package intulid

import (
	"encoding/binary"
	"fmt"

	"github.com/oklog/ulid/v2"
	"golang.org/x/crypto/sha3"
)

type entropy []byte

func New(ms uint64, num int64, salt []byte) (ulid.ULID, error) {
	if len(salt) > 120 {
		return ulid.ULID{}, fmt.Errorf("salt len could not be longer than 120 bytes")
	}

	e := make(entropy, 8, 128)
	binary.LittleEndian.PutUint64(e[:8], uint64(num))
	e = append(e, salt...)

	return ulid.New(ms, e)
}

func (e entropy) Read(p []byte) (n int, err error) {
	sha3.ShakeSum256(p, e)
	return len(p), nil
}