package slasherkv

import (
	"bytes"
	"context"
	"encoding/binary"
	"fmt"
	"sort"
	"sync"

	ssz "github.com/ferranbt/fastssz"
	"github.com/golang/snappy"
	"github.com/pkg/errors"
	types "github.com/prysmaticlabs/eth2-types"
	slashertypes "github.com/prysmaticlabs/prysm/beacon-chain/slasher/types"
	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
	bolt "go.etcd.io/bbolt"
	"go.opencensus.io/trace"
	"golang.org/x/sync/errgroup"
)

const (
	// Signing root (32 bytes)
	attestationRecordKeySize = 32 // Bytes.
	signingRootSize          = 32 // Bytes.
)

// LastEpochWrittenForValidators given a list of validator indices returns the latest
// epoch we have recorded the validators writing data for.
func (s *Store) LastEpochWrittenForValidators(
	ctx context.Context, validatorIndices []types.ValidatorIndex,
) ([]*slashertypes.AttestedEpochForValidator, error) {
	_, span := trace.StartSpan(ctx, "BeaconDB.LastEpochWrittenForValidators")
	defer span.End()
	attestedEpochs := make([]*slashertypes.AttestedEpochForValidator, 0)
	encodedIndices := make([][]byte, len(validatorIndices))
	for i, valIdx := range validatorIndices {
		encodedIndices[i] = encodeValidatorIndex(valIdx)
	}
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(attestedEpochsByValidator)
		for i, encodedIndex := range encodedIndices {
			var epoch types.Epoch
			epochBytes := bkt.Get(encodedIndex)
			if epochBytes != nil {
				if err := epoch.UnmarshalSSZ(epochBytes); err != nil {
					return err
				}
			}
			attestedEpochs = append(attestedEpochs, &slashertypes.AttestedEpochForValidator{
				ValidatorIndex: validatorIndices[i],
				Epoch:          epoch,
			})
		}
		return nil
	})
	return attestedEpochs, err
}

// SaveLastEpochsWrittenForValidators updates the latest epoch a slice
// of validator indices has attested to.
func (s *Store) SaveLastEpochsWrittenForValidators(
	ctx context.Context, epochByValidator map[types.ValidatorIndex]types.Epoch,
) error {
	_, span := trace.StartSpan(ctx, "BeaconDB.SaveLastEpochsWrittenForValidators")
	defer span.End()
	encodedIndices := make([][]byte, 0, len(epochByValidator))
	encodedEpochs := make([][]byte, 0, len(epochByValidator))
	for valIdx, epoch := range epochByValidator {
		if ctx.Err() != nil {
			return ctx.Err()
		}
		encodedEpoch, err := epoch.MarshalSSZ()
		if err != nil {
			return err
		}
		encodedIndices = append(encodedIndices, encodeValidatorIndex(valIdx))
		encodedEpochs = append(encodedEpochs, encodedEpoch)
	}
	// The list of validators might be too massive for boltdb to handle in a single transaction,
	// so instead we split it into batches and write each batch.
	batchSize := 10000
	for i := 0; i < len(encodedIndices); i += batchSize {
		if ctx.Err() != nil {
			return ctx.Err()
		}
		if err := s.db.Update(func(tx *bolt.Tx) error {
			if ctx.Err() != nil {
				return ctx.Err()
			}
			bkt := tx.Bucket(attestedEpochsByValidator)
			min := i + batchSize
			if min > len(encodedIndices) {
				min = len(encodedIndices)
			}
			for j, encodedIndex := range encodedIndices[i:min] {
				if ctx.Err() != nil {
					return ctx.Err()
				}
				if err := bkt.Put(encodedIndex, encodedEpochs[j]); err != nil {
					return err
				}
			}
			return nil
		}); err != nil {
			return err
		}
	}
	return nil
}

