package main

import (
	"fmt"
	"net"
	"os"
	"os/signal"
	"strconv"
	"syscall"
	"time"

	"github.com/gofiber/fiber/v2"
	"github.com/kanna5/qrtxt"
)

func getLocalAddr() (string, error) {
	conn, err := net.Dial("udp", "1.0.0.1:53")
	if err != nil {
		return "", err
	}
	defer conn.Close()

	host, _, err := net.SplitHostPort(conn.LocalAddr().String())
	return host, err
}

func serve(port int) (*fiber.App, <-chan error) {
	ch := make(chan error)

	app := fiber.New(fiber.Config{
		AppName:               "StaticFileServer",
		BodyLimit:             1,
		DisableStartupMessage: true,
		ReadTimeout:           5 * time.Second,
		RequestMethods:        []string{"GET", "HEAD"},
		ServerHeader:          "StaticFileServer",
	})
	app.Static("/", "./", fiber.Static{
		Browse:    true,
		ByteRange: true,
	})

	go func() {
		defer close(ch)
		ch <- app.Listen(":" + strconv.Itoa(port))
	}()

	return app, ch
}

func main() {
	listenPort := 8080

	var err error
	if len(os.Args) >= 2 {
		portStr := os.Args[1]
		listenPort, err = strconv.Atoi(portStr)
	}
	if err != nil {
		panic(fmt.Errorf("Cannot parse port number: %w", err))
	}
	if listenPort < 1 || listenPort > 65535 {
		panic(fmt.Errorf("Invalid port number: %d", listenPort))
	}

	localAddr, err := getLocalAddr()
	if err != nil {
		panic(fmt.Errorf("Cannot get local address: %w", err))
	}

	fullAddress := fmt.Sprintf("http://%s:%d/", localAddr, listenPort)

	app, errCh := serve(listenPort)
	// Early check to see if the server is started successfully. This might not be reliable
	select {
	case err := <-errCh:
		panic(fmt.Errorf("Cannot start server: %w", err))
	case <-time.After(1 * time.Millisecond):
	}

	if qrText, err := qrtxt.Encode(fullAddress, qrtxt.Low); err == nil {
		fmt.Println(qrText)
	}
	fmt.Printf("\nListening on %s\n", fullAddress)

	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, os.Interrupt, syscall.SIGTERM)
	go func() {
		<-sigCh
		_ = app.Shutdown()
	}()

	err, ok := <-errCh
	if !ok {
		panic("Server closed unexpectedly")
	}
	if err != nil {
		panic(fmt.Errorf("Failed to run server: %w", err))
	}

	fmt.Println("Bye!")
}