// 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 vm

import (
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/params"
)

type (
    CanTransferFunc func(StateDB, common.Address, *big.Int) bool
    TransferFunc    func(StateDB, common.Address, common.Address, *big.Int)
    // GetHashFunc returns the nth block hash in the blockchain
    // and is used by the BLOCKHASH EVM op code.
    GetHashFunc func(uint64) common.Hash
)

// Context provides the EVM with auxilary information. Once provided it shouldn't be modified.
type Context struct {
    // CanTransfer returns whether the account contains
    // sufficient ether to transfer the value
    CanTransfer CanTransferFunc
    // Transfer transfers ether from one account to the other
    Transfer TransferFunc
    // GetHash returns the hash corresponding to n
    GetHash GetHashFunc

    // Message information
    Origin   common.Address // Provides information for ORIGIN
    GasPrice *big.Int       // Provides information for GASPRICE

    // Block information
    Coinbase    common.Address // Provides information for COINBASE
    GasLimit    *big.Int       // Provides information for GASLIMIT
    BlockNumber *big.Int       // Provides information for NUMBER
    Time        *big.Int       // Provides information for TIME
    Difficulty  *big.Int       // Provides information for DIFFICULTY
}

// Environment provides information about external sources for the EVM
//
// The Environment should never be reused and is not thread safe.
type Environment struct {
    // Context provides auxiliary blockchain related information
    Context
    // StateDB gives access to the underlying state
    StateDB StateDB
    // Depth is the current call stack
    Depth int

    // evm is the ethereum virtual machine
    evm Vm
    // chainConfig contains information about the current chain
    chainConfig *params.ChainConfig
    vmConfig    Config
}

// NewEnvironment retutrns a new EVM environment.
func NewEnvironment(context Context, statedb StateDB, chainConfig *params.ChainConfig, vmConfig Config) *Environment {
    env := &Environment{
        Context:     context,
        StateDB:     statedb,
        vmConfig:    vmConfig,
        chainConfig: chainConfig,
    }
    env.evm = New(env, vmConfig)
    return env
}

// Call executes the contract associated with the addr with the given input as paramaters. It also handles any
// necessary value transfer required and takes the necessary steps to create accounts and reverses the state in
// case of an execution error or failed value transfer.
func (env *Environment) Call(caller ContractRef, addr common.Address, input []byte, gas, value *big.Int) ([]byte, error) {
    if env.vmConfig.NoRecursion && env.Depth > 0 {
        caller.ReturnGas(gas)

        return nil, nil
    }

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

        return nil, DepthError
    }
    if !env.Context.CanTransfer(env.StateDB, caller.Address(), value) {
        caller.ReturnGas(gas)

        return nil, ErrInsufficientBalance
    }

    var (
        to                  Account
        snapshotPreTransfer = env.StateDB.Snapshot()
    )
    if !env.StateDB.Exist(addr) {
        if Precompiled[addr.Str()] == nil && env.ChainConfig().IsEIP158(env.BlockNumber) && value.BitLen() == 0 {
            caller.ReturnGas(gas)
            return nil, nil
        }

        to = env.StateDB.CreateAccount(addr)
    } else {
        to = env.StateDB.GetAccount(addr)
    }
    env.Transfer(env.StateDB, caller.Address(), to.Address(), value)

    // initialise a new contract and set the code that is to be used by the
    // E The contract is a scoped environment for this execution context
    // only.
    contract := NewContract(caller, to, value, gas)
    contract.SetCallCode(&addr, env.StateDB.GetCodeHash(addr), env.StateDB.GetCode(addr))
    defer contract.Finalise()

    ret, err := env.EVM().Run(contract, input)
    // When an error was returned by the EVM or when setting the creation code
    // above we revert to the snapshot and consume any gas remaining. Additionally
    // when we're in homestead this also counts for code storage gas errors.
    if err != nil {
        contract.UseGas(contract.Gas)

        env.StateDB.RevertToSnapshot(snapshotPreTransfer)
    }
    return ret, err
}

// CallCode executes the contract associated with the addr with the given input as paramaters. It also handles any
// necessary value transfer required and takes the necessary steps to create accounts and reverses the state in
// case of an execution error or failed value transfer.
//
// CallCode differs from Call in the sense that it executes the given address' code with the caller as context.
func (env *Environment) CallCode(caller ContractRef, addr common.Address, input []byte, gas, value *big.Int) ([]byte, error) {
    if env.vmConfig.NoRecursion && env.Depth > 0 {
        caller.ReturnGas(gas)

        return nil, nil
    }

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

        return nil, DepthError
    }
    if !env.CanTransfer(env.StateDB, caller.Address(), value) {
        caller.ReturnGas(gas)

        return nil, fmt.Errorf("insufficient funds to transfer value. Req %v, has %v", value, env.StateDB.GetBalance(caller.Address()))
    }

