package backup

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/aritmolab/thothii/tools/tht/internal/authconfig"
	"github.com/aritmolab/thothii/tools/tht/internal/compose"
	"github.com/aritmolab/thothii/tools/tht/internal/config"
	"github.com/aritmolab/thothii/tools/tht/internal/doctor"
	"github.com/aritmolab/thothii/tools/tht/internal/lifecycle"
	"github.com/aritmolab/thothii/tools/tht/internal/pi"
	"github.com/aritmolab/thothii/tools/tht/internal/safeio"
	"github.com/aritmolab/thothii/tools/tht/internal/service"
)

func productionRestoreDependencies(installation config.Installation) restoreDependencies {
	runner := hostRunner{runner: compose.NewRunner(""), binary: "docker", profile: installation.Profile}
	deps := restoreDependencies{
		preflight: func(ctx context.Context, target config.Installation, request PreflightRequest) (PreflightResult, error) {
			return Preflight(ctx, target, request, PreflightDependencies{
				FreeBytes:                 restoreFreeBytes,
				CheckOwnershipPermissions: validateRestoreTargets,
				CheckVolumeMapping: func(ctx context.Context, target config.Installation, manifest Manifest) error {
					return validateRestoreVolumes(ctx, target, manifest, runner)
				},
				CheckImageConfigCompatibility: func(ctx context.Context, target config.Installation, manifest Manifest) error {
					return validateRestoreImages(ctx, target, manifest, runner)
				},
			})
		},
		checkpointLocked: func(ctx context.Context, target config.Installation, request CreateRequest) (Result, error) {
			path, err := restoreCheckpointPath(target, time.Now().UTC())
			if err != nil {
				return Result{}, err
			}
			request.Output = path
			return createWithDependenciesLockHeld(ctx, target, request, productionCreateDependencies(target))
		},
		cleanupCheckpoint: cleanupRecoveryCheckpoint,
		acquireLock: func(target config.Installation) (restoreLock, error) {
			return lifecycle.Acquire(target)
		},
		runner:      runner,
		sleep:       time.Sleep,
		restoreFile: restoreFilePayload,
		restoreVolume: func(ctx context.Context, _ config.Installation, volume VolumeMetadata, input io.Reader) error {
			result, err := runner.Stream(ctx, volumeRestoreCommand(volume.Name), input, io.Discard)
			if err != nil || result.ExitCode != 0 {
				if err == nil {
					err = errors.New("Docker volume helper returned a nonzero exit status")
				}
				return fmt.Errorf("restore volume %s: %w", volume.LogicalName, dockerError("stream volume", result, err))
			}
			return nil
		},
		resetAuthenticationState: resetAuthenticationState,
		verify: map[string]restoreVerify{
			"health":    verifyRestoreHealth,
			"doctor":    verifyRestoreDoctor,
			"pi":        verifyRestorePi,
			"workspace": verifyRestoreWorkspace,
		},
	}
	deps.prepareRecovery = func(ctx context.Context, target config.Installation, path string) (PreflightResult, error) {
		return deps.preflight(ctx, target, PreflightRequest{Archive: path, Confirm: true, AllowExternalSecrets: true})
	}
	deps.recover = func(ctx context.Context, target config.Installation, recovery PreflightResult, wasRunning bool) error {
		return recoverRestoreTransaction(ctx, target, recovery, wasRunning, deps)
	}
	return deps
}

func cleanupRecoveryCheckpoint(path string) error {
	if err := safeio.RemoveCanonicalPrivateRegular(path); err != nil {
		return errors.New("private recovery checkpoint could not be destroyed safely")
	}
	return nil
}

func recoverRestoreTransaction(ctx context.Context, installation config.Installation, recovery PreflightResult, wasRunning bool, deps restoreDependencies) error {
	var resultErr error
	if err := runCompose(ctx, installation, deps.runner, "stop"); err != nil {
		resultErr = errors.Join(resultErr, err)
		// The first stop may already have taken effect before Docker lost its response. Retry the
		// idempotent command so no recovery mutation starts while the candidate core is running.
		if retryErr := runCompose(ctx, installation, deps.runner, "stop"); retryErr != nil {
			return errors.Join(resultErr, retryErr)
		}
	}
	archive, err := recovery.RevalidateArchive()
	if err != nil {
		return errors.Join(resultErr, err)
	}
	if err := restoreVerifiedEntries(ctx, installation, recovery, archive, deps.restoreFile, deps.restoreVolume); err != nil {
		return errors.Join(resultErr, err)
	}
	// Recovery restores only configuration/secret files and durable application volumes. Runtime
	// authentication state is deliberately reset again so neither sessions nor OIDC transactions
	// survive a failed restore attempt.
	if err := deps.resetAuthenticationState(ctx, installation, deps.runner); err != nil {
		return errors.Join(resultErr, err)
	}
	if wasRunning {
		if err := composeStartAndVerify(ctx, installation, deps.runner); err != nil {
			resultErr = errors.Join(resultErr, err)
			// As with stop, a start can succeed while the client loses its response. A successful
			// retry includes its own health check before recovery verification proceeds.
			if retryErr := composeStartAndVerify(ctx, installation, deps.runner); retryErr != nil {
				return errors.Join(resultErr, retryErr)
			}
		}
	}
	if err := verifyRestoreTransaction(ctx, installation, deps); err != nil {
		return errors.Join(resultErr, err)
	}
	if resultErr != nil {
		// A prior response was lost, but the checkpoint has been restored and fully verified. The
		// caller may safely remove maintenance while still returning every observed error.
		return &verifiedRecoveryError{err: resultErr}
	}
	return nil
}

