package useCases

import (
	"RenewCMS/internal/domain/update"
	"errors"
	"fmt"
	"path"
	"time"
)

type ApplyRestartRequestUseCase struct {
	requests update.RestartRequestStore
	results  update.ResultStore
	running  update.RunningInfoStore
	files    update.HelperFilesystem
	service  update.ServiceControl
	health   update.HealthChecker
	verifier update.SignatureVerifier
	clock    update.Clock
	logger   update.Logger
	layout   update.HelperLayout
	platform update.Platform
}

type ApplyRestartRequestDependencies struct {
	Requests update.RestartRequestStore
	Results  update.ResultStore
	Running  update.RunningInfoStore
	Files    update.HelperFilesystem
	Service  update.ServiceControl
	Health   update.HealthChecker
	Verifier update.SignatureVerifier
	Clock    update.Clock
	Logger   update.Logger
	Layout   update.HelperLayout
	Platform update.Platform
}

func NewApplyRestartRequestUseCase(dependencies ApplyRestartRequestDependencies) *ApplyRestartRequestUseCase {
	return &ApplyRestartRequestUseCase{
		requests: dependencies.Requests,
		results:  dependencies.Results,
		running:  dependencies.Running,
		files:    dependencies.Files,
		service:  dependencies.Service,
		health:   dependencies.Health,
		verifier: dependencies.Verifier,
		clock:    dependencies.Clock,
		logger:   dependencies.Logger,
		layout:   dependencies.Layout,
		platform: dependencies.Platform,
	}
}

type helperRun struct {
	apply     *ApplyRestartRequestUseCase
	result    update.Result
	tempDir   string
	stagedTag string
}

type verifiedCopy struct {
	binaryPath string
	checksum   string
}

func (a *ApplyRestartRequestUseCase) Apply() (err error) {
	request, readErr := a.requests.Read()
	if errors.Is(readErr, update.ErrNoRestartRequest) {
		a.logger.Printf("no restart request found, nothing to do")
		return nil
	}
	run := &helperRun{apply: a, result: update.Result{
		Outcome:   update.OutcomeRunning,
		Kind:      request.Kind,
		Tag:       request.Tag,
		StartedAt: a.clock.Now().UTC(),
	}}
	defer run.recoverPanic(&err)

	deleteErr := a.requests.Delete()
	symlinkErr := a.symlinkedDataFile()
	if info, found := a.running.Read(); found {
		run.result.FromVersion = info.Version
	}
	run.record()

	for _, refusal := range []error{readErr, deleteErr, symlinkErr} {
		if refusal != nil {
			return run.fail(refusal)
		}
	}
	return run.dispatch()
}

func (a *ApplyRestartRequestUseCase) symlinkedDataFile() error {
	for _, candidate := range []string{a.layout.ResultPath(), a.layout.ResultTempPath()} {
		if info, err := a.files.Lstat(candidate); err == nil && info.IsSymlink {
			return update.SymlinkError{Path: candidate}
		}
	}
	return nil
}

func (r *helperRun) dispatch() error {
	switch r.result.Kind {
	case update.RestartKindRestart:
		return r.plainRestart()
	case update.RestartKindUpdate:
		return r.installUpdate()
	}
	return r.fail(fmt.Errorf("unknown restart kind %q", r.result.Kind))
}

func (r *helperRun) plainRestart() error {
	if !r.apply.restartAndAwait("") {
		return r.failLoudly(errors.New("the site did not come back after the restart"))
	}
	return r.finish(update.OutcomeSucceeded)
}

func (r *helperRun) installUpdate() error {
	a := r.apply
	tag := r.result.Tag
	if r.result.FromVersion == "" {
		return r.fail(errors.New("the running version could not be read from update-running.json"))
	}
	if err := update.ValidateRestartTag(tag, r.result.FromVersion); err != nil {
		return r.fail(fmt.Errorf("tag %q: %w", tag, err))
	}
	r.stagedTag = tag

	assetName := update.AssetName(tag, a.platform)
	if err := a.requireStagedFiles(tag, assetName); err != nil {
		return r.fail(err)
	}
	verified, err := r.copyAndVerify(tag, assetName)
	if err != nil {
		return r.fail(err)
	}
	if err := a.swapBinary(verified); err != nil {
		return r.fail(err)
	}
	if a.restartAndAwait(tag) {
		return r.finish(update.OutcomeSucceeded)
	}
	return r.rollBack()
}

