package kv

import (
	"bytes"
	"context"
	"fmt"

	"github.com/pkg/errors"
	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
	"github.com/prysmaticlabs/prysm/beacon-chain/db/filters"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/prysmaticlabs/prysm/shared/params"
	"github.com/prysmaticlabs/prysm/shared/sliceutil"
	bolt "go.etcd.io/bbolt"
	"go.opencensus.io/trace"
)

// used to represent errors for inconsistent slot ranges.
var errInvalidSlotRange = errors.New("invalid end slot and start slot provided")

// Block retrieval by root.
func (s *Store) Block(ctx context.Context, blockRoot [32]byte) (*ethpb.SignedBeaconBlock, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.Block")
	defer span.End()
	// Return block from cache if it exists.
	if v, ok := s.blockCache.Get(string(blockRoot[:])); v != nil && ok {
		return v.(*ethpb.SignedBeaconBlock), nil
	}
	var block *ethpb.SignedBeaconBlock
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		enc := bkt.Get(blockRoot[:])
		if enc == nil {
			return nil
		}
		block = &ethpb.SignedBeaconBlock{}
		return decode(ctx, enc, block)
	})
	return block, err
}

// HeadBlock returns the latest canonical block in eth2.
func (s *Store) HeadBlock(ctx context.Context) (*ethpb.SignedBeaconBlock, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.HeadBlock")
	defer span.End()
	var headBlock *ethpb.SignedBeaconBlock
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		headRoot := bkt.Get(headBlockRootKey)
		if headRoot == nil {
			return nil
		}
		enc := bkt.Get(headRoot)
		if enc == nil {
			return nil
		}
		headBlock = &ethpb.SignedBeaconBlock{}
		return decode(ctx, enc, headBlock)
	})
	return headBlock, err
}

// Blocks retrieves a list of beacon blocks and its respective roots by filter criteria.
func (s *Store) Blocks(ctx context.Context, f *filters.QueryFilter) ([]*ethpb.SignedBeaconBlock, [][32]byte, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.Blocks")
	defer span.End()
	blocks := make([]*ethpb.SignedBeaconBlock, 0)
	blockRoots := make([][32]byte, 0)

	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)

		keys, err := getBlockRootsByFilter(ctx, tx, f)
		if err != nil {
			return err
		}

		for i := 0; i < len(keys); i++ {
			encoded := bkt.Get(keys[i])
			block := &ethpb.SignedBeaconBlock{}
			if err := decode(ctx, encoded, block); err != nil {
				return err
			}
			blocks = append(blocks, block)
			blockRoots = append(blockRoots, bytesutil.ToBytes32(keys[i]))
		}
		return nil
	})
	return blocks, blockRoots, err
}

// BlockRoots retrieves a list of beacon block roots by filter criteria. If the caller
// requires both the blocks and the block roots for a certain filter they should instead
// use the Blocks function rather than use BlockRoots. During periods of non finality
// there are potential race conditions which leads to differing roots when calling the db
// multiple times for the same filter.
func (s *Store) BlockRoots(ctx context.Context, f *filters.QueryFilter) ([][32]byte, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.BlockRoots")
	defer span.End()
	blockRoots := make([][32]byte, 0)
	err := s.db.View(func(tx *bolt.Tx) error {
		keys, err := getBlockRootsByFilter(ctx, tx, f)
		if err != nil {
			return err
		}

		for i := 0; i < len(keys); i++ {
			blockRoots = append(blockRoots, bytesutil.ToBytes32(keys[i]))
		}
		return nil
	})
	if err != nil {
		return nil, errors.Wrap(err, "could not retrieve block roots")
	}
	return blockRoots, nil
}

// HasBlock checks if a block by root exists in the db.
func (s *Store) HasBlock(ctx context.Context, blockRoot [32]byte) bool {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.HasBlock")
	defer span.End()
	if v, ok := s.blockCache.Get(string(blockRoot[:])); v != nil && ok {
		return true
	}
	exists := false
	if err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		exists = bkt.Get(blockRoot[:]) != nil
		return nil
	}); err != nil { // This view never returns an error, but we'll handle anyway for sanity.
		panic(err)
	}
	return exists
}

