package util

import (
	"github.com/google/uuid"
	"math/rand" // not crypto secure
	"regexp"
	"strings"
)

const randHostnameCharset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-"
const randStringCharset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

var (
	// Up to 15 characters; only letters, digits, and hyphens (with hyphens not at the start or end).
	randHostnameRegex = regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9-]{0,14}[a-zA-Z0-9]$`)
)

func RandomHostname() (hostname string) {
	for {
		// between 2 and 10 characters
		if hostname = RandomStringFromCharset(randHostnameCharset, rand.Intn(8)+2); randHostnameRegex.MatchString(hostname) {
			return
		}
	}
}

func RandomWindowsTempFile() string {
	return `\Windows\Temp\` + strings.ToUpper(uuid.New().String())
}

func RandomString() string {
	return RandomStringFromCharset(randStringCharset, rand.Intn(10)+6)
}

func RandomStringFromCharset(charset string, length int) string {
	b := make([]byte, length)
	for i := range length {
		b[i] = charset[rand.Intn(len(charset))]
	}
	return string(b)
}