// 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"
	"sync/atomic"

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

// Config are the configuration options for the Interpreter
// 解释器配置类
type Config struct {
	// Debug enabled debugging Interpreter options
	// 启用调试
	Debug bool
	// Tracer is the op code logger
	// 操作码记录器
	Tracer Tracer
	// NoRecursion disabled Interpreter call, callcode,
	// delegate call and create.
	// 禁用解释器调用，代码库调用，委托调用
	NoRecursion bool
	// Enable recording of SHA3/keccak preimages
	// 启用SHA3/keccak
	EnablePreimageRecording bool
	// JumpTable contains the EVM instruction table. This
	// may be left uninitialised and will be set to the default
	// table.
	// 操作码opcode对应的操作表
	JumpTable [256]operation
}

// Interpreter is used to run Ethereum based contracts and will utilise the
// passed environment to query external sources for state information.
// The Interpreter will run the byte code VM based on the passed
// configuration.
// 用来运行智能合约的字节码
type Interpreter struct {
	evm      *EVM
	// 解释器配置
	cfg      Config
	// gas价格表，根据不同的以太坊阶段来决定
	gasTable params.GasTable
	intPool  *intPool

	readOnly   bool   // Whether to throw on stateful modifications
	// 最后一个call调用的返回值
	returnData []byte // Last CALL's return data for subsequent reuse
}

// NewInterpreter returns a new instance of the Interpreter.
// 3.创建解释器
func NewInterpreter(evm *EVM, cfg Config) *Interpreter {
	// We use the STOP instruction whether to see
	// the jump table was initialised. If it was not
	// we'll set the default jump table.
	if !cfg.JumpTable[STOP].valid {
		switch {
		case evm.ChainConfig().IsConstantinople(evm.BlockNumber):
			cfg.JumpTable = constantinopleInstructionSet
		case evm.ChainConfig().IsByzantium(evm.BlockNumber):
			cfg.JumpTable = byzantiumInstructionSet
		case evm.ChainConfig().IsHomestead(evm.BlockNumber):
			cfg.JumpTable = homesteadInstructionSet
		default:
			cfg.JumpTable = frontierInstructionSet
		}
	}

	return &Interpreter{
		evm:      evm,
		cfg:      cfg,
		gasTable: evm.ChainConfig().GasTable(evm.BlockNumber),
	}
}

func (in *Interpreter) enforceRestrictions(op OpCode, operation operation, stack *Stack) error {
	if in.evm.chainRules.IsByzantium {
		if in.readOnly {
			// If the interpreter is operating in readonly mode, make sure no
			// state-modifying operation is performed. The 3rd stack item
			// for a call operation is the value. Transferring value from one
			// account to the others means the state is modified and should also
			// return with an error.
			if operation.writes || (op == CALL && stack.Back(2).BitLen() > 0) {
				return errWriteProtection
			}
		}
	}
	return nil
}

// Run loops and evaluates the contract's code with the given input data and returns
// the return byte-slice and an error if one occurred.
//
// It's important to note that any errors returned by the interpreter should be
// considered a revert-and-consume-all-gas operation except for
// errExecutionReverted which means revert-and-keep-gas-left.
// 执行合约代码
func (in *Interpreter) Run(contract *Contract, input []byte) (ret []byte, err error) {
	if in.intPool == nil {
		in.intPool = poolOfIntPools.get()
		defer func() {
			poolOfIntPools.put(in.intPool)
			in.intPool = nil
		}()
	}

	// Increment the call depth which is restricted to 1024
	// 调用深度递增，evm执行栈的深度不能超过1024
	in.evm.depth++
	defer func() { in.evm.depth-- }()

	// Reset the previous call's return data. It's unimportant to preserve the old buffer
	// as every returning call will return new data anyway.
	// 重置上一个call的返回数据
	in.returnData = nil