// deleteBlock by block root.
func (s *Store) deleteBlock(ctx context.Context, blockRoot [32]byte) error {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.deleteBlock")
	defer span.End()
	return s.db.Update(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		enc := bkt.Get(blockRoot[:])
		if enc == nil {
			return nil
		}
		block := &ethpb.SignedBeaconBlock{}
		if err := decode(ctx, enc, block); err != nil {
			return err
		}
		indicesByBucket := createBlockIndicesFromBlock(ctx, block.Block)
		if err := deleteValueForIndices(ctx, indicesByBucket, blockRoot[:], tx); err != nil {
			return errors.Wrap(err, "could not delete root for DB indices")
		}
		s.blockCache.Del(string(blockRoot[:]))
		return bkt.Delete(blockRoot[:])
	})
}

// deleteBlocks by block roots.
func (s *Store) deleteBlocks(ctx context.Context, blockRoots [][32]byte) error {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.deleteBlocks")
	defer span.End()

	return s.db.Update(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		for _, blockRoot := range blockRoots {
			enc := bkt.Get(blockRoot[:])
			if enc == nil {
				return nil
			}
			block := &ethpb.SignedBeaconBlock{}
			if err := decode(ctx, enc, block); err != nil {
				return err
			}
			indicesByBucket := createBlockIndicesFromBlock(ctx, block.Block)
			if err := deleteValueForIndices(ctx, indicesByBucket, blockRoot[:], tx); err != nil {
				return errors.Wrap(err, "could not delete root for DB indices")
			}
			s.blockCache.Del(string(blockRoot[:]))
			if err := bkt.Delete(blockRoot[:]); err != nil {
				return err
			}
		}
		return nil
	})
}

// SaveBlock to the db.
func (s *Store) SaveBlock(ctx context.Context, signed *ethpb.SignedBeaconBlock) error {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.SaveBlock")
	defer span.End()
	blockRoot, err := signed.Block.HashTreeRoot()
	if err != nil {
		return err
	}
	if v, ok := s.blockCache.Get(string(blockRoot[:])); v != nil && ok {
		return nil
	}

	return s.SaveBlocks(ctx, []*ethpb.SignedBeaconBlock{signed})
}

// SaveBlocks via bulk updates to the db.
func (s *Store) SaveBlocks(ctx context.Context, blocks []*ethpb.SignedBeaconBlock) error {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.SaveBlocks")
	defer span.End()

	return s.db.Update(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		for _, block := range blocks {
			blockRoot, err := block.Block.HashTreeRoot()
			if err != nil {
				return err
			}

			if existingBlock := bkt.Get(blockRoot[:]); existingBlock != nil {
				continue
			}
			enc, err := encode(ctx, block)
			if err != nil {
				return err
			}
			indicesByBucket := createBlockIndicesFromBlock(ctx, block.Block)
			if err := updateValueForIndices(ctx, indicesByBucket, blockRoot[:], tx); err != nil {
				return errors.Wrap(err, "could not update DB indices")
			}
			s.blockCache.Set(string(blockRoot[:]), block, int64(len(enc)))

			if err := bkt.Put(blockRoot[:], enc); err != nil {
				return err
			}
		}
		return nil
	})
}

// SaveHeadBlockRoot to the db.
func (s *Store) SaveHeadBlockRoot(ctx context.Context, blockRoot [32]byte) error {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.SaveHeadBlockRoot")
	defer span.End()
	return s.db.Update(func(tx *bolt.Tx) error {
		hasStateSummaryInDB := s.HasStateSummary(ctx, blockRoot)
		hasStateInDB := tx.Bucket(stateBucket).Get(blockRoot[:]) != nil
		if !(hasStateInDB || hasStateSummaryInDB) {
			return errors.New("no state or state summary found with head block root")
		}

		bucket := tx.Bucket(blocksBucket)
		return bucket.Put(headBlockRootKey, blockRoot[:])
	})
}

// GenesisBlock retrieves the genesis block of the beacon chain.
func (s *Store) GenesisBlock(ctx context.Context) (*ethpb.SignedBeaconBlock, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.GenesisBlock")
	defer span.End()
	var block *ethpb.SignedBeaconBlock
	err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blocksBucket)
		root := bkt.Get(genesisBlockRootKey)
		enc := bkt.Get(root)
		if enc == nil {
			return nil
		}
		block = &ethpb.SignedBeaconBlock{}
		return decode(ctx, enc, block)
	})
	return block, err
}

