// Author: Yurij Gera

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;
}