package totpT

import (
	"crypto/hmac"
	"crypto/sha512"
	"encoding/binary"
	"errors"
	"hash"
	"math"
	"math/rand"
	"strconv"
	"time"
	
	"gitee.com/Jiudan0905/go-tools/logT"
)

func HOTP(h func() hash.Hash, key []byte, count uint64, digits int) (string, error) {
	if digits < 1 {
		return "", errors.New("数字值必须大于 0, 建议至少为 6 位数字的值")
	}
	hash := hmacGenerator(h, key, count)
	offset := hash[len(hash)-1] & 0xf
	dbc := hash[offset : offset+4]
	dbc[0] = dbc[0] & 0x7f
	code := binary.BigEndian.Uint32(dbc)
	otp := code % uint32(math.Pow10(digits))
	value := strconv.Itoa(int(otp))
	for i := 0; i < digits-len(value); i++ {
		value = "0" + value
	}
	return value, nil
}

func TOTP(h func() hash.Hash, secret []byte, t time.Time, interval int, digits int) (string, error) {
	if interval < 1 {
		return "", errors.New("间隔值必须大于 0, 建议默认为 30")
	}
	count := numTimeSteps(t, interval, 0)
	return HOTP(h, secret, count, digits)
}

// GenTotpToken 获取数字密钥
func GenTotpToken(secret string) (string, error) {
	ti := time.Now().Unix()
	t := time.Unix(ti, 0)
	totp, err := TOTP(func() hash.Hash {
		return sha512.New()
	}, []byte(secret), t, 30, 7)
	if err != nil {
		logT.Error(err.Error())
		return "", err
	}
	totp64, err := strconv.ParseInt(totp, 10, 64)
	if err != nil {
		logT.Error(err.Error())
	}
	return GenRandomToken(totp64), nil
}

// GenRandomToken 获取加密密钥
func GenRandomToken(totp int64) string {
	token := make([]byte, 6)
	LetterBytes := "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
	rand.Seed(totp)
	for i := range token {
		token[i] = LetterBytes[rand.Intn(len(LetterBytes))]
	}
	return string(token)
}

// GetTotpToken 忽略错误，直接获取token
func GetTotpToken(secret string) string {
	token, err := GenTotpToken(secret)
	if err != nil {
		logT.Error(err.Error())
		return "ERROR-TOKEN"
	}
	return token
}

// VerifyTotpToken 验证token
func VerifyTotpToken(secret string, token string) (ok bool) {
	// 验证Token是否正确
	realToken := GetTotpToken(secret)
	if token != realToken {
		return false
	}
	return true
}

// numTimeSteps 初始计数器时间 T0 和当前 Unix 时间之间的时间步长数
func numTimeSteps(t time.Time, interval int, t0 int64) uint64 {
	return uint64(math.Floor(float64(t.Unix()-t0) / float64(interval)))
}

// hmacGenerator 使用指定的算法生成密钥和计数的 HMAC。
func hmacGenerator(h func() hash.Hash, key []byte, count uint64) []byte {
	mac := hmac.New(h, key)
	buf := make([]byte, 8)
	binary.BigEndian.PutUint64(buf, count)
	mac.Write(buf)
	return mac.Sum(nil)
}