package main

import (
	"io"
	"log"
	"net"
	"net/http"
	"os"
	"strings"
	"time"
)

func main() {
	entries := os.Args[1:]
	c := make(chan error)
	d := Downloader{}
	d.HTTPClient.Transport = &http.Transport{
		Proxy: http.ProxyFromEnvironment,
		DialContext: (&net.Dialer{
			Timeout:   30 * time.Second,
			KeepAlive: 30 * time.Second,
		}).DialContext,
		ForceAttemptHTTP2:     true,
		MaxIdleConns:          100,
		IdleConnTimeout:       90 * time.Second,
		TLSHandshakeTimeout:   90 * time.Second,
		ExpectContinueTimeout: 1 * time.Second,
	}
	for _, u := range entries {
		splits := strings.Split(u, ";")
		url := splits[0]
		output := splits[1]
		go d.download(url, output, c)
	}

	for range entries {
		err := <-c
		if err != nil {
			log.Panic(err)
		}
	}
}

type Downloader struct {
	HTTPClient http.Client
}

func (d *Downloader) download(url string, output string, doneChan chan error) {
	res, err := d.HTTPClient.Get(url)
	if err != nil {
		doneChan <- err
		return
	}
	if res.StatusCode != http.StatusOK {
		doneChan <- nil
		return
	}
	f, err := os.Create(output)
	if err != nil {
		doneChan <- err
		return
	}
	_, err = io.Copy(f, res.Body)
	if err != nil {
		doneChan <- err
		return
	}
	doneChan <- nil
}