Untitled

package main

import (
	"http"
	"io"
	"log"
	"strconv"
	"fmt"
)

const (
	width = 320
	height = 200
)

// returns a javascript command, must not use ' without escaping
func drawSomething(x string, y string) string {
	return "ctx.lineTo(" + x + ", " + y + ");"
}

// hello world, the web server
func GoDrawServer(w http.ResponseWriter, req *http.Request) {
	keypress := req.FormValue("key")
	x := req.FormValue("x")
	y := req.FormValue("y")
	if x == "" || y == "" {
		// Starting point for the drawing
		x = strconv.Itoa(width / 3)
		y = strconv.Itoa(height / 3)
  }
	const stepsize = 10
	var newcommand string = "" // can not use ' without escaping
	switch keypress {
		case "up":
			ynum, _ := strconv.Atoi(y)
			y = strconv.Itoa(ynum - stepsize)
			newcommand = drawSomething(x, y);
		case "down":
			ynum, _ := strconv.Atoi(y)
			y = strconv.Itoa(ynum + stepsize)
			newcommand = drawSomething(x, y);
		case "left":
			xnum, _ := strconv.Atoi(x)
			x = strconv.Itoa(xnum - stepsize)
			newcommand = drawSomething(x, y);
		case "right":
			xnum, _ := strconv.Atoi(x)
			x = strconv.Itoa(xnum + stepsize)
			newcommand = drawSomething(x, y);
	}
	fmt.Println("x:", x, "y:", y);

	drawstart := `
	var elem = document.getElementById('myCanvas');
	if (elem && elem.getContext) {
	  var ctx = elem.getContext('2d');
	  if (ctx) {

			ctx.fillStyle = '#808080';
			ctx.fillRect(0, 0, ` + strconv.Itoa(width) + ", " + strconv.Itoa(height) + `);

			ctx.fillStyle   = '#0000ff';
			ctx.strokeStyle = '#ff0000';
			ctx.lineWidth   = 4;

			ctx.beginPath();
  `
	drawcommands := req.FormValue("drawcommands") + newcommand
	drawend := `
			ctx.fill();
			ctx.stroke();
			ctx.closePath();
		}}
  `

	js := `

function postwith (to,p) {
  var myForm = document.createElement("form");
  myForm.method="post" ;
  myForm.action = to ;
  for (var k in p) {
    var myInput = document.createElement("input") ;
    myInput.setAttribute("name", k) ;
    myInput.setAttribute("value", p[k]);
    myForm.appendChild(myInput) ;
  }
  document.body.appendChild(myForm) ;
  myForm.submit() ;
  document.body.removeChild(myForm) ;
}

function checkKey(e) {
     switch (e.keyCode) {
        case 40:
						postwith('', {key:'down', x:'` + x + `', y:'` + y + `', drawcommands:'` + drawcommands + `'});
						top.focus();
            break;
        case 38:
						postwith('', {key:'up', x:'` + x + `', y:'` + y + `', drawcommands:'` + drawcommands + `'});
						top.focus();
            break;
        case 37:
						postwith('', {key:'left', x:'` + x + `', y:'` + y + `', drawcommands:'` + drawcommands + `'});
						top.focus();
            break;
        case 39:
						postwith('', {key:'right', x:'` + x + `', y:'` + y + `', drawcommands:'` + drawcommands + `'});
						top.focus();
            break;
		}
}

function main() {
	document.onkeydown = checkKey;
	top.focus();
}


`
	title := "GoDraw 1"
  // keypress is the fallback text for those that does not have canvas-support
	body := "<h1>" + title + "</h1>Try the arrow keys<br><br><canvas id=\"myCanvas\" width=\"" + strconv.Itoa(width) + "\" height=\"" + strconv.Itoa(height) + "\">" + keypress + "</canvas><br><a href=\"/\">Clear</a>"
	document := "<!doctype html><html><head><title>" + title + "</title></head><body style=\"font-family: sans-serif; margin: 10em;\"onload=\"main()\">" + body + "<script type=\"text/javascript\">" + js + drawstart + drawcommands + drawend + "</script></body></html>"
	io.WriteString(w, document)
}

func main() {
	http.HandleFunc("/", GoDrawServer)
	if err := http.ListenAndServe(":7777", nil); err != nil {
		log.Fatal("ListenAndServe: ", err.String())
	}
}