package helpers

import (
	"github.com/pkg/errors"
	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
	stateTrie "github.com/prysmaticlabs/prysm/beacon-chain/state"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	"github.com/prysmaticlabs/prysm/shared/bls"
	"github.com/prysmaticlabs/prysm/shared/bytesutil"
	"github.com/prysmaticlabs/prysm/shared/hashutil"
	"github.com/prysmaticlabs/prysm/shared/params"
)

// IsActiveValidator returns the boolean value on whether the validator
// is active or not.
//
// Spec pseudocode definition:
//  def is_active_validator(validator: Validator, epoch: Epoch) -> bool:
//    """
//    Check if ``validator`` is active.
//    """
//    return validator.activation_epoch <= epoch < validator.exit_epoch
func IsActiveValidator(validator *ethpb.Validator, epoch uint64) bool {
	return checkValidatorActiveStatus(validator.ActivationEpoch, validator.ExitEpoch, epoch)
}

// IsActiveValidatorUsingTrie checks if a read only validator is active.
func IsActiveValidatorUsingTrie(validator *stateTrie.ReadOnlyValidator, epoch uint64) bool {
	return checkValidatorActiveStatus(validator.ActivationEpoch(), validator.ExitEpoch(), epoch)
}

func checkValidatorActiveStatus(activationEpoch uint64, exitEpoch uint64, epoch uint64) bool {
	return activationEpoch <= epoch && epoch < exitEpoch
}

// IsSlashableValidator returns the boolean value on whether the validator
// is slashable or not.
//
// Spec pseudocode definition:
//  def is_slashable_validator(validator: Validator, epoch: Epoch) -> bool:
//    """
//    Check if ``validator`` is slashable.
//    """
//    return (
//        validator.activation_epoch <= epoch < validator.withdrawable_epoch and
//        validator.slashed is False
// 		)
func IsSlashableValidator(validator *ethpb.Validator, epoch uint64) bool {
	active := validator.ActivationEpoch <= epoch
	beforeWithdrawable := epoch < validator.WithdrawableEpoch
	return beforeWithdrawable && active && !validator.Slashed
}

// ActiveValidatorIndices filters out active validators based on validator status
// and returns their indices in a list.
//
// WARNING: This method allocates a new copy of the validator index set and is
// considered to be very memory expensive. Avoid using this unless you really
// need the active validator indices for some specific reason.
//
// Spec pseudocode definition:
//  def get_active_validator_indices(state: BeaconState, epoch: Epoch) -> Sequence[ValidatorIndex]:
//    """
//    Return the sequence of active validator indices at ``epoch``.
//    """
//    return [ValidatorIndex(i) for i, v in enumerate(state.validators) if is_active_validator(v, epoch)]
func ActiveValidatorIndices(state *stateTrie.BeaconState, epoch uint64) ([]uint64, error) {
	seed, err := Seed(state, epoch, params.BeaconConfig().DomainBeaconAttester)
	if err != nil {
		return nil, errors.Wrap(err, "could not get seed")
	}
	activeIndices, err := committeeCache.ActiveIndices(seed)
	if err != nil {
		return nil, errors.Wrap(err, "could not interface with committee cache")
	}
	if activeIndices != nil {
		return activeIndices, nil
	}
	var indices []uint64
	state.ReadFromEveryValidator(func(idx int, val *stateTrie.ReadOnlyValidator) error {
		if IsActiveValidatorUsingTrie(val, epoch) {
			indices = append(indices, uint64(idx))
		}
		return nil
	})

	if err := UpdateCommitteeCache(state, epoch); err != nil {
		return nil, errors.Wrap(err, "could not update committee cache")
	}

	return indices, nil
}

// ActiveValidatorCount returns the number of active validators in the state
// at the given epoch.
func ActiveValidatorCount(state *stateTrie.BeaconState, epoch uint64) (uint64, error) {
	count := uint64(0)
	state.ReadFromEveryValidator(func(idx int, val *stateTrie.ReadOnlyValidator) error {
		if IsActiveValidatorUsingTrie(val, epoch) {
			count++
		}
		return nil
	})
	return count, nil
}

