package bor

import (
	"context"
	"encoding/json"

	"github.com/ethereum/go-ethereum/consensus/bor/valset"

	lru "github.com/hashicorp/golang-lru"

	"github.com/ethereum/go-ethereum/common"
	borSpan "github.com/ethereum/go-ethereum/consensus/bor/heimdall/span"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethdb"
	"github.com/ethereum/go-ethereum/params"
)

// Snapshot is the state of the authorization voting at a given point in time.
type Snapshot struct {
	chainConfig *params.ChainConfig

	sigcache *lru.ARCCache // Cache of recent block signatures to speed up ecrecover

	Number       uint64                    `json:"number"`       // Block number where the snapshot was created
	Hash         common.Hash               `json:"hash"`         // Block hash where the snapshot was created
	ValidatorSet *valset.ValidatorSet      `json:"validatorSet"` // Validator set at this moment
	Recents      map[uint64]common.Address `json:"recents"`      // Set of recent signers for spam protections
}

// newSnapshot creates a new snapshot with the specified startup parameters. This
// method does not initialize the set of recent signers, so only ever use if for
// the genesis block.
func newSnapshot(
	chainConfig *params.ChainConfig,
	sigcache *lru.ARCCache,
	number uint64,
	hash common.Hash,
	validators []*valset.Validator,
) *Snapshot {
	snap := &Snapshot{
		chainConfig:  chainConfig,
		sigcache:     sigcache,
		Number:       number,
		Hash:         hash,
		ValidatorSet: valset.NewValidatorSet(validators),
		Recents:      make(map[uint64]common.Address),
	}

	return snap
}

// loadSnapshot loads an existing snapshot from the database.
func loadSnapshot(chainConfig *params.ChainConfig, config *params.BorConfig, sigcache *lru.ARCCache, db ethdb.Database, hash common.Hash) (*Snapshot, error) {
	blob, err := db.Get(append([]byte("bor-"), hash[:]...))
	if err != nil {
		return nil, err
	}

	snap := new(Snapshot)

	if err := json.Unmarshal(blob, snap); err != nil {
		return nil, err
	}

	snap.ValidatorSet.UpdateValidatorMap()

	snap.chainConfig = chainConfig
	snap.sigcache = sigcache

	// update total voting power
	if err := snap.ValidatorSet.UpdateTotalVotingPower(); err != nil {
		return nil, err
	}

	return snap, nil
}

// store inserts the snapshot into the database.
func (s *Snapshot) store(db ethdb.Database) error {
	blob, err := json.Marshal(s)
	if err != nil {
		return err
	}

	return db.Put(append([]byte("bor-"), s.Hash[:]...), blob)
}

// copy creates a deep copy of the snapshot, though not the individual votes.
func (s *Snapshot) copy() *Snapshot {
	cpy := &Snapshot{
		chainConfig:  s.chainConfig,
		sigcache:     s.sigcache,
		Number:       s.Number,
		Hash:         s.Hash,
		ValidatorSet: s.ValidatorSet.Copy(),
		Recents:      make(map[uint64]common.Address),
	}
	for block, signer := range s.Recents {
		cpy.Recents[block] = signer
	}

	return cpy
}

func (s *Snapshot) apply(headers []*types.Header, c *Bor) (*Snapshot, error) {
	// Allow passing in no headers for cleaner code
	if len(headers) == 0 {
		return s, nil
	}
	// Sanity check that the headers can be applied
	for i := 0; i < len(headers)-1; i++ {
		if headers[i+1].Number.Uint64() != headers[i].Number.Uint64()+1 {
			return nil, errOutOfRangeChain
		}
	}

	if headers[0].Number.Uint64() != s.Number+1 {
		return nil, errOutOfRangeChain
	}
	// Iterate through the headers and create a new snapshot
	snap := s.copy()

	for _, header := range headers {
		// Remove any votes on checkpoint blocks
		number := header.Number.Uint64()