// CheckAttesterDoubleVotes retries any slashable double votes that exist
// for a series of input attestations.
func (s *Store) CheckAttesterDoubleVotes(
	ctx context.Context, attestations []*slashertypes.IndexedAttestationWrapper,
) ([]*slashertypes.AttesterDoubleVote, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.CheckAttesterDoubleVotes")
	defer span.End()
	doubleVotes := make([]*slashertypes.AttesterDoubleVote, 0)
	doubleVotesMu := sync.Mutex{}
	eg, egctx := errgroup.WithContext(ctx)
	for _, att := range attestations {
		// Copy the iteration instance to a local variable to give each go-routine its own copy to play with.
		// See https://golang.org/doc/faq#closures_and_goroutines for more details.
		attToProcess := att
		// process every attestation parallelly.
		eg.Go(func() error {
			err := s.db.View(func(tx *bolt.Tx) error {
				signingRootsBkt := tx.Bucket(attestationDataRootsBucket)
				attRecordsBkt := tx.Bucket(attestationRecordsBucket)
				encEpoch := encodeTargetEpoch(attToProcess.IndexedAttestation.Data.Target.Epoch)
				localDoubleVotes := make([]*slashertypes.AttesterDoubleVote, 0)
				for _, valIdx := range attToProcess.IndexedAttestation.AttestingIndices {
					encIdx := encodeValidatorIndex(types.ValidatorIndex(valIdx))
					validatorEpochKey := append(encEpoch, encIdx...)
					attRecordsKey := signingRootsBkt.Get(validatorEpochKey)
					// An attestation record key is comprised of a signing root (32 bytes).
					if len(attRecordsKey) < attestationRecordKeySize {
						continue
					}
					encExistingAttRecord := attRecordsBkt.Get(attRecordsKey)
					if encExistingAttRecord == nil {
						continue
					}
					existingSigningRoot := bytesutil.ToBytes32(attRecordsKey[:signingRootSize])
					if existingSigningRoot != attToProcess.SigningRoot {
						existingAttRecord, err := decodeAttestationRecord(encExistingAttRecord)
						if err != nil {
							return err
						}
						slashAtt := &slashertypes.AttesterDoubleVote{
							ValidatorIndex:         types.ValidatorIndex(valIdx),
							Target:                 attToProcess.IndexedAttestation.Data.Target.Epoch,
							PrevAttestationWrapper: existingAttRecord,
							AttestationWrapper:     attToProcess,
						}
						localDoubleVotes = append(localDoubleVotes, slashAtt)
					}
				}
				// if any routine is cancelled, then cancel this routine too
				select {
				case <-egctx.Done():
					return egctx.Err()
				default:
				}
				// if there are any doible votes in this attestation, add it to the global double votes
				if len(localDoubleVotes) > 0 {
					doubleVotesMu.Lock()
					defer doubleVotesMu.Unlock()
					doubleVotes = append(doubleVotes, localDoubleVotes...)
				}
				return nil
			})
			return err
		})
	}
	return doubleVotes, eg.Wait()
}

// AttestationRecordForValidator given a validator index and a target epoch,
// retrieves an existing attestation record we have stored in the database.
func (s *Store) AttestationRecordForValidator(
	ctx context.Context, validatorIdx types.ValidatorIndex, targetEpoch types.Epoch,
) (*slashertypes.IndexedAttestationWrapper, error) {
	_, span := trace.StartSpan(ctx, "BeaconDB.AttestationRecordForValidator")
	defer span.End()
	var record *slashertypes.IndexedAttestationWrapper
	encIdx := encodeValidatorIndex(validatorIdx)
	encEpoch := encodeTargetEpoch(targetEpoch)
	key := append(encEpoch, encIdx...)
	err := s.db.View(func(tx *bolt.Tx) error {
		signingRootsBkt := tx.Bucket(attestationDataRootsBucket)
		attRecordKey := signingRootsBkt.Get(key)
		if attRecordKey == nil {
			return nil
		}
		attRecordsBkt := tx.Bucket(attestationRecordsBucket)
		indexedAttBytes := attRecordsBkt.Get(attRecordKey)
		if indexedAttBytes == nil {
			return nil
		}
		decoded, err := decodeAttestationRecord(indexedAttBytes)
		if err != nil {
			return err
		}
		record = decoded
		return nil
	})
	return record, err
}

