package main

import (
	"fmt"
	"log"
	"strconv"
)

const (
	ClassControl uint8 = iota
	ClassReserved
	ClassDebug
	ClassReserved2
)

var (
	classStr map[uint8]string = map[uint8]string{
		ClassControl:   "Control",
		ClassReserved:  "Reserved (1)",
		ClassDebug:     "Debugging/Measurement",
		ClassReserved2: "Reserved (2)",
	}
)

const (
	/// This is the same type from examples/v4optspad.go.
	ip4OptTypBits string = "10010100" // [1001 0100], or 148 (0x94)
)

var (
	v4TypCpyOffset uint8 = 0x80             // 128
	v4TypCpyMask   uint8 = 0x01             // Mask to 1 bit
	v4TypCpyPos    uint8 = 8 - v4TypCpyMask // 7 or 0x07 (8 (bits) - mask = Shifted to 7th bit)

	v4TypClsOffset uint8 = 0x60 // 96
	v4TypClsMask   uint8 = 0x05 // mask to 5 bits
	v4TypClsPos    uint8 = 8 - v4TypClsMask

	v4TypNumOffset uint8 = 0x1f // 31
)

func ToV4OptTyp(copied, class, num uint8) (typ uint8) {

	typ = ((copied & v4TypCpyMask) << v4TypCpyPos) | ((class & v4TypClsMask) << v4TypClsPos) | (num & v4TypNumOffset)

	return
}

func FromV4OptTyp(typ uint8) (copied, class, num uint8) {

	copied = (typ & v4TypCpyOffset) >> v4TypCpyPos
	class = (typ & v4TypClsOffset) >> v4TypClsPos
	num = (typ & v4TypNumOffset)

	return
}

func main() {

	var err error
	var u64 uint64
	var typ uint8
	var cpd uint8
	var cls uint8
	var num uint8

	// Given a type of ip4OptTypBits (see const at top)...
	if u64, err = strconv.ParseUint(ip4OptTypBits, 2, 8); err != nil {
		log.Panicln(err)
	}
	typ = uint8(u64)
	// Prints:
	/*
		Type is:	148 (0x0094)
	*/
	fmt.Printf("Type is:\t%d (%#04x)\n", typ, typ)

	cpd, cls, num = FromV4OptTyp(typ)
	// Prints:
	/*
		Copied:		1 (0x0001)
		Class:		0 (0x0000)
		Number:		20 (0x0014)
	*/
	fmt.Printf(
		"Copied:\t\t%d %#04x)\n"+
			"Class:\t\t%d (%#04x)\n"+
			"Number:\t\t%d (%#04x)\n",
		cpd, cpd,
		cls, cls,
		num, num,
	)

	typ = ToV4OptTyp(cpd, cls, num)
	// Prints:
	/*
		Confirmed Type:	148 (0x94)
	*/
	fmt.Printf("Confirmed Type:\t%d (%#02x)\n\n", typ, typ)

	fmt.Println("Class Name:")
	// Prints:
	/*
		Control
	*/
	for c, cNm := range classStr {
		if c == cls {
			fmt.Println(cNm)
		}
	}
}