package backup

import (
	"archive/zip"
	"context"
	"errors"
	"fmt"
	"io"
	"time"

	"github.com/aritmolab/thothii/tools/tht/internal/authconfig"
	"github.com/aritmolab/thothii/tools/tht/internal/config"
	"github.com/aritmolab/thothii/tools/tht/internal/lifecycle"
)

var ErrRestoreConfirmationRequired = errors.New("restore requires --yes")

// RestoreRequest describes the deliberately-confirmed archive restoration.
type RestoreRequest struct {
	Archive string
	Confirm bool
	Drain   bool
}

// RestoreResult records the final service state. Secret-bearing recovery checkpoints are always
// destroyed internally and are therefore never exposed to callers.
type RestoreResult struct {
	// Deprecated: always empty. Recovery checkpoints are private transaction internals.
	Checkpoint string
	Restarted  bool
	Verified   bool
}

type restoreVerify func(context.Context, config.Installation, archiveRunner) error

type authProjectionRestoreTransaction interface {
	PublishCanonical() (authconfig.ProjectionStatus, error)
	RestorePriorIfCanonicalUnchanged() error
	Close() error
}

type restoreDependencies struct {
	preflight func(context.Context, config.Installation, PreflightRequest) (PreflightResult, error)
	// checkpoint requires the opaque capability created by lifecycle acquisition. It must not call
	// public Create, which would re-acquire the non-reentrant lock and deadlock the transaction.
	checkpoint               func(context.Context, *lifecycle.Transaction, config.Installation, CreateRequest) (Result, error)
	prepareRecovery          func(context.Context, config.Installation, string) (PreflightResult, error)
	recover                  func(context.Context, config.Installation, PreflightResult, *stagedArchive, bool, authProjectionRestoreTransaction) error
	requireAuthProjection    func() error
	beginAuthProjection      func(context.Context, config.Installation) (authProjectionRestoreTransaction, error)
	cleanupCheckpoint        func(string) error
	acquireTransaction       func(config.Installation) (*lifecycle.Transaction, error)
	runner                   archiveRunner
	sleep                    func(duration time.Duration)
	restoreFile              func(context.Context, config.Installation, ArchiveEntryMetadata, io.Reader) error
	restoreVolume            func(context.Context, config.Installation, VolumeMetadata, io.Reader) error
	resetAuthenticationState func(context.Context, config.Installation, archiveRunner) error
	verify                   map[string]restoreVerify
}

// restoreTransactionState is the restore admission state machine. The durable maintenance
// barrier is released only after the target archive has been verified, or after a separately
// verified checkpoint recovery. Every mutable Docker command is tracked before it is invoked.
type restoreTransactionState struct {
	wasRunning           bool
	maintenanceAttempted bool
	stopAttempted        bool
	mutated              bool
	verified             bool
	recovered            bool
}

func (state restoreTransactionState) recoveryRequired(resultErr error) bool {
	return resultErr != nil && state.mutated && !state.verified
}

func (state restoreTransactionState) mayDeactivateMaintenance() bool {
	return !state.mutated || state.verified || state.recovered
}

// Restore runs the host transaction through the same concrete Docker/filesystem boundaries used
// by backup creation. The injectable core below exists only to make every failure boundary
// deterministic in tests.
func Restore(ctx context.Context, installation config.Installation, request RestoreRequest) (RestoreResult, error) {
	return restoreWithDependencies(ctx, installation, request, productionRestoreDependencies(installation))
}

func restoreWithDependencies(ctx context.Context, installation config.Installation, request RestoreRequest, deps restoreDependencies) (result RestoreResult, resultErr error) {
	if !request.Confirm {
		return RestoreResult{}, ErrRestoreConfirmationRequired
	}
	if request.Archive == "" {
		return RestoreResult{}, errors.New("restore archive is required")
	}
	if deps.preflight == nil || deps.checkpoint == nil || deps.prepareRecovery == nil || deps.recover == nil || deps.requireAuthProjection == nil || deps.cleanupCheckpoint == nil || deps.acquireTransaction == nil || deps.runner == nil || deps.restoreFile == nil || deps.restoreVolume == nil || deps.resetAuthenticationState == nil || deps.verify == nil {
		return RestoreResult{}, errors.New("restore dependencies are incomplete")
	}