	// Don't bother with the execution if there's no code.
	// 合约代码为空
	if len(contract.Code) == 0 {
		return nil, nil
	}

	var (
		op    OpCode        // current opcode
		mem   = NewMemory() // bound memory
		stack = newstack()  // local stack
		// For optimisation reason we're using uint64 as the program counter.
		// It's theoretically possible to go above 2^64. The YP defines the PC
		// to be uint256. Practically much less so feasible.
		pc   = uint64(0) // program counter
		cost uint64
		// copies used by tracer
		pcCopy  uint64 // needed for the deferred Tracer
		gasCopy uint64 // for Tracer to log gas remaining before execution
		logged  bool   // deferred Tracer should ignore already logged steps
	)
	contract.Input = input

	// Reclaim the stack as an int pool when the execution stops
	// 执行停止时将栈回收为int值缓存池
	defer func() { in.intPool.put(stack.data...) }()

	if in.cfg.Debug {
		defer func() {
			if err != nil {
				if !logged {
					in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
				} else {
					in.cfg.Tracer.CaptureFault(in.evm, pcCopy, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
				}
			}
		}()
	}
	// The Interpreter main run loop (contextual). This loop runs until either an
	// explicit STOP, RETURN or SELFDESTRUCT is executed, an error occurred during
	// the execution of one of the operations or until the done flag is set by the
	// parent context.
	// 解释器主循环，循环运行直到执行显式STOP，RETURN或SELFDESTRUCT，发生错误
	for atomic.LoadInt32(&in.evm.abort) == 0 {
		if in.cfg.Debug {
			// Capture pre-execution values for tracing.
			// 捕获预执行的值进行跟踪
			logged, pcCopy, gasCopy = false, pc, contract.Gas
		}

		// Get the operation from the jump table and validate the stack to ensure there are
		// enough stack items available to perform the operation.
		// 从合约的二进制数据i获取第pc个opcode操作符 opcode是以太坊虚拟机指令，一共不超过256个，正好一个byte大小能装下
		op = contract.GetOp(pc)
		// 从JumpTable表中查询op对应的操作
		operation := in.cfg.JumpTable[op]
		if !operation.valid {
			return nil, fmt.Errorf("invalid opcode 0x%x", int(op))
		}
		if err := operation.validateStack(stack); err != nil {
			return nil, err
		}
		// If the operation is valid, enforce and write restrictions
		// 操作有效，强制执行
		if err := in.enforceRestrictions(op, operation, stack); err != nil {
			return nil, err
		}

		var memorySize uint64
		// calculate the new memory size and expand the memory to fit
		// the operation
		// 计算新的内存大小以适应操作，必要时进行扩容
		if operation.memorySize != nil {
			// memSize不能大于64位
			memSize, overflow := bigUint64(operation.memorySize(stack))
			if overflow {
				return nil, errGasUintOverflow
			}
			// memory is expanded in words of 32 bytes. Gas
			// is also calculated in words.
			// 扩容按32字节的字扩展
			if memorySize, overflow = math.SafeMul(toWordSize(memSize), 32); overflow {
				return nil, errGasUintOverflow
			}
		}
		// consume the gas and return an error if not enough gas is available.
		// cost is explicitly set so that the capture state defer method can get the proper cost
		// 计算执行操作所需要的gas
		cost, err = operation.gasCost(in.gasTable, in.evm, contract, stack, mem, memorySize)
		// gas不足
		if err != nil || !contract.UseGas(cost) {
			return nil, ErrOutOfGas
		}
		if memorySize > 0 {
			mem.Resize(memorySize)
		}

		if in.cfg.Debug {
			in.cfg.Tracer.CaptureState(in.evm, pc, op, gasCopy, cost, mem, stack, contract, in.evm.depth, err)
			logged = true
		}

		// execute the operation
		// 执行操作
		res, err := operation.execute(&pc, in.evm, contract, mem, stack)
		// verifyPool is a build flag. Pool verification makes sure the integrity
		// of the integer pool by comparing values to a default value.
		// 验证int值缓存池
		if verifyPool {
			verifyIntegerPool(in.intPool)
		}
		// if the operation clears the return data (e.g. it has returning data)
		// set the last return to the result of the operation.
		// 将最后一次返回设为操作结果
		if operation.returns {
			in.returnData = res
		}

		switch {
		case err != nil:
			return nil, err
		case operation.reverts:
			return res, errExecutionReverted
		case operation.halts:
			return res, nil
		case !operation.jumps:
			pc++
		}
	}
	return nil, nil
}
