// add a new canvas element to this page
canvas = document.createElement('canvas')
canvas.setAttribute('width',  '500')
canvas.setAttribute('height', '275')
$('playArea').appendChild(canvas)
ctxt = canvas.getContext('2d')

// scheduler
tasks = []
schedule = function(task) { tasks.push(task) }
setInterval(function() { if (tasks.length > 0) tasks.shift()() }, 20)

// the turtle
smiley = {
  x: 250,
  y: 60,
  angle: 0,
  color: 'blue',
  penDown: true,
  forwardBy: function(n) {
    schedule(function() {
      ctxt.beginPath()
      ctxt.moveTo(smiley.x, smiley.y)
      smiley.x += n * Math.cos(smiley.angle)
      smiley.y += n * Math.sin(smiley.angle)
      if (smiley.penDown) { ctxt.lineTo(smiley.x, smiley.y); ctxt.stroke() }
    })
  },
  turnBy: function(n) {
    schedule(function() { smiley.angle += n * Math.PI / 180 })
  },
  setPenDown: function(penDown) {
    schedule(function() { smiley.penDown = penDown })
  },
  rt: function(n) { smiley.turnBy(n) },
  lt: function(n) { smiley.turnBy(-n) },
  fd: function(n) { smiley.forwardBy(n) },
  bk: function(n) { smiley.forwardBy(-n) },
  pu: function() { smiley.setPenDown(false) },
  pd: function() { smiley.setPenDown(true) },
  "if": function(cond, block) { if (cond) block() }
}

ometa LogoTranslator <: Parser {
  name     = spaces <letter (letter | digit)*>,
  cmdName  = ~("to" | "end" | "output") name,
  number   = spaces <digit+>,
  arg      = ":" name,
  cmds     = cmd*:xs                                       -> xs.join(';'),
  block    = "[" cmds:xs "]"                               -> ('(function() {' + xs + '})'),
  primExpr = arg | number | block | "(" (expr | cmd):x ")" -> x,
  mulExpr  = mulExpr:x "*" primExpr:y                      -> (x + '*' + y)
           | mulExpr:x "/" primExpr:y                      -> (x + '/' + y)
           | primExpr,
  addExpr  = addExpr:x "+" mulExpr:y                       -> (x + '+' + y)
           | addExpr:x "-" mulExpr:y                       -> (x + '-' + y)
           | mulExpr,
  expr     = addExpr:x "<"  addExpr:y                      -> (x + '<'  + y)
           | addExpr:x "<=" addExpr:y                      -> (x + '<=' + y)
           | addExpr:x ">"  addExpr:y                      -> (x + '>'  + y)
           | addExpr:x ">=" addExpr:y                      -> (x + '>=' + y)
           | addExpr,
  cmd      = "output" expr:x                               -> ('return ' + x)
           | cmdName:n expr*:args                          -> ('smiley["' + n + '"](' + args.join(',') + ')'),
  decl     = "to" cmdName:n arg*:args cmds:body "end"      -> ('smiley["' + n + '"]=function(' + args.join(',') + '){' + body + '}'),
  prog     = (decl | cmd)*:xs spaces end                   -> xs.join(';')
}

translateCode = function(code) {
  return LogoTranslator.matchAll(code, 'prog')
}



to spiral :size :angle
  if :size < 100 [
    fd :size
    rt :angle
    spiral :size + 2 :angle
  ]
end

spiral 1 89
spiral 1 30