package meta

import (
	"context"
	"time"

	objectcore "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/object"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/internal/metaerr"
	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/util/logicerr"
	"git.frostfs.info/TrueCloudLab/frostfs-observability/tracing"
	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
	"go.etcd.io/bbolt"
	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/trace"
)

// ErrEndOfListing is returned from object listing with cursor
// when storage can't return any more objects after provided
// cursor. Use nil cursor object to start listing again.
var ErrEndOfListing = logicerr.New("end of object listing")

// Cursor is a type for continuous object listing.
type Cursor struct {
	bucketName     []byte
	inBucketOffset []byte
}

// ListPrm contains parameters for ListWithCursor operation.
type ListPrm struct {
	count  int
	cursor *Cursor
}

// SetCount sets maximum amount of addresses that ListWithCursor should return.
func (l *ListPrm) SetCount(count uint32) {
	l.count = int(count)
}

// SetCursor sets cursor for ListWithCursor operation. For initial request
// ignore this param or use nil value. For consecutive requests, use value
// from ListRes.
func (l *ListPrm) SetCursor(cursor *Cursor) {
	l.cursor = cursor
}

// ListRes contains values returned from ListWithCursor operation.
type ListRes struct {
	addrList []objectcore.AddressWithType
	cursor   *Cursor
}

// AddressList returns addresses selected by ListWithCursor operation.
func (l ListRes) AddressList() []objectcore.AddressWithType {
	return l.addrList
}

// Cursor returns cursor for consecutive listing requests.
func (l ListRes) Cursor() *Cursor {
	return l.cursor
}

// ListWithCursor lists physical objects available in metabase starting from
// cursor. Includes objects of all types. Does not include inhumed objects.
// Use cursor value from response for consecutive requests.
//
// Returns ErrEndOfListing if there are no more objects to return or count
// parameter set to zero.
func (db *DB) ListWithCursor(ctx context.Context, prm ListPrm) (res ListRes, err error) {
	var (
		startedAt = time.Now()
		success   = false
	)
	defer func() {
		db.metrics.AddMethodDuration("ListWithCursor", time.Since(startedAt), success)
	}()
	_, span := tracing.StartSpanFromContext(ctx, "metabase.ListWithCursor",
		trace.WithAttributes(
			attribute.Int("count", prm.count),
			attribute.Bool("has_cursor", prm.cursor != nil),
		))
	defer span.End()

	db.modeMtx.RLock()
	defer db.modeMtx.RUnlock()

	if db.mode.NoMetabase() {
		return res, ErrDegradedMode
	}

	result := make([]objectcore.AddressWithType, 0, prm.count)

	err = db.boltDB.View(func(tx *bbolt.Tx) error {
		res.addrList, res.cursor, err = db.listWithCursor(tx, result, prm.count, prm.cursor)
		return err
	})
	success = err == nil
	return res, metaerr.Wrap(err)
}

func (db *DB) listWithCursor(tx *bbolt.Tx, result []objectcore.AddressWithType, count int, cursor *Cursor) ([]objectcore.AddressWithType, *Cursor, error) {
	threshold := cursor == nil // threshold is a flag to ignore cursor
	var bucketName []byte
	var err error

	c := tx.Cursor()
	name, _ := c.First()

	if !threshold {
		name, _ = c.Seek(cursor.bucketName)
	}

	var containerID cid.ID
	var offset []byte
	graveyardBkt := tx.Bucket(graveyardBucketName)
	garbageBkt := tx.Bucket(garbageBucketName)

	rawAddr := make([]byte, cidSize, addressKeySize)

loop:
	for ; name != nil; name, _ = c.Next() {
		cidRaw, prefix := parseContainerIDWithPrefix(&containerID, name)
		if cidRaw == nil {
			continue
		}

		var objType objectSDK.Type

		switch prefix {
		case primaryPrefix:
			objType = objectSDK.TypeRegular
		case lockersPrefix:
			objType = objectSDK.TypeLock
		case tombstonePrefix:
			objType = objectSDK.TypeTombstone
		default:
			continue
		}

		bkt := tx.Bucket(name)
		if bkt != nil {
			copy(rawAddr, cidRaw)
			result, offset, cursor, err = selectNFromBucket(bkt, objType, graveyardBkt, garbageBkt, rawAddr, containerID,
				result, count, cursor, threshold)
			if err != nil {
				return nil, nil, err
			}
		}
		bucketName = name
		if len(result) >= count {
			break loop
		}

		// set threshold flag after first `selectNFromBucket` invocation
		// first invocation must look for cursor object
		threshold = true
	}

	if offset != nil {
		// new slice is much faster but less memory efficient
		// we need to copy, because offset exists during bbolt tx
		cursor.inBucketOffset = make([]byte, len(offset))
		copy(cursor.inBucketOffset, offset)
	}

	if len(result) == 0 {
		return nil, nil, ErrEndOfListing
	}

	// new slice is much faster but less memory efficient
	// we need to copy, because bucketName exists during bbolt tx
	cursor.bucketName = make([]byte, len(bucketName))
	copy(cursor.bucketName, bucketName)

	return result, cursor, nil
}

// selectNFromBucket similar to selectAllFromBucket but uses cursor to find
// object to start selecting from. Ignores inhumed objects.
func selectNFromBucket(bkt *bbolt.Bucket, // main bucket
	objType objectSDK.Type, // type of the objects stored in the main bucket
	graveyardBkt, garbageBkt *bbolt.Bucket, // cached graveyard buckets
	cidRaw []byte, // container ID prefix, optimization
	cnt cid.ID, // container ID
	to []objectcore.AddressWithType, // listing result
	limit int, // stop listing at `limit` items in result
	cursor *Cursor, // start from cursor object
	threshold bool, // ignore cursor and start immediately
) ([]objectcore.AddressWithType, []byte, *Cursor, error) {
	if cursor == nil {
		cursor = new(Cursor)
	}

	count := len(to)
	c := bkt.Cursor()
	k, v := c.First()

	offset := cursor.inBucketOffset

	if !threshold {
		c.Seek(offset)
		k, v = c.Next() // we are looking for objects _after_ the cursor
	}

	for ; k != nil; k, v = c.Next() {
		if count >= limit {
			break
		}

		var obj oid.ID
		if err := obj.Decode(k); err != nil {
			break
		}

		offset = k
		if inGraveyardWithKey(append(cidRaw, k...), graveyardBkt, garbageBkt) > 0 {
			continue
		}

		var isLinkingObj bool
		if objType == objectSDK.TypeRegular {
			var o objectSDK.Object
			if err := o.Unmarshal(v); err != nil {
				return nil, nil, nil, err
			}
			isLinkingObj = isLinkObject(&o)
		}

		var a oid.Address
		a.SetContainer(cnt)
		a.SetObject(obj)
		to = append(to, objectcore.AddressWithType{Address: a, Type: objType, IsLinkingObject: isLinkingObj})
		count++
	}

	return to, offset, cursor, nil
}

func parseContainerIDWithPrefix(containerID *cid.ID, name []byte) ([]byte, byte) {
	if len(name) < bucketKeySize {
		return nil, 0
	}

	rawID := name[1:bucketKeySize]

	if err := containerID.Decode(rawID); err != nil {
		return nil, 0
	}

	return rawID, name[0]
}