package chain

import (
	"math/big"
	"sync"

	"github.com/ethereum/go-ethereum/common"
	"github.com/harmony-one/bls/ffi/go/bls"
	"github.com/harmony-one/harmony/block"
	"github.com/harmony-one/harmony/common/denominations"
	"github.com/harmony-one/harmony/consensus/engine"
	"github.com/harmony-one/harmony/consensus/reward"
	"github.com/harmony-one/harmony/core/state"
	bls2 "github.com/harmony-one/harmony/crypto/bls"
	common2 "github.com/harmony-one/harmony/internal/common"
	"github.com/harmony-one/harmony/internal/ctxerror"
	"github.com/harmony-one/harmony/internal/utils"
	"github.com/harmony-one/harmony/shard"
	"github.com/harmony-one/harmony/staking/slash"
	"github.com/pkg/errors"
)

var (
	// BlockReward is the block reward, to be split evenly among block signers.
	BlockReward                  = new(big.Int).Mul(big.NewInt(24), big.NewInt(denominations.One))
	errPayoutNotEqualBlockReward = errors.New("total payout not equal to blockreward")
)

// 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(
	bc engine.ChainReader, state *state.DB,
	header *block.Header, rewarder reward.Distributor,
	slasher slash.Slasher,
) error {
	blockNum := header.Number().Uint64()
	if blockNum == 0 {
		// Epoch block has no parent to reward.
		return nil
	}
	// TODO ek – retrieving by parent number (blockNum - 1) doesn't work,
	//  while it is okay with hash.  Sounds like DB inconsistency.
	//  Figure out why.
	parentHeader := bc.GetHeaderByHash(header.ParentHash())
	if parentHeader == nil {
		return ctxerror.New("cannot find parent block header in DB",
			"parentHash", header.ParentHash())
	}
	if parentHeader.Number().Cmp(common.Big0) == 0 {
		// Parent is an epoch block,
		// which is not signed in the usual manner therefore rewards nothing.
		return nil
	}
	parentShardState, err := bc.ReadShardState(parentHeader.Epoch())
	if err != nil {
		return ctxerror.New("cannot read shard state",
			"epoch", parentHeader.Epoch(),
		).WithCause(err)
	}
	parentCommittee := parentShardState.FindCommitteeByID(parentHeader.ShardID())
	if parentCommittee == nil {
		return ctxerror.New("cannot find shard in the shard state",
			"parentBlockNumber", parentHeader.Number(),
			"shardID", parentHeader.ShardID(),
		)
	}
	var committerKeys []*bls.PublicKey
	for _, member := range parentCommittee.Slots {
		committerKey := new(bls.PublicKey)
		err := member.BlsPublicKey.ToLibBLSPublicKey(committerKey)
		if err != nil {
			return ctxerror.New("cannot convert BLS public key",
				"blsPublicKey", member.BlsPublicKey).WithCause(err)
		}
		committerKeys = append(committerKeys, committerKey)
	}
	mask, err := bls2.NewMask(committerKeys, nil)
	if err != nil {
		return ctxerror.New("cannot create group sig mask").WithCause(err)
	}
	if err := mask.SetMask(header.LastCommitBitmap()); err != nil {
		return ctxerror.New("cannot set group sig mask bits").WithCause(err)
	}

	accounts := []common.Address{}
	missing := shard.SlotList{}

	for idx, member := range parentCommittee.Slots {
		switch signed, err := mask.IndexEnabled(idx); true {
		case err != nil:
			return ctxerror.New("cannot check for committer bit",
				"committerIndex", idx,
			).WithCause(err)
		case signed:
			accounts = append(accounts, member.EcdsaAddress)
		default:
			missing = append(missing, member)
		}
	}

	// do it quickly
	w := sync.WaitGroup{}
	for i := range missing {
		w.Add(1)
		go func(member int) {
			defer w.Done()
			// Slash if missing block was long enough
			if slasher.ShouldSlash(missing[member].BlsPublicKey) {
				// TODO Logic
			}
		}(i)
	}

	w.Wait()

	payable := []struct {
		string
		common.Address
		*big.Int
	}{}

	totalAmount := rewarder.Award(
		BlockReward, accounts, func(receipient common.Address, amount *big.Int) {
			payable = append(payable, struct {
				string
				common.Address
				*big.Int
			}{
				common2.MustAddressToBech32(receipient), receipient, amount,
			},
			)
		},
	)

	if totalAmount.Cmp(BlockReward) != 0 {
		utils.Logger().Error().
			Int64("block-reward", BlockReward.Int64()).
			Int64("total-amount-paid-out", totalAmount.Int64()).
			Msg("Total paid out was not equal to block-reward")
		return errors.Wrapf(errPayoutNotEqualBlockReward, "payout "+totalAmount.String())
	}

	signers := make([]string, len(payable))

	for i := range payable {
		signers[i] = payable[i].string
		state.AddBalance(payable[i].Address, payable[i].Int)
	}

	header.Logger(utils.Logger()).Debug().
		Int("NumAccounts", len(accounts)).
		Str("TotalAmount", totalAmount.String()).
		Strs("Signers", signers).
		Msg("[Block Reward] Successfully paid out block reward")
	return nil
}