// SaveGenesisBlockRoot to the db.
func (s *Store) SaveGenesisBlockRoot(ctx context.Context, blockRoot [32]byte) error {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.SaveGenesisBlockRoot")
	defer span.End()
	return s.db.Update(func(tx *bolt.Tx) error {
		bucket := tx.Bucket(blocksBucket)
		return bucket.Put(genesisBlockRootKey, blockRoot[:])
	})
}

// HighestSlotBlocksBelow returns the block with the highest slot below the input slot from the db.
func (s *Store) HighestSlotBlocksBelow(ctx context.Context, slot uint64) ([]*ethpb.SignedBeaconBlock, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.HighestSlotBlocksBelow")
	defer span.End()

	var best []byte
	if err := s.db.View(func(tx *bolt.Tx) error {
		bkt := tx.Bucket(blockSlotIndicesBucket)
		// Iterate through the index, which is in byte sorted order.
		c := bkt.Cursor()
		for s, root := c.First(); s != nil; s, root = c.Next() {
			if ctx.Err() != nil {
				return ctx.Err()
			}
			key := bytesutil.BytesToUint64BigEndian(s)
			if root == nil {
				continue
			}
			if key >= slot {
				break
			}
			best = root
		}
		return nil
	}); err != nil {
		return nil, err
	}

	var blk *ethpb.SignedBeaconBlock
	var err error
	if best != nil {
		blk, err = s.Block(ctx, bytesutil.ToBytes32(best))
		if err != nil {
			return nil, err
		}
	}
	if blk == nil {
		blk, err = s.GenesisBlock(ctx)
		if err != nil {
			return nil, err
		}
	}

	return []*ethpb.SignedBeaconBlock{blk}, nil
}

// getBlockRootsByFilter retrieves the block roots given the filter criteria.
func getBlockRootsByFilter(ctx context.Context, tx *bolt.Tx, f *filters.QueryFilter) ([][]byte, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.getBlockRootsByFilter")
	defer span.End()

	// If no filter criteria are specified, return an error.
	if f == nil {
		return nil, errors.New("must specify a filter criteria for retrieving blocks")
	}

	// Creates a list of indices from the passed in filter values, such as:
	// []byte("0x2093923") in the parent root indices bucket to be used for looking up
	// block roots that were stored under each of those indices for O(1) lookup.
	indicesByBucket, err := createBlockIndicesFromFilters(ctx, f)
	if err != nil {
		return nil, errors.Wrap(err, "could not determine lookup indices")
	}

	// We retrieve block roots that match a filter criteria of slot ranges, if specified.
	filtersMap := f.Filters()
	rootsBySlotRange, err := fetchBlockRootsBySlotRange(
		ctx,
		tx.Bucket(blockSlotIndicesBucket),
		filtersMap[filters.StartSlot],
		filtersMap[filters.EndSlot],
		filtersMap[filters.StartEpoch],
		filtersMap[filters.EndEpoch],
		filtersMap[filters.SlotStep],
	)
	if err != nil {
		return nil, err
	}

	// Once we have a list of block roots that correspond to each
	// lookup index, we find the intersection across all of them and use
	// that list of roots to lookup the block. These block will
	// meet the filter criteria.
	indices := lookupValuesForIndices(ctx, indicesByBucket, tx)
	keys := rootsBySlotRange
	if len(indices) > 0 {
		// If we have found indices that meet the filter criteria, and there are also
		// block roots that meet the slot range filter criteria, we find the intersection
		// between these two sets of roots.
		if len(rootsBySlotRange) > 0 {
			joined := append([][][]byte{keys}, indices...)
			keys = sliceutil.IntersectionByteSlices(joined...)
		} else {
			// If we have found indices that meet the filter criteria, but there are no block roots
			// that meet the slot range filter criteria, we find the intersection
			// of the regular filter indices.
			keys = sliceutil.IntersectionByteSlices(indices...)
		}
	}

	return keys, nil
}

// fetchBlockRootsBySlotRange looks into a boltDB bucket and performs a binary search
// range scan using sorted left-padded byte keys using a start slot and an end slot.
// However, if step is one, the implemented logic won’t skip half of the slots in the range.
func fetchBlockRootsBySlotRange(
	ctx context.Context,
	bkt *bolt.Bucket,
	startSlotEncoded, endSlotEncoded, startEpochEncoded, endEpochEncoded, slotStepEncoded interface{},
) ([][]byte, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.fetchBlockRootsBySlotRange")
	defer span.End()

