package shell

func isGBK(data []byte) bool {
	length := len(data)
	var i int = 0
	for i < length {
		if data[i] <= 0x7f {
			i++
			continue
		} else {
			if data[i] >= 0x81 &&
				data[i] <= 0xfe &&
				data[i+1] >= 0x40 &&
				data[i+1] <= 0xfe &&
				data[i+1] != 0xf7 {
				i += 2
				continue
			} else {
				return false
			}
		}
	}
	return true
}

func preNUm(data byte) int {
	var mask byte = 0x80
	var num int = 0
	for i := 0; i < 8; i++ {
		if (data & mask) == mask {
			num++
			mask = mask >> 1
		} else {
			break
		}
	}
	return num
}

func isUtf8(data []byte) bool {
	i := 0
	for i < len(data) {
		if (data[i] & 0x80) == 0x00 {
			i++
			continue
		} else if num := preNUm(data[i]); num > 2 {
			i++
			for j := 0; j < num-1; j++ {
				if (data[i] & 0xc0) != 0x80 {
					return false
				}
				i++
			}
		} else {
			return false
		}
	}
	return true
}