// license that can be found in the LICENSE file.

package bytes

import (
	"errors"
	"io"
	"unicode/utf8"
)

// A Reader implements the [io.Reader], [io.ReaderAt], [io.WriterTo], [io.Seeker],
// [io.ByteScanner], and [io.RuneScanner] interfaces by reading from
// a byte slice.
// Unlike a [Buffer], a Reader is read-only and supports seeking.

	var buf strings.Builder
	buf.Grow(n)
	// Copy full pieces and fragment in.
	for _, fb := range full {
		buf.Write(fb)
	}
	buf.Write(frag)
	return buf.String(), err
}

// WriteTo implements io.WriterTo.
// This may make multiple calls to the [Reader.Read] method of the underlying [Reader].
// If the underlying reader supports the [Reader.WriteTo] method,
// this calls the underlying [Reader.WriteTo] without buffering.

	return b2[:i]
}

// WriteTo writes data to w until the buffer is drained or an error occurs.
// The return value n is the number of bytes written; it always fits into an
// int, but it is int64 to match the [io.WriterTo] interface. Any error
// encountered during the write is also returned.
func (b *Buffer) WriteTo(w io.Writer) (n int64, err error) {
	b.lastRead = opInvalid
	if nBytes := b.Len(); nBytes > 0 {

		t.Fatalf("Buffered = %v; want %v", buffered, wantBuffered)
	}
}

func BenchmarkReaderCopyOptimal(b *testing.B) {
	// Optimal case is where the underlying reader implements io.WriterTo
	srcBuf := bytes.NewBuffer(make([]byte, 8192))
	src := NewReader(srcBuf)
	dstBuf := new(bytes.Buffer)
	dst := onlyWriter{dstBuf}
	for i := 0; i < b.N; i++ {
		srcBuf.Reset()
		src.Reset(srcBuf)