func restoreCheckpointPath(installation config.Installation, now time.Time) (string, error) {
	suffix := make([]byte, 8)
	if _, err := rand.Read(suffix); err != nil {
		return "", errors.New("recovery checkpoint name is unavailable")
	}
	name := fmt.Sprintf("restore-checkpoint-%s-%s.zip", now.Format("20060102T150405.000000000Z"), hex.EncodeToString(suffix))
	return filepath.Join(installation.ControlDirectory(), name), nil
}

func validateRestoreTargets(_ context.Context, installation config.Installation, manifest Manifest) error {
	for _, entry := range manifest.Entries {
		if entry.Kind == EntryVolume {
			continue
		}
		if !entry.Archived {
			if entry.Kind == EntrySecretReference || entry.Kind == EntryPreservationReference {
				if err := validateRestoreReference(installation, entry); err != nil {
					return err
				}
			}
			continue
		}
		metadata := ArchiveEntryMetadata{
			Path: entry.Path, Kind: entry.Kind, Owner: entry.Owner, LogicalName: entry.LogicalName,
			SourcePath: entry.SourcePath, Size: entry.Size, SHA256: entry.SHA256, Mode: entry.Mode,
			Sensitive: entry.Sensitive,
		}
		target, err := restoreFileTarget(installation, metadata)
		if err != nil || !safeRestoreParent(target) {
			return errors.New("restore target ownership or permissions are invalid")
		}
	}
	return nil
}

func validateRestoreReference(installation config.Installation, entry Entry) error {
	metadata := ArchiveEntryMetadata{
		Path: entry.Path, Kind: entry.Kind, Owner: entry.Owner, SourcePath: entry.SourcePath,
		Size: entry.Size, SHA256: entry.SHA256, Mode: entry.Mode, Sensitive: entry.Sensitive,
	}
	if entry.Kind == EntryPreservationReference {
		return nil
	}
	if _, err := restoreExternalTarget(installation, metadata); err != nil {
		return errors.New("restore external prerequisite is invalid")
	}
	contents, err := safeio.ReadCanonicalRegular(entry.SourcePath, entry.Size)
	if err != nil || int64(len(contents)) != entry.Size {
		return errors.New("restore external prerequisite is unavailable or unsafe")
	}
	digest := sha256.Sum256(contents)
	if "sha256:"+hex.EncodeToString(digest[:]) != entry.SHA256 {
		return errors.New("restore external prerequisite has changed")
	}
	return nil
}

func validateRestoreVolumes(ctx context.Context, installation config.Installation, manifest Manifest, runner archiveRunner) error {
	if len(manifest.Volumes) != len(requiredBackupVolumes(installation)) {
		return errors.New("backup volume set is incomplete")
	}
	rendered, err := renderedConfiguration(ctx, installation, runner)
	if err != nil {
		return err
	}
	current, err := inspectRequiredVolumes(ctx, installation, runner, rendered)
	if err != nil {
		return err
	}
	archived := make(map[string]VolumeMetadata, len(manifest.Volumes))
	for _, volume := range manifest.Volumes {
		archived[volume.LogicalName] = volume
	}
	for _, volume := range current {
		previous, found := archived[volume.LogicalName]
		if !found || previous.Name != volume.Name || previous.Driver != volume.Driver {
			return errors.New("backup volume ownership does not match the installation")
		}
		if volume.Labels["com.docker.compose.project"] != installation.ProjectName() {
			return errors.New("current volume is not owned by the installation")
		}
	}
	return nil
}

func validateRestoreImages(ctx context.Context, installation config.Installation, manifest Manifest, runner archiveRunner) error {
	rendered, err := renderedConfiguration(ctx, installation, runner)
	if err != nil {
		return err
	}
	for _, image := range manifest.Images {
		serviceDefinition, found := rendered.Services[image.Service]
		if !found || serviceDefinition.Image == "" || serviceDefinition.Image != image.Reference {
			return errors.New("backup image configuration does not match the installation")
		}
	}
	return nil
}

