var shader = (function(){
  var fn_str, fn, lex
  var exports = {}
  var animating = false
  
  exports.init = function(){
    lex = new Lex (0, 0)
    exports.build(demo_shader.innerHTML)
  }
  exports.build = function (fn_str){
    try {
      new_fn = new Function('lex', 'x', 'y', 'w', 'h', 't', fn_str)
      new_fn(lex, 0, 0, 1, 1, 0)
    }
    catch (e) {
      throw 'Shader execution error'
    }
    exports.fn = fn = new_fn
    return fn
  }
  exports.run = function(canvas){
    var t = +new Date
    shader.canvas = shader.canvas || canvas
    var w = shader.canvas.w, h = shader.canvas.h
    shader.canvas.forEach(function(lex, x, y){
      fn(lex, x, y, w, h, t)
      lex.build()
    })
  }
  exports.toggle = function(state){
    animating = typeof state == "boolean" ? state : ! animating
    shader_fps_el.classList.toggle('hidden')
    return animating
  }
  exports.pause = function(){
    animating = false
    shader_fps_el.classList.add('hidden')
    shader.fps_time = 0
  }
  exports.play = function(){
    animating = true
    shader_fps_el.classList.remove('hidden')
  }
  exports.animate = function (t){
    requestAnimationFrame(exports.animate)
    if (! animating) { return } 
    if (shader.fps_time){
      var ms = Date.now() - shader.fps_time
      fps = 1000 / ms
      shader_fps_el.innerHTML = (fps | 0) + ' fps'
    }
    shader.fps_time = Date.now()
    exports.run(canvas)
  }
  
  return exports

})()

var blit = (function(){
  var blit = {}
  blit.and = blit.atop = function(A, B, x, y){
    x = x || 0 ; y = y || 0
    B.forEach(function(lex, u, v){
      var cell = A.getCell(u+x, v+y)
      if (cell && lex.opacity > 0) {
        cell.assign(lex)
      }
    })
  }
  blit.or = blit.under = function(A, B, x, y){
    x = x || 0 ; y = y || 0
    B.forEach(function(lex, u, v){
      var cell = A.getCell(u+x, v+y)
      if (cell && cell.opacity == 0) {
        cell.assign(lex)
      }
    })
  }
  // copy the region of A beginning at x,y into B
  blit.copy_from = function(A, B, x, y){
    x = x || 0 ; y = y || 0
    B.forEach(function(lex, u, v){
      var cell = A.getCell(u+x, v+y)
      if (cell) {
        lex.assign(cell)
      }
    })
  }
  blit.copy_toroidal_from = function(A, B, x, y){
    x = x || 0 ; y = y || 0
    B.forEach(function(lex, u, v){
      var cell = A.get(u+x, v+y)
      if (cell) {
        lex.assign(cell)
      }
    })
  }
  blit.copy_to = function(A, B, x, y){
    x = x || 0 ; y = y || 0
    B.forEach(function(lex, u, v){
      var cell = A.getCell(u+x, v+y)
      if (cell) {
        cell.assign(lex)
      }
    })
  }
  blit.invert = function(A, B, x, y){
    x = x || 0 ; y = y || 0
    B.forEach(function(lex, u, v){
      var cell = A.getCell(u+x, v+y)
      if (cell && lex.opacity > 0) {
        cell.fg = get_inverse(cell.fg)
        cell.bg = get_inverse(cell.bg)
      }
    })
  }
  var distance_rect = function(x, y, ratio){
    return Math.sqrt((Math.pow(y * ratio, 2)) + Math.pow(x, 2))
  }
  var distance_square = function(x, y, ratio){
    return Math.sqrt((Math.pow(y * ratio, 2)) + Math.pow(x * ratio, 2))
  }
  blit.circle = function(A, lex){
    var hw = brush.w/2, hh = brush.h/2
    var ratio, distance
    
    if (brush.w === brush.h){
      distance = distance_square
      ratio = hw / hh * (brush.w === 3 || brush.w === 5 ? 1.2 : 1.05)
    } else {
      distance = distance_rect
      ratio = hw / hh
    }

    A.forEach(function(lex,x,y) {
      if (distance(x - hw + 0.5, y - hh + 0.5, ratio) > hw){
        lex.clear()
      }
    })
  }
  blit.cross = function(A, lex){
    A.forEach(function(lex,x,y) {
      if ((x+y)%2) {
        lex.clear()
      }
    })
  }
  blit.inverted_cross = function(A, lex){
    // 1x1 brush should still draw something
    if (A.w == 1 && A.h == 1) {
      return
    }
    A.forEach(function(lex,x,y) {
      if (!((x+y)%2)) {
        lex.clear()
      }
    })
  }
  blit.square = function(A, lex){
  	// i.e. no transparency
  }
  return blit
})()