package message

//rssp 协议中crc校验，查表法实现

// Crc16Table G(x)=X16+X11+X4+1，计算初始值为0
var crc16Table []uint32 = nil
var crc32C1Table []uint32 = nil
var crc32C2Table []uint32 = nil

const (
	RsspCrc16GX uint32 = 0b1_0000_1000_0001_0001 //生成多项式 G(X)=X16+X11+X4+1
	RsspCrc32C1 uint32 = 0x100d4e63              //安全通道1 CRC32生成多项式
	RsspCrc32C2 uint32 = 0x8ce56011              //安全通道1 CRC32生成多项式
)

func CreateRsspCrcTable() {
	if crc16Table == nil {
		var table = make([]uint32, 0, 256)
		for bt := 0x00; bt <= 0xff; bt++ {
			table = append(table, Lookup(uint32(bt), RsspCrc16GX, 16, false))
		}
		crc16Table = table
	}
	if crc32C1Table == nil {
		var table = make([]uint32, 0, 256)
		for bt := 0x00; bt <= 0xff; bt++ {
			table = append(table, Lookup(uint32(bt), RsspCrc32C1, 32, false))
		}
		crc32C1Table = table
	}
	if crc32C2Table == nil {
		var table = make([]uint32, 0, 256)
		for bt := 0x00; bt <= 0xff; bt++ {
			table = append(table, Lookup(uint32(bt), RsspCrc32C2, 32, false))
		}
		crc32C2Table = table
	}
}
func RsspCrc16(data []byte) uint16 {
	return uint16(CrcTableBased(data, 16, 0, false, false, 0, crc16Table))
}
func RsspC1Crc32(data []byte) uint32 {
	return CrcTableBased(data, 32, 0, false, false, 0, crc32C1Table)
}
func RsspC2Crc32(data []byte) uint32 {
	return CrcTableBased(data, 32, 0, false, false, 0, crc32C2Table)
}

/////////////////////////////////////////////////////////////////////////////

// 反转(0b00001010->0b01010000)
func reflect(data uint32, width int) uint32 {
	var register1 uint32 = 0
	var significant_mask uint32 = 0xffffffff >> (32 - width)
	var register_msb_mask uint32 = 1 << (width - 1)
	var register_lsb_mask uint32 = 1

	for i := 0; i < width; i++ {
		need_or := (data>>i)&register_lsb_mask == register_lsb_mask
		if need_or {
			register1 |= register_msb_mask >> i
		}
	}
	return register1 & significant_mask
}

// Lookup 计算单个数值的crc
func Lookup(data uint32,
	polynomial uint32,
	width int,
	input_reflected bool) uint32 {
	var register1 uint32 = 0
	var significant_mask uint32 = 0xffffffff >> (32 - width)
	var register_msb_mask uint32 = 1 << (width - 1)
	var register_lsb_mask uint32 = 1
	var byte_msb_mask uint32 = 0x80
	var byte_lsb_mask uint32 = 1

	if input_reflected {
		polynomial = reflect(polynomial, width)
	}

	for i := 0; i < 1+(width/8); i++ {
		var byteData uint32 = 0

		if i < 1 {
			byteData = data
		}

		for j := 0; j < 8; j++ {
			need_xor := false

			if input_reflected {
				need_xor = (register1 & register_lsb_mask) == register_lsb_mask
				register1 >>= 1

				need_or := (byteData & byte_lsb_mask) == byte_lsb_mask
				byteData >>= 1

				if need_or {
					register1 |= register_msb_mask
				}
			} else {
				need_xor = (register1 & register_msb_mask) == register_msb_mask
				register1 <<= 1

				need_or := (byteData & byte_msb_mask) == byte_msb_mask
				byteData <<= 1

				if need_or {
					register1 |= register_lsb_mask
				}
			}

			if need_xor {
				register1 ^= polynomial
			}
		}
	}
	return register1 & significant_mask
}

// CrcTableBased 查表法计算字节数组的crc
func CrcTableBased(
	data []byte,
	width int,
	initial_value uint32,
	input_reflected bool,
	result_reflected bool,
	final_xor_value uint32,
	table []uint32) uint32 {
	//
	length := len(data)
	var register1 uint32 = initial_value
	var significant_mask uint32 = 0xffffffff >> (32 - width)
	var register_lsb_mask uint32 = 0xff

	if input_reflected {
		register1 = reflect(register1, width)
	}

	for i := 0; i < length; i++ {
		var byteData = uint32(data[i])
		var shift_out uint32 = 0

		if input_reflected {
			shift_out = register1 & register_lsb_mask
			register1 = (register1 >> 8) ^ table[shift_out^byteData]
		} else {
			shift_out = (register1 >> (width - 8)) & register_lsb_mask
			register1 = (register1 << 8) ^ table[shift_out^byteData]
		}
	}

	if input_reflected != result_reflected {
		register1 = reflect(register1, width)
	}
	return (register1 ^ final_xor_value) & significant_mask
}

// MSB优先(字节中高位bit即最左侧bit优先)
func CrcBitOrientedMsbFirst(data []byte, polynomial uint32, width int) uint32 {
	var register1 uint32 = 0
	var significant_mask uint32 = 0xffffffff >> (32 - width)
	var register_msb_mask uint32 = 1 << (width - 1)
	var register_lsb_mask uint32 = 1
	var byte_msb_mask uint32 = 0x80
	length := len(data)

	for i := 0; i < length+(width/8); i++ {
		var byteData uint32 = 0
		if i < length {
			byteData = uint32(data[i])
		}
		for j := 0; j < 8; j++ {
			need_xor := (register1 & register_msb_mask) == register_msb_mask
			register1 <<= 1

			need_or := (byteData & byte_msb_mask) == byte_msb_mask
			byteData <<= 1

			if need_or {
				register1 |= register_lsb_mask
			}
			if need_xor {
				register1 ^= polynomial
			}
		}
	}
	return register1 & significant_mask
}
func Crc(data []byte,
	polynomial uint32,
	width int,
	initial_value uint32,
	input_reflected bool,
	result_reflected bool,
	final_xor_value uint32) uint32 {
	length := len(data)
	var register1 uint32 = initial_value
	var significant_mask uint32 = 0xffffffff >> (32 - width)
	var register_lsb_mask uint32 = 0xff

	if input_reflected {
		register1 = reflect(register1, width)
	}

	for i := 0; i < length; i++ {
		var byteData uint32 = uint32(data[i])
		var shift_out uint32 = 0
		var value uint32 = 0

		if input_reflected {
			shift_out = register1 & register_lsb_mask
			value = Lookup(shift_out^byteData, polynomial, width, input_reflected)
			register1 = (register1 >> 8) ^ value
		} else {
			shift_out = (register1 >> (width - 8)) & register_lsb_mask
			value = Lookup(shift_out^byteData, polynomial, width, input_reflected)
			register1 = (register1 << 8) ^ value
		}
	}

	if input_reflected != result_reflected {
		register1 = reflect(register1, width)
	}
	return (register1 ^ final_xor_value) & significant_mask
}