(function(global) {

  'use strict';

  var fabric = global.fabric || (global.fabric = { }),
      toFixed = fabric.util.toFixed;

  if (fabric.Shadow) {
    fabric.warn('fabric.Shadow is already defined.');
    return;
  }

  /**
   * Shadow class
   * @class fabric.Shadow
   * @see {@link http://fabricjs.com/shadows|Shadow demo}
   * @see {@link fabric.Shadow#initialize} for constructor definition
   */
  fabric.Shadow = fabric.util.createClass(/** @lends fabric.Shadow.prototype */ {

    /**
     * Shadow color
     * @type String
     * @default
     */
    color: 'rgb(0,0,0)',

    /**
     * Shadow blur
     * @type Number
     */
    blur: 0,

    /**
     * Shadow horizontal offset
     * @type Number
     * @default
     */
    offsetX: 0,

    /**
     * Shadow vertical offset
     * @type Number
     * @default
     */
    offsetY: 0,

    /**
     * Whether the shadow should affect stroke operations
     * @type Boolean
     * @default
     */
    affectStroke: false,

    /**
     * Indicates whether toObject should include default values
     * @type Boolean
     * @default
     */
    includeDefaultValues: true,

    /**
     * Constructor
     * @param {Object|String} [options] Options object with any of color, blur, offsetX, offsetY properties or string (e.g. "rgba(0,0,0,0.2) 2px 2px 10px")
     * @return {fabric.Shadow} thisArg
     */
    initialize: function(options) {

      if (typeof options === 'string') {
        options = this._parseShadow(options);
      }

      for (var prop in options) {
        this[prop] = options[prop];
      }

      this.id = fabric.Object.__uid++;
    },

    /**
     * @private
     * @param {String} shadow Shadow value to parse
     * @return {Object} Shadow object with color, offsetX, offsetY and blur
     */
    _parseShadow: function(shadow) {
      var shadowStr = shadow.trim(),
          offsetsAndBlur = fabric.Shadow.reOffsetsAndBlur.exec(shadowStr) || [],
          color = shadowStr.replace(fabric.Shadow.reOffsetsAndBlur, '') || 'rgb(0,0,0)';

      return {
        color: color.trim(),
        offsetX: parseInt(offsetsAndBlur[1], 10) || 0,
        offsetY: parseInt(offsetsAndBlur[2], 10) || 0,
        blur: parseInt(offsetsAndBlur[3], 10) || 0
      };
    },

    /**
     * Returns a string representation of an instance
     * @see http://www.w3.org/TR/css-text-decor-3/#text-shadow
     * @return {String} Returns CSS3 text-shadow declaration
     */
    toString: function() {
      return [this.offsetX, this.offsetY, this.blur, this.color].join('px ');
    },

    /* _TO_SVG_START_ */
    /**
     * Returns SVG representation of a shadow
     * @param {fabric.Object} object
     * @return {String} SVG representation of a shadow
     */
    toSVG: function(object) {
      var fBoxX = 40, fBoxY = 40, NUM_FRACTION_DIGITS = fabric.Object.NUM_FRACTION_DIGITS,
          offset = fabric.util.rotateVector(
            { x: this.offsetX, y: this.offsetY },
            fabric.util.degreesToRadians(-object.angle)),
          BLUR_BOX = 20, color = new fabric.Color(this.color);

      if (object.width && object.height) {
        //http://www.w3.org/TR/SVG/filters.html#FilterEffectsRegion
        // we add some extra space to filter box to contain the blur ( 20 )
        fBoxX = toFixed((Math.abs(offset.x) + this.blur) / object.width, NUM_FRACTION_DIGITS) * 100 + BLUR_BOX;
        fBoxY = toFixed((Math.abs(offset.y) + this.blur) / object.height, NUM_FRACTION_DIGITS) * 100 + BLUR_BOX;
      }
      if (object.flipX) {
        offset.x *= -1;
      }
      if (object.flipY) {
        offset.y *= -1;
      }

      return (
        '<filter id="SVGID_' + this.id + '" y="-' + fBoxY + '%" height="' + (100 + 2 * fBoxY) + '%" ' +
          'x="-' + fBoxX + '%" width="' + (100 + 2 * fBoxX) + '%" ' + '>\n' +
          '\t<feGaussianBlur in="SourceAlpha" stdDeviation="' +
            toFixed(this.blur ? this.blur / 2 : 0, NUM_FRACTION_DIGITS) + '"></feGaussianBlur>\n' +
          '\t<feOffset dx="' + toFixed(offset.x, NUM_FRACTION_DIGITS) +
          '" dy="' + toFixed(offset.y, NUM_FRACTION_DIGITS) + '" result="oBlur" ></feOffset>\n' +
          '\t<feFlood flood-color="' + color.toRgb() + '" flood-opacity="' + color.getAlpha() + '"/>\n' +
          '\t<feComposite in2="oBlur" operator="in" />\n' +
          '\t<feMerge>\n' +
            '\t\t<feMergeNode></feMergeNode>\n' +
            '\t\t<feMergeNode in="SourceGraphic"></feMergeNode>\n' +
          '\t</feMerge>\n' +
        '</filter>\n');
    },
    /* _TO_SVG_END_ */

    /**
     * Returns object representation of a shadow
     * @return {Object} Object representation of a shadow instance
     */
    toObject: function() {
      if (this.includeDefaultValues) {
        return {
          color: this.color,
          blur: this.blur,
          offsetX: this.offsetX,
          offsetY: this.offsetY,
          affectStroke: this.affectStroke
        };
      }
      var obj = { }, proto = fabric.Shadow.prototype;

      ['color', 'blur', 'offsetX', 'offsetY', 'affectStroke'].forEach(function(prop) {
        if (this[prop] !== proto[prop]) {
          obj[prop] = this[prop];
        }
      }, this);

      return obj;
    }
  });

  /**
   * Regex matching shadow offsetX, offsetY and blur (ex: "2px 2px 10px rgba(0,0,0,0.2)", "rgb(0,255,0) 2px 2px")
   * @static
   * @field
   * @memberOf fabric.Shadow
   */
  // eslint-disable-next-line max-len
  fabric.Shadow.reOffsetsAndBlur = /(?:\s|^)(-?\d+(?:px)?(?:\s?|$))?(-?\d+(?:px)?(?:\s?|$))?(\d+(?:px)?)?(?:\s?|$)(?:$|\s)/;

})(typeof exports !== 'undefined' ? exports : this);