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// 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 runtime

import (
    "math/big"
    "time"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/state"
    "github.com/ethereum/go-ethereum/core/vm"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/ethdb"
)

// Config is a basic type specifing certain configuration flags for running
// the EVM.
type Config struct {
    Difficulty  *big.Int
    Origin      common.Address
    Coinbase    common.Address
    BlockNumber *big.Int
    Time        *big.Int
    GasLimit    *big.Int
    GasPrice    *big.Int
    Value       *big.Int
    DisableJit  bool // "disable" so it's enabled by default
    Debug       bool

    GetHashFn func(n uint64) common.Hash
}

// sets defaults on the config
func setDefaults(cfg *Config) {
    if cfg.Difficulty == nil {
        cfg.Difficulty = new(big.Int)
    }
    if cfg.Time == nil {
        cfg.Time = big.NewInt(time.Now().Unix())
    }
    if cfg.GasLimit == nil {
        cfg.GasLimit = new(big.Int).Set(common.MaxBig)
    }
    if cfg.GasPrice == nil {
        cfg.GasPrice = new(big.Int)
    }
    if cfg.Value == nil {
        cfg.Value = new(big.Int)
    }
    if cfg.BlockNumber == nil {
        cfg.BlockNumber = new(big.Int)
    }
    if cfg.GetHashFn == nil {
        cfg.GetHashFn = func(n uint64) common.Hash {
            return common.BytesToHash(crypto.Sha3([]byte(new(big.Int).SetUint64(n).String())))
        }
    }
}

// Execute executes the code using the input as call data during the execution.
// It returns the EVM's return value, the new state and an error if it failed.
//
// Executes sets up a in memory, temporarily, environment for the execution of
// the given code. It enabled the JIT by default and make sure that it's restored
// to it's original state afterwards.
func Execute(code, input []byte, cfg *Config) ([]byte, *state.StateDB, error) {
    if cfg == nil {
        cfg = new(Config)
    }
    setDefaults(cfg)

    // defer the call to setting back the original values
    defer func(debug, forceJit, enableJit bool) {
        vm.Debug = debug
        vm.ForceJit = forceJit
        vm.EnableJit = enableJit
    }(vm.Debug, vm.ForceJit, vm.EnableJit)

    vm.ForceJit = !cfg.DisableJit
    vm.EnableJit = !cfg.DisableJit
    vm.Debug = cfg.Debug

    var (
        db, _      = ethdb.NewMemDatabase()
        statedb, _ = state.New(common.Hash{}, db)
        vmenv      = NewEnv(cfg, statedb)
        sender     = statedb.CreateAccount(cfg.Origin)
        receiver   = statedb.CreateAccount(common.StringToAddress("contract"))
    )
    // set the receiver's (the executing contract) code for execution.
    receiver.SetCode(code)

    // Call the code with the given configuration.
    ret, err := vmenv.Call(
        sender,
        receiver.Address(),
        input,
        cfg.GasLimit,
        cfg.GasPrice,
        cfg.Value,
    )

    if cfg.Debug {
        vm.StdErrFormat(vmenv.StructLogs())
    }
    return ret, statedb, err
}