// Copyright 2016 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 core

import (
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/consensus"
	"github.com/ethereum/go-ethereum/consensus/misc/eip4844"
	"github.com/ethereum/go-ethereum/core/tracing"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/core/vm"
	"github.com/ethereum/go-ethereum/params"
	"github.com/holiman/uint256"
)

// ChainContext supports retrieving headers and consensus parameters from the
// current blockchain to be used during transaction processing.
type ChainContext interface {
	consensus.ChainHeaderReader

	// Engine retrieves the chain's consensus engine.
	Engine() consensus.Engine
}

// NewEVMBlockContext creates a new context for use in the EVM.
func NewEVMBlockContext(header *types.Header, chain ChainContext, author *common.Address) vm.BlockContext {
	var (
		beneficiary common.Address
		baseFee     *big.Int
		blobBaseFee *big.Int
		random      *common.Hash
		slotNum     uint64
	)

	// If we don't have an explicit author (i.e. not mining), extract from the header
	if author == nil {
		beneficiary, _ = chain.Engine().Author(header) // Ignore error, we're past header validation
	} else {
		beneficiary = *author
	}
	if header.BaseFee != nil {
		baseFee = new(big.Int).Set(header.BaseFee)
	}
	if header.ExcessBlobGas != nil {
		blobBaseFee = eip4844.CalcBlobFee(chain.Config(), header)
	}
	// CHANGE(taiko): Unzen blocks have non-zero difficulty (zk gas) but still need
	// Random for PREVRANDAO, and BlobBaseFee=1 for BLOBBASEFEE opcode compatibility.
	// Note: chainCfg guards against nil interface values AND nil concrete pointers
	// behind a non-nil interface (e.g. (*BlockChain)(nil) passed from test helpers).
	chainCfg := getChainConfig(chain)
	if chainCfg != nil && chainCfg.IsUnzen(header.Time) {
		random = &header.MixDigest
		blobBaseFee = big.NewInt(1)
	} else if header.Difficulty.Sign() == 0 {
		random = &header.MixDigest
	}
	if header.SlotNumber != nil {
		slotNum = *header.SlotNumber
	}

	return vm.BlockContext{
		CanTransfer: CanTransfer,
		Transfer:    Transfer,
		GetHash:     GetHashFn(header, chain),
		Coinbase:    beneficiary,
		BlockNumber: new(big.Int).Set(header.Number),
		Time:        header.Time,
		Difficulty:  new(big.Int).Set(header.Difficulty),
		BaseFee:     baseFee,
		BlobBaseFee: blobBaseFee,
		GasLimit:    header.GasLimit,
		Random:      random,
		SlotNum:     slotNum,
	}
}

// NewEVMTxContext creates a new transaction context for a single transaction.
func NewEVMTxContext(msg *Message) vm.TxContext {
	ctx := vm.TxContext{
		Origin:     msg.From,
		GasPrice:   uint256.MustFromBig(msg.GasPrice),
		BlobHashes: msg.BlobHashes,
	}
	return ctx
}

// CHANGE(taiko): getChainConfig safely extracts the chain config, returning nil when the
// chain context is nil or wraps a nil concrete pointer (common in test helpers).
func getChainConfig(chain ChainContext) *params.ChainConfig {
	if chain == nil {
		return nil
	}
	defer func() { recover() }() //nolint:errcheck
	return chain.Config()
}

// GetHashFn returns a GetHashFunc which retrieves header hashes by number
func GetHashFn(ref *types.Header, chain ChainContext) func(n uint64) common.Hash {
	// Cache will initially contain [refHash.parent],
	// Then fill up with [refHash.p, refHash.pp, refHash.ppp, ...]
	var cache []common.Hash

	return func(n uint64) common.Hash {
		if ref.Number.Uint64() <= n {
			// This situation can happen if we're doing tracing and using
			// block overrides.
			return common.Hash{}
		}
		// If there's no hash cache yet, make one
		if len(cache) == 0 {
			cache = append(cache, ref.ParentHash)
		}
		if idx := ref.Number.Uint64() - n - 1; idx < uint64(len(cache)) {
			return cache[idx]
		}
		// No luck in the cache, but we can start iterating from the last element we already know
		lastKnownHash := cache[len(cache)-1]
		lastKnownNumber := ref.Number.Uint64() - uint64(len(cache))

		for {
			header := chain.GetHeader(lastKnownHash, lastKnownNumber)
			if header == nil {
				break
			}
			cache = append(cache, header.ParentHash)
			lastKnownHash = header.ParentHash
			lastKnownNumber = header.Number.Uint64() - 1
			if n == lastKnownNumber {
				return lastKnownHash
			}
		}
		return common.Hash{}
	}
}

// CanTransfer checks whether there are enough funds in the address' account to make a transfer.
// This does not take the necessary gas in to account to make the transfer valid.
func CanTransfer(db vm.StateDB, addr common.Address, amount *uint256.Int) bool {
	return db.GetBalance(addr).Cmp(amount) >= 0
}

// Transfer subtracts amount from sender and adds amount to recipient using the given Db
func Transfer(db vm.StateDB, sender, recipient common.Address, amount *uint256.Int, rules *params.Rules) {
	db.SubBalance(sender, amount, tracing.BalanceChangeTransfer)
	db.AddBalance(recipient, amount, tracing.BalanceChangeTransfer)
	if rules.IsAmsterdam && !amount.IsZero() && sender != recipient {
		db.AddLog(types.EthTransferLog(sender, recipient, amount))
	}
}
