package authconfig

import (
	"context"
	"errors"
	"sync"

	"github.com/aritmolab/thothii/tools/tht/internal/authprojection"
)

const transactionLockFileName = ".auth-transaction.lock"

var (
	errProjectionMutation  = errors.New("authentication projection mutation failed")
	errProjectionPublish   = errors.New("authentication projection publication failed")
	errProjectionCleanup   = errors.New("authentication projection cleanup failed")
	errProjectionIntegrity = errors.New("authentication projection coordination failed")
)

var runtimeProjectionBegin = authprojection.BeginContext

func setRuntimeProjectionBeginForTest(begin func(context.Context, authprojection.Spec, *authprojection.Snapshot, bool) (*authprojection.Transaction, error)) func() {
	previous := runtimeProjectionBegin
	runtimeProjectionBegin = begin
	return func() { runtimeProjectionBegin = previous }
}

type ProjectionSpec struct {
	RuntimeRoot string
	UID         uint32
	GID         uint32
}

type ProjectionStatus struct {
	State             string
	Generation        string
	CanonicalRevision string
	Equal             bool
}

type ExternalProjectionTransaction struct {
	ctx           context.Context
	canonicalRoot string
	spec          authprojection.Spec
	outerLock     *transactionLock
	projection    *authprojection.Transaction
	before        authprojection.Snapshot
	hasBefore     bool
	published     bool
	closed        bool
}

type projectionCoordinatorHooks struct {
	onOuterLockContention     func()
	onCanonicalLockContention func()
	beforeProjectionBegin     func()
	verifyCommittedProjection func(authprojection.Status, authprojection.Snapshot) error
}

var projectionCoordinatorHookState struct {
	sync.Mutex
	hooks projectionCoordinatorHooks
}

func setProjectionCoordinatorHooksForTest(hooks projectionCoordinatorHooks) func() {
	projectionCoordinatorHookState.Lock()
	previous := projectionCoordinatorHookState.hooks
	projectionCoordinatorHookState.hooks = hooks
	projectionCoordinatorHookState.Unlock()
	return func() {
		projectionCoordinatorHookState.Lock()
		projectionCoordinatorHookState.hooks = previous
		projectionCoordinatorHookState.Unlock()
	}
}

func coordinatorHooks() projectionCoordinatorHooks {
	projectionCoordinatorHookState.Lock()
	defer projectionCoordinatorHookState.Unlock()
	return projectionCoordinatorHookState.hooks
}

func RunProjectedMutation(ctx context.Context, canonicalRoot string, spec ProjectionSpec, mutate func() error) (err error) {
	if mutate == nil {
		return errProjectionMutation
	}
	transaction, err := BeginExternalProjectionTransaction(ctx, canonicalRoot, spec)
	if err != nil {
		return errProjectionIntegrity
	}
	defer func() {
		if closeErr := transaction.Close(); closeErr != nil {
			if err == nil {
				err = errProjectionCleanup
			} else {
				err = errors.Join(err, errProjectionCleanup)
			}
		}
	}()
	if mutateErr := mutate(); mutateErr != nil {
		if restoreErr := transaction.restorePriorIfCanonicalUnchanged(ctx); restoreErr != nil {
			return errors.Join(errProjectionMutation, errProjectionCleanup)
		}
		return errProjectionMutation
	}
	if _, publishErr := transaction.publishCanonicalContext(ctx); publishErr != nil {
		return errProjectionPublish
	}
	return nil
}

func PublishProjectedCanonical(ctx context.Context, canonicalRoot string, spec ProjectionSpec) (status ProjectionStatus, err error) {
	transaction, err := BeginExternalProjectionTransaction(ctx, canonicalRoot, spec)
	if err != nil {
		return ProjectionStatus{}, errProjectionIntegrity
	}
	defer func() {
		if closeErr := transaction.Close(); closeErr != nil {
			if err == nil {
				err = errProjectionCleanup
			} else {
				err = errors.Join(err, errProjectionCleanup)
			}
		}
	}()
	return transaction.publishCanonicalContext(ctx)
}

func BeginExternalProjectionTransaction(ctx context.Context, canonicalRoot string, spec ProjectionSpec) (transaction *ExternalProjectionTransaction, err error) {
	if ctx == nil {
		return nil, errProjectionIntegrity
	}
	if err := requirePrivateDirectory(canonicalRoot); err != nil {
		return nil, errProjectionIntegrity
	}
	outerLock, err := acquireTransactionLock(ctx, canonicalRoot)
	if err != nil {
		return nil, errProjectionIntegrity
	}
	transaction = &ExternalProjectionTransaction{
		ctx:           ctx,
		canonicalRoot: canonicalRoot,
		spec:          authprojection.Spec{RuntimeRoot: spec.RuntimeRoot, UID: spec.UID, GID: spec.GID},
		outerLock:     outerLock,
	}
	created := transaction
	defer func() {
		if err != nil {
			if closeErr := created.closeProjectionAndOuterLock(); closeErr != nil {
				err = errors.Join(errProjectionIntegrity, errProjectionCleanup)
			} else {
				err = errProjectionIntegrity
			}
		}
	}()
	if err = transaction.beginProjection(ctx); err != nil {
		return nil, err
	}
	return transaction, nil
}

func (transaction *ExternalProjectionTransaction) PublishCanonical() (ProjectionStatus, error) {
	if transaction == nil {
		return ProjectionStatus{}, errProjectionIntegrity
	}
	return transaction.publishCanonicalContext(transaction.ctx)
}

