var Ci = Components.interfaces;

var gSetBackground = {
  _position        : "",
  _backgroundColor : 0,
  _screenWidth     : 0,
  _screenHeight    : 0,
  _image           : null,
  _canvas          : null,

  get _shell()
  {
    return Components.classes["@mozilla.org/browser/shell-service;1"]
                     .getService(Ci.nsIShellService);
  },

  load: function ()
  {
    this._canvas = document.getElementById("screen");
    this._screenWidth = screen.width;
    this._screenHeight = screen.height;
    if (this._screenWidth / this._screenHeight >= 1.6)
      document.getElementById("monitor").setAttribute("aspectratio", "16:10");

    // make sure that the correct dimensions will be used
    setTimeout(function(self) {
      self.init(window.arguments[0]);
    }, 0, this);
  },

  init: function (aImage)
  {
    this._image = aImage;

    // set the size of the coordinate space
    this._canvas.width = this._canvas.clientWidth;
    this._canvas.height = this._canvas.clientHeight;

    var ctx = this._canvas.getContext("2d");
    ctx.scale(this._canvas.clientWidth / this._screenWidth, this._canvas.clientHeight / this._screenHeight);

    this._initColor();
    this.updatePosition();
  },

  setDesktopBackground: function ()
  {
    document.persist("menuPosition", "value");
    this._shell.desktopBackgroundColor = this._hexStringToLong(this._backgroundColor);
    this._shell.setDesktopBackground(this._image,
                                     Ci.nsIShellService["BACKGROUND_" + this._position]);
  },

  updatePosition: function ()
  {
    var ctx = this._canvas.getContext("2d");
    ctx.clearRect(0, 0, this._screenWidth, this._screenHeight);

    this._position = document.getElementById("menuPosition").value;

    switch (this._position) {
      case "TILE":
        ctx.save();
        ctx.fillStyle = ctx.createPattern(this._image, "repeat");
        ctx.fillRect(0, 0, this._screenWidth, this._screenHeight);
        ctx.restore();
        break;
      case "STRETCH":
        ctx.drawImage(this._image, 0, 0, this._screenWidth, this._screenHeight);
        break;
      case "CENTER": {
        let x = (this._screenWidth - this._image.naturalWidth) / 2;
        let y = (this._screenHeight - this._image.naturalHeight) / 2;
        ctx.drawImage(this._image, x, y);
        break;
      }
      case "FILL": {
        // Try maxing width first, overflow height.
        let widthRatio = this._screenWidth / this._image.naturalWidth;
        let width = this._image.naturalWidth * widthRatio;
        let height = this._image.naturalHeight * widthRatio;
        if (height < this._screenHeight) {
          // Height less than screen, max height and overflow width.
          let heightRatio = this._screenHeight / this._image.naturalHeight;
          width = this._image.naturalWidth * heightRatio;
          height = this._image.naturalHeight * heightRatio;
        }
        let x = (this._screenWidth - width) / 2;
        let y = (this._screenHeight - height) / 2;
        ctx.drawImage(this._image, x, y, width, height);
        break;
      }
      case "FIT": {
        // Try maxing width first, top and bottom borders.
        let widthRatio = this._screenWidth / this._image.naturalWidth;
        let width = this._image.naturalWidth * widthRatio;
        let height = this._image.naturalHeight * widthRatio;
        let x = 0;
        let y = (this._screenHeight - height) / 2;
        if (height > this._screenHeight) {
          // Height overflow, maximise height, side borders.
          let heightRatio = this._screenHeight / this._image.naturalHeight;
          width = this._image.naturalWidth * heightRatio;
          height = this._image.naturalHeight * heightRatio;
          x = (this._screenWidth - width) / 2;
          y = 0;
        }
        ctx.drawImage(this._image, x, y, width, height);
        break;
      }
    }
  }
};

gSetBackground["_initColor"] = function ()
{
  var color = this._shell.desktopBackgroundColor;

  const rMask = 4294901760;
  const gMask = 65280;
  const bMask = 255;
  var r = (color & rMask) >> 16;
  var g = (color & gMask) >> 8;
  var b = (color & bMask);
  this.updateColor(this._rgbToHex(r, g, b));

  var colorpicker = document.getElementById("desktopColor");
  colorpicker.color = this._backgroundColor;
};

gSetBackground["updateColor"] = function (aColor)
{
  this._backgroundColor = aColor;
  this._canvas.style.backgroundColor = aColor;
};

// Converts a color string in the format "#RRGGBB" to an integer.
gSetBackground["_hexStringToLong"] = function (aString)
{
  return parseInt(aString.substring(1, 3), 16) << 16 |
         parseInt(aString.substring(3, 5), 16) << 8 |
         parseInt(aString.substring(5, 7), 16);
};

gSetBackground["_rgbToHex"] = function (aR, aG, aB)
{
  return "#" + [aR, aG, aB].map(aInt => aInt.toString(16).replace(/^(.)$/, "0$1"))
                           .join("").toUpperCase();
};