package netstring

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

type Encoder struct {
	w io.Writer
}

type Decoder struct {
	r io.Reader
}

var errBadFormat = errors.New("netstring: bad format")

func NewEncoder(w io.Writer) *Encoder {
	return &Encoder{w: w}
}

func NewDecoder(r io.Reader) *Decoder {
	return &Decoder{r: r}
}

func (e *Encoder) Encode(s string) error {
	_, err := fmt.Fprintf(e.w, "%d:%s,", len(s), s)
	return err
}

func (d *Decoder) Decode() (out string, err error) {
	var n int

	_, err = fmt.Fscanf(d.r, "%d:", &n)
	if err != nil {
		return
	}

	buf := make([]byte, n + 1)

	_, err = io.ReadFull(d.r, buf)
	if err != nil {
		if err == io.EOF {
			err = io.ErrUnexpectedEOF
		}
		return
	}

	if buf[n] != ',' {
		return "", errBadFormat
	}

	return string(buf[:n]), nil
}