	// Lock ordering is lifecycle lock -> Compose/operator maintenance barrier. The core operator
	// command never acquires the host lifecycle lock, so this order cannot form a lock cycle with
	// Docker Compose or the durable maintenance marker.
	transaction, err := deps.acquireTransaction(installation)
	if err != nil {
		return result, err
	}
	defer func() {
		if releaseErr := transaction.Release(); releaseErr != nil {
			result = RestoreResult{}
			resultErr = errors.Join(resultErr, fmt.Errorf("release restore lifecycle lock: %w", releaseErr))
		}
	}()
	// Target-dependent preflight is intentionally inside the lifecycle transaction. This binds
	// target ownership, volume, image, and free-space checks to the later mutation.
	preflight, err := deps.preflight(ctx, installation, PreflightRequest{Archive: request.Archive, Confirm: true, AllowExternalSecrets: true})
	if err != nil {
		return RestoreResult{}, err
	}
	defer preflight.CloseArchive()
	authRestoreRequired := installation.HasRuntimeAuthProjection() && manifestArchivesAuthentication(preflight.Manifest)
	if authRestoreRequired {
		if err := deps.requireAuthProjection(); err != nil {
			return result, err
		}
	}

	checkpoint, err := deps.checkpoint(ctx, transaction, installation, CreateRequest{IncludeSecrets: true, Confirm: true})
	if err != nil {
		return result, fmt.Errorf("create recovery checkpoint: %w", err)
	}
	recovery, err := deps.prepareRecovery(ctx, installation, checkpoint.Path)
	if err != nil {
		cleanupErr := deps.cleanupCheckpoint(checkpoint.Path)
		return result, errors.Join(fmt.Errorf("validate recovery checkpoint: %w", err), cleanupErr)
	}
	defer recovery.CloseArchive()

	// Both immutable archives are staged while the lifecycle transaction is held and before
	// maintenance, service stops, or destination writes. Keeping both files open reserves their
	// combined staging capacity, so checkpoint recovery never needs a new allocation after a
	// candidate mutation has begun.
	candidateStage, err := preflight.StageArchive(ctx)
	if err != nil {
		cleanupErr := deps.cleanupCheckpoint(checkpoint.Path)
		return result, errors.Join(err, cleanupErr)
	}
	defer func() {
		if closeErr := candidateStage.Close(); closeErr != nil {
			result = RestoreResult{}
			resultErr = errors.Join(resultErr, closeErr)
		}
	}()
	recoveryStage, err := recovery.stageArchiveAlongside(ctx, candidateStage)
	if err != nil {
		cleanupErr := deps.cleanupCheckpoint(checkpoint.Path)
		return result, errors.Join(err, cleanupErr)
	}
	defer func() {
		if closeErr := recoveryStage.Close(); closeErr != nil {
			result = RestoreResult{}
			resultErr = errors.Join(resultErr, closeErr)
		}
	}()
	if err := ensureCombinedRestoreCapacity(preflight, recovery); err != nil {
		cleanupErr := deps.cleanupCheckpoint(checkpoint.Path)
		return result, errors.Join(err, cleanupErr)
	}

	var authTransaction authProjectionRestoreTransaction
	if authRestoreRequired {
		if deps.beginAuthProjection == nil {
			cleanupErr := deps.cleanupCheckpoint(checkpoint.Path)
			return result, errors.Join(errors.New("restore authentication projection dependency is unavailable"), cleanupErr)
		}
		authTransaction, err = deps.beginAuthProjection(ctx, installation)
		if err != nil {
			cleanupErr := deps.cleanupCheckpoint(checkpoint.Path)
			return result, errors.Join(errors.New("restore authentication projection could not be blocked"), cleanupErr)
		}
	}

	state := restoreTransactionState{}
	defer func() {
		if state.recoveryRequired(resultErr) {
			recoveryContext, cancel := boundedCleanupContext()
			recoveryErr := deps.recover(recoveryContext, installation, recovery, recoveryStage, state.wasRunning, authTransaction)
			cancel()
			if recoveryErr != nil {
				resultErr = errors.Join(resultErr, fmt.Errorf("restore recovery checkpoint: %w", recoveryErr))
				if recoveryReachedVerifiedState(recoveryErr) {
					state.recovered = true
					state.stopAttempted = false
				}
			} else {
				state.recovered = true
				state.stopAttempted = false
			}
		}

