package state

import (
	v "github.com/prysmaticlabs/prysm/beacon-chain/core/validators"
	pb "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
	pbcomm "github.com/prysmaticlabs/prysm/proto/common"
	"github.com/prysmaticlabs/prysm/shared/params"
)

// NewGenesisBeaconState initializes the beacon chain state for slot 0.
func NewGenesisBeaconState(genesisValidatorRegistry []*pb.ValidatorRecord) (*pb.BeaconState, error) {
	// We seed the genesis state with a bunch of validators to
	// bootstrap the system.
	var err error
	if genesisValidatorRegistry == nil {
		genesisValidatorRegistry = v.InitialValidatorRegistry()

	}
	// Bootstrap attester indices for slots, each slot contains an array of attester indices.
	shardAndCommitteesForSlots, err := v.InitialShardAndCommitteesForSlots(genesisValidatorRegistry)
	if err != nil {
		return nil, err
	}

	// Bootstrap cross link records.
	var crosslinks []*pb.CrosslinkRecord
	for i := uint64(0); i < params.BeaconConfig().ShardCount; i++ {
		crosslinks = append(crosslinks, &pb.CrosslinkRecord{
			ShardBlockRootHash32: make([]byte, 0, 32),
			Slot:                 0,
		})
	}

	var latestBlockHashes [][]byte
	for i := 0; i < 2*int(params.BeaconConfig().CycleLength); i++ {
		latestBlockHashes = append(latestBlockHashes, make([]byte, 0, 32))
	}

	return &pb.BeaconState{
		ValidatorRegistry:                    genesisValidatorRegistry,
		ValidatorRegistryLastChangeSlot:      0,
		ValidatorRegistryExitCount:           0,
		ValidatorRegistryDeltaChainTipHash32: make([]byte, 0, 32),
		RandaoMixHash32:                      make([]byte, 0, 32),
		NextSeedHash32:                       make([]byte, 0, 32),
		ShardAndCommitteesAtSlots:            shardAndCommitteesForSlots,
		PersistentCommittees:                 []*pbcomm.Uint32List{},
		PersistentCommitteeReassignments:     []*pb.ShardReassignmentRecord{},
		PreviousJustifiedSlot:                0,
		JustifiedSlot:                        0,
		JustifiedSlotBitfield:                0,
		FinalizedSlot:                        0,
		LatestCrosslinks:                     crosslinks,
		LastStateRecalculationSlot:           0,
		LatestBlockRootHash32S:               latestBlockHashes,
		LatestPenalizedExitBalances:          []uint64{},
		LatestAttestations:                   []*pb.PendingAttestationRecord{},
		ProcessedPowReceiptRootHash32:        []byte{},
		CandidatePowReceiptRoots:             []*pb.CandidatePoWReceiptRootRecord{},
		GenesisTime:                          0,
		ForkData: &pb.ForkData{
			PreForkVersion:  params.BeaconConfig().InitialForkVersion,
			PostForkVersion: params.BeaconConfig().InitialForkVersion,
			ForkSlot:        params.BeaconConfig().InitialForkSlot,
		},
		Slot: 0,
	}, nil
}

// CalculateNewBlockHashes builds a new slice of recent block hashes with the
// provided block and the parent slot number.
//
// The algorithm is:
//   1) shift the array by block.SlotNumber - parentSlot (i.e. truncate the
//     first by the number of slots that have occurred between the block and
//     its parent).
//
//   2) fill the array with the parent block hash for all values between the parent
//     slot and the block slot.
//
// Computation of the state hash depends on this feature that slots with
// missing blocks have the block hash of the next block hash in the chain.
//
// For example, if we have a segment of recent block hashes that look like this
//   [0xF, 0x7, 0x0, 0x0, 0x5]
//
// Where 0x0 is an empty or missing hash where no block was produced in the
// alloted slot. When storing the list (or at least when computing the hash of
// the active state), the list should be back-filled as such:
//
//   [0xF, 0x7, 0x5, 0x5, 0x5]
func CalculateNewBlockHashes(state *pb.BeaconState, block *pb.BeaconBlock, parentSlot uint64) ([][]byte, error) {
	distance := block.GetSlot() - parentSlot
	existing := state.GetLatestBlockRootHash32S()
	update := existing[distance:]
	for len(update) < 2*int(params.BeaconConfig().CycleLength) {
		update = append(update, block.GetParentRootHash32())
	}
	return update, nil
}

// IsValidatorSetChange checks if a validator set change transition can be processed. At that point,
// validator shuffle will occur.
func IsValidatorSetChange(state *pb.BeaconState, slotNumber uint64) bool {
	if state.GetFinalizedSlot() <= state.GetValidatorRegistryLastChangeSlot() {
		return false
	}
	if slotNumber-state.GetValidatorRegistryLastChangeSlot() < params.BeaconConfig().MinValidatorSetChangeInterval {
		return false
	}

	shardProcessed := map[uint64]bool{}
	for _, shardAndCommittee := range state.GetShardAndCommitteesAtSlots() {
		for _, committee := range shardAndCommittee.ArrayShardAndCommittee {
			shardProcessed[committee.Shard] = true
		}
	}

	crosslinks := state.GetLatestCrosslinks()
	for shard := range shardProcessed {
		if state.GetValidatorRegistryLastChangeSlot() >= crosslinks[shard].Slot {
			return false
		}
	}
	return true
}

// ClearAttestations removes attestations older than last state recalculation slot.
func ClearAttestations(state *pb.BeaconState, lastStateRecalc uint64) []*pb.PendingAttestationRecord {
	existing := state.GetLatestAttestations()
	updatedAttestations := make([]*pb.PendingAttestationRecord, 0, len(existing))
	for _, a := range existing {
		if a.GetData().GetSlot() >= lastStateRecalc {
			updatedAttestations = append(updatedAttestations, a)
		}
	}
	return updatedAttestations
}

// IsCycleTransition checks if a new cycle has been reached. At that point,
// a new state transition will occur in the beacon chain.
func IsCycleTransition(lastRecalcSlot uint64, slotNumber uint64) bool {
	return slotNumber >= lastRecalcSlot+params.BeaconConfig().CycleLength
}