// Copyright 2017 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/>.

// Provides support for dealing with EVM assembly instructions (e.g., disassembling them).
package asm

import (
	"encoding/hex"
	"fmt"

	"github.com/ethereum/go-ethereum/core/vm"
)

// Apply function to each disassembled EVM instruction.
func ForEachDisassembledInstruction(script []byte, fun func(uint64, vm.OpCode, []byte)) error {
	for pc := uint64(0); pc < uint64(len(script)); pc++ {
		op := vm.OpCode(script[pc])
		if op.IsPush() {
			a := uint64(op) - uint64(vm.PUSH1) + 1
			u := pc + 1 + a
			if uint64(len(script)) <= pc || uint64(len(script)) < u {
				return fmt.Errorf("incomplete push instruction at %v", pc)
			}
			fun(pc, op, script[pc+1:u])
			pc += a
		} else {
			fun(pc, op, make([]byte, 0))
		}
	}
	return nil
}

// Pretty-print all disassembled EVM instructions to stdout.
func PrintDisassembled(code string) error {
	script, err := hex.DecodeString(code)
	if err != nil {
		return err
	}

	return ForEachDisassembledInstruction(script, func(pc uint64, op vm.OpCode, args []byte) {
		if args != nil && 0 < len(args) {
			fmt.Printf("%06v: %v 0x%x\n", pc, op, args)
		} else {
			fmt.Printf("%06v: %v\n", pc, op)
		}
	})
}

// Return all disassembled EVM instructions in human-readable format.
func Disassemble(script []byte) ([]string, error) {
	instrs := make([]string, 0)
	err := ForEachDisassembledInstruction(script, func(pc uint64, op vm.OpCode, args []byte) {
		if args != nil && 0 < len(args) {
			instrs = append(instrs, fmt.Sprintf("%06v: %v 0x%x\n", pc, op, args))
		} else {
			instrs = append(instrs, fmt.Sprintf("%06v: %v\n", pc, op))
		}
	})

	if err != nil {
		return nil, err
	}
	return instrs, nil
}