// SaveAttestationRecordsForValidators saves attestation records for the specified indices.
func (s *Store) SaveAttestationRecordsForValidators(
	ctx context.Context,
	attestations []*slashertypes.IndexedAttestationWrapper,
) error {
	_, span := trace.StartSpan(ctx, "BeaconDB.SaveAttestationRecordsForValidators")
	defer span.End()
	encodedTargetEpoch := make([][]byte, len(attestations))
	encodedRecords := make([][]byte, len(attestations))
	encodedIndices := make([][]byte, len(attestations))
	for i, att := range attestations {
		encEpoch := encodeTargetEpoch(att.IndexedAttestation.Data.Target.Epoch)
		value, err := encodeAttestationRecord(att)
		if err != nil {
			return err
		}
		indicesBytes := make([]byte, len(att.IndexedAttestation.AttestingIndices)*8)
		for _, idx := range att.IndexedAttestation.AttestingIndices {
			encodedIdx := encodeValidatorIndex(types.ValidatorIndex(idx))
			indicesBytes = append(indicesBytes, encodedIdx...)
		}
		encodedIndices[i] = indicesBytes
		encodedTargetEpoch[i] = encEpoch
		encodedRecords[i] = value
	}
	return s.db.Update(func(tx *bolt.Tx) error {
		attRecordsBkt := tx.Bucket(attestationRecordsBucket)
		signingRootsBkt := tx.Bucket(attestationDataRootsBucket)
		for i, att := range attestations {
			if err := attRecordsBkt.Put(att.SigningRoot[:], encodedRecords[i]); err != nil {
				return err
			}
			for _, valIdx := range att.IndexedAttestation.AttestingIndices {
				encIdx := encodeValidatorIndex(types.ValidatorIndex(valIdx))
				key := append(encodedTargetEpoch[i], encIdx...)
				if err := signingRootsBkt.Put(key, att.SigningRoot[:]); err != nil {
					return err
				}
			}
		}
		return nil
	})
}

// LoadSlasherChunks given a chunk kind and a disk keys, retrieves chunks for a validator
// min or max span used by slasher from our database.
func (s *Store) LoadSlasherChunks(
	ctx context.Context, kind slashertypes.ChunkKind, diskKeys [][]byte,
) ([][]uint16, []bool, error) {
	_, span := trace.StartSpan(ctx, "BeaconDB.LoadSlasherChunk")
	defer span.End()
	chunks := make([][]uint16, 0)
	var exists []bool
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(slasherChunksBucket)
		for _, diskKey := range diskKeys {
			key := append(ssz.MarshalUint8(make([]byte, 0), uint8(kind)), diskKey...)
			chunkBytes := bkt.Get(key)
			if chunkBytes == nil {
				chunks = append(chunks, []uint16{})
				exists = append(exists, false)
				continue
			}
			chunk, err := decodeSlasherChunk(chunkBytes)
			if err != nil {
				return err
			}
			chunks = append(chunks, chunk)
			exists = append(exists, true)
		}
		return nil
	})
	return chunks, exists, err
}