		// Delete the oldest signer from the recent list to allow it signing again
		if number >= s.chainConfig.Bor.CalculateSprint(number) {
			delete(snap.Recents, number-s.chainConfig.Bor.CalculateSprint(number))
		}

		// Resolve the authorization key and check against signers
		signer, err := ecrecover(header, s.sigcache, s.chainConfig.Bor)
		if err != nil {
			return nil, err
		}

		// check if signer is in validator set
		if !snap.ValidatorSet.HasAddress(signer) {
			return nil, &UnauthorizedSignerError{number, signer.Bytes(), snap.ValidatorSet.Validators}
		}

		if _, err = snap.GetSignerSuccessionNumber(signer); err != nil {
			return nil, err
		}

		// add recents
		snap.Recents[number] = signer

		// change validator set and change proposer
		if number > 0 && (number+1)%s.chainConfig.Bor.CalculateSprint(number) == 0 {
			if err := validateHeaderExtraField(header.Extra); err != nil {
				return nil, err
			}

			validatorBytes := header.GetValidatorBytes(s.chainConfig)

			// get validators from headers and use that for new validator set
			newVals, _ := valset.ParseValidators(validatorBytes)

			v := getUpdatedValidatorSet(snap.ValidatorSet.Copy(), newVals)
			v.IncrementProposerPriority(1)

			if v.CheckEmptyId() {
				// Fetch the validator set from span
				span, err := c.spanStore.spanByBlockNumber(context.Background(), number+1)
				if err != nil {
					return nil, err
				}
				v.IncludeIds(borSpan.ConvertHeimdallValSetToBorValSet(span.ValidatorSet).Validators)
			}
			snap.ValidatorSet = v
		}
	}

	snap.Number += uint64(len(headers))
	snap.Hash = headers[len(headers)-1].Hash()

	return snap, nil
}

// GetSignerSuccessionNumber returns the relative position of signer in terms of the in-turn proposer
func (s *Snapshot) GetSignerSuccessionNumber(signer common.Address) (int, error) {
	validators := s.ValidatorSet.Validators
	proposer := s.ValidatorSet.GetProposer().Address
	proposerIndex, _ := s.ValidatorSet.GetByAddress(proposer)

	if proposerIndex == -1 {
		return -1, &UnauthorizedProposerError{s.Number, proposer.Bytes()}
	}

	signerIndex, _ := s.ValidatorSet.GetByAddress(signer)

	if signerIndex == -1 {
		return -1, &UnauthorizedSignerError{s.Number, signer.Bytes(), s.ValidatorSet.Validators}
	}

	tempIndex := signerIndex
	if proposerIndex != tempIndex {
		if tempIndex < proposerIndex {
			tempIndex = tempIndex + len(validators)
		}
	}

	return tempIndex - proposerIndex, nil
}

// signers retrieves the list of authorized signers in ascending order.
func (s *Snapshot) signers() []common.Address {
	sigs := make([]common.Address, 0, len(s.ValidatorSet.Validators))
	for _, sig := range s.ValidatorSet.Validators {
		sigs = append(sigs, sig.Address)
	}

	return sigs
}

// Difficulty returns the difficulty for a particular signer at the current snapshot number
func Difficulty(validatorSet *valset.ValidatorSet, signer common.Address) uint64 {
	// if signer is empty
	if signer == (common.Address{}) {
		return 1
	}

	validators := validatorSet.Validators
	proposer := validatorSet.GetProposer().Address
	totalValidators := len(validators)

	proposerIndex, _ := validatorSet.GetByAddress(proposer)
	signerIndex, _ := validatorSet.GetByAddress(signer)

	// temp index
	tempIndex := signerIndex
	if tempIndex < proposerIndex {
		tempIndex = tempIndex + totalValidators
	}

	return uint64(totalValidators - (tempIndex - proposerIndex))
}
