package codec

import (
	"bufio"
	"io"
)

const DefaultFirstByte = 0xab

type XorEncoder struct {
	wr   io.Writer
	wb   *bufio.Writer
	last byte
}

func (x *XorEncoder) Write(p []byte) (n int, err error) {
	var next byte
	for _, v := range p {
		next = v ^ x.last
		x.last = next
		err = x.wb.WriteByte(next)
		if err != nil {
			return
		}
		n = n + 1
	}
	err = x.wb.Flush()
	return
}

func NewXorEncoder(wr io.Writer, first byte) *XorEncoder {
	return &XorEncoder{
		wr:   wr,
		wb:   bufio.NewWriter(wr),
		last: first,
	}
}

type XorDecoder struct {
	rd   io.Reader
	last byte
}

func (x *XorDecoder) Read(p []byte) (n int, err error) {
	n, err = x.rd.Read(p)
	if err != nil {
		return n, err
	}
	var next byte
	for idx := 0; idx < n; idx++ {
		next = p[idx]
		p[idx] ^= x.last
		x.last = next
	}
	return n, nil
}

func NewXorDecoder(rd io.Reader, first byte) *XorDecoder {
	return &XorDecoder{
		rd:   rd,
		last: first,
	}
}