// Package incentives defines Casper Proof of Stake rewards and penalties for validator
// records based on Vitalik Buterin's Friendly Finality Gadget protocol. Validator balances
// depend on time to finality as well as deposit-weighted functions. This package provides
// pure functions that can then be incorporated into a beacon chain state transition.
package incentives

import (
	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	"github.com/prysmaticlabs/prysm/shared/mathutil"
	"github.com/prysmaticlabs/prysm/shared/params"
)

// RewardQuotient returns the reward quotient for validators which will be used to
// reward validators for voting on blocks, or penalise them for being offline.
func RewardQuotient(totalActiveValidatorDeposit uint64) uint64 {
	totalDepositETH := totalActiveValidatorDeposit / params.BeaconConfig().Gwei
	return params.BeaconConfig().BaseRewardQuotient * mathutil.IntegerSquareRoot(totalDepositETH)
}

// QuadraticPenaltyQuotient is the quotient that will be used to apply penalties to offline
// validators.
func QuadraticPenaltyQuotient() uint64 {
	dropTimeFactor := params.BeaconConfig().SqrtExpDropTime
	return dropTimeFactor * dropTimeFactor
}

// QuadraticPenalty returns the penalty that will be applied to an offline validator
// based on the number of slots that they are offline.
func QuadraticPenalty(numberOfSlots uint64) uint64 {
	slotFactor := (numberOfSlots * numberOfSlots) / 2
	penaltyQuotient := QuadraticPenaltyQuotient()
	return slotFactor / penaltyQuotient
}

// RewardValidatorCrosslink applies rewards to validators part of a shard committee for voting on a shard.
// TODO(#538): Change this to big.Int as tests using 64 bit integers fail due to integer overflow.
func RewardValidatorCrosslink(
	totalDeposit uint64,
	participatedDeposits uint64,
	rewardQuotient uint64,
	validator *pb.ValidatorRecord,
) *pb.ValidatorRecord {
	currentBalance := int64(validator.Balance)
	currentBalance += int64(currentBalance) / int64(rewardQuotient) * (2*int64(participatedDeposits) - int64(totalDeposit)) / int64(totalDeposit)
	return &pb.ValidatorRecord{
		Pubkey:                 validator.Pubkey,
		RandaoCommitmentHash32: validator.RandaoCommitmentHash32,
		Balance:                uint64(currentBalance),
		Status:                 validator.Status,
		LatestStatusChangeSlot: validator.LatestStatusChangeSlot,
	}
}

// PenaliseValidatorCrosslink applies penalties to validators part of a shard committee for not voting on a shard.
func PenaliseValidatorCrosslink(
	timeSinceLastConfirmation uint64,
	rewardQuotient uint64,
	validator *pb.ValidatorRecord,
) *pb.ValidatorRecord {
	newBalance := validator.Balance
	quadraticQuotient := QuadraticPenaltyQuotient()
	newBalance -= newBalance/rewardQuotient + newBalance*timeSinceLastConfirmation/quadraticQuotient
	return &pb.ValidatorRecord{
		Pubkey:                 validator.Pubkey,
		RandaoCommitmentHash32: validator.RandaoCommitmentHash32,
		Balance:                uint64(newBalance),
		Status:                 validator.Status,
		LatestStatusChangeSlot: validator.LatestStatusChangeSlot,
	}
}