// Copyright 2014 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/core/vm"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/params"
)

// Call executes within the given contract
func Call(env vm.Environment, caller vm.ContractRef, addr common.Address, input []byte, gas, gasPrice, value *big.Int) (ret []byte, err error) {
	ret, _, err = exec(env, caller, &addr, &addr, input, env.Db().GetCode(addr), gas, gasPrice, value)
	return ret, err
}

// CallCode executes the given address' code as the given contract address
func CallCode(env vm.Environment, caller vm.ContractRef, addr common.Address, input []byte, gas, gasPrice, value *big.Int) (ret []byte, err error) {
	prev := caller.Address()
	ret, _, err = exec(env, caller, &prev, &addr, input, env.Db().GetCode(addr), gas, gasPrice, value)
	return ret, err
}

// Create creates a new contract with the given code
func Create(env vm.Environment, caller vm.ContractRef, code []byte, gas, gasPrice, value *big.Int) (ret []byte, address common.Address, err error) {
	ret, address, err = exec(env, caller, nil, nil, nil, code, gas, gasPrice, value)
	// Here we get an error if we run into maximum stack depth,
	// See: https://github.com/ethereum/yellowpaper/pull/131
	// and YP definitions for CREATE instruction
	if err != nil {
		return nil, address, err
	}
	return ret, address, err
}

func exec(env vm.Environment, caller vm.ContractRef, address, codeAddr *common.Address, input, code []byte, gas, gasPrice, value *big.Int) (ret []byte, addr common.Address, err error) {
	evm := vm.NewVm(env)

	// Depth check execution. Fail if we're trying to execute above the
	// limit.
	if env.Depth() > int(params.CallCreateDepth.Int64()) {
		caller.ReturnGas(gas, gasPrice)

		return nil, common.Address{}, vm.DepthError
	}

	if !env.CanTransfer(caller.Address(), value) {
		caller.ReturnGas(gas, gasPrice)

		return nil, common.Address{}, ValueTransferErr("insufficient funds to transfer value. Req %v, has %v", value, env.Db().GetBalance(caller.Address()))
	}

	var createAccount bool
	if address == nil {
		// Generate a new address
		nonce := env.Db().GetNonce(caller.Address())
		env.Db().SetNonce(caller.Address(), nonce+1)

		addr = crypto.CreateAddress(caller.Address(), nonce)

		address = &addr
		createAccount = true
	}
	snapshot := env.MakeSnapshot()

	var (
		from = env.Db().GetAccount(caller.Address())
		to   vm.Account
	)
	if createAccount {
		to = env.Db().CreateAccount(*address)
	} else {
		if !env.Db().Exist(*address) {
			to = env.Db().CreateAccount(*address)
		} else {
			to = env.Db().GetAccount(*address)
		}
	}
	env.Transfer(from, to, value)

	contract := vm.NewContract(caller, to, value, gas, gasPrice)
	contract.SetCallCode(codeAddr, code)

	ret, err = evm.Run(contract, input)
	if err != nil {
		env.SetSnapshot(snapshot) //env.Db().Set(snapshot)
	}

	return ret, addr, err
}

// generic transfer method
func Transfer(from, to vm.Account, amount *big.Int) {
	from.SubBalance(amount)
	to.AddBalance(amount)
}