// SaveSlasherChunks given a chunk kind, list of disk keys, and list of chunks,
// saves the chunks to our database for use by slasher in slashing detection.
func (s *Store) SaveSlasherChunks(
	ctx context.Context, kind slashertypes.ChunkKind, chunkKeys [][]byte, chunks [][]uint16,
) error {
	_, span := trace.StartSpan(ctx, "BeaconDB.SaveSlasherChunks")
	defer span.End()
	encodedKeys := make([][]byte, len(chunkKeys))
	encodedChunks := make([][]byte, len(chunkKeys))
	for i := 0; i < len(chunkKeys); i++ {
		encodedKeys[i] = append(ssz.MarshalUint8(make([]byte, 0), uint8(kind)), chunkKeys[i]...)
		encodedChunk, err := encodeSlasherChunk(chunks[i])
		if err != nil {
			return err
		}
		encodedChunks[i] = encodedChunk
	}
	return s.db.Update(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(slasherChunksBucket)
		for i := 0; i < len(chunkKeys); i++ {
			if err := bkt.Put(encodedKeys[i], encodedChunks[i]); err != nil {
				return err
			}
		}
		return nil
	})
}

// CheckDoubleBlockProposals takes in a list of proposals and for each,
// checks if there already exists a proposal at the same slot+validatorIndex combination. If so,
// We check if the existing signing root is not-empty and is different than the incoming
// proposal signing root. If so, we return a double block proposal object.
func (s *Store) CheckDoubleBlockProposals(
	ctx context.Context, proposals []*slashertypes.SignedBlockHeaderWrapper,
) ([]*ethpb.ProposerSlashing, error) {
	_, span := trace.StartSpan(ctx, "BeaconDB.CheckDoubleBlockProposals")
	defer span.End()
	proposerSlashings := make([]*ethpb.ProposerSlashing, 0, len(proposals))
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(proposalRecordsBucket)
		for _, proposal := range proposals {
			key, err := keyForValidatorProposal(
				proposal.SignedBeaconBlockHeader.Header.Slot,
				proposal.SignedBeaconBlockHeader.Header.ProposerIndex,
			)
			if err != nil {
				return err
			}
			encExistingProposalWrapper := bkt.Get(key)
			if len(encExistingProposalWrapper) < signingRootSize {
				continue
			}
			existingSigningRoot := bytesutil.ToBytes32(encExistingProposalWrapper[:signingRootSize])
			if existingSigningRoot != proposal.SigningRoot {
				existingProposalWrapper, err := decodeProposalRecord(encExistingProposalWrapper)
				if err != nil {
					return err
				}
				proposerSlashings = append(proposerSlashings, &ethpb.ProposerSlashing{
					Header_1: existingProposalWrapper.SignedBeaconBlockHeader,
					Header_2: proposal.SignedBeaconBlockHeader,
				})
			}
		}
		return nil
	})
	return proposerSlashings, err
}

// BlockProposalForValidator given a validator index and a slot
// retrieves an existing proposal record we have stored in the database.
func (s *Store) BlockProposalForValidator(
	ctx context.Context, validatorIdx types.ValidatorIndex, slot types.Slot,
) (*slashertypes.SignedBlockHeaderWrapper, error) {
	_, span := trace.StartSpan(ctx, "BeaconDB.BlockProposalForValidator")
	defer span.End()
	var record *slashertypes.SignedBlockHeaderWrapper
	key, err := keyForValidatorProposal(slot, validatorIdx)
	if err != nil {
		return nil, err
	}
	err = s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(proposalRecordsBucket)
		encProposal := bkt.Get(key)
		if encProposal == nil {
			return nil
		}
		decoded, err := decodeProposalRecord(encProposal)
		if err != nil {
			return err
		}
		record = decoded
		return nil
	})
	return record, err
}

