package main

import (
	"flag"
	"fmt"
	"math/rand/v2"
	"strings"
)

func main() {
	onlyNum := flag.Bool("num", false, "generate only numbers (no formatting)")
	flag.Parse()

	cpf := generateCPF()

	if *onlyNum {
		fmt.Println(cpf)
	} else {
		fmt.Printf("%s.%s.%s-%s\n", cpf[:3], cpf[3:6], cpf[6:9], cpf[9:])
	}
}

func generateCPF() string {
	digits := make([]int, 11)

	for i := range 9 {
		digits[i] = rand.IntN(10)
	}

	sum := 0
	for i := range 9 {
		sum += digits[i] * (10 - i)
	}
	rem := sum % 11
	if rem < 2 {
		digits[9] = 0
	} else {
		digits[9] = 11 - rem
	}

	sum = 0
	for i := range 10 {
		sum += digits[i] * (11 - i)
	}
	rem = sum % 11
	if rem < 2 {
		digits[10] = 0
	} else {
		digits[10] = 11 - rem
	}

	var result strings.Builder
	for _, d := range digits {
		fmt.Fprintf(&result, "%d", d)
	}
	return result.String()
}