// DelayedActivationExitEpoch takes in epoch number and returns when
// the validator is eligible for activation and exit.
//
// Spec pseudocode definition:
//  def compute_activation_exit_epoch(epoch: Epoch) -> Epoch:
//    """
//    Return the epoch during which validator activations and exits initiated in ``epoch`` take effect.
//    """
//    return Epoch(epoch + 1 + ACTIVATION_EXIT_DELAY)
func DelayedActivationExitEpoch(epoch uint64) uint64 {
	return epoch + 1 + params.BeaconConfig().MaxSeedLookahead
}

// ValidatorChurnLimit returns the number of validators that are allowed to
// enter and exit validator pool for an epoch.
//
// Spec pseudocode definition:
//   def get_validator_churn_limit(state: BeaconState) -> uint64:
//    """
//    Return the validator churn limit for the current epoch.
//    """
//    active_validator_indices = get_active_validator_indices(state, get_current_epoch(state))
//    return max(MIN_PER_EPOCH_CHURN_LIMIT, len(active_validator_indices) // CHURN_LIMIT_QUOTIENT)
func ValidatorChurnLimit(activeValidatorCount uint64) (uint64, error) {
	churnLimit := activeValidatorCount / params.BeaconConfig().ChurnLimitQuotient
	if churnLimit < params.BeaconConfig().MinPerEpochChurnLimit {
		churnLimit = params.BeaconConfig().MinPerEpochChurnLimit
	}
	return churnLimit, nil
}

// BeaconProposerIndex returns proposer index of a current slot.
//
// Spec pseudocode definition:
//  def get_beacon_proposer_index(state: BeaconState) -> ValidatorIndex:
//    """
//    Return the beacon proposer index at the current slot.
//    """
//    epoch = get_current_epoch(state)
//    seed = hash(get_seed(state, epoch, DOMAIN_BEACON_PROPOSER) + int_to_bytes(state.slot, length=8))
//    indices = get_active_validator_indices(state, epoch)
//    return compute_proposer_index(state, indices, seed)
func BeaconProposerIndex(state *stateTrie.BeaconState) (uint64, error) {
	e := CurrentEpoch(state)

	seed, err := Seed(state, e, params.BeaconConfig().DomainBeaconAttester)
	if err != nil {
		return 0, errors.Wrap(err, "could not generate seed")
	}
	proposerIndices, err := committeeCache.ProposerIndices(seed)
	if err != nil {
		return 0, errors.Wrap(err, "could not interface with committee cache")
	}
	if proposerIndices != nil {
		return proposerIndices[state.Slot()%params.BeaconConfig().SlotsPerEpoch], nil
	}

	seed, err = Seed(state, e, params.BeaconConfig().DomainBeaconProposer)
	if err != nil {
		return 0, errors.Wrap(err, "could not generate seed")
	}

	seedWithSlot := append(seed[:], bytesutil.Bytes8(state.Slot())...)
	seedWithSlotHash := hashutil.Hash(seedWithSlot)

	indices, err := ActiveValidatorIndices(state, e)
	if err != nil {
		return 0, errors.Wrap(err, "could not get active indices")
	}

	if err := UpdateProposerIndicesInCache(state, CurrentEpoch(state)); err != nil {
		return 0, errors.Wrap(err, "could not update committee cache")
	}

