// Author: Yurij Gera
// TODO: make @media print... work for Mozilla and Opera

var SnowCount     = exAutoCalculate();
var SnowMinSize   = 12;   // Minimum Snow-Font Size [Pixel]
var SnowMaxSize   = 28;   // Maximum Snow-Font Size [Pixel]
var SnowMinYSpeed = 0.5;  // Maximum Y Speed [Pixel/Frame]
var SnowMaxYSpeed = 2.5;  // Maximum Y Speed [Pixel/Frame]
var SnowMinXSpeed = 0.05; // Minumum Radial Speed [Radian/Frame]
var SnowMaxXSpeed = 0.15; // Maximum Radial Speed [Radian/Frame]
var SnowMinXDelta = 10;   // Minimum X Delta [Pixel]
var SnowMaxXDelta = 20;   // Maximum X Delta [Pixel]
var SnowMoveDelay = 25;   // Delay [Milliseconds]
var SnowColors    = ['#BBBBBB', '#DDDDDD', '#FFFFFF', '#BBBBFF']; // Snow Colors [Array]

exSnowInit();

function exSnowInit() {
        SnowMoveDelay = 25; // Delay [Milliseconds]
        exAddEvent(window, 'load', exSnowStart);
        exAddEvent(window, 'resize', exSnowRefresh);
        document.createStyleSheet().cssText = "@media print {.exSnowClass { DISPLAY: none; }}"; // IE only
}

function exAutoCalculate() {
        var start = new Date();
        for (var i = 0; i < 50000; i++) {
                Math.random();
        }
        var end = new Date();
        var delta = end.valueOf() - start.valueOf();
        var EstimatedSnowCount = Math.min(Math.floor(10000 / delta), 500);
        if (navigator.userAgent.match(/Opera/)) EstimatedSnowCount *= 0.5; // Hot fix opera
        return EstimatedSnowCount;
}

function exRandom(Min, Max, Natural) {
        if (typeof Natural == 'undefined')
                Natural = false;
        if (Natural) {
                return Math.floor(Min + (Max - Min + 0.999999) * Math.random());
        }
        else
                return Min + (Max - Min) * Math.random();
}

function exSnowStart() {
        Snow = new Array();
        for (i = 0; i < SnowCount; i++) {
                var e = document.createElement("span");
                e.className = 'exSnowClass';
                e.style.fontFamily = 'Times';
                e.style.fontSize = (SnowMinSize + Math.floor((SnowMaxSize - SnowMinSize) * Math.random())) + 'px';
                e.style.color = SnowColors[exRandom(0, SnowColors.length-1, true)];
                e.style.cursor = 'default';
                e.style.position = 'absolute';
                e.onselectstart = function () { return false; };
                var t = document.createTextNode("*");
                e.appendChild(t);
                Snow[i] = document.body.appendChild(e);
        }
        exSnowRefresh();
        exSnowMove();
}

function exSnowRefresh() {
        SnowBoxWidth = document.body.clientWidth;
        SnowBoxHeight = document.body.clientHeight;
        for (i = 0; i < Snow.length; i++) {
                var e = Snow[i];
                e.YSpeed = exRandom(SnowMinYSpeed, SnowMaxYSpeed);
                e.XSpeed = exRandom(SnowMinXSpeed, SnowMaxXSpeed);
                e.XMaxDelta = exRandom(SnowMinXDelta, SnowMaxXDelta);
                e.XDelta = Math.PI * Math.random(); // Stored Radial Delta (Radian)
                e.X = exRandom(SnowMaxXDelta, SnowBoxWidth - SnowMaxXDelta - SnowMaxSize);
                e.Y = exRandom(0, SnowBoxHeight - SnowMaxSize);
                e.style.left = e.X + 'px';
                e.style.top = e.Y + 'px';
        }
}

function exSnowMove() {
        for (i = 0; i < Snow.length; i++) {
                with (Snow[i]) {
                        Y = (Y + YSpeed < SnowBoxHeight - SnowMaxSize) ? Y + YSpeed : 0;
                        XDelta += XSpeed;
                        style.left = X + Math.sin(XDelta) * XMaxDelta + 'px';
                        style.top = Y + 'px';
                }
        }
        setTimeout("exSnowMove()", SnowMoveDelay);
}

function exAddEvent(o, e, f) {
        if (typeof o.addEventListener != 'undefined')
                o.addEventListener(e, f, false);
        else if (typeof o.attachEvent != 'undefined')
                o.attachEvent("on" + e, f);
        else
                return false;
        return true;
}