package dummy

import (
	"errors"
	"fmt"
	"golang.org/x/crypto/sha3"
	"math/big"
	"runtime"
	"time"

	mapset "github.com/deckarep/golang-set"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/core/state"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/params"
	"github.com/ethereum/go-ethereum/rlp"
	"github.com/ethereum/go-ethereum/rpc"
)

type OnFinalizeCallbackType = func(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, uncles []*types.Header)
type OnFinalizeAndAssembleCallbackType = func(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction, uncles []*types.Header, receipts []*types.Receipt)
type OnAPIsCallbackType = func(consensus.ChainReader) []rpc.API

type ConsensusCallbacks struct {
	OnSeal                func(*types.Block) error
	OnAPIs                OnAPIsCallbackType
	OnFinalize            OnFinalizeCallbackType
	OnFinalizeAndAssemble OnFinalizeAndAssembleCallbackType
}

type DummyEngine struct {
	cb *ConsensusCallbacks
}

func NewDummyEngine(cb *ConsensusCallbacks) *DummyEngine {
	return &DummyEngine{cb: cb}
}

var (
	allowedFutureBlockTime = 15 * time.Second // Max time from current time allowed for blocks, before they're considered future blocks
)

var (
	maxUncles = 2 // Maximum number of uncles allowed in a single block

	errTooManyUncles   = errors.New("too many uncles")
	errZeroBlockTime   = errors.New("timestamp equals parent's")
	errDuplicateUncle  = errors.New("duplicate uncle")
	errUncleIsAncestor = errors.New("uncle is ancestor")
	errDanglingUncle   = errors.New("uncle's parent is not ancestor")
)

// modified from consensus.go
func (self *DummyEngine) verifyHeader(chain consensus.ChainReader, header, parent *types.Header, uncle bool, seal bool) error {
	// Ensure that the header's extra-data section is of a reasonable size
	if uint64(len(header.Extra)) > params.MaximumExtraDataSize {
		return fmt.Errorf("extra-data too long: %d > %d", len(header.Extra), params.MaximumExtraDataSize)
	}
	// Verify the header's timestamp
	if !uncle {
		if header.Time > uint64(time.Now().Add(allowedFutureBlockTime).Unix()) {
			return consensus.ErrFutureBlock
		}
	}
	if header.Time <= parent.Time {
		return errZeroBlockTime
	}
	// Verify that the gas limit is <= 2^63-1
	cap := uint64(0x7fffffffffffffff)
	if header.GasLimit > cap {
		return fmt.Errorf("invalid gasLimit: have %v, max %v", header.GasLimit, cap)
	}
	// Verify that the gasUsed is <= gasLimit
	if header.GasUsed > header.GasLimit {
		return fmt.Errorf("invalid gasUsed: have %d, gasLimit %d", header.GasUsed, header.GasLimit)
	}

	// Verify that the gas limit remains within allowed bounds
	diff := int64(parent.GasLimit) - int64(header.GasLimit)
	if diff < 0 {
		diff *= -1
	}
	limit := parent.GasLimit / params.GasLimitBoundDivisor

	if uint64(diff) >= limit || header.GasLimit < params.MinGasLimit {
		return fmt.Errorf("invalid gas limit: have %d, want %d += %d", header.GasLimit, parent.GasLimit, limit)
	}
	// Verify that the block number is parent's +1
	if diff := new(big.Int).Sub(header.Number, parent.Number); diff.Cmp(big.NewInt(1)) != 0 {
		return consensus.ErrInvalidNumber
	}
	// Verify the engine specific seal securing the block
	if seal {
		if err := self.VerifySeal(chain, header); err != nil {
			return err
		}
	}
	return nil
}

func (self *DummyEngine) verifyHeaderWorker(chain consensus.ChainReader, headers []*types.Header, seals []bool, index int) error {
	var parent *types.Header
	if index == 0 {
		parent = chain.GetHeader(headers[0].ParentHash, headers[0].Number.Uint64()-1)
	} else if headers[index-1].Hash() == headers[index].ParentHash {
		parent = headers[index-1]
	}
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}
	if chain.GetHeader(headers[index].Hash(), headers[index].Number.Uint64()) != nil {
		return nil // known block
	}
	return self.verifyHeader(chain, headers[index], parent, false, seals[index])
}

func (self *DummyEngine) Author(header *types.Header) (common.Address, error) {
	return header.Coinbase, nil
}

func (self *DummyEngine) VerifyHeader(chain consensus.ChainReader, header *types.Header, seal bool) error {
	// Short circuit if the header is known, or it's parent not
	number := header.Number.Uint64()
	if chain.GetHeader(header.Hash(), number) != nil {
		return nil
	}
	parent := chain.GetHeader(header.ParentHash, number-1)
	if parent == nil {
		return consensus.ErrUnknownAncestor
	}
	// Sanity checks passed, do a proper verification
	return self.verifyHeader(chain, header, parent, false, seal)
}

func (self *DummyEngine) VerifyHeaders(chain consensus.ChainReader, headers []*types.Header, seals []bool) (chan<- struct{}, <-chan error) {
	// Spawn as many workers as allowed threads
	workers := runtime.GOMAXPROCS(0)
	if len(headers) < workers {
		workers = len(headers)
	}

