main.go

package main

import (
	"crypto/rand"
	"encoding/binary"
	"fmt"
	"time"
)

const (
	randLen = 4
)

func main() {
	for i := 0; i < 10; i++ {
		id, _ := newID("UK")
		fmt.Println(id)
	}
}

type id struct {
	country    string
	timestsamp uint32
	random     []byte
}

func newID(country string) (i id, err error) {
	r, err := random(randLen)
	if err != nil {
		return
	}

	return id{
		country:    country,
		timestsamp: uint32(time.Now().UTC().Unix()),
		random:     r,
	}, nil
}

func (i id) String() string {
	bytes := make([]byte, 4+randLen)
	binary.BigEndian.PutUint32(bytes, i.timestsamp)
	copy(bytes[4:], i.random)

	return fmt.Sprintf("%s-%x-%x", i.country, bytes[:4], bytes[4:])
}

func random(l int) (b []byte, err error) {
	b = make([]byte, l)
	_, err = rand.Read(b)

	return
}