    var (
        snapshotPreTransfer = env.StateDB.Snapshot()
        to                  = env.StateDB.GetAccount(caller.Address())
    )
    // initialise a new contract and set the code that is to be used by the
    // E The contract is a scoped environment for this execution context
    // only.
    contract := NewContract(caller, to, value, gas)
    contract.SetCallCode(&addr, env.StateDB.GetCodeHash(addr), env.StateDB.GetCode(addr))
    defer contract.Finalise()

    ret, err := env.EVM().Run(contract, input)
    if err != nil {
        contract.UseGas(contract.Gas)

        env.StateDB.RevertToSnapshot(snapshotPreTransfer)
    }

    return ret, err
}

// DelegateCall executes the contract associated with the addr with the given input as paramaters.
// It reverses the state in case of an execution error.
//
// DelegateCall differs from CallCode in the sense that it executes the given address' code with the caller as context
// and the caller is set to the caller of the caller.
func (env *Environment) DelegateCall(caller ContractRef, addr common.Address, input []byte, gas *big.Int) ([]byte, error) {
    if env.vmConfig.NoRecursion && env.Depth > 0 {
        caller.ReturnGas(gas)

        return nil, nil
    }

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

    var (
        snapshot = env.StateDB.Snapshot()
        to       = env.StateDB.GetAccount(caller.Address())
    )

    // Iinitialise a new contract and make initialise the delegate values
    contract := NewContract(caller, to, caller.Value(), gas).AsDelegate()
    contract.SetCallCode(&addr, env.StateDB.GetCodeHash(addr), env.StateDB.GetCode(addr))
    defer contract.Finalise()

    ret, err := env.EVM().Run(contract, input)
    if err != nil {
        contract.UseGas(contract.Gas)

        env.StateDB.RevertToSnapshot(snapshot)
    }

    return ret, err
}

// Create creates a new contract using code as deployment code.
func (env *Environment) Create(caller ContractRef, code []byte, gas, value *big.Int) ([]byte, common.Address, error) {
    if env.vmConfig.NoRecursion && env.Depth > 0 {
        caller.ReturnGas(gas)

        return nil, common.Address{}, nil
    }

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

        return nil, common.Address{}, DepthError
    }
    if !env.CanTransfer(env.StateDB, caller.Address(), value) {
        caller.ReturnGas(gas)

        return nil, common.Address{}, ErrInsufficientBalance
    }

    // Create a new account on the state
    nonce := env.StateDB.GetNonce(caller.Address())
    env.StateDB.SetNonce(caller.Address(), nonce+1)

    snapshotPreTransfer := env.StateDB.Snapshot()
    var (
        addr = crypto.CreateAddress(caller.Address(), nonce)
        to   = env.StateDB.CreateAccount(addr)
    )
    if env.ChainConfig().IsEIP158(env.BlockNumber) {
        env.StateDB.SetNonce(addr, 1)
    }
    env.Transfer(env.StateDB, caller.Address(), to.Address(), value)

    // initialise a new contract and set the code that is to be used by the
    // E The contract is a scoped environment for this execution context
    // only.
    contract := NewContract(caller, to, value, gas)
    contract.SetCallCode(&addr, crypto.Keccak256Hash(code), code)
    defer contract.Finalise()

    ret, err := env.EVM().Run(contract, nil)
    // check whether the max code size has been exceeded
    maxCodeSizeExceeded := len(ret) > params.MaxCodeSize
    // if the contract creation ran successfully and no errors were returned
    // calculate the gas required to store the code. If the code could not
    // be stored due to not enough gas set an error and let it be handled
    // by the error checking condition below.
    if err == nil && !maxCodeSizeExceeded {
        dataGas := big.NewInt(int64(len(ret)))
        dataGas.Mul(dataGas, params.CreateDataGas)
        if contract.UseGas(dataGas) {
            env.StateDB.SetCode(addr, ret)
        } else {
            err = CodeStoreOutOfGasError
        }
    }

    // When an error was returned by the EVM or when setting the creation code
    // above we revert to the snapshot and consume any gas remaining. Additionally
    // when we're in homestead this also counts for code storage gas errors.
    if maxCodeSizeExceeded ||
        (err != nil && (env.ChainConfig().IsHomestead(env.BlockNumber) || err != CodeStoreOutOfGasError)) {
        contract.UseGas(contract.Gas)
        env.StateDB.RevertToSnapshot(snapshotPreTransfer)

        // Nothing should be returned when an error is thrown.
        return nil, addr, err
    }
    // If the vm returned with an error the return value should be set to nil.
    // This isn't consensus critical but merely to for behaviour reasons such as
    // tests, RPC calls, etc.
    if err != nil {
        ret = nil
    }

    return ret, addr, err
}

// ChainConfig returns the environment's chain configuration
func (env *Environment) ChainConfig() *params.ChainConfig { return env.chainConfig }

// EVM returns the environments EVM
func (env *Environment) EVM() Vm { return env.evm }