////////////////////////////////////////////////////////////////////////
// SnowFlakes-Script (c) 2011, Dominik Scholz / go4u.de Webdesign
////////////////////////////////////////////////////////////////////////

var snowflakes = {

        ///////////////////////////// configuration ////////////////////////////

        // amout of flakes
        _amount: 30,
        // random colors
        _color: ['#DDDDFF', '#CCCCDD', '#F3F3F3', '#F0FFFF', '#FDFAFA', '#FFFFFF'],
        // random fonts
        _type: ['Arial Black', 'Arial Narrow', 'Times', 'Comic Sans MS'],
        // char used for flake
        _flakeChar: '*',
        // speed of flakes
        _speed: .2,
        // minimum flake font size
        _minSize: 8,
        // maximum flake font size
        _maxSize: 35,
        // horizontal drift
        _drift: 12,
        // zIndex of flakes
        _zIndex: 20000,



        ///////////////////////////// private vars /////////////////////////////

        _flakes: [],
        _bodyWidth: 0,
        _bodyHeight: 0,
        _range: null,
        _count: 0,
        _timeout: 20,
        _lastInterval: 0,
        _eventHandlerResize: window.onresize,
        _eventHandlerLoad: window.onload,



        ////////////////////////////// functions ///////////////////////////////

        // start snow
        start: function()
        {
                if (this._eventHandlerLoad != null) this._eventHandlerLoad();

                // calculate range
                this._range = this._maxSize - this._minSize;

                // init window size
                this._windowSize();

                // add new flakes
                while (this._amount > this._flakes.length)
                        this._createFlake(this._flakes.length);

                // start to move snow
                this._lastInterval = this._time();
                window.setInterval(function() { snowflakes._move(); }, this._timeout);
        },


        // get current time
        _time: function()
        {
                return +new Date();
        },


        // return a random number bewtween 0 and range
        _random: function(range)
        {
                return Math.floor(Math.random() * range);
        },


        // creates a new snowflake
        _createFlake: function(i)
        {
                // select body tag
                var insertBody = document.getElementsByTagName('body')[0];

                // create span child for flake
                var f = document.createElement('div');
                f.id                 = 'flake' + i;
                f.style.zIndex       = '99999999999999999999';
                f.style.position     = 'absolute';
                f.style.left         = '0px';
                f.style.top          = '-' + this._maxSize + 'px';
                f.style.color        = this._color[this._random(this._color.length - 1)];
                f.style.family       = this._type[this._random(this._type.length - 1)];
                f.style.fontSize     = (this._random(this._range) + this._minSize) + 'px';
                f.style.zIndex       = this._zIndex;
                f.innerHTML          = this._flakeChar;
                insertBody.appendChild(f);

                // create array element
                this._flakes[i] = {
                        x: this._random(this._bodyWidth - this._drift - this._maxSize - 3) + this._drift + 1,
                        y: -this._maxSize - this._random(this._bodyHeight),
                        size: this._random(this._range) + this._minSize,
                        count: this._random(10000)
                };
        },


        // restart an existing snow flake
        _restartFlake: function(i)
        {
                this._flakes[i] = {
                        x: this._random(this._bodyWidth - this._drift - this._maxSize - 3) + this._drift + 1,
                        y: -this._maxSize,
                        size: this._random(this._range) + this._minSize,
                        count: this._random(10000)
                };
        },


        // move existing flakes
        _move: function()
        {
                // calculate movement factor
                var dif = this._time() - this._lastInterval;
                this._lastInterval = this._time();
                var f = dif * this._speed;

                this._count += f / 80;

                for (var i = 0; i < this._flakes.length; i++)
                {
                        var flake = this._flakes[i];
                        flake.y += f * this._speed * this._maxSize / flake.size;

                        // restart existing flake
                        if (flake.y + flake.size >= this._bodyHeight)
                        {
                                this._restartFlake(i);
                                continue;
                        }

                        var flakeDiv = document.getElementById('flake' + i);
                        flakeDiv.style.left = Math.floor(flake.x + Math.sin(flake.count + this._count) * this._drift) + 'px';
                        flakeDiv.style.top  = Math.floor(flake.y) + 'px';
                }
        },


        // calculate new positions for all flakes
        _windowSize: function()
        {
                // save old width
                var oldWidth = this._bodyWidth;

                // get new width and height
                this._bodyWidth = this._getWindowWidth() - this._maxSize;
                this._bodyHeight = this._getWindowHeight() - this._maxSize;

                // calculate correction ratio
                var ratio = this._bodyWidth / oldWidth;

                // for all flakes
                for (var i = 0; i < this._flakes.length; i++)
                {
                        var flake = this._flakes[i];

                        // do width correction
                        flake.x *= ratio;

                        // restart existing flake
                        if ((flake.y + flake.size) >= this._bodyHeight)
                                this._restartFlake(i);
                }
        },


        // get window width
        _getWindowWidth: function()
        {
                var w = Math.max(self.innerWidth || 0, window.innerWidth || 0);

                if (document.documentElement)
                        w = Math.max(w, document.documentElement.clientWidth || 0);
                if (document.body)
                {
                        w = Math.max(w, document.body.clientWidth || 0);
                        w = Math.max(w, document.body.scrollWidth || 0);
                        w = Math.max(w, document.body.offsetWidth || 0);
                }

                return w;
        },


        // get window height
        _getWindowHeight: function()
        {
                var h = Math.max(self.innerHeight || 0, window.innerHeight || 0);

                if (document.documentElement)
                        h = Math.max(h, document.documentElement.clientHeight || 0);
                if (document.body)
                {
                        h = Math.max(h, document.body.clientHeight || 0);
                        h = Math.max(h, document.body.scrollHeight || 0);
                        h = Math.max(h, document.body.offsetHeight || 0);
                }

                return h;
        },


        // handle resize event
        resize: function()
        {
                if (this._eventHandlerResize != null)
                        this._eventHandlerResize();
                this._windowSize();
        }

};


// register window resize event
window.onresize = function() { snowflakes.resize(); }
window.onload = function() { snowflakes.start(); }