// Copyright 2023 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 directory

import (
	"errors"
	"fmt"

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

const (
	memoryPadLimit = 1024 * 1024
)

// GetMemoryCopyPadded returns offset + size as a new slice.
// It zero-pads the slice if it extends beyond memory bounds.
func GetMemoryCopyPadded(m *vm.Memory, offset, size int64) ([]byte, error) {
	if offset < 0 || size < 0 {
		return nil, errors.New("offset or size must not be negative")
	}
	if int(offset+size) < m.Len() { // slice fully inside memory
		return m.GetCopy(offset, size), nil
	}
	paddingNeeded := int(offset+size) - m.Len()
	if paddingNeeded > memoryPadLimit {
		return nil, fmt.Errorf("reached limit for padding memory slice: %d", paddingNeeded)
	}
	cpy := make([]byte, size)
	if overlap := int64(m.Len()) - offset; overlap > 0 {
		copy(cpy, m.GetPtr(offset, overlap))
	}
	return cpy, nil
}