package consensus

import (
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/crypto/sha3"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/harmony-one/harmony/core/state"
	"github.com/harmony-one/harmony/core/types"
)

type Bft struct {
}

func NewFaker() *Bft {
	return &Bft{}
}

// Author implements Engine, returning the header's coinbase as the
// proof-of-work verified author of the block.
func (bft *Bft) Author(header *types.Header) (common.Address, error) {
	return header.Coinbase, nil
}

// VerifyHeader checks whether a header conforms to the consensus rules of the
// stock Ethereum bft engine.
func (bft *Bft) VerifyHeader(chain ChainReader, header *types.Header, seal bool) error {
	return nil
}

// VerifyHeaders is similar to VerifyHeader, but verifies a batch of headers
// concurrently. The method returns a quit channel to abort the operations and
// a results channel to retrieve the async verifications.
func (bft *Bft) VerifyHeaders(chain ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error) {
	abort, results := make(chan struct{}), make(chan error, len(headers))
	for i := 0; i < len(headers); i++ {
		results <- nil
	}
	return abort, results
}

func (bft *Bft) verifyHeaderWorker(chain ChainReader, headers []*types.Header, seals []bool, index int) error {
	var parent *types.Header
	if index == 0 {
		parent = chain.GetHeader(headers[0].ParentHash, headers[0].Number.Uint64()-1)
	} else if headers[index-1].Hash() == headers[index].ParentHash {
		parent = headers[index-1]
	}
	if parent == nil {
		return ErrUnknownAncestor
	}
	if chain.GetHeader(headers[index].Hash(), headers[index].Number.Uint64()) != nil {
		return nil // known block
	}
	return bft.verifyHeader(chain, headers[index], parent, false, seals[index])
}

// verifyHeader checks whether a header conforms to the consensus rules of the
// stock Ethereum bft engine.
// See YP section 4.3.4. "Block Header Validity"
func (bft *Bft) verifyHeader(chain ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
	return nil
}

// VerifySeal implements consensus.Engine, checking whether the given block satisfies
// the PoW difficulty requirements.
func (bft *Bft) VerifySeal(chain ChainReader, header *types.Header) error {
	return nil
}

// Prepare implements consensus.Engine, initializing the difficulty field of a
// header to conform to the ethash protocol. The changes are done inline.
func (bft *Bft) Prepare(chain ChainReader, header *types.Header) error {
	return nil
}

// Finalize implements consensus.Engine, accumulating the block and uncle rewards,
// setting the final state and assembling the block.
func (bft *Bft) Finalize(chain ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, receipts []*types.Receipt) (*types.Block, error) {
	// Accumulate any block and uncle rewards and commit the final state root
	// Header seems complete, assemble into a block and return
	accumulateRewards(chain.Config(), state, header)
	header.Root = state.IntermediateRoot(false)
	return types.NewBlock(header, txs, receipts), nil
}

// SealHash returns the hash of a block prior to it being sealed.
func (bft *Bft) SealHash(header *types.Header) (hash common.Hash) {
	hasher := sha3.NewKeccak256()

	rlp.Encode(hasher, []interface{}{
		header.ParentHash,
		header.UncleHash,
		header.Coinbase,
		header.Root,
		header.TxHash,
		header.ReceiptHash,
		header.Bloom,
		header.Difficulty,
		header.Number,
		header.GasLimit,
		header.GasUsed,
		header.Time,
		header.Extra,
	})
	hasher.Sum(hash[:0])
	return hash
}

func (bft *Bft) Seal(chain ChainReader, block *types.Block, results chan<- *types.Block, stop <-chan struct{}) error {
	return nil
}

// AccumulateRewards credits the coinbase of the given block with the mining
// reward. The total reward consists of the static block reward and rewards for
// included uncles. The coinbase of each uncle block is also rewarded.
func accumulateRewards(config *params.ChainConfig, state *state.StateDB, header *types.Header) {

}