	var startSlot, endSlot, step uint64
	var ok bool
	if startSlot, ok = startSlotEncoded.(uint64); !ok {
		startSlot = 0
	}
	if endSlot, ok = endSlotEncoded.(uint64); !ok {
		endSlot = 0
	}
	if step, ok = slotStepEncoded.(uint64); !ok || step == 0 {
		step = 1
	}
	startEpoch, startEpochOk := startEpochEncoded.(uint64)
	endEpoch, endEpochOk := endEpochEncoded.(uint64)
	var err error
	if startEpochOk && endEpochOk {
		startSlot, err = helpers.StartSlot(startEpoch)
		if err != nil {
			return nil, err
		}
		endSlot, err = helpers.StartSlot(endEpoch)
		if err != nil {
			return nil, err
		}
		endSlot = endSlot + params.BeaconConfig().SlotsPerEpoch - 1
	}
	min := bytesutil.Uint64ToBytesBigEndian(startSlot)
	max := bytesutil.Uint64ToBytesBigEndian(endSlot)

	conditional := func(key, max []byte) bool {
		return key != nil && bytes.Compare(key, max) <= 0
	}
	if endSlot < startSlot {
		return nil, errInvalidSlotRange
	}
	// Return nothing with an end slot of 0.
	if endSlot == 0 {
		return [][]byte{}, nil
	}
	rootsRange := (endSlot - startSlot) / step
	roots := make([][]byte, 0, rootsRange)
	c := bkt.Cursor()
	for k, v := c.Seek(min); conditional(k, max); k, v = c.Next() {
		if step > 1 {
			slot := bytesutil.BytesToUint64BigEndian(k)
			if (slot-startSlot)%step != 0 {
				continue
			}
		}
		numOfRoots := len(v) / 32
		splitRoots := make([][]byte, 0, numOfRoots)
		for i := 0; i < len(v); i += 32 {
			splitRoots = append(splitRoots, v[i:i+32])
		}
		roots = append(roots, splitRoots...)
	}
	return roots, nil
}

// createBlockIndicesFromBlock takes in a beacon block and returns
// a map of bolt DB index buckets corresponding to each particular key for indices for
// data, such as (shard indices bucket -> shard 5).
func createBlockIndicesFromBlock(ctx context.Context, block *ethpb.BeaconBlock) map[string][]byte {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.createBlockIndicesFromBlock")
	defer span.End()
	indicesByBucket := make(map[string][]byte)
	// Every index has a unique bucket for fast, binary-search
	// range scans for filtering across keys.
	buckets := [][]byte{
		blockSlotIndicesBucket,
	}
	indices := [][]byte{
		bytesutil.Uint64ToBytesBigEndian(block.Slot),
	}
	if block.ParentRoot != nil && len(block.ParentRoot) > 0 {
		buckets = append(buckets, blockParentRootIndicesBucket)
		indices = append(indices, block.ParentRoot)
	}
	for i := 0; i < len(buckets); i++ {
		indicesByBucket[string(buckets[i])] = indices[i]
	}
	return indicesByBucket
}

// createBlockFiltersFromIndices takes in filter criteria and returns
// a map with a single key-value pair: "block-parent-root-indices” -> parentRoot (array of bytes).
//
// For blocks, these are list of signing roots of block
// objects. If a certain filter criterion does not apply to
// blocks, an appropriate error is returned.
func createBlockIndicesFromFilters(ctx context.Context, f *filters.QueryFilter) (map[string][]byte, error) {
	ctx, span := trace.StartSpan(ctx, "BeaconDB.createBlockIndicesFromFilters")
	defer span.End()
	indicesByBucket := make(map[string][]byte)
	for k, v := range f.Filters() {
		switch k {
		case filters.ParentRoot:
			parentRoot, ok := v.([]byte)
			if !ok {
				return nil, errors.New("parent root is not []byte")
			}
			indicesByBucket[string(blockParentRootIndicesBucket)] = parentRoot
		// The following cases are passthroughs for blocks, as they are not used
		// for filtering indices.
		case filters.StartSlot:
		case filters.EndSlot:
		case filters.StartEpoch:
		case filters.EndEpoch:
		case filters.SlotStep:
		default:
			return nil, fmt.Errorf("filter criterion %v not supported for blocks", k)
		}
	}
	return indicesByBucket, nil
}