package sign

import "time"

func GetACSignature(oneSite, oneNonce, uaN string, oneTimeStamp int64) string {
	if oneTimeStamp == 0 {
		oneTimeStamp = time.Now().Unix()
	}

	calOneStr := func(s string, iv int) int {
		k := iv
		for _, ch := range s {
			k = int(((k ^ int(ch)) * 65599) & 0xFFFFFFFF)
		}
		return k
	}

	calOneStr3 := func(s string, iv int) int {
		k := iv
		for _, ch := range s {
			k = int((int64(k)*65599 + int64(ch)) & 0xFFFFFFFF)
		}
		return k
	}

	getOneChr := func(code int) string {
		code &= 0x3F
		if code < 26 {
			return string(rune('A' + code))
		} else if code < 52 {
			return string(rune('a' + code - 26))
		} else if code < 62 {
			return string(rune('0' + code - 52))
		} else if code == 62 {
			return "+"
		}
		return "/"
	}

	encNumToStr := func(val uint32) string {
		var s string
		for i := 24; i >= 0; i -= 6 {
			s += getOneChr(int((val >> uint(i)) & 0x3F))
		}
		return s
	}

	signHead := "_02B4Z6wo00f01"
	timeStampS := itoa(oneTimeStamp)

	a := calOneStr(oneSite, calOneStr(timeStampS, 0)) % 65521

	xorVal := uint32(oneTimeStamp) ^ uint32(a*65521)
	b := uint64(0x80F0) << 32 | uint64(xorVal)
	bStr := itoa(int64(b))

	c := calOneStr(bStr, 0)

	d := encNumToStr(uint32(b >> 2))
	e := uint32((b >> 32) & 0xFFFFFFFF)
	f := encNumToStr(uint32((b << 28) | (uint64(e) >> 4)))
	g := uint32(0x22AA7A58) ^ uint32(b&0xFFFFFFFF)
	h := encNumToStr(uint32((e << 26) | (g >> 6)))
	i := getOneChr(int(g & 0x3F))

	j := (uint32(calOneStr(uaN, c)%65521) << 16) | uint32(calOneStr(oneNonce, c)%65521)
	k := encNumToStr(j >> 2)
	l := encNumToStr(uint32((j << 28) | ((0x8000 ^ uint32(b&0xFFFFFFFF)) >> 4)))
	m := encNumToStr(uint32(a))

	n := signHead + d + f + h + i + k + l + m

	oHex := itoa(int64(calOneStr3(n, 0)))
	if len(oHex) < 2 {
		oHex = "00"
	}
	o := oHex[len(oHex)-2:]

	return n + o
}

func itoa(v int64) string {
	if v == 0 {
		return "0"
	}
	var digits []byte
	n := v
	if n < 0 {
		n = -n
	}
	for n > 0 {
		digits = append([]byte{byte('0' + n%10)}, digits...)
		n /= 10
	}
	return string(digits)
}