package rpc

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

type Decoder struct {
	mutex sync.Mutex
	r     io.Reader
	buf   bytes.Buffer
}

func NewDecoder(r io.Reader) *Decoder {
	if _, ok := r.(io.ByteReader); !ok {
		r = bufio.NewReader(r)
	}
	return &Decoder{
		r: r,
	}
}

func (dec *Decoder) Decode(vs Vars) error {
	h := make([]byte, 5)
	n, err := dec.r.Read(h)
	if n != 5 || err != nil {
		return errors.New(fmt.Sprintf(
			"Did not retrieve 5 bytes for the msg header, got %d bytes for %+v", n, h))
	}
	size, err := decodeHeader(h)
	if err != nil {
		return err
	}
	buf := make([]byte, size)

	n, err = dec.r.Read(buf)
	if n != size {
		return errors.New("MsgRpc::Wrong Byte length read")
	}

	vs.UnmarshalBinary(buf)

	return nil
}

func decodeHeader(h []byte) (l int, err error) {
	if h[0] != (h[1] ^ h[2] ^ h[3] ^ h[4]) {
		return -1, errors.New("MsgRpc::NotP4::MagicNumber")
	}
	l = int(h[1])*0x1 +
		int(h[2])*0x100 +
		int(h[3])*0x10000 +
		int(h[4])*0x1000000

		// Lengths < 11 are not enough for a func variable... bzzzz...
	if l < 11 || l >= 0x1fffffff {
		return -1, errors.New(fmt.Sprintf("MsgRpc::NotP4 %d", l))
	}
	return l, nil
}