		checkpointCleanupSucceeded := true
		var cleanupErr error
		if checkpointErr := deps.cleanupCheckpoint(checkpoint.Path); checkpointErr != nil {
			checkpointCleanupSucceeded = false
			cleanupErr = errors.Join(cleanupErr, fmt.Errorf("destroy recovery checkpoint: %w", checkpointErr))
		}
		authCleanupSucceeded := true
		if authTransaction != nil {
			if resultErr != nil && !state.mutated {
				if restoreErr := authTransaction.RestorePriorIfCanonicalUnchanged(); restoreErr != nil {
					authCleanupSucceeded = false
					cleanupErr = errors.Join(cleanupErr, errors.New("restore authentication projection could not restore its prior selector"))
				}
			}
			if closeErr := authTransaction.Close(); closeErr != nil {
				authCleanupSucceeded = false
				cleanupErr = errors.Join(cleanupErr, errors.New("restore authentication projection transaction could not be closed"))
			}
			authTransaction = nil
		}
		if !state.maintenanceAttempted {
			if cleanupErr != nil {
				result = RestoreResult{}
				resultErr = errors.Join(resultErr, cleanupErr)
			}
			return
		}
		// A recovery checkpoint remains secret-bearing transaction state. Do not reopen
		// admissions until it has been safely deleted, even if the restored target verified.
		if !checkpointCleanupSucceeded {
			result = RestoreResult{}
			resultErr = errors.Join(resultErr, cleanupErr)
			return
		}
		restartCompleted := true
		if state.wasRunning && state.stopAttempted && state.mayDeactivateMaintenance() {
			startErr, started := retryBoundedCleanup(func(cleanupContext context.Context) error {
				return composeStartAndVerify(cleanupContext, installation, deps.runner)
			})
			if startErr != nil {
				cleanupErr = errors.Join(cleanupErr, fmt.Errorf("restore maintenance cleanup restart: %w", startErr))
			}
			if started {
				state.stopAttempted = false
			} else {
				restartCompleted = false
			}
		}
		// A failed checkpoint recovery deliberately leaves admissions blocked. Starting or
		// deactivating at that point would expose an unverified, possibly partial restore.
		if state.mayDeactivateMaintenance() && restartCompleted && authCleanupSucceeded {
			deactivateErr, deactivated := retryBoundedCleanup(func(cleanupContext context.Context) error {
				return maintenance(cleanupContext, installation, deps.runner, false)
			})
			if deactivateErr != nil {
				cleanupErr = errors.Join(cleanupErr, fmt.Errorf("restore maintenance cleanup: %w", deactivateErr))
			}
			if deactivated {
				state.maintenanceAttempted = false
			}
		}
		if cleanupErr != nil {
			result = RestoreResult{}
			resultErr = errors.Join(resultErr, cleanupErr)
		}
	}()

	wasRunning, err := installationRunning(ctx, installation, deps.runner)
	if err != nil {
		return result, err
	}
	state.wasRunning = wasRunning
	if state.wasRunning {
		// The activation command may take effect even when its response is lost. Track the attempt,
		// not merely a successful return, so every subsequent path compensates from durable state.
		state.maintenanceAttempted = true
		if err := maintenance(ctx, installation, deps.runner, true); err != nil {
			return result, err
		}
		if err := waitForNoActiveSessions(ctx, installation, deps.runner, request.Drain, deps.sleep); err != nil {
			return result, err
		}
		// Compose may stop the core and then lose its response. Cleanup must therefore restart after
		// any stop attempt, including a command that returns an error.
		state.stopAttempted = true
		if err := runCompose(ctx, installation, deps.runner, "stop"); err != nil {
			return result, err
		}
	}
	state.mutated = true
	if err := restoreVerifiedEntries(ctx, installation, preflight, candidateStage.file, deps.restoreFile, deps.restoreVolume); err != nil {
		return result, err
	}
	if err := deps.resetAuthenticationState(ctx, installation, deps.runner); err != nil {
		return result, fmt.Errorf("reset authentication state: %w", err)
	}
	if authTransaction != nil {
		if err := publishRestoredAuthentication(authTransaction); err != nil {
			return result, err
		}
	}
	if state.wasRunning {
		if err := composeStartAndVerify(ctx, installation, deps.runner); err != nil {
			return result, err
		}
		state.stopAttempted = false
		result.Restarted = true
	}
	if err := verifyRestoreTransaction(ctx, installation, deps); err != nil {
		return result, err
	}
	state.verified = true
	result.Verified = true
	return result, nil
}

func manifestArchivesAuthentication(manifest Manifest) bool {
	for _, entry := range manifest.Entries {
		if entry.Archived && entry.Kind == EntryExternalSecret && entry.Owner == "authentication-configuration" {
			return true
		}
	}
	return false
}

func publishRestoredAuthentication(transaction authProjectionRestoreTransaction) error {
	status, err := transaction.PublishCanonical()
	if err != nil || status.State != "ready" || !status.Equal {
		if err != nil {
			return fmt.Errorf("publish restored authentication projection: %w", err)
		}
		return errors.New("publish restored authentication projection")
	}
	return nil
}

