type recommendation struct {
	p2s map[uint16]byte
	s2p map[byte]uint16
}

func apply(rec *recommendation, reader io.Reader) {
	symbolReader := iou.SizedReader(iou.ReaderFunc(func(output []byte) (int, error) {
		var i int = 0
		for ; i < len(output)-1; i++ {
			// Read a byte from the underlying reader
			count, err := reader.Read(output[i : i+1])

			// If we can't read anything else - return immediatelly
			if count == 0 {
				return i, err
			}

			// Convert the byte to a pair if there is a mapping for it
			if pair, ok := rec.s2p[output[i]]; ok {
				output[i] = byte(pair >> 8) // extract the high byte from the pair
				i++
				output[i] = byte(pair) // leave only the low byte from the pair
			}

			// Return on error
			if err != nil {
				return i + 1, err
			}
		}
		return i + 1, nil
	}), 2)

	pairReader := iou.ReaderFunc(func(output []byte) (int, error) {
		for i := 0; i < len(output); i++ {

		}
	})
}

func recommend(pairs pairSlice, symbols symbolSlice) *recommendation {
	var (
		rec         recommendation
		pairsLength = len(pairs)
	)

// An function alias type that implements io.Reader.
type ReaderFunc func([]byte) (int, error)

// Delegates the call to the WriterFunc while implementing io.Reader.
func (r ReaderFunc) Read(b []byte) (int, error) {
	return r(b)
}

// Reads a single byte from the provided io.Reader
func ReadByte(reader io.Reader) (byte, error) {
	var (
		arr [1]byte
		err error
	)
	_, err = reader.Read(arr[:])
	return arr[0], err
}

// Returns a writer that delegates calls to Write(...) while ensuring
// that it is never called with less bytes than the specified amount.
//
// Calls with fewer bytes are buffered while a call with a nil slice
// causes the buffer to be flushed to the underlying writer.
func SizedWriter(writer io.Writer, size int) io.Writer {

	// Diff the result against the initial input
	delta := diff.Diff(diff.D{len(input), len(output),
		func(i, j int) bool { return input[i] == output[j] }})
	if len(delta.Added) > 0 || len(delta.Removed) > 0 {
		t.Error("Differences detected ", delta)
	}
}

func TestReadByte(t *testing.T) {
	var (
		input  []byte        = []byte{255}
		reader *bytes.Reader = bytes.NewReader(input)
	)

	result, err := ReadByte(reader)
	if result != input[0] {
		t.Error("Unexpected read result from ReadByte", result)
	}
	if err != nil {
		t.Error("Unexpected error from ReadByte", err)
	}

	result, err = ReadByte(reader)
	if err != io.EOF {
		t.Error("Unexpected nil error from ReadByte, read value:", result)
	}
}

func TestSizedWriter(t *testing.T) {
	var (
		buffer bytes.Buffer
		writer io.Writer = SizedWriter(&buffer, 4)
	)