state, err := worker.registeredState()
		if err != nil {
			return err
		}
		length := input.ChunkSizeBytes
		if remaining := input.SizeBytes - offset; int64(length) > remaining {
			length = int(remaining)
		}
		chunk, err := worker.client.ReadRunUpdateChunk(ctx, protocol.RunUpdateChunkRequest{RunEndpointID: state.RunEndpointID, SessionToken: state.SessionToken, JobID: assignment.JobID, LeaseToken: assignment.LeaseToken, Attempt: assignment.Attempt, Offset: offset, Length: length})
		if err != nil {
			return err
		}
		if chunk.JobID != assignment.JobID || chunk.ArtifactID != input.ArtifactID || chunk.Offset != offset || chunk.TotalBytes != input.SizeBytes || chunk.Checksum != input.Checksum || len(chunk.Payload) == 0 || len(chunk.Payload) > length {
			return fmt.Errorf("Run update chunk acknowledgement does not match request")
		}
		if _, err := file.Write(chunk.Payload); err != nil {
			return err
		}
		if err := file.Sync(); err != nil {
			return err
		}
		offset += int64(len(chunk.Payload))
		manifest.DownloadedBytes = offset
		manifest.UpdatedAt = time.Now().UTC()
		if err := persistSelfUpdateManifest(manifestPath, *manifest); err != nil {
			return err
		}
	}
	if err := file.Close(); err != nil {
		return err
	}
	checksum, size, err := checksumFile(archivePath)
	if err != nil {
		return err
	}
	if size != input.SizeBytes || checksum != input.Checksum {
		_ = os.Remove(archivePath)
		return fmt.Errorf("Run update artifact checksum mismatch")
	}
	return nil
}

func stageRunUpdateBinary(artifactPath, format, executableName, destination string) (string, error) {
	if format != "raw-executable" {
		return extractRunUpdateBinary(artifactPath, format, executableName, destination)
	}
	info, err := os.Stat(artifactPath)
	if err != nil {
		return "", err
	}
	if !info.Mode().IsRegular() || info.Size() <= 0 || info.Size() > maxSelfUpdateBytes {
		return "", fmt.Errorf("Run update executable exceeds bounds")
	}
	input, err := os.Open(artifactPath)
	if err != nil {
		return "", err
	}
	defer input.Close()
	temporary := destination + ".tmp"
	output, err := os.OpenFile(temporary, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o700)
	if err != nil {
		return "", err
	}
	written, copyErr := io.Copy(output, io.LimitReader(input, maxSelfUpdateBytes+1))
	if copyErr == nil && written != info.Size() {
		copyErr = fmt.Errorf("Run update executable size does not match artifact")
	}
	if syncErr := output.Sync(); copyErr == nil {
		copyErr = syncErr
	}
	if closeErr := output.Close(); copyErr == nil {
		copyErr = closeErr
	}
	if copyErr != nil {
		_ = os.Remove(temporary)
		return "", copyErr
	}
	if err := os.Rename(temporary, destination); err != nil {
		_ = os.Remove(temporary)
		return "", err
	}
	if err := os.Chmod(destination, 0o700); err != nil {
		return "", err
	}
	checksum, _, err := checksumFile(destination)
	return checksum, err
}

func extractRunUpdateBinary(archivePath, format, executableName, destination string) (string, error) {
	found := false
	entries := 0
	writeEntry := func(name string, mode os.FileMode, reader io.Reader, size int64) error {
		entries++
		if entries > maxSelfUpdateEntries || size < 0 || size > maxSelfUpdateBytes {
			return fmt.Errorf("Run update archive exceeds bounds")
		}
		clean := filepath.ToSlash(filepath.Clean(name))
		if clean != name || strings.Contains(clean, "../") || strings.HasPrefix(clean, "/") || strings.Contains(clean, `\`) {
			return fmt.Errorf("Run update archive entry is unsafe")
		}
		if clean == "config.json" {
			_, err := io.Copy(io.Discard, io.LimitReader(reader, size+1))
			return err
		}
		if clean != executableName || found || mode&os.ModeSymlink != 0 {
			return fmt.Errorf("Run update archive contains unexpected entry")
		}
		found = true
		temporary := destination + ".tmp"
		file, err := os.OpenFile(temporary, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o700)
		if err != nil {
			return err
		}
		written, copyErr := io.Copy(file, io.LimitReader(reader, maxSelfUpdateBytes+1))
		if copyErr == nil && written != size {
			copyErr = fmt.Errorf("Run update binary size does not match archive")
		}
		if syncErr := file.Sync(); copyErr == nil {
			copyErr = syncErr
		}
		if closeErr := file.Close(); copyErr == nil {
			copyErr = closeErr
		}
		if copyErr != nil {
			_ = os.Remove(temporary)
			return copyErr
		}
		if err := os.Rename(temporary, destination); err != nil {
			_ = os.Remove(temporary)
			return err
		}
		return os.Chmod(destination, 0o700)
	}

