// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// Package consensus implements different Ethereum consensus engines.
package consensus

import (
	"context"
	"math/big"

	"github.com/ledgerwatch/erigon/common"
	"github.com/ledgerwatch/erigon/core/state"
	"github.com/ledgerwatch/erigon/core/types"
	"github.com/ledgerwatch/erigon/params"
	"github.com/ledgerwatch/erigon/rlp"
	"github.com/ledgerwatch/erigon/rpc"
)

// ChainHeaderReader defines a small collection of methods needed to access the local
// blockchain during header verification.
type ChainHeaderReader interface {
	// Config retrieves the blockchain's chain configuration.
	Config() *params.ChainConfig

	// CurrentHeader retrieves the current header from the local chain.
	CurrentHeader() *types.Header

	// GetHeader retrieves a block header from the database by hash and number.
	GetHeader(hash common.Hash, number uint64) *types.Header

	// GetHeaderByNumber retrieves a block header from the database by number.
	GetHeaderByNumber(number uint64) *types.Header

	// GetHeaderByHash retrieves a block header from the database by its hash.
	GetHeaderByHash(hash common.Hash) *types.Header

	// GetTd retrieves the total difficulty from the database by hash and number.
	GetTd(hash common.Hash, number uint64) *big.Int
}

// ChainReader defines a small collection of methods needed to access the local
// blockchain during header and/or uncle verification.
type ChainReader interface {
	ChainHeaderReader

	// GetBlock retrieves a block from the database by hash and number.
	GetBlock(hash common.Hash, number uint64) *types.Block
	GetHeader(hash common.Hash, number uint64) *types.Header

	HasBlock(hash common.Hash, number uint64) bool
}

type EpochReader interface {
	GetEpoch(blockHash common.Hash, blockN uint64) (transitionProof []byte, err error)
	PutEpoch(blockHash common.Hash, blockN uint64, transitionProof []byte) (err error)
	GetPendingEpoch(blockHash common.Hash, blockN uint64) (transitionProof []byte, err error)
	PutPendingEpoch(blockHash common.Hash, blockN uint64, transitionProof []byte) (err error)
	FindBeforeOrEqualNumber(number uint64) (blockNum uint64, blockHash common.Hash, transitionProof []byte, err error)
}

type SystemCall func(contract common.Address, data []byte) ([]byte, error)
type Call func(contract common.Address, data []byte) ([]byte, error)

// Engine is an algorithm agnostic consensus engine.
type Engine interface {
	// Author retrieves the Ethereum address of the account that minted the given
	// block, which may be different from the header's coinbase if a consensus
	// engine is based on signatures.
	Author(header *types.Header) (common.Address, error)

	// VerifyHeader checks whether a header conforms to the consensus rules of a
	// given engine. Verifying the seal may be done optionally here, or explicitly
	// via the VerifySeal method.
	VerifyHeader(chain ChainHeaderReader, header *types.Header, seal bool) error

	// VerifyUncles verifies that the given block's uncles conform to the consensus
	// rules of a given engine.
	VerifyUncles(chain ChainReader, header *types.Header, uncles []*types.Header) error

	// Prepare initializes the consensus fields of a block header according to the
	// rules of a particular engine. The changes are executed inline.
	Prepare(chain ChainHeaderReader, header *types.Header, state *state.IntraBlockState) error

	// Initialize runs any pre-transaction state modifications (e.g. epoch start)
	Initialize(config *params.ChainConfig, chain ChainHeaderReader, e EpochReader, header *types.Header, txs []types.Transaction, uncles []*types.Header, syscall SystemCall)

	// Finalize runs any post-transaction state modifications (e.g. block rewards)
	// but does not assemble the block.
	//
	// Note: The block header and state database might be updated to reflect any
	// consensus rules that happen at finalization (e.g. block rewards).
	Finalize(config *params.ChainConfig, header *types.Header, state *state.IntraBlockState,
		txs types.Transactions, uncles []*types.Header, receipts types.Receipts,
		e EpochReader, chain ChainHeaderReader, syscall SystemCall,
	) (types.Transactions, types.Receipts, error)

	// FinalizeAndAssemble runs any post-transaction state modifications (e.g. block
	// rewards) and assembles the final block.
	//
	// Note: The block header and state database might be updated to reflect any
	// consensus rules that happen at finalization (e.g. block rewards).
	FinalizeAndAssemble(config *params.ChainConfig, header *types.Header, state *state.IntraBlockState,
		txs types.Transactions, uncles []*types.Header, receipts types.Receipts,
		e EpochReader, chain ChainHeaderReader, syscall SystemCall, call Call,
	) (*types.Block, types.Transactions, types.Receipts, error)

	// Seal generates a new sealing request for the given input block and pushes
	// the result into the given channel.
	//
	// Note, the method returns immediately and will send the result async. More
	// than one result may also be returned depending on the consensus algorithm.
	Seal(chain ChainHeaderReader, block *types.Block, results chan<- *types.Block, stop <-chan struct{}) error

	// SealHash returns the hash of a block prior to it being sealed.
	SealHash(header *types.Header) common.Hash

	// CalcDifficulty is the difficulty adjustment algorithm. It returns the difficulty
	// that a new block should have.
	CalcDifficulty(chain ChainHeaderReader, time, parentTime uint64, parentDifficulty *big.Int, parentNumber uint64, parentHash, parentUncleHash common.Hash, parentSeal []rlp.RawValue) *big.Int

	GenerateSeal(chain ChainHeaderReader, currnt, parent *types.Header, call Call) []rlp.RawValue

	// APIs returns the RPC APIs this consensus engine provides.
	APIs(chain ChainHeaderReader) []rpc.API

	Type() params.ConsensusType
	// Close terminates any background threads maintained by the consensus engine.
	Close() error
}

// PoW is a consensus engine based on proof-of-work.
type PoW interface {
	Engine

	// Hashrate returns the current mining hashrate of a PoW consensus engine.
	Hashrate() float64
}

var (
	SystemAddress = common.HexToAddress("0xffffFFFfFFffffffffffffffFfFFFfffFFFfFFfE")
)

type PoSA interface {
	Engine

	IsSystemTransaction(tx types.Transaction, header *types.Header) (bool, error)
	IsSystemContract(to *common.Address) bool
	EnoughDistance(chain ChainReader, header *types.Header) bool
	IsLocalBlock(header *types.Header) bool
	AllowLightProcess(chain ChainReader, currentHeader *types.Header) bool
}

type AsyncEngine interface {
	Engine

	WithExecutionContext(context.Context) AsyncEngine
}