func restoreFilePayload(_ context.Context, installation config.Installation, entry ArchiveEntryMetadata, input io.Reader) error {
	if entry.Size < 0 || uint64(entry.Size) > defaultPreflightMaxUncompressedBytes {
		return errors.New("restore file size is invalid")
	}
	contents, err := io.ReadAll(io.LimitReader(input, entry.Size+1))
	if err != nil || int64(len(contents)) != entry.Size {
		return errors.New("restore file payload is invalid")
	}
	target, err := restoreFileTarget(installation, entry)
	if err != nil {
		return err
	}
	if err := replaceRestoreFile(target, contents, os.FileMode(entry.Mode)); err != nil {
		return errors.New("restore file could not be replaced safely")
	}
	return nil
}

func restoreFileTarget(installation config.Installation, entry ArchiveEntryMetadata) (string, error) {
	if entry.Kind == EntryExternalSecret {
		return restoreExternalTarget(installation, entry)
	}
	if entry.Kind != EntryFile {
		return "", errors.New("restore file kind is unsupported")
	}
	switch entry.Path {
	case "configuration/installation/thothii-installation.yaml":
		return installation.Path, nil
	case "configuration/environment/operator.env":
		return installation.EnvFile, nil
	case "configuration/pi/models.json":
		return filepath.Join(installation.ProjectDirectory, "deploy", "pi", "models.json"), nil
	case "configuration/pi/settings.json":
		return filepath.Join(installation.ProjectDirectory, "deploy", "pi", "settings.json"), nil
	case "configuration/generated/current-image.yaml":
		return installation.CurrentImageOverridePath(), nil
	}
	if strings.HasPrefix(entry.Path, "configuration/overrides/") {
		name := strings.TrimPrefix(entry.Path, "configuration/overrides/")
		indexText, base, found := strings.Cut(name, "-")
		index, parseErr := strconv.Atoi(indexText)
		if !found || parseErr != nil || len(indexText) != 2 || index < 0 || index >= len(installation.Overrides) || filepath.Base(installation.Overrides[index]) != base {
			return "", errors.New("restore override target is invalid")
		}
		return installation.Overrides[index], nil
	}
	if strings.HasPrefix(entry.Owner, "preservation-root:") && strings.HasPrefix(entry.Path, "preservation/") {
		variable := strings.TrimPrefix(entry.Owner, "preservation-root:")
		allowed := variable == "THT_DATA_ROOT" || variable == "THT_PI_STATE_ROOT" || variable == "THT_WORKSPACE_REGISTRY_ROOT"
		parts := strings.SplitN(entry.Path, "/", 3)
		root, rootErr := installation.EnvironmentValue(variable)
		if !allowed || len(parts) != 3 || rootErr != nil || root == "" {
			return "", errors.New("restore preservation target is invalid")
		}
		target := filepath.Join(root, filepath.FromSlash(parts[2]))
		relative, relErr := filepath.Rel(root, target)
		if relErr != nil || relative == ".." || strings.HasPrefix(relative, ".."+string(filepath.Separator)) {
			return "", errors.New("restore preservation target escapes its root")
		}
		return target, nil
	}
	return "", errors.New("restore file target is not declared")
}

func restoreExternalTarget(installation config.Installation, entry ArchiveEntryMetadata) (string, error) {
	if entry.SourcePath == "" || filepath.Clean(entry.SourcePath) != entry.SourcePath || !filepath.IsAbs(entry.SourcePath) {
		return "", errors.New("restore external target is invalid")
	}
	if entry.Owner == "external-secret" {
		paths, err := installation.SecretFiles()
		if err != nil {
			return "", errors.New("restore external secret declarations are unavailable")
		}
		for _, path := range paths {
			if path == entry.SourcePath {
				return path, nil
			}
		}
		return "", errors.New("restore external secret target is not declared")
	}
	if entry.Owner == "authentication-configuration" {
		for _, name := range []string{"auth.yaml", "users.yaml"} {
			path := filepath.Join(installation.AuthenticationDirectory(), name)
			if entry.SourcePath == path {
				return path, nil
			}
		}
	}
	return "", errors.New("restore external target owner is invalid")
}

func safeRestoreParent(target string) bool {
	if target == "" || !filepath.IsAbs(target) || filepath.Clean(target) != target {
		return false
	}
	parent := filepath.Dir(target)
	resolved, err := filepath.EvalSymlinks(parent)
	if err != nil || resolved != parent {
		return false
	}
	info, err := os.Stat(parent)
	if err != nil || !info.IsDir() {
		return false
	}
	if targetInfo, err := os.Lstat(target); err == nil {
		return targetInfo.Mode().IsRegular() && targetInfo.Mode()&os.ModeSymlink == 0
	} else {
		return errors.Is(err, os.ErrNotExist)
	}
}