	return ComputeProposerIndex(state.Validators(), indices, seedWithSlotHash)
}

// ComputeProposerIndex returns the index sampled by effective balance, which is used to calculate proposer.
//
// Note: This method signature deviates slightly from the spec recommended definition. The full
// state object is not required to compute the proposer index.
//
// Spec pseudocode definition:
//  def compute_proposer_index(state: BeaconState, indices: Sequence[ValidatorIndex], seed: Hash) -> ValidatorIndex:
//    """
//    Return from ``indices`` a random index sampled by effective balance.
//    """
//    assert len(indices) > 0
//    MAX_RANDOM_BYTE = 2**8 - 1
//    i = 0
//    while True:
//        candidate_index = indices[compute_shuffled_index(ValidatorIndex(i % len(indices)), len(indices), seed)]
//        random_byte = hash(seed + int_to_bytes(i // 32, length=8))[i % 32]
//        effective_balance = state.validators[candidate_index].effective_balance
//        if effective_balance * MAX_RANDOM_BYTE >= MAX_EFFECTIVE_BALANCE * random_byte:
//            return ValidatorIndex(candidate_index)
//        i += 1
func ComputeProposerIndex(validators []*ethpb.Validator, activeIndices []uint64, seed [32]byte) (uint64, error) {
	length := uint64(len(activeIndices))
	if length == 0 {
		return 0, errors.New("empty active indices list")
	}
	maxRandomByte := uint64(1<<8 - 1)
	hashFunc := hashutil.CustomSHA256Hasher()

	for i := uint64(0); ; i++ {
		candidateIndex, err := ComputeShuffledIndex(i%length, length, seed, true /* shuffle */)
		if err != nil {
			return 0, err
		}
		candidateIndex = activeIndices[candidateIndex]
		if int(candidateIndex) >= len(validators) {
			return 0, errors.New("active index out of range")
		}
		b := append(seed[:], bytesutil.Bytes8(i/32)...)
		randomByte := hashFunc(b)[i%32]
		v := validators[candidateIndex]
		var effectiveBal uint64
		if v != nil {
			effectiveBal = v.EffectiveBalance
		}
		if effectiveBal*maxRandomByte >= params.BeaconConfig().MaxEffectiveBalance*uint64(randomByte) {
			return candidateIndex, nil
		}
	}
}

// Domain returns the domain version for BLS private key to sign and verify.
//
// Spec pseudocode definition:
//  def get_domain(state: BeaconState,
//               domain_type: int,
//               message_epoch: Epoch=None) -> int:
//    """
//    Return the signature domain (fork version concatenated with domain type) of a message.
//    """
//    epoch = get_current_epoch(state) if message_epoch is None else message_epoch
//    fork_version = state.fork.previous_version if epoch < state.fork.epoch else state.fork.current_version
//    return bls_domain(domain_type, fork_version)
func Domain(fork *pb.Fork, epoch uint64, domainType []byte) uint64 {
	var forkVersion []byte
	if epoch < fork.Epoch {
		forkVersion = fork.PreviousVersion
	} else {
		forkVersion = fork.CurrentVersion
	}
	return bls.Domain(domainType, forkVersion)
}

// IsEligibleForActivationQueue checks if the validator is eligible to
// be places into the activation queue.
//
// Spec pseudocode definition:
//  def is_eligible_for_activation_queue(validator: Validator) -> bool:
//    """
//    Check if ``validator`` is eligible to be placed into the activation queue.
//    """
//    return (
//        validator.activation_eligibility_epoch == FAR_FUTURE_EPOCH
//        and validator.effective_balance == MAX_EFFECTIVE_BALANCE
//    )
func IsEligibleForActivationQueue(validator *ethpb.Validator) bool {
	return validator.ActivationEligibilityEpoch == params.BeaconConfig().FarFutureEpoch &&
		validator.EffectiveBalance == params.BeaconConfig().MaxEffectiveBalance
}

// IsEligibleForActivation checks if the validator is eligible for activation.
//
// Spec pseudocode definition:
//  def is_eligible_for_activation(state: BeaconState, validator: Validator) -> bool:
//    """
//    Check if ``validator`` is eligible for activation.
//    """
//    return (
//        # Placement in queue is finalized
//        validator.activation_eligibility_epoch <= state.finalized_checkpoint.epoch
//        # Has not yet been activated
//        and validator.activation_epoch == FAR_FUTURE_EPOCH
//    )
func IsEligibleForActivation(state *stateTrie.BeaconState, validator *ethpb.Validator) bool {
	finalizedEpoch := state.FinalizedCheckpointEpoch()
	return validator.ActivationEligibilityEpoch <= finalizedEpoch &&
		validator.ActivationEpoch == params.BeaconConfig().FarFutureEpoch
}