golang - Christmas tree

main.go

package main

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

const (
	defaultBushChar  = "*"
	defaultLightChar = "O"
	defaultPadChar   = " "
)

var (
	lightColors = []string{
		"0;31",
		"0;33",
		"0;34",
		"0;35",
		"0;36",
		"1;31",
		"1;33",
		"1;34",
		"1;35",
		"1;36",
	}

	greetings = []string{
		"Wishing you a very merry Christmas :)",
		" ",
		"@dhaninugraha",
	}

	/* start with lit lights */
	isLit = true
)

func getTermSize() (rows int, cols int) {
	size := []string{}

	cmdGetSize := exec.Command("stty", "size")
	cmdGetSize.Stdin = os.Stdin
	outSize, err := cmdGetSize.Output()
	if err == nil {
		cleanSize := strings.TrimSuffix(string(outSize), "\n")
		size = strings.Split(cleanSize, " ")

		if len(size) != 2 {
			return 0, 0
		}

		r, eR := strconv.Atoi(size[0])
		c, eC := strconv.Atoi(size[1])

		if eR != nil || eC != nil {
			return 0, 0
		}

		return r, c
	}

	return 0, 0
}

func drawTree(termHeight int, termWidth int, greetings []string) {
	if termHeight == 0 || termWidth == 0 {
		return
	}

	/*
		we use string builder since it's more
		efficient than appending chars to a string
	*/
	var b strings.Builder

	/* clear screen */
	fmt.Fprintf(&b, "%s", "\033[H\033[2J")

	/* top padding: 1/5 terminal height */
	for i := 0; i < termHeight/5; i++ {
		fmt.Fprintf(&b, "%s", "\n")
	}

	/* tree bush */
	bushHeight := termHeight / 2
	for i := 0; i < bushHeight; i++ {
		bushCharLen := (i * 2) + 1
		padding := (termWidth / 2) - bushCharLen + i

		/* align to the center by using spaces to left-pad */
		fmt.Fprintf(&b, "%s", strings.Repeat(defaultPadChar, padding))

		for j := 0; j < bushCharLen; j++ {
			if !isLit {
				fmt.Fprintf(&b, "\033[0;32m%s\033[0m", defaultBushChar)
			} else {
				rand.Seed(time.Now().UnixNano())

				if rand.Intn(5) == 1 {
					rand.Seed(time.Now().UnixNano())

					colorIdx := rand.Intn(len(lightColors))

					fmt.Fprintf(&b, "\033[%sm%s\033[0m", lightColors[colorIdx], defaultLightChar)
				} else {
					fmt.Fprintf(&b, "\033[0;32m%s\033[0m", defaultBushChar)
				}
			}
		}

		fmt.Fprintf(&b, "%s", "\n")
	}

	/* tree base */
	baseW := 5
	baseH := 5
	for i := 0; i < baseH; i++ {
		padding := (termWidth / 2) - baseW

		if i < baseH-1 {
			fmt.Fprintf(&b, "\033[33m%s|%s|\033[0m\n", strings.Repeat(defaultPadChar, padding), strings.Repeat("/", (baseW-1)*2))
		} else {
			fmt.Fprintf(&b, "\033[33m%s%s\033[0m\n", strings.Repeat(defaultPadChar, padding), strings.Repeat("-", baseW*2))
		}
	}

	/* gap between tree & greetings: 1/20 terminal height */
	for i := 0; i < termHeight/20; i++ {
		fmt.Fprintf(&b, "%s", "\n")
	}

	/* greetings */
	for i := 0; i < len(greetings); i++ {
		width := len(greetings[i])
		padding := (termWidth / 2) - width

		fmt.Fprintf(&b, "%s%s\n", strings.Repeat(defaultPadChar, padding+(width/2)), greetings[i])
	}

	/* bottom padding: 1/20 terminal height */
	for i := 0; i < termHeight/20; i++ {
		fmt.Fprintf(&b, "%s", "\n")
	}

	/* print everything */
	fmt.Println(b.String())
}

func main() {
	termHeight, termWidth := getTermSize()

	for {
		drawTree(termHeight, termWidth, greetings)

		time.Sleep(250 * time.Millisecond)

		/* toggle light state */
		isLit = !isLit
	}
}