package t

import (
	"encoding/binary"
)

type digest struct {
	h   [5]uint32
	x   [chunk]byte
	nx  int
	len uint64
}

const (
	chunk         = 64
	magic         = "sha\x01"
	marshaledSize = len(magic) + 5*4 + chunk + 8
)

func (d *digest) MarshalBinary() ([]byte, error) {
	b := make([]byte, 0, marshaledSize)
	b = append(b, magic...)
	b = binary.BigEndian.AppendUint32(b, d.h[0])
	b = binary.BigEndian.AppendUint32(b, d.h[1])
	b = binary.BigEndian.AppendUint32(b, d.h[2])
	b = binary.BigEndian.AppendUint32(b, d.h[3])
	b = binary.BigEndian.AppendUint32(b, d.h[4])
	b = append(b, d.x[:d.nx]...)
	b = b[:len(b)+len(d.x)-d.nx] // already zero
	b = binary.BigEndian.AppendUint64(b, d.len)
	return b, nil
}