package coupon

import (
	"encoding/binary"
	"encoding/hex"
	"math/rand"
	"strings"
)

func DisolveCouponCode(code string) (round string, key string) {
	var final []byte
	for _, n := range strings.Split(code, "-") {
		nb, err := hex.DecodeString(n)
		if err != nil {
			// 형식 오류
			return "", ""
		}
		final = append(final, nb...)
	}

	if len(final) != 8 {
		// 형식 오류
		return "", ""
	}

	uid := final[4:]
	left := binary.BigEndian.Uint16(uid[0:2])
	right := binary.BigEndian.Uint16(uid[2:4])

	final = final[0:4]
	xor := binary.LittleEndian.Uint32(final)
	roundhashnum := xor ^ (uint32(left) * uint32(right))

	roundhash := make([]byte, 4)
	binary.BigEndian.PutUint32(roundhash, roundhashnum)

	round = hex.EncodeToString(roundhash)
	key = hex.EncodeToString(uid)

	return
}

func MakeCouponRoundHash(name string) (hash string, roundNumber uint32) {
	roundbt := make([]byte, 8)
	copy(roundbt, []byte(strings.ToLower(name)))

	roundseed := int64(binary.BigEndian.Uint64(roundbt))
	roundhash := make([]byte, 4)
	rand.New(rand.NewSource(roundseed)).Read(roundhash)
	roundNumber = binary.BigEndian.Uint32(roundhash)
	hash = hex.EncodeToString(roundhash)

	return
}