

 This page uses content from Wikipedia. The original article was at Snake_(video_game). The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)


Snake is a game where the player maneuvers a line which grows in length every time the snake reaches a food source.



Task
Implement a variant of the Snake game, in any interactive environment, in which a sole player attempts to eat items by running into them with the head of the snake.

Each item eaten makes the snake longer and a new item is randomly generated somewhere else on the plane.

The game ends when the snake attempts to eat himself.




package main
 
import (
	"errors"
	"fmt"
	"log"
	"math/rand"
	"time"
 
	termbox "github.com/nsf/termbox-go"
)
 
func main() {
	rand.Seed(time.Now().UnixNano())
	score, err := playSnake()
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println("Final score:", score)
}
 
type snake struct {
	body          []position // tail to head positions of the snake
	heading       direction
	width, height int
	cells         []termbox.Cell
}
 
type position struct {
	X int
	Y int
}
 
type direction int
 
const (
	North direction = iota
	East
	South
	West
)
 
func (p position) next(d direction) position {
	switch d {
	case North:
		p.Y--
	case East:
		p.X++
	case South:
		p.Y++
	case West:
		p.X--
	}
	return p
}
 
func playSnake() (int, error) {
	err := termbox.Init()
	if err != nil {
		return 0, err
	}
	defer termbox.Close()
 
	termbox.Clear(fg, bg)
	termbox.HideCursor()
	s := &snake{
		// It would be more efficient to use a circular
		// buffer instead of a plain slice for s.body.
		body:  make([]position, 0, 32),
		cells: termbox.CellBuffer(),
	}
	s.width, s.height = termbox.Size()
	s.drawBorder()
	s.startSnake()
	s.placeFood()
	s.flush()
 
	moveCh, errCh := s.startEventLoop()
	const delay = 125 * time.Millisecond
	for t := time.NewTimer(delay); ; t.Reset(delay) {
		var move direction
		select {
		case err = <-errCh:
			return len(s.body), err
		case move = <-moveCh:
			if !t.Stop() {
				<-t.C // handles race between moveCh and t.C
			}
		case <-t.C:
			move = s.heading
		}
		if s.doMove(move) {
			time.Sleep(1 * time.Second)
			break
		}
	}
 
	return len(s.body), err
}
 
func (s *snake) startEventLoop() (<-chan direction, <-chan error) {
	moveCh := make(chan direction)
	errCh := make(chan error, 1)
	go func() {
		defer close(errCh)
		for {
			switch ev := termbox.PollEvent(); ev.Type {
			case termbox.EventKey:
				switch ev.Ch { // WSAD and HJKL movement
				case 'w', 'W', 'k', 'K':
					moveCh <- North
				case 'a', 'A', 'h', 'H':
					moveCh <- West
				case 's', 'S', 'j', 'J':
					moveCh <- South
				case 'd', 'D', 'l', 'L':
					moveCh <- East
				case 0:
					switch ev.Key { // Cursor key movement
					case termbox.KeyArrowUp:
						moveCh <- North
					case termbox.KeyArrowDown:
						moveCh <- South
					case termbox.KeyArrowLeft:
						moveCh <- West
					case termbox.KeyArrowRight:
						moveCh <- East
					case termbox.KeyEsc: // Quit
						return
					}
				}
			case termbox.EventResize:
				// TODO
				errCh <- errors.New("terminal resizing unsupported")
				return
			case termbox.EventError:
				errCh <- ev.Err
				return
			case termbox.EventInterrupt:
				return
			}
		}
	}()
	return moveCh, errCh
}
 
func (s *snake) flush() {
	termbox.Flush()
	s.cells = termbox.CellBuffer()
}
 
func (s *snake) getCellRune(p position) rune {
	i := p.Y*s.width + p.X
	return s.cells[i].Ch
}
func (s *snake) setCell(p position, c termbox.Cell) {
	i := p.Y*s.width + p.X
	s.cells[i] = c
}
 
func (s *snake) drawBorder() {
	for x := 0; x < s.width; x++ {
		s.setCell(position{x, 0}, border)
		s.setCell(position{x, s.height - 1}, border)
	}
	for y := 0; y < s.height-1; y++ {
		s.setCell(position{0, y}, border)
		s.setCell(position{s.width - 1, y}, border)
	}
}
 
func (s *snake) placeFood() {
	for {
		// a random empty cell
		x := rand.Intn(s.width-2) + 1
		y := rand.Intn(s.height-2) + 1
		foodp := position{x, y}
		r := s.getCellRune(foodp)
		if r != ' ' {
			continue
		}
		s.setCell(foodp, food)
		return
	}
}
 
func (s *snake) startSnake() {
	// a random cell somewhat near the center
	x := rand.Intn(s.width/2) + s.width/4
	y := rand.Intn(s.height/2) + s.height/4
	head := position{x, y}
	s.setCell(head, snakeHead)
	s.body = append(s.body[:0], head)
	s.heading = direction(rand.Intn(4))
}
 
func (s *snake) doMove(move direction) bool {
	head := s.body[len(s.body)-1]
	s.setCell(head, snakeBody)
	head = head.next(move)
	s.heading = move
	s.body = append(s.body, head)
	r := s.getCellRune(head)
	s.setCell(head, snakeHead)
	gameOver := false
	switch r {
	case food.Ch:
		s.placeFood()
	case border.Ch, snakeBody.Ch:
		gameOver = true
		fallthrough
	case empty.Ch:
		s.setCell(s.body[0], empty)
		s.body = s.body[1:]
	default:
		panic(r)
	}
	s.flush()
	return gameOver
}
 
const (
	fg = termbox.ColorWhite
	bg = termbox.ColorBlack
)
 
// Symbols to use.
// Could use Unicode instead of simple ASCII.
var (
	empty     = termbox.Cell{Ch: ' ', Bg: bg, Fg: fg}
	border    = termbox.Cell{Ch: '+', Bg: bg, Fg: termbox.ColorBlue}
	snakeBody = termbox.Cell{Ch: '#', Bg: bg, Fg: termbox.ColorGreen}
	snakeHead = termbox.Cell{Ch: 'O', Bg: bg, Fg: termbox.ColorYellow | termbox.AttrBold}
	food      = termbox.Cell{Ch: '@', Bg: bg, Fg: termbox.ColorRed}
)