package sharding

import (
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/rlp"
)

// Shard base struct.
type Shard struct {
	shardDB *shardBackend
	shardID *big.Int
}

// ValidateShardID checks if header belongs to shard.
func (s *Shard) ValidateShardID(h *CollationHeader) error {
	if s.shardID.Cmp(h.shardID) != 0 {
		return fmt.Errorf("Error: Collation Does Not Belong to Shard %d but Instead Has ShardID %d", h.shardID, s.shardID)
	}
	return nil
}

// GetHeaderByHash of collation.
func (s *Shard) GetHeaderByHash(hash *common.Hash) (*CollationHeader, error) {
	encoded := s.shardDB.Get(hash)
	var header CollationHeader
	if err := rlp.DecodeBytes(encoded, &header); err != nil {
		return nil, fmt.Errorf("Error Decoding Header: %v", err)
	}
	return &header, nil
}

// GetHeaderByPeriod the header was added.
func (s *Shard) GetHeaderByPeriod(period *big.Int) *CollationHeader {
	return nil
}

// GetCollationByHash fetches full collation.
func (s *Shard) GetCollationByHash(hash *common.Hash) (*Collation, error) {
	header, err := s.GetHeaderByHash(hash)
	if err != nil {
		return nil, err
	}
	body, err := s.GetBodyByChunkRoot(header.chunkRoot)
	if err != nil {
		return nil, err
	}
	return &Collation{header: header, body: body}, nil
}

// GetBodyByChunkRoot fetches a collation body
func (s *Shard) GetBodyByChunkRoot(chunkRoot *common.Hash) ([]byte, error) {
	body := s.shardDB.Get(chunkRoot)
	if body == nil {
		return nil, fmt.Errorf("Error: No Corresponding Body With Chunk Root Found")
	}
	return body, nil
}

// CheckAvailability is used by notaries to confirm a header's data availability.
func (s *Shard) CheckAvailability(header *CollationHeader) bool {
	return true
}

// SetUnavailable ensures to set a collation as unavailable in the shardDB.
func (s *Shard) SetUnavailable(header *CollationHeader) error {
	return nil
}

// SetCanonical is called after >= 2/3 notaries vote on header and period ends.
func (s *Shard) SetCanonical(header *CollationHeader) error {
	return nil
}

// Set Header and Set Body Methods
// TODO: error in Get from the kv store