beer-rain.go

package main

import (
	"errors"
	"flag"
	"log"
	"math/rand"
	"os"
	"time"

	termbox "github.com/nsf/termbox-go"
)

var (
	numBeers    = flag.Int("num-beers", 100, "a number of beers")
	timeRaining = flag.Int64("time", 10, "a time raining beers [second]")
)

func main() {
	flag.Parse()
	os.Exit(_main())
}

func printError(err error) {
	log.Println("error:", err)
}

var invalidArguments = errors.New("invalid arguments")

func _main() int {
	if *numBeers <= 0 || *timeRaining <= 0 {
		printError(invalidArguments)
		flag.PrintDefaults()
		return 1
	}

	err := termbox.Init()
	if err != nil {
		printError(err)
		return 1
	}
	defer termbox.Close()
	go mainLoop()
	<-time.After(time.Duration(*timeRaining) * time.Second)
	return 0
}

type point struct {
	x, y int
	vy   int
}

func cheers(beers []point) {
	w, h := termbox.Size()
	for i := range beers {
		beers[i].x = rand.Intn(w)
		beers[i].y = rand.Intn(h)
		beers[i].vy = rand.Intn(3) + 1
	}
}

func printBeers(beers []point) {
	for _, b := range beers {
		termbox.SetCell(b.x, b.y, rune('🍺'), termbox.ColorDefault, termbox.ColorDefault)
	}
}

func moveBeers(beers []point) {
	w, h := termbox.Size()
	for i := range beers {
		b := &beers[i]
		b.y += b.vy
		if b.y >= h {
			b.x = rand.Intn(w)
			b.y = 0
			b.vy = rand.Intn(3) + 1
		}
	}
}

func mainLoop() {
	beers := make([]point, *numBeers)
	cheers(beers)
	for {
		c := time.After(50 * time.Millisecond)
		termbox.SetCursor(-1, -1)
		termbox.Clear(termbox.ColorDefault, termbox.ColorDefault)
		printBeers(beers)
		moveBeers(beers)
		termbox.Flush()
		<-c
	}
}