package kv

import (
	"context"

	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	bolt "go.etcd.io/bbolt"
	"go.opencensus.io/trace"
)

// EpochSpans accepts epoch and returns the corresponding spans byte array
// for slashing detection.
// Returns span byte array, and error in case of db error.
// returns empty byte array if no entry for this epoch exists in db.
func (db *Store) EpochSpans(ctx context.Context, epoch uint64) (EpochStore, error) {
	ctx, span := trace.StartSpan(ctx, "slasherDB.EpochSpans")
	defer span.End()

	var err error
	var spans []byte
	err = db.view(func(tx *bolt.Tx) error {
		b := tx.Bucket(validatorsMinMaxSpanBucketNew)
		if b == nil {
			return nil
		}
		spans = b.Get(bytesutil.Bytes8(epoch))
		return nil
	})
	if spans == nil {
		spans = []byte{}
	}
	return spans, err
}

// SaveEpochSpans accepts a epoch and span byte array and writes it to disk.
func (db *Store) SaveEpochSpans(ctx context.Context, epoch uint64, es EpochStore) error {
	ctx, span := trace.StartSpan(ctx, "slasherDB.SaveEpochSpans")
	defer span.End()

	if len(es)%spannerEncodedLength != 0 {
		return ErrWrongSize
	}
	return db.update(func(tx *bolt.Tx) error {
		b, err := tx.CreateBucketIfNotExists(validatorsMinMaxSpanBucketNew)
		if err != nil {
			return err
		}
		return b.Put(bytesutil.Bytes8(epoch), es)
	})
}