window.onload = function() {
	function randomChar(charSet) {
		var rand = charSet[Math.floor(Math.random() * charSet.length)];

		//var rand = String.fromCharCode(1e2+Math.random()*33);

		return rand;
	}
	function randomRange(min, max) {
		return Math.floor(Math.random() * (max - min + 1)) + min;

	}
	function newMatrixLine( speed, charSet, charLength, charHeight){
		var elemLine = document.createElement('div');
		elemLine.style.top = '-'+(charLength * charHeight)+'px';
		elemLine.style.left = randomRange(0, window.innerWidth)+'px';
		elemLine.style.position = 'fixed';
		document.body.appendChild(elemLine);

		for(let i = 0; i < charLength; i++){
			var elemLetter = document.createElement('div);
			elemLetter.innerHtml = randomChar(charSet);
			elemLetter.style.color = linesColor;
			elemLine.appendChild(elemLetter);
		}

		var interval1 = setInterval(function(){
			var elemLineTop = parseInt(elemLine.style.top);

			if(elemLineTop < (window.innerHeight)) {
				elemLine.style.top = elemLineTop + moveByNumPixels + 'px';
					//console.log('moving');
			}
			else {
				elemLine.remove();
			clearInterval(interval1);}
			}, speed);
		}
		var moveByNumPixels = 8.6;
		var linesGroupCreationInterval = 1;
		var maxLinesPerGroup = 1;
		var charSet = ['a', 'b', 'c'];
		var charHeight = 18.6;
		var bodyColor = '#000';
		var linesColor = 'lime';
		var minLineSpeedInterval = 16;
		var maxLineSpeedInterval = 28;
		var minCharLength = 4;
		var maxCharLength = 150;
		var maxLines = 40;

		var interval2 = setInterval(function(){
		if(document.body.children.length < maxLines) {
			for(let i = 0; i < randomRange(1, maxLinesPerGroup); i++) {
				newMatrixLine(randomRange(minLineSpeedInterval, maxLineSpeedInterval), charSet, randomRange(minCharLength, maxCharLength), charHeight);
			}
		}
		}, linesGroupCreationInterval);
		document.body.style.background = bodyColor;
		}
	}
}