/*
Copyright The ORAS Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package content

import (
	"io"

	"github.com/containerd/containerd/content"
)

// ensure interface
var (
	_ content.ReaderAt = sizeReaderAt{}
)

type readAtCloser interface {
	io.ReaderAt
	io.Closer
}

type sizeReaderAt struct {
	readAtCloser
	size int64
}

func (ra sizeReaderAt) Size() int64 {
	return ra.size
}

func NopCloserAt(r io.ReaderAt) nopCloserAt {
	return nopCloserAt{r}
}

type nopCloserAt struct {
	io.ReaderAt
}

func (n nopCloserAt) Close() error {
	return nil
}

// readerAtWrapper wraps a ReaderAt to give a Reader
type ReaderAtWrapper struct {
	offset   int64
	readerAt io.ReaderAt
}

func (r *ReaderAtWrapper) Read(p []byte) (n int, err error) {
	n, err = r.readerAt.ReadAt(p, r.offset)
	r.offset += int64(n)
	return
}

func NewReaderAtWrapper(readerAt io.ReaderAt) *ReaderAtWrapper {
	return &ReaderAtWrapper{readerAt: readerAt}
}