package altair

import (
	"github.com/pkg/errors"
	types "github.com/prysmaticlabs/eth2-types"
	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
	"github.com/prysmaticlabs/prysm/beacon-chain/state"
	"github.com/prysmaticlabs/prysm/config/params"
	"github.com/prysmaticlabs/prysm/math"
)

// BaseReward takes state and validator index and calculate
// individual validator's base reward.
//
// Spec code:
//  def get_base_reward(state: BeaconState, index: ValidatorIndex) -> Gwei:
//    """
//    Return the base reward for the validator defined by ``index`` with respect to the current ``state``.
//
//    Note: An optimally performing validator can earn one base reward per epoch over a long time horizon.
//    This takes into account both per-epoch (e.g. attestation) and intermittent duties (e.g. block proposal
//    and sync committees).
//    """
//    increments = state.validators[index].effective_balance // EFFECTIVE_BALANCE_INCREMENT
//    return Gwei(increments * get_base_reward_per_increment(state))
func BaseReward(s state.ReadOnlyBeaconState, index types.ValidatorIndex) (uint64, error) {
	totalBalance, err := helpers.TotalActiveBalance(s)
	if err != nil {
		return 0, errors.Wrap(err, "could not calculate active balance")
	}
	return BaseRewardWithTotalBalance(s, index, totalBalance)
}

// BaseRewardWithTotalBalance calculates the base reward with the provided total balance.
func BaseRewardWithTotalBalance(s state.ReadOnlyBeaconState, index types.ValidatorIndex, totalBalance uint64) (uint64, error) {
	val, err := s.ValidatorAtIndexReadOnly(index)
	if err != nil {
		return 0, err
	}
	cfg := params.BeaconConfig()
	increments := val.EffectiveBalance() / cfg.EffectiveBalanceIncrement
	baseRewardPerInc, err := BaseRewardPerIncrement(totalBalance)
	if err != nil {
		return 0, err
	}
	return increments * baseRewardPerInc, nil
}

// BaseRewardPerIncrement of the beacon state
//
// Spec code:
// def get_base_reward_per_increment(state: BeaconState) -> Gwei:
//    return Gwei(EFFECTIVE_BALANCE_INCREMENT * BASE_REWARD_FACTOR // integer_squareroot(get_total_active_balance(state)))
func BaseRewardPerIncrement(activeBalance uint64) (uint64, error) {
	if activeBalance == 0 {
		return 0, errors.New("active balance can't be 0")
	}
	cfg := params.BeaconConfig()
	return cfg.EffectiveBalanceIncrement * cfg.BaseRewardFactor / math.IntegerSquareRoot(activeBalance), nil
}
