package main

import (
	"flag"
	"fmt"
	"log"
	"os"
)

const (
	defaultLimit  = 1_000_000_000
	defaultOutput = "primes.txt"
)

func main() {
	limit := flag.Int("n", defaultLimit, "upper limit, inclusive, to sieve")
	out := flag.String("out", defaultOutput, "output file path")
	flag.Parse()

	f, err := os.Create(*out)
	if err != nil {
		log.Fatalf("create %s: %v", *out, err)
	}
	defer f.Close()

	count, err := writePrimes(f, sieve(*limit))
	if err != nil {
		log.Fatalf("write %s: %v", *out, err)
	}
	if err := f.Close(); err != nil {
		log.Fatalf("close %s: %v", *out, err)
	}

	fmt.Printf("Wrote %d prime numbers up to %d to %s\n", count, *limit, *out)
}