	if format == "zip" {
		info, err := os.Stat(archivePath)
		if err != nil {
			return "", err
		}
		reader, err := zip.OpenReader(archivePath)
		if err != nil {
			return "", err
		}
		defer reader.Close()
		if info.Size() > maxSelfUpdateBytes {
			return "", fmt.Errorf("Run update archive exceeds size limit")
		}
		for _, entry := range reader.File {
			if entry.FileInfo().IsDir() || entry.Mode()&os.ModeType != 0 {
				return "", fmt.Errorf("Run update archive contains non-regular entry")
			}
			stream, err := entry.Open()
			if err != nil {
				return "", err
			}
			err = writeEntry(entry.Name, entry.Mode(), stream, int64(entry.UncompressedSize64))
			_ = stream.Close()
			if err != nil {
				return "", err
			}
		}
	} else {
		file, err := os.Open(archivePath)
		if err != nil {
			return "", err
		}
		defer file.Close()
		gzipReader, err := gzip.NewReader(file)
		if err != nil {
			return "", err
		}
		defer gzipReader.Close()
		tarReader := tar.NewReader(gzipReader)
		for {
			header, err := tarReader.Next()
			if errors.Is(err, io.EOF) {
				break
			}
			if err != nil {
				return "", err
			}
			if header.Typeflag != tar.TypeReg && header.Typeflag != tar.TypeRegA {
				return "", fmt.Errorf("Run update archive contains non-regular entry")
			}
			if err := writeEntry(header.Name, os.FileMode(header.Mode), tarReader, header.Size); err != nil {
				return "", err
			}
		}
	}
	if !found {
		return "", fmt.Errorf("Run update archive does not contain expected executable")
	}
	checksum, _, err := checksumFile(destination)
	return checksum, err
}

func ApplySelfUpdateManifest(manifestPath string) error {
	manifest, err := loadSelfUpdateManifest(manifestPath)
	if err != nil {
		return err
	}
	helper, err := os.Executable()
	if err != nil {
		return err
	}
	helper, _ = filepath.Abs(helper)
	staged, _ := filepath.Abs(manifest.StagedExecutable)
	if helper != staged || manifest.TargetOS != runtime.GOOS || manifest.TargetArch != runtime.GOARCH || manifest.Phase != "staged" {
		return fmt.Errorf("self-update helper scope does not match staged transaction")
	}
	manifest.Phase = "activating"
	manifest.UpdatedAt = time.Now().UTC()
	if err := persistSelfUpdateManifest(manifestPath, manifest); err != nil {
		return err
	}
	if err := replaceRunExecutable(manifest); err != nil {
		manifest.Phase = "rolled-back"
		manifest.UpdatedAt = time.Now().UTC()
		_ = persistSelfUpdateManifest(manifestPath, manifest)
		_, _ = startRunAfterUpdate(manifest, "rolled-back")
		return err
	}
	_ = os.Remove(manifest.HealthFile)
	command, err := startRunAfterUpdate(manifest, "succeeded")
	if err != nil {
		_ = rollbackRunExecutable(manifest)
		_, _ = startRunAfterUpdate(manifest, "rolled-back")
		return err
	}
	wait := defaultUpdateHealthWait
	if value, parseErr := strconv.Atoi(os.Getenv("RUN_UPDATE_HEALTH_TIMEOUT_MS")); parseErr == nil && value > 0 && value <= 300000 {
		wait = time.Duration(value) * time.Millisecond
	}
	deadline := time.Now().Add(wait)
	for time.Now().Before(deadline) {
		if _, err := os.Stat(manifest.HealthFile); err == nil {
			manifest.Phase = "succeeded"
			manifest.UpdatedAt = time.Now().UTC()
			return persistSelfUpdateManifest(manifestPath, manifest)
		}
		time.Sleep(100 * time.Millisecond)
	}
	_ = command.Process.Kill()
	if err := rollbackRunExecutable(manifest); err != nil {
		return fmt.Errorf("updated Run health timed out and rollback failed: %w", err)
	}
	manifest.Phase = "rolled-back"
	manifest.UpdatedAt = time.Now().UTC()
	_ = persistSelfUpdateManifest(manifestPath, manifest)
	_, _ = startRunAfterUpdate(manifest, "rolled-back")
	return fmt.Errorf("updated Run did not become healthy before timeout")
}

func replaceRunExecutable(manifest SelfUpdateManifest) error {
	if checksum, _, err := checksumFile(manifest.StagedExecutable); err != nil || checksum != manifest.BinaryChecksum {
		return fmt.Errorf("staged Run binary checksum changed")
	}
	_ = os.Remove(manifest.BackupExecutable)
	var lastErr error
	for deadline := time.Now().Add(30 * time.Second); time.Now().Before(deadline); time.Sleep(100 * time.Millisecond) {
		if err := os.Rename(manifest.CurrentExecutable, manifest.BackupExecutable); err != nil {
			lastErr = err
			continue
		}
		if err := copyExecutable(manifest.StagedExecutable, manifest.CurrentExecutable); err != nil {
			_ = os.Rename(manifest.BackupExecutable, manifest.CurrentExecutable)
			return err
		}
		return nil
	}
	return fmt.Errorf("could not back up current Run executable: %w", lastErr)
}

