package algos

// getBit 获取指定位的值
func getBit(val uint64, pos int) uint64 {
	if val&(1<<pos) != 0 {
		return 1
	}
	return 0
}

// rotateLeft64 64位左循环移位
func rotateLeft64(v uint64, n int) uint64 {
	r := (v << n) | (v >> (64 - n))
	return r & 0xFFFFFFFFFFFFFFFF
}

// rotateRight64 64位右循环移位
func rotateRight64(v uint64, n int) uint64 {
	r := (v << (64 - n)) | (v >> n)
	return r & 0xFFFFFFFFFFFFFFFF
}

// keyExpansion 密钥扩展
func keyExpansion(key []uint64) []uint64 {
	expandedKey := make([]uint64, 72)
	copy(expandedKey, key[:4])

	var tmp uint64
	for i := 4; i < 72; i++ {
		tmp = rotateRight64(expandedKey[i-1], 3)
		tmp = tmp ^ expandedKey[i-3]
		tmp = tmp ^ rotateRight64(tmp, 1)
		expandedKey[i] = (^expandedKey[i-4]) ^ tmp ^ getBit(0x3DC94C3A046D678B, (i-4)%62) ^ 3
	}
	return expandedKey
}

// SimonEnc Simon加密
func SimonEnc(pt []uint64, k []uint64, c int) []uint64 {
	key := make([]uint64, 72)
	copy(key[:4], k[:4])
	key = keyExpansion(key)

	xi := pt[0]
	xi1 := pt[1]

	var tmp, f uint64
	for i := 0; i < 72; i++ {
		tmp = xi1
		if c == 1 {
			f = rotateLeft64(xi1, 1)
		} else {
			f = rotateLeft64(xi1, 1) & rotateLeft64(xi1, 8)
		}
		xi1 = xi ^ f ^ rotateLeft64(xi1, 2) ^ key[i]
		xi = tmp
	}

	return []uint64{xi, xi1}
}

// SimonDec Simon解密
func SimonDec(ct []uint64, k []uint64, c int) []uint64 {
	key := make([]uint64, 72)
	copy(key[:4], k[:4])
	key = keyExpansion(key)

	xi := ct[0]
	xi1 := ct[1]

	var tmp, f uint64
	for i := 71; i >= 0; i-- {
		tmp = xi
		if c == 1 {
			f = rotateLeft64(xi, 1)
		} else {
			f = rotateLeft64(xi, 1) & rotateLeft64(xi, 8)
		}
		xi = xi1 ^ f ^ rotateLeft64(xi, 2) ^ key[i]
		xi1 = tmp
	}

	return []uint64{xi, xi1}
}