package godis

var lookupTable = []uint16{0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5,
	0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231,
	0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A,
	0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4,
	0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672,
	0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF,
	0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
	0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7,
	0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58,
	0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE,
	0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4,
	0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59,
	0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1,
	0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D,
	0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
	0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0,
	0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E,
	0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634, 0xD94C,
	0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827,
	0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB,
	0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F,
	0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2,
	0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
	0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0}

// CRC16 Implementation according to CCITT standard Polynomial : 1021 (x^16 + x^12 + x^5 + 1) See <a
// href="http://redis.io/topics/cluster-spec">Appendix A. CRC16 reference implementation in ANSIC</a>
type crc16 struct {
	tagUtil *redisClusterHashTagUtil
}

//new construct
func newCRC16() *crc16 {
	return &crc16{tagUtil: newRedisClusterHashTagUtil()}
}

func (c *crc16) getStringSlot(key string) uint16 {
	key = c.tagUtil.getHashTag(key)
	// optimization with modulo operator with power of 2
	// equivalent to getCRC16(key) % 16384
	return c.getStringCRC16(key) & (16384 - 1)
}

func (c *crc16) getByteSlot(key []byte) uint16 {
	s := -1
	e := -1
	sFound := false
	for i := 0; i < len(key); i++ {
		if key[i] == '{' && !sFound {
			s = i
			sFound = true
		}
		if key[i] == '}' && sFound {
			e = i
			break
		}
	}
	if s > -1 && e > -1 && e != s+1 {
		return c.getCRC16(key, s+1, e) & (16384 - 1)
	}
	return c.getBytesCRC16(key) & (16384 - 1)
}

func (c *crc16) getCRC16(bytes []byte, s, e int) uint16 {
	var crc uint16 = 0x0000
	for i := s; i < e; i++ {
		crc = (crc << uint16(8)) ^ lookupTable[((crc>>uint16(8))^uint16(bytes[i]))&0x00FF]
	}
	return crc
}

func (c *crc16) getBytesCRC16(bytes []byte) uint16 {
	return c.getCRC16(bytes, 0, len(bytes))
}

func (c *crc16) getStringCRC16(key string) uint16 {
	bytesKey := []byte(key)
	return c.getCRC16(bytesKey, 0, len(bytesKey))
}