	// Create a task channel and spawn the verifiers
	var (
		inputs = make(chan int)
		done   = make(chan int, workers)
		errors = make([]error, len(headers))
		abort  = make(chan struct{})
	)
	for i := 0; i < workers; i++ {
		go func() {
			for index := range inputs {
				errors[index] = self.verifyHeaderWorker(chain, headers, seals, index)
				done <- index
			}
		}()
	}

	errorsOut := make(chan error, len(headers))
	go func() {
		defer close(inputs)
		var (
			in, out = 0, 0
			checked = make([]bool, len(headers))
			inputs  = inputs
		)
		for {
			select {
			case inputs <- in:
				if in++; in == len(headers) {
					// Reached end of headers. Stop sending to workers.
					inputs = nil
				}
			case index := <-done:
				for checked[index] = true; checked[out]; out++ {
					errorsOut <- errors[out]
					if out == len(headers)-1 {
						return
					}
				}
			case <-abort:
				return
			}
		}
	}()
	return abort, errorsOut
}

func (self *DummyEngine) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {
	// Verify that there are at most 2 uncles included in this block
	if len(block.Uncles()) > maxUncles {
		return errTooManyUncles
	}
	if len(block.Uncles()) == 0 {
		return nil
	}
	// Gather the set of past uncles and ancestors
	uncles, ancestors := mapset.NewSet(), make(map[common.Hash]*types.Header)

	number, parent := block.NumberU64()-1, block.ParentHash()
	for i := 0; i < 7; i++ {
		ancestor := chain.GetBlock(parent, number)
		if ancestor == nil {
			break
		}
		ancestors[ancestor.Hash()] = ancestor.Header()
		for _, uncle := range ancestor.Uncles() {
			uncles.Add(uncle.Hash())
		}
		parent, number = ancestor.ParentHash(), number-1
	}
	ancestors[block.Hash()] = block.Header()
	uncles.Add(block.Hash())

	// Verify each of the uncles that it's recent, but not an ancestor
	for _, uncle := range block.Uncles() {
		// Make sure every uncle is rewarded only once
		hash := uncle.Hash()
		if uncles.Contains(hash) {
			return errDuplicateUncle
		}
		uncles.Add(hash)

		// Make sure the uncle has a valid ancestry
		if ancestors[hash] != nil {
			return errUncleIsAncestor
		}
		if ancestors[uncle.ParentHash] == nil || uncle.ParentHash == block.ParentHash() {
			return errDanglingUncle
		}
		if err := self.verifyHeader(chain, uncle, ancestors[uncle.ParentHash], true, true); err != nil {
			return err
		}
	}
	return nil
}

func (self *DummyEngine) VerifySeal(chain consensus.ChainReader, header *types.Header) error {
	return nil
}

func (self *DummyEngine) Prepare(chain consensus.ChainReader, header *types.Header) error {
	header.Difficulty = big.NewInt(1)
	return nil
}

func (self *DummyEngine) Finalize(
	chain consensus.ChainReader, header *types.Header,
	state *state.StateDB, txs []*types.Transaction,
	uncles []*types.Header) {
	if self.cb.OnFinalize != nil {
		self.cb.OnFinalize(chain, header, state, txs, uncles)
	}
	// commit the final state root
	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))
}

func (self *DummyEngine) FinalizeAndAssemble(chain consensus.ChainReader, header *types.Header, state *state.StateDB, txs []*types.Transaction,
	uncles []*types.Header, receipts []*types.Receipt) (*types.Block, error) {
	if self.cb.OnFinalizeAndAssemble != nil {
		self.cb.OnFinalizeAndAssemble(chain, header, state, txs, uncles, receipts)
	}
	// commit the final state root
	header.Root = state.IntermediateRoot(chain.Config().IsEIP158(header.Number))

	// Header seems complete, assemble into a block and return
	return types.NewBlock(header, txs, uncles, receipts), nil
}

func (self *DummyEngine) Seal(chain consensus.ChainReader, block *types.Block, results chan<- *types.Block, stop <-chan struct{}) (err error) {
	if self.cb.OnSeal != nil {
		err = self.cb.OnSeal(block)
	} else {
		err = nil
	}
	results <- block
	return
}

func (self *DummyEngine) SealHash(header *types.Header) (hash common.Hash) {
	hasher := sha3.NewLegacyKeccak256()

	rlp.Encode(hasher, []interface{}{
		header.ParentHash,
		header.UncleHash,
		header.Coinbase,
		header.Root,
		header.TxHash,
		header.ReceiptHash,
		header.Bloom,
		header.Difficulty,
		header.Number,
		header.GasLimit,
		header.GasUsed,
		header.Time,
		header.Extra,
	})
	hasher.Sum(hash[:0])
	return hash
}

func (self *DummyEngine) CalcDifficulty(chain consensus.ChainReader, time uint64, parent *types.Header) *big.Int {
	return big.NewInt(1)
}

func (self *DummyEngine) APIs(chain consensus.ChainReader) (res []rpc.API) {
	res = nil
	if self.cb.OnAPIs != nil {
		res = self.cb.OnAPIs(chain)
	}
	return
}

func (self *DummyEngine) Close() error {
	return nil
}