func (transaction *ExternalProjectionTransaction) publishCanonicalContext(ctx context.Context) (ProjectionStatus, error) {
	if transaction == nil || transaction.closed {
		return ProjectionStatus{}, errProjectionIntegrity
	}
	if transaction.projection == nil {
		if err := transaction.beginProjection(ctx); err != nil {
			return ProjectionStatus{}, errProjectionIntegrity
		}
	}
	var published authprojection.Status
	var expected authprojection.Snapshot
	committed := false
	err := transaction.withCanonicalLock(ctx, func() error {
		snapshot, err := loadSnapshotBytes(transaction.canonicalRoot)
		if err != nil {
			return err
		}
		expected = snapshot
		published, err = transaction.projection.Commit(snapshot)
		if err != nil {
			return err
		}
		committed = true
		if !equalProjection(published, snapshot) {
			return errProjectionIntegrity
		}
		if verify := coordinatorHooks().verifyCommittedProjection; verify != nil {
			return verify(published, snapshot)
		}
		return nil
	})
	if err != nil {
		if committed {
			if blockErr := transaction.ensureBlocked(); blockErr != nil {
				return ProjectionStatus{}, errors.Join(errProjectionPublish, errProjectionCleanup)
			}
		}
		return ProjectionStatus{}, errProjectionPublish
	}
	transaction.published = true
	if err := transaction.releaseProjection(); err != nil {
		if blockErr := transaction.ensureBlocked(); blockErr != nil {
			return ProjectionStatus{}, errors.Join(errProjectionCleanup, errProjectionIntegrity)
		}
		return ProjectionStatus{}, errProjectionCleanup
	}
	return projectionStatus(published, expected), nil
}

func (transaction *ExternalProjectionTransaction) RestorePriorIfCanonicalUnchanged() error {
	if transaction == nil {
		return errProjectionIntegrity
	}
	return transaction.restorePriorIfCanonicalUnchanged(transaction.ctx)
}

func (transaction *ExternalProjectionTransaction) restorePriorIfCanonicalUnchanged(ctx context.Context) error {
	if transaction == nil || transaction.closed || transaction.projection == nil || !transaction.hasBefore {
		return errProjectionIntegrity
	}
	err := transaction.withCanonicalLock(ctx, func() error {
		current, err := loadSnapshotBytes(transaction.canonicalRoot)
		if err != nil {
			return err
		}
		if current.Generation != transaction.before.Generation {
			return errProjectionIntegrity
		}
		return transaction.projection.RestoreIfUnchanged(current)
	})
	if err != nil {
		return errProjectionIntegrity
	}
	return transaction.releaseProjection()
}

func (transaction *ExternalProjectionTransaction) Close() (err error) {
	if transaction == nil || transaction.closed {
		return nil
	}
	defer func() {
		transaction.closed = true
		err = errors.Join(err, transaction.closeProjectionAndOuterLock())
	}()
	if transaction.projection == nil && transaction.published {
		if beginErr := transaction.beginProjection(context.Background()); beginErr != nil {
			return errProjectionIntegrity
		}
		if restoreErr := transaction.restorePriorIfCanonicalUnchanged(context.Background()); restoreErr != nil {
			return errProjectionIntegrity
		}
	}
	return nil
}

func (transaction *ExternalProjectionTransaction) beginProjection(ctx context.Context) error {
	status, err := authprojection.Inspect(transaction.spec)
	var before *authprojection.Snapshot
	requireReadyMatch := false
	if err == nil {
		captured := status.Snapshot
		before = &captured
		requireReadyMatch = true
	}
	if hook := coordinatorHooks().beforeProjectionBegin; hook != nil {
		hook()
	}
	projection, err := runtimeProjectionBegin(ctx, transaction.spec, before, requireReadyMatch)
	if err != nil {
		return errProjectionIntegrity
	}
	transaction.projection = projection
	transaction.hasBefore = before != nil
	if before != nil {
		transaction.before = *before
	} else {
		transaction.before = authprojection.Snapshot{}
	}
	return nil
}

func (transaction *ExternalProjectionTransaction) ensureBlocked() error {
	if transaction.projection != nil {
		if err := transaction.releaseProjection(); err != nil {
			return err
		}
	}
	return transaction.beginProjection(context.Background())
}

func (transaction *ExternalProjectionTransaction) releaseProjection() error {
	if transaction.projection == nil {
		return nil
	}
	projection := transaction.projection
	transaction.projection = nil
	if err := projection.Close(); err != nil {
		return errProjectionIntegrity
	}
	return nil
}

func (transaction *ExternalProjectionTransaction) closeProjectionAndOuterLock() error {
	var err error
	if closeErr := transaction.releaseProjection(); closeErr != nil {
		err = errors.Join(err, closeErr)
	}
	if transaction.outerLock != nil {
		if unlockErr := transaction.outerLock.Close(); unlockErr != nil {
			err = errors.Join(err, errProjectionCleanup)
		}
		transaction.outerLock = nil
	}
	return err
}

func (transaction *ExternalProjectionTransaction) withCanonicalLock(ctx context.Context, callback func() error) (err error) {
	lock, err := acquireLockContext(ctx, transaction.canonicalRoot)
	if err != nil {
		return errProjectionIntegrity
	}
	defer func() {
		if unlockErr := lock.Unlock(); unlockErr != nil {
			err = errors.Join(err, errProjectionCleanup)
		}
	}()
	return callback()
}

func equalProjection(status authprojection.Status, snapshot authprojection.Snapshot) bool {
	return status.Selector.State == "ready" && status.Snapshot.Generation == snapshot.Generation && status.Snapshot.CanonicalRevision == snapshot.CanonicalRevision
}

func projectionStatus(status authprojection.Status, expected authprojection.Snapshot) ProjectionStatus {
	return ProjectionStatus{
		State:             status.Selector.State,
		Generation:        status.Snapshot.Generation,
		CanonicalRevision: status.Snapshot.CanonicalRevision,
		Equal:             equalProjection(status, expected),
	}
}