package iotest

import (
	"bytes"
	"errors"
	"fmt"
	"io"
)

// OneByteReader returns a Reader that implements
// each non-empty Read by reading one byte from r.
func OneByteReader(r io.Reader) io.Reader { return &oneByteReader{r} }

type oneByteReader struct {
	r io.Reader
}

func (r *oneByteReader) Read(p []byte) (int, error) {
	if len(p) == 0 {
		return 0, nil
	}
	return r.r.Read(p[0:1])
}

import (
	"bytes"
	"errors"
	"io"
	"strings"
	"testing"
)

func TestOneByteReader_nonEmptyReader(t *testing.T) {
	msg := "Hello, World!"
	buf := new(bytes.Buffer)
	buf.WriteString(msg)

	obr := OneByteReader(buf)
	var b []byte
	n, err := obr.Read(b)
	if err != nil || n != 0 {
		t.Errorf("Empty buffer read returned n=%d err=%v", n, err)
	}

	b = make([]byte, 3)
	// Read from obr until EOF.