// SaveBlockProposals takes in a list of block proposals and saves them to our
// proposal records bucket in the database.
func (s *Store) SaveBlockProposals(
	ctx context.Context, proposals []*slashertypes.SignedBlockHeaderWrapper,
) error {
	_, span := trace.StartSpan(ctx, "BeaconDB.SaveBlockProposals")
	defer span.End()
	encodedKeys := make([][]byte, len(proposals))
	encodedProposals := make([][]byte, len(proposals))
	for i, proposal := range proposals {
		key, err := keyForValidatorProposal(
			proposal.SignedBeaconBlockHeader.Header.Slot,
			proposal.SignedBeaconBlockHeader.Header.ProposerIndex,
		)
		if err != nil {
			return err
		}
		enc, err := encodeProposalRecord(proposal)
		if err != nil {
			return err
		}
		encodedKeys[i] = key
		encodedProposals[i] = enc
	}
	return s.db.Update(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(proposalRecordsBucket)
		for i := range proposals {
			if err := bkt.Put(encodedKeys[i], encodedProposals[i]); err != nil {
				return err
			}
		}
		return nil
	})
}

// HighestAttestations retrieves the last attestation data from the database for all indices.
func (s *Store) HighestAttestations(
	_ context.Context,
	indices []types.ValidatorIndex,
) ([]*ethpb.HighestAttestation, error) {
	if len(indices) == 0 {
		return nil, nil
	}
	// Sort indices to keep DB interactions short.
	sort.SliceStable(indices, func(i, j int) bool {
		return uint64(indices[i]) < uint64(indices[j])
	})

	var err error
	encodedIndices := make([][]byte, len(indices))
	for i, valIdx := range indices {
		encodedIndices[i] = encodeValidatorIndex(valIdx)
	}

	history := make([]*ethpb.HighestAttestation, 0, len(encodedIndices))
	err = s.db.View(func(tx *bolt.Tx) error {
		signingRootsBkt := tx.Bucket(attestationDataRootsBucket)
		attRecordsBkt := tx.Bucket(attestationRecordsBucket)
		for i := 0; i < len(encodedIndices); i++ {
			c := signingRootsBkt.Cursor()
			for k, v := c.Last(); k != nil; k, v = c.Prev() {
				if suffixForAttestationRecordsKey(k, encodedIndices[i]) {
					encodedAttRecord := attRecordsBkt.Get(v)
					if encodedAttRecord == nil {
						continue
					}
					attWrapper, err := decodeAttestationRecord(encodedAttRecord)
					if err != nil {
						return err
					}
					highestAtt := &ethpb.HighestAttestation{
						ValidatorIndex:     uint64(indices[i]),
						HighestSourceEpoch: attWrapper.IndexedAttestation.Data.Source.Epoch,
						HighestTargetEpoch: attWrapper.IndexedAttestation.Data.Target.Epoch,
					}
					history = append(history, highestAtt)
					break
				}
			}
		}
		return nil
	})
	return history, err
}

func suffixForAttestationRecordsKey(key, encodedValidatorIndex []byte) bool {
	encIdx := key[8:]
	return bytes.Equal(encIdx, encodedValidatorIndex)
}

// Disk key for a validator proposal, including a slot+validatorIndex as a byte slice.
func keyForValidatorProposal(slot types.Slot, proposerIndex types.ValidatorIndex) ([]byte, error) {
	encSlot, err := slot.MarshalSSZ()
	if err != nil {
		return nil, err
	}
	encValidatorIdx := encodeValidatorIndex(proposerIndex)
	return append(encSlot, encValidatorIdx...), nil
}

func encodeSlasherChunk(chunk []uint16) ([]byte, error) {
	val := make([]byte, 0)
	for i := 0; i < len(chunk); i++ {
		val = append(val, ssz.MarshalUint16(make([]byte, 0), chunk[i])...)
	}
	if len(val) == 0 {
		return nil, errors.New("cannot encode empty chunk")
	}
	return snappy.Encode(nil, val), nil
}

func decodeSlasherChunk(enc []byte) ([]uint16, error) {
	chunkBytes, err := snappy.Decode(nil, enc)
	if err != nil {
		return nil, err
	}
	if len(chunkBytes)%2 != 0 {
		return nil, fmt.Errorf(
			"cannot decode slasher chunk with length %d, must be a multiple of 2",
			len(chunkBytes),
		)
	}
	chunk := make([]uint16, 0)
	for i := 0; i < len(chunkBytes); i += 2 {
		distance := ssz.UnmarshallUint16(chunkBytes[i : i+2])
		chunk = append(chunk, distance)
	}
	return chunk, nil
}