func rollbackRunExecutable(manifest SelfUpdateManifest) error {
	if _, err := os.Stat(manifest.BackupExecutable); err != nil {
		return err
	}
	_ = os.Remove(manifest.CurrentExecutable)
	return os.Rename(manifest.BackupExecutable, manifest.CurrentExecutable)
}

func startRunAfterUpdate(manifest SelfUpdateManifest, outcome string) (*exec.Cmd, error) {
	command := exec.Command(manifest.CurrentExecutable)
	command.Dir = manifest.WorkingDirectory
	environment := cleanUpdateEnvironment(os.Environ())
	environment = append(environment, "RUN_MODE=worker", "RUN_UPDATE_JOB_ID="+manifest.JobID, "RUN_UPDATE_OUTCOME="+outcome, "RUN_UPDATE_ATTEMPT="+strconv.Itoa(manifest.Attempt), "RUN_UPDATE_LEASE_TOKEN="+manifest.LeaseToken)
	if outcome == "succeeded" {
		environment = append(environment, "RUN_VERSION="+manifest.TargetRelease, "RUN_UPDATE_HEALTH_FILE="+manifest.HealthFile)
	}
	command.Env = environment
	command.Stdout = io.Discard
	command.Stderr = io.Discard
	if err := command.Start(); err != nil {
		return command, err
	}
	return command, nil
}

func MarkSelfUpdateHealthy(path string) error {
	if strings.TrimSpace(path) == "" {
		return nil
	}
	return writeRuntimeAtomicFile(path, []byte("healthy\n"), 0o600)
}

func loadSelfUpdateManifest(path string) (SelfUpdateManifest, error) {
	body, err := os.ReadFile(path)
	if err != nil {
		return SelfUpdateManifest{}, err
	}
	var manifest SelfUpdateManifest
	if err := json.Unmarshal(body, &manifest); err != nil {
		return SelfUpdateManifest{}, fmt.Errorf("decode self-update manifest: %w", err)
	}
	if manifest.Version != selfUpdateManifestVersion || manifest.JobID == "" || manifest.Attempt <= 0 || manifest.LeaseToken == "" || manifest.ArtifactID == "" || !validSHA256(manifest.ArtifactChecksum) || manifest.ArtifactSizeBytes <= 0 || manifest.ArtifactSizeBytes > maxSelfUpdateBytes || !protocol.ValidLogicalFileKey(manifest.TargetRelease) {
		return SelfUpdateManifest{}, fmt.Errorf("self-update manifest is invalid")
	}
	return manifest, nil
}

func persistSelfUpdateManifest(path string, manifest SelfUpdateManifest) error {
	body, err := json.MarshalIndent(manifest, "", "  ")
	if err != nil {
		return err
	}
	return writeRuntimeAtomicFile(path, body, 0o600)
}

func checksumFile(path string) (string, int64, error) {
	file, err := os.Open(path)
	if err != nil {
		return "", 0, err
	}
	defer file.Close()
	hash := sha256.New()
	size, err := io.Copy(hash, io.LimitReader(file, maxSelfUpdateBytes+1))
	if err != nil {
		return "", 0, err
	}
	if size > maxSelfUpdateBytes {
		return "", size, fmt.Errorf("file exceeds self-update size limit")
	}
	return "sha256:" + hex.EncodeToString(hash.Sum(nil)), size, nil
}

func copyExecutable(source, destination string) error {
	input, err := os.Open(source)
	if err != nil {
		return err
	}
	defer input.Close()
	temporary := destination + ".update-tmp"
	output, err := os.OpenFile(temporary, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o700)
	if err != nil {
		return err
	}
	if _, err := io.Copy(output, io.LimitReader(input, maxSelfUpdateBytes+1)); err != nil {
		_ = output.Close()
		_ = os.Remove(temporary)
		return err
	}
	if err := output.Sync(); err != nil {
		_ = output.Close()
		_ = os.Remove(temporary)
		return err
	}
	if err := output.Close(); err != nil {
		_ = os.Remove(temporary)
		return err
	}
	if err := os.Rename(temporary, destination); err != nil {
		_ = os.Remove(temporary)
		return err
	}
	return os.Chmod(destination, 0o700)
}

func cleanUpdateEnvironment(environment []string) []string {
	blocked := map[string]bool{"RUN_UPDATE_MANIFEST": true, "RUN_UPDATE_HEALTH_FILE": true, "RUN_UPDATE_HEALTH_TIMEOUT_MS": true, "RUN_UPDATE_JOB_ID": true, "RUN_UPDATE_OUTCOME": true, "RUN_UPDATE_ATTEMPT": true, "RUN_UPDATE_LEASE_TOKEN": true, "RUN_MODE": true, "RUN_VERSION": true}
	out := make([]string, 0, len(environment))
	for _, entry := range environment {
		key, _, _ := strings.Cut(entry, "=")
		if !blocked[key] {
			out = append(out, entry)
		}
	}
	return out
}