func ensureCombinedRestoreCapacity(candidate, recovery PreflightResult) error {
	if candidate.freeBytes == nil || candidate.stagingRoot == "" || candidate.stagingRoot != recovery.stagingRoot {
		return errors.New("candidate and recovery archives do not share controlled restore staging")
	}
	if recovery.RequiredBytes > ^uint64(0)-candidate.RequiredBytes {
		return errors.New("combined candidate and recovery restore capacity exceeds supported size")
	}
	required := candidate.RequiredBytes + recovery.RequiredBytes
	freeBytes, err := candidate.freeBytes(candidate.stagingRoot)
	if err != nil {
		return errors.New("check combined candidate and recovery staging capacity")
	}
	if freeBytes < required {
		return fmt.Errorf("insufficient free disk space for combined candidate and recovery staging: need %d bytes, have %d", required, freeBytes)
	}
	return nil
}

func verifyRestoreTransaction(ctx context.Context, installation config.Installation, deps restoreDependencies) error {
	for _, name := range []string{"health", "doctor", "pi", "workspace"} {
		check := deps.verify[name]
		if check == nil {
			return fmt.Errorf("restore verification %q is unavailable", name)
		}
		if err := check(ctx, installation, deps.runner); err != nil {
			return fmt.Errorf("restore verification %s: %w", name, err)
		}
	}
	return nil
}

type verifiedRecoveryError struct{ err error }

func (err *verifiedRecoveryError) Error() string { return err.err.Error() }

func (err *verifiedRecoveryError) Unwrap() error { return err.err }

func recoveryReachedVerifiedState(err error) bool {
	var verifiedErr *verifiedRecoveryError
	return errors.As(err, &verifiedErr)
}

func restoreVerifiedEntries(
	ctx context.Context,
	installation config.Installation,
	preflight PreflightResult,
	archive io.ReaderAt,
	restoreFile func(context.Context, config.Installation, ArchiveEntryMetadata, io.Reader) error,
	restoreVolume func(context.Context, config.Installation, VolumeMetadata, io.Reader) error,
) error {
	reader, err := zip.NewReader(archive, preflight.ArchiveSize)
	if err != nil {
		return fmt.Errorf("read verified restore archive: %w", err)
	}
	members := make(map[string]*zip.File, len(reader.File))
	for _, member := range reader.File {
		members[member.Name] = member
	}
	for _, entry := range preflight.Entries {
		member := members[entry.Path]
		if member == nil {
			return fmt.Errorf("verified archive is missing %q", entry.Path)
		}
		stream, openErr := member.Open()
		if openErr != nil {
			return fmt.Errorf("open verified archive member %q: %w", entry.Path, openErr)
		}
		var restoreErr error
		if entry.Kind == EntryVolume {
			volume, found := restoreVolumeMetadata(preflight.Manifest, entry.LogicalName)
			if !found {
				_ = stream.Close()
				return errors.New("verified volume metadata is incomplete")
			}
			restoreErr = restoreVolume(ctx, installation, volume, stream)
		} else {
			restoreErr = restoreFile(ctx, installation, entry, stream)
		}
		closeErr := stream.Close()
		if restoreErr != nil {
			return restoreErr
		}
		if closeErr != nil {
			return closeErr
		}
	}
	return nil
}

func restoreVolumeMetadata(manifest Manifest, logicalName string) (VolumeMetadata, bool) {
	if logicalName == "" {
		return VolumeMetadata{}, false
	}
	for _, volume := range manifest.Volumes {
		if volume.LogicalName == logicalName {
			return volume, true
		}
	}
	return VolumeMetadata{}, false
}

// resetAuthenticationState clears browser sessions and pending OIDC transactions without touching
// installation-global auth.yaml or users.yaml. A root-scoped one-shot repairs ownership and mode
// before clearing children; links and malformed roots are rejected before any recursive removal.
func resetAuthenticationState(ctx context.Context, installation config.Installation, runner archiveRunner) error {
	result, err := runner.Run(ctx, installation.ComposeArgs(
		"run", "--rm", "--no-deps", "--no-TTY", "--user", "0:0", "--entrypoint", "sh", "core", "-ceu",
		"test ! -L /data/auth && { test ! -e /data/auth || test -d /data/auth; } && install -d -o 10001 -g 10001 -m 0700 /data/auth && find /data/auth -mindepth 1 -maxdepth 1 -exec rm -rf -- {} + && install -d -o 10001 -g 10001 -m 0700 /data/auth/sessions /data/auth/oidc && chmod 0700 /data/auth /data/auth/sessions /data/auth/oidc && chown 10001:10001 /data/auth /data/auth/sessions /data/auth/oidc && test -z \"$(find /data/auth/sessions /data/auth/oidc -mindepth 1 -print -quit)\"",
	), nil)
	if err != nil {
		return dockerError("reset authentication state", result, err)
	}
	if result.ExitCode != 0 {
		return dockerError("reset authentication state", result, errors.New("Compose returned a nonzero exit status"))
	}
	return nil
}