func volumeRestoreCommand(volume string) []string {
	return []string{
		"run", "--rm", "--interactive", "--network", "none", "--mount", "type=volume,src=" + volume + ",dst=/target",
		helperImage, "sh", "-ceu",
		"rm -rf -- /target/* /target/.[!.]* /target/..?*; tar --numeric-owner -C /target -xf -",
	}
}

func restoreVerificationRunning(ctx context.Context, installation config.Installation, runner archiveRunner) (bool, error) {
	return installationRunning(ctx, installation, runner)
}

func verifyRestoreHealth(ctx context.Context, installation config.Installation, runner archiveRunner) error {
	running, err := restoreVerificationRunning(ctx, installation, runner)
	if err != nil || !running {
		return err
	}
	return service.WaitForHealthy(ctx, installation, runner)
}

func verifyRestoreDoctor(ctx context.Context, installation config.Installation, runner archiveRunner) error {
	running, err := restoreVerificationRunning(ctx, installation, runner)
	if err != nil {
		return err
	}
	if !running {
		result, configErr := runner.Run(ctx, installation.ComposeArgs("config", "--quiet"), nil)
		if configErr != nil {
			return dockerError("verify restored Compose configuration", result, configErr)
		}
		diagnostics, diagnosticErr := authconfig.Check(ctx, installation, runner, false, false)
		if diagnosticErr != nil || !diagnostics.Ready {
			if diagnosticErr != nil {
				return diagnosticErr
			}
			return errors.New("authentication diagnostics did not pass after restore")
		}
		return nil
	}
	report, err := doctor.Run(ctx, installation, runner)
	if err != nil {
		return err
	}
	if !report.OK {
		failed := make([]string, 0, len(report.Checks))
		for _, check := range report.Checks {
			if check.Status == doctor.StatusFailed {
				failed = append(failed, check.Name)
			}
		}
		if len(failed) == 0 {
			return errors.New("aggregate doctor did not pass after restore")
		}
		return fmt.Errorf("aggregate doctor failed checks: %s", strings.Join(failed, ","))
	}
	return nil
}

func verifyRestorePi(ctx context.Context, installation config.Installation, runner archiveRunner) error {
	running, err := restoreVerificationRunning(ctx, installation, runner)
	if err != nil || !running {
		if err != nil {
			return err
		}
		result, runErr := runner.Run(ctx, installation.ComposeArgs(
			"run", "--rm", "--no-deps", "--no-TTY", "core", "pi", "--version",
		), nil)
		if runErr != nil || strings.TrimSpace(result.Stdout) == "" {
			if runErr == nil {
				runErr = errors.New("Pi version probe returned no version")
			}
			return dockerError("verify restored Pi runtime", result, runErr)
		}
		return nil
	}
	return pi.Doctor(ctx, compose.InstallationRunner{Installation: installation, Runner: runner})
}

func verifyRestoreWorkspace(ctx context.Context, installation config.Installation, runner archiveRunner) error {
	running, err := restoreVerificationRunning(ctx, installation, runner)
	if err != nil {
		return err
	}
	command := []string{"exec", "-T", "core", "node", "/app/backend/dist/operator-command.js", "workspace-integrity"}
	if !running {
		command = []string{"run", "--rm", "--no-deps", "--no-TTY", "core", "node", "/app/backend/dist/operator-command.js", "workspace-integrity"}
	}
	result, err := runner.Run(ctx, installation.ComposeArgs(command...), nil)
	if err != nil || result.ExitCode != 0 {
		return dockerError("validate restored workspace registry", result, err)
	}
	if len(result.Stdout) == 0 || len(result.Stdout) > 4096 {
		return errors.New("restored workspace registry returned an invalid result")
	}
	var payload struct {
		Ready       bool   `json:"ready"`
		State       string `json:"state"`
		Workspaces  int    `json:"workspaces"`
		Fingerprint string `json:"fingerprint"`
	}
	decoder := json.NewDecoder(strings.NewReader(result.Stdout))
	decoder.DisallowUnknownFields()
	if decodeErr := decoder.Decode(&payload); decodeErr != nil {
		return errors.New("restored workspace registry returned an invalid result")
	}
	var trailing any
	if decodeErr := decoder.Decode(&trailing); !errors.Is(decodeErr, io.EOF) {
		return errors.New("restored workspace registry returned an invalid result")
	}
	if !payload.Ready || payload.Workspaces < 0 ||
		!regexp.MustCompile(`^sha256:[0-9a-f]{64}$`).MatchString(payload.Fingerprint) ||
		(payload.State != "active" && payload.State != "uninitialized") ||
		(payload.State == "uninitialized" && payload.Workspaces != 0) {
		return errors.New("restored workspace registry did not pass integrity validation")
	}
	return nil
}