LifeGame for Go

lifegame.go

// Run: go build /path/to/lifegame/go/index.go; ./index
// Environment variables:
// - LIFEGAME_WIDTH: int(default is terminal width)
// - LIFEGAME_HEIGHT: int(default is terminal height)

package main

import (
	"fmt"
	"math/rand"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"
)

const FPS = 20
const LIVE = 1
const DEAD = 0

var WIDTH = width()
var HEIGHT = height()

func main() {
	rand.Seed(time.Now().UnixNano())

	board := make([]int, WIDTH*HEIGHT)

	// random cell birth
	for i := 0; i < (WIDTH*HEIGHT)/3; i++ {
		board[rand.Intn(WIDTH*HEIGHT)] = 1
	}

	// main loop
	for true {
		board = simulate(board)
		fmt.Println(render(board))
		time.Sleep((1000 / FPS) * time.Millisecond)
	}
}

func width() int {
	width, _ := strconv.Atoi(size()[1])

	return width
}

func height() int {
	height, _ := strconv.Atoi(size()[0])

	return height
}

func size() []string {
	cmd := exec.Command("stty", "size")
	cmd.Stdin = os.Stdin
	out, _ := cmd.Output()
	sizes := strings.Split(strings.Trim(string(out), "\n"), " ")

	width := os.Getenv("LIFEGAME_WIDTH")
	height := os.Getenv("LIFEGAME_HEIGHT")

	if width != "" {
		sizes[0] = width
	}
	if height != "" {
		sizes[1] = height
	}

	fmt.Println(sizes)

	return sizes
}

func render(board []int) string {
	str := ""

	for i := 0; i < HEIGHT; i++ {
		for j := 0; j < WIDTH; j++ {
			cell := " "
			if board[i*HEIGHT+j] == LIVE {
				cell = "#"
			}

			str += cell
		}
		str += "\n"
	}

	return str
}

func simulate(board []int) []int {
	next := make([]int, WIDTH*HEIGHT)

	for i := 0; i < HEIGHT; i++ {
		for j := 0; j < WIDTH; j++ {
			idx := i*HEIGHT + j
			neighbor := moore_neighborhood(board, i, j)

			birth := (board[idx] == DEAD && neighbor == 3)
			stay := (board[idx] == LIVE && 2 <= neighbor && neighbor <= 3)

			if birth || stay {
				next[idx] = LIVE
			}
		}
	}

	return next
}

func moore_neighborhood(board []int, y int, x int) int {
	living := 0
	for i := y - 1; i <= y+1; i++ {
		for j := x - 1; j <= x+1; j++ {
			idx := i*HEIGHT + j
			if i < 0 || i >= HEIGHT || j < 0 || j >= WIDTH || (i == y && j == x) {
				continue
			}

			if board[idx] == LIVE {
				living++
			}
		}
	}

	return living
}