package buffer

import (
	"errors"
	"io"
	"slices"
)

type bytesReader struct {
	bs    []byte
	index int64
}

func newBytesReader(bs []byte) *bytesReader {
	return &bytesReader{bs: bs, index: 0}
}

// Read implements the io.Reader interface.
func (r *bytesReader) Read(b []byte) (n int, err error) {
	if r.index >= int64(len(r.bs)) {
		return 0, io.EOF
	}
	n = copy(b, r.bs[r.index:])
	r.index += int64(n)
	return
}

// Seek implements the io.Seeker interface.
func (r *bytesReader) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case io.SeekStart:
		r.index = offset
	case io.SeekCurrent:
		r.index += offset
	case io.SeekEnd:
		r.index = int64(len(r.bs)) + offset
	}
	return r.index, nil
}

// ReadAt implements the io.ReaderAt interface.
func (r *bytesReader) ReadAt(b []byte, offset int64) (n int, err error) {
	if offset < 0 {
		return 0, errors.New("buffer.bytesReader.ReadAt: negative offset")
	}
	if offset >= int64(len(r.bs)) {
		return 0, io.EOF
	}
	n = copy(b, r.bs[offset:])
	if n < len(b) {
		err = io.EOF
	}
	return
}

func (r *bytesReader) insert(offset int64, b byte) {
	r.bs = slices.Insert(r.bs, int(offset), b)
}

func (r *bytesReader) delete(offset int64) {
	r.bs = slices.Delete(r.bs, int(offset), int(offset+1))
}

func (r *bytesReader) clone() *bytesReader {
	return newBytesReader(slices.Clone(r.bs))
}