package engine

import (
	"context"
	"errors"

	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util/logicerr"
	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
	"go.uber.org/zap"
)

// GetPrm groups the parameters of Get operation.
type GetPrm struct {
	addr oid.Address
}

// GetRes groups the resulting values of Get operation.
type GetRes struct {
	obj *objectSDK.Object
}

// WithAddress is a Get option to set the address of the requested object.
//
// Option is required.
func (p *GetPrm) WithAddress(addr oid.Address) {
	p.addr = addr
}

// Object returns the requested object.
func (r GetRes) Object() *objectSDK.Object {
	return r.obj
}

// Get reads an object from local storage.
//
// Returns any error encountered that
// did not allow to completely read the object part.
//
// Returns an error of type apistatus.ObjectNotFound if the requested object is missing in local storage.
// Returns an error of type apistatus.ObjectAlreadyRemoved if the object has been marked as removed.
//
// Returns an error if executions are blocked (see BlockExecution).
func (e *StorageEngine) Get(ctx context.Context, prm GetPrm) (res GetRes, err error) {
	ctx, span := tracing.StartSpanFromContext(ctx, "StorageEngine.Get",
		trace.WithAttributes(
			attribute.String("address", prm.addr.EncodeToString()),
		))
	defer span.End()

	err = e.execIfNotBlocked(func() error {
		res, err = e.get(ctx, prm)
		return err
	})

	return
}

func (e *StorageEngine) get(ctx context.Context, prm GetPrm) (GetRes, error) {
	if e.metrics != nil {
		defer elapsed("Get", e.metrics.AddMethodDuration)()
	}

	var errNotFound apistatus.ObjectNotFound

	var shPrm shard.GetPrm
	shPrm.SetAddress(prm.addr)

	it := &getShardIterator{
		OutError: errNotFound,
		ShardPrm: shPrm,
		Address:  prm.addr,
		Engine:   e,
	}

	it.tryGetWithMeta(ctx)

	if it.SplitInfo != nil {
		return GetRes{}, logicerr.Wrap(objectSDK.NewSplitInfoError(it.SplitInfo))
	}

	if it.ObjectExpired {
		return GetRes{}, errNotFound
	}

	if it.Object == nil {
		if !it.HasDegraded && it.ShardWithMeta.Shard == nil || !shard.IsErrNotFound(it.OutError) {
			return GetRes{}, it.OutError
		}

		it.tryGetFromBlobstore(ctx)

		if it.Object == nil {
			return GetRes{}, it.OutError
		}
		if it.ShardWithMeta.Shard != nil {
			e.reportShardError(it.ShardWithMeta, "meta info was present, but object is missing",
				it.MetaError, zap.Stringer("address", prm.addr))
		}
	}

	return GetRes{
		obj: it.Object,
	}, nil
}

type getShardIterator struct {
	Object        *objectSDK.Object
	SplitInfo     *objectSDK.SplitInfo
	OutError      error
	ShardWithMeta hashedShard
	MetaError     error
	HasDegraded   bool
	ObjectExpired bool

	ShardPrm shard.GetPrm
	Address  oid.Address
	Engine   *StorageEngine

	splitInfoErr *objectSDK.SplitInfoError
}

func (i *getShardIterator) tryGetWithMeta(ctx context.Context) {
	i.Engine.iterateOverSortedShards(i.Address, func(_ int, sh hashedShard) (stop bool) {
		noMeta := sh.GetMode().NoMetabase()
		i.ShardPrm.SetIgnoreMeta(noMeta)

		i.HasDegraded = i.HasDegraded || noMeta

		res, err := sh.Get(ctx, i.ShardPrm)
		if err == nil {
			i.Object = res.Object()
			return true
		}

		if res.HasMeta() {
			i.ShardWithMeta = sh
			i.MetaError = err
		}
		switch {
		case shard.IsErrNotFound(err):
			return false // ignore, go to next shard
		case errors.As(err, &i.splitInfoErr):
			if i.SplitInfo == nil {
				i.SplitInfo = objectSDK.NewSplitInfo()
			}

			util.MergeSplitInfo(i.splitInfoErr.SplitInfo(), i.SplitInfo)

			_, withLink := i.SplitInfo.Link()
			_, withLast := i.SplitInfo.LastPart()

			// stop iterating over shards if SplitInfo structure is complete
			return withLink && withLast
		case shard.IsErrRemoved(err):
			i.OutError = err
			return true // stop, return it back
		case shard.IsErrObjectExpired(err):
			// object is found but should not be returned
			i.ObjectExpired = true
			return true
		default:
			i.Engine.reportShardError(sh, "could not get object from shard", err)
			return false
		}
	})
}

func (i *getShardIterator) tryGetFromBlobstore(ctx context.Context) {
	// If the object is not found but is present in metabase,
	// try to fetch it from blobstor directly. If it is found in any
	// blobstor, increase the error counter for the shard which contains the meta.
	i.ShardPrm.SetIgnoreMeta(true)

	i.Engine.iterateOverSortedShards(i.Address, func(_ int, sh hashedShard) (stop bool) {
		if sh.GetMode().NoMetabase() {
			// Already visited.
			return false
		}

		res, err := sh.Get(ctx, i.ShardPrm)
		i.Object = res.Object()
		return err == nil
	})
}

// Get reads object from local storage by provided address.
func Get(ctx context.Context, storage *StorageEngine, addr oid.Address) (*objectSDK.Object, error) {
	var getPrm GetPrm
	getPrm.WithAddress(addr)

	res, err := storage.Get(ctx, getPrm)
	if err != nil {
		return nil, err
	}

	return res.Object(), nil
}