func (r *helperRun) copyAndVerify(tag string, assetName string) (verifiedCopy, error) {
	a := r.apply
	tempDir, err := a.files.MakePrivateTempDir()
	if err != nil {
		return verifiedCopy{}, err
	}
	r.tempDir = tempDir
	stagedDir := a.layout.StagedDir(tag)
	for _, name := range []string{assetName, update.ChecksumsAssetName, update.SignatureAssetName} {
		original := path.Join(stagedDir, name)
		if err := a.files.Copy(original, path.Join(tempDir, name), update.PrivateFileMode); err != nil {
			return verifiedCopy{}, fmt.Errorf("copying %s: %w", original, err)
		}
	}
	return a.verifyCopy(tempDir, assetName)
}

func (a *ApplyRestartRequestUseCase) verifyCopy(tempDir string, assetName string) (verifiedCopy, error) {
	checksumsPath := path.Join(tempDir, update.ChecksumsAssetName)
	if err := a.verifier.Verify(checksumsPath, path.Join(tempDir, update.SignatureAssetName)); err != nil {
		return verifiedCopy{}, fmt.Errorf("signature check: %w", err)
	}
	checksums, err := a.files.ReadFile(checksumsPath)
	if err != nil {
		return verifiedCopy{}, err
	}
	expected, found := update.ChecksumFor(string(checksums), assetName)
	if !found {
		return verifiedCopy{}, fmt.Errorf("checksums.txt has no line for %q", assetName)
	}
	binaryPath := path.Join(tempDir, assetName)
	content, err := a.files.ReadFile(binaryPath)
	if err != nil {
		return verifiedCopy{}, err
	}
	if update.SHA256Hex(content) != expected {
		return verifiedCopy{}, fmt.Errorf("sha-256 mismatch for the staged %q", assetName)
	}
	return verifiedCopy{binaryPath: binaryPath, checksum: expected}, nil
}

func (a *ApplyRestartRequestUseCase) requireStagedFiles(tag string, assetName string) error {
	for _, directory := range []string{a.layout.UpdatesDir(), a.layout.StagedDir(tag)} {
		if err := a.requireDirectory(directory); err != nil {
			return err
		}
	}
	for _, name := range []string{assetName, update.ChecksumsAssetName, update.SignatureAssetName} {
		if err := a.requireRegularFile(path.Join(a.layout.StagedDir(tag), name)); err != nil {
			return err
		}
	}
	return nil
}

func (a *ApplyRestartRequestUseCase) requireDirectory(target string) error {
	return a.requireEntry(target, "a directory", func(info update.FileInfo) bool { return info.IsDir })
}

func (a *ApplyRestartRequestUseCase) requireRegularFile(target string) error {
	return a.requireEntry(target, "a regular file", func(info update.FileInfo) bool { return info.IsRegular })
}

func (a *ApplyRestartRequestUseCase) requireEntry(target string, description string, matches func(update.FileInfo) bool) error {
	info, err := a.files.Lstat(target)
	if err != nil {
		return fmt.Errorf("%s: %w", target, err)
	}
	if info.IsSymlink {
		return update.SymlinkError{Path: target}
	}
	if !matches(info) {
		return fmt.Errorf("%s is not %s", target, description)
	}
	return nil
}

func (a *ApplyRestartRequestUseCase) swapBinary(verified verifiedCopy) error {
	binary := a.layout.BinaryPath
	if err := a.replaceViaTemp(binary, a.layout.PreviousPath(), binary+update.PreviousTempSuffix); err != nil {
		return fmt.Errorf("keeping the previous binary: %w", err)
	}
	installTemp := binary + update.InstallTempSuffix
	a.removeQuietly(installTemp)
	if err := a.files.Copy(verified.binaryPath, installTemp, update.ExecutableMode); err != nil {
		a.removeQuietly(installTemp)
		return fmt.Errorf("writing the new binary: %w", err)
	}
	if err := a.installIfUnchanged(installTemp, verified.checksum); err != nil {
		a.removeQuietly(installTemp)
		return err
	}
	return nil
}

func (a *ApplyRestartRequestUseCase) installIfUnchanged(installTemp string, checksum string) error {
	content, err := a.files.ReadFile(installTemp)
	if err != nil {
		return err
	}
	if update.SHA256Hex(content) != checksum {
		return fmt.Errorf("%s changed after it was verified", installTemp)
	}
	if err := a.files.Chmod(installTemp, update.ExecutableMode); err != nil {
		return err
	}
	if err := a.files.Rename(installTemp, a.layout.BinaryPath); err != nil {
		return fmt.Errorf("installing the new binary: %w", err)
	}
	return nil
}