// Decode attestation record from bytes.
func encodeAttestationRecord(att *slashertypes.IndexedAttestationWrapper) ([]byte, error) {
	if att == nil || att.IndexedAttestation == nil {
		return []byte{}, errors.New("nil proposal record")
	}
	encodedAtt, err := att.IndexedAttestation.MarshalSSZ()
	if err != nil {
		return nil, err
	}
	compressedAtt := snappy.Encode(nil, encodedAtt)
	return append(att.SigningRoot[:], compressedAtt...), nil
}

// Decode attestation record from bytes.
func decodeAttestationRecord(encoded []byte) (*slashertypes.IndexedAttestationWrapper, error) {
	if len(encoded) < signingRootSize {
		return nil, fmt.Errorf("wrong length for encoded attestation record, want 32, got %d", len(encoded))
	}
	signingRoot := encoded[:signingRootSize]
	decodedAtt := &ethpb.IndexedAttestation{}
	decodedAttBytes, err := snappy.Decode(nil, encoded[signingRootSize:])
	if err != nil {
		return nil, err
	}
	if err := decodedAtt.UnmarshalSSZ(decodedAttBytes); err != nil {
		return nil, err
	}
	return &slashertypes.IndexedAttestationWrapper{
		IndexedAttestation: decodedAtt,
		SigningRoot:        bytesutil.ToBytes32(signingRoot),
	}, nil
}

func encodeProposalRecord(blkHdr *slashertypes.SignedBlockHeaderWrapper) ([]byte, error) {
	if blkHdr == nil || blkHdr.SignedBeaconBlockHeader == nil {
		return []byte{}, errors.New("nil proposal record")
	}
	encodedHdr, err := blkHdr.SignedBeaconBlockHeader.MarshalSSZ()
	if err != nil {
		return nil, err
	}
	compressedHdr := snappy.Encode(nil, encodedHdr)
	return append(blkHdr.SigningRoot[:], compressedHdr...), nil
}

func decodeProposalRecord(encoded []byte) (*slashertypes.SignedBlockHeaderWrapper, error) {
	if len(encoded) < signingRootSize {
		return nil, fmt.Errorf(
			"wrong length for encoded proposal record, want %d, got %d", signingRootSize, len(encoded),
		)
	}
	signingRoot := encoded[:signingRootSize]
	decodedBlkHdr := &ethpb.SignedBeaconBlockHeader{}
	decodedHdrBytes, err := snappy.Decode(nil, encoded[signingRootSize:])
	if err != nil {
		return nil, err
	}
	if err := decodedBlkHdr.UnmarshalSSZ(decodedHdrBytes); err != nil {
		return nil, err
	}
	return &slashertypes.SignedBlockHeaderWrapper{
		SignedBeaconBlockHeader: decodedBlkHdr,
		SigningRoot:             bytesutil.ToBytes32(signingRoot),
	}, nil
}

// Encodes an epoch into little-endian bytes.
func encodeTargetEpoch(epoch types.Epoch) []byte {
	buf := make([]byte, 8)
	binary.LittleEndian.PutUint64(buf, uint64(epoch))
	return buf
}

// Encodes a validator index using 5 bytes instead of 8 as a
// client optimization to save space in the database. Because the max validator
// registry size is 2**40, this is a safe optimization.
func encodeValidatorIndex(index types.ValidatorIndex) []byte {
	buf := make([]byte, 5)
	v := uint64(index)
	buf[0] = byte(v)
	buf[1] = byte(v >> 8)
	buf[2] = byte(v >> 16)
	buf[3] = byte(v >> 24)
	buf[4] = byte(v >> 32)
	return buf
}
