// Copyright 2021 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 eip1559

import (
	"fmt"
	"math/big"

	"github.com/XinFinOrg/XDPoSChain/common"
	"github.com/XinFinOrg/XDPoSChain/core/types"
	"github.com/XinFinOrg/XDPoSChain/params"
)

// VerifyEip1559Header verifies some header attributes which were changed in EIP-1559,
// - gas limit check
// - basefee check
func VerifyEip1559Header(config *params.ChainConfig, header *types.Header) error {
	if !config.IsEIP1559(header.Number) {
		if header.BaseFee != nil {
			return fmt.Errorf("invalid baseFee: have %s, want <nil>",
				header.BaseFee)
		}
		return nil
	}

	// Verify the header is not malformed
	if header.BaseFee == nil {
		return fmt.Errorf("header is missing baseFee")
	}

	// Verify the baseFee is correct based on the current header.
	expectedBaseFee := CalcBaseFee(config, header)
	if header.BaseFee.Cmp(expectedBaseFee) != 0 {
		return fmt.Errorf("invalid baseFee: have %s, want %s",
			header.BaseFee, expectedBaseFee)
	}
	return nil
}

// CalcBaseFee calculates the basefee of the header.
func CalcBaseFee(config *params.ChainConfig, header *types.Header) *big.Int {
	// If the current block is the first EIP-1559 block, return the InitialBaseFee.
	if config.IsEIP1559(header.Number) {
		return new(big.Int).Set(common.BaseFee)
	} else {
		return nil
	}
}