func (a *ApplyRestartRequestUseCase) replaceViaTemp(source string, destination string, temporary string) error {
	a.removeQuietly(temporary)
	if err := a.files.Copy(source, temporary, update.ExecutableMode); err != nil {
		a.removeQuietly(temporary)
		return err
	}
	if err := a.files.Rename(temporary, destination); err != nil {
		a.removeQuietly(temporary)
		return err
	}
	return nil
}

func (r *helperRun) rollBack() error {
	a := r.apply
	a.logger.Printf("version %s did not come up, restoring %s", r.result.Tag, a.layout.PreviousPath())
	restoreTemp := a.layout.BinaryPath + update.RestoreTempSuffix
	if err := a.replaceViaTemp(a.layout.PreviousPath(), a.layout.BinaryPath, restoreTemp); err != nil {
		return r.failLoudly(fmt.Errorf("the previous binary could not be restored, the site may be down: %w", err))
	}
	if !a.restartAndAwait(r.result.FromVersion) {
		return r.failLoudly(errors.New("the previous version did not come back after the rollback"))
	}
	return r.finish(update.OutcomeRolledBack)
}

func (a *ApplyRestartRequestUseCase) restartAndAwait(expectedVersion string) bool {
	baseline, _ := a.running.Read()
	restartedAt := a.clock.Now()
	if err := a.service.Restart(); err != nil {
		a.logger.Printf("restarting the service failed: %v", err)
		return false
	}
	for a.clock.Now().Sub(restartedAt) < update.RestartWindow {
		if a.isBackUp(baseline, restartedAt, expectedVersion) {
			return true
		}
		a.clock.Sleep(update.PollInterval)
	}
	return false
}

func (a *ApplyRestartRequestUseCase) isBackUp(baseline update.RunningInfo, restartedAt time.Time, expectedVersion string) bool {
	if !a.health.Healthy() {
		return false
	}
	info, found := a.running.Read()
	if !found || !info.IsNewerThan(baseline, restartedAt) {
		return false
	}
	return expectedVersion == "" || info.Version == expectedVersion
}

func (r *helperRun) record() {
	if err := r.apply.results.Write(r.result); err != nil {
		r.apply.logger.Printf("update-result.json could not be written: %v", err)
	}
}

func (r *helperRun) finish(outcome string) error {
	finishedAt := r.apply.clock.Now().UTC()
	r.result.Outcome = outcome
	r.result.FinishedAt = &finishedAt
	r.record()
	r.cleanUp()
	return nil
}

func (r *helperRun) fail(reason error) error {
	r.apply.logger.Printf("restart request refused or failed: %v", reason)
	return r.finish(update.OutcomeFailed)
}

func (r *helperRun) failLoudly(reason error) error {
	r.apply.logger.Printf("restart request failed: %v", reason)
	_ = r.finish(update.OutcomeFailed)
	return reason
}

func (r *helperRun) recoverPanic(err *error) {
	if recovered := recover(); recovered != nil {
		*err = r.failLoudly(fmt.Errorf("panic: %v", recovered))
	}
}

func (r *helperRun) cleanUp() {
	a := r.apply
	if r.tempDir != "" {
		a.removeTreeQuietly(r.tempDir)
	}
	if r.stagedTag != "" {
		a.removeStaged(r.stagedTag)
	}
}

func (a *ApplyRestartRequestUseCase) removeStaged(tag string) {
	if err := a.requireDirectory(a.layout.UpdatesDir()); err != nil {
		a.logger.Printf("staged files left in place: %v", err)
		return
	}
	staged := a.layout.StagedDir(tag)
	info, err := a.files.Lstat(staged)
	if err != nil {
		return
	}
	if info.IsSymlink {
		a.removeQuietly(staged)
		return
	}
	a.removeTreeQuietly(staged)
}

func (a *ApplyRestartRequestUseCase) removeQuietly(target string) {
	_ = a.files.Remove(target)
}

func (a *ApplyRestartRequestUseCase) removeTreeQuietly(target string) {
	if err := a.files.RemoveAll(target); err != nil {
		a.logger.Printf("could not remove %s: %v", target, err)
	}
}