var goL = (function(){
	var goL ={},bits=64*128;
	var dt; // grid bits
	var i;  // which dt is current?
	var sp=20; // speed of animation. smaller = faster.
	var timeClr ;// for clearing Timeout.
	var editMode=false;
	
	goL.clearGrid = function(){
		dt = [  Array.apply(0, Array(bits/32)).map(function() { return 0; }),
				Array.apply(0, Array(bits/32)).map(function() { return 0; })]; //enough bits for 64x128 grid
		i =0;// 0 is current
	}
	
	goL.get = function(p){ // get status of pth bit
		return (dt[i][p>>>5]&(0x80000000>>>(p&31))) ==0?0:1;
	}
	
	goL.put = function(p,s,j){ // set status of pth bit to s
		s ? (dt[j][p>>>5]|=(0x80000000>>>(p&31))): (dt[j][p>>>5]&=~(0x80000000>>>(p&31)));
	}
	
	goL.clearTimeout = function(){
		clearTimeout(timeClr);
	}
	
	goL.editMode = function(f){
		editMode=f;
		f? rects.attr('class',"edit") : rects.attr('class',"");
	}
	
	function switchSq(p){
		if(!editMode) return;
		goL.put(p,1-goL.get(p),i);
		rects.style("fill",function(d){ return goL.get(d)==1? "steelblue":"white";});
	}
	
	goL.clearGrid();
	var rects = d3.select("svg").selectAll("rect").data(d3.range(0,bits)).enter().append("rect")
			.attr("x",function(d){ return (d&127)*7;})
			.attr("y",function(d){ return (d>>>7)*7;})
			.attr("width",7).attr("height",7)
			.style("fill",function(d){ return goL.get(d)==1? "steelblue":"white";})
			.on("click",function(d){ return switchSq(d);});
	
	goL.setGrid = function(ar){  //set the initial bits
		goL.clearGrid();
		goL.clearTimeout();
		
		if(arguments.length > 0){
			d3.range(0,ar.length).forEach(function(y){d3.range(0,ar[0].length)
				.forEach(function(x){goL.put(y*128+x,ar[y][x],i)})});
		}	
		rects.style("fill",function(d){ return goL.get(d)==1? "steelblue":"white";});
	}
	
	goL.update = function(){
		for(var p=0; p<bits; p++){
			var q = p>>>7, r=p&127;// quotient and reminder
			var n= 	(q>0 && r>0 ? goL.get(p-129): 0) + // number of neighbours
					(q>0 ? goL.get(p-128): 0) + 
					(q>0 && r<127 ? goL.get(p-127): 0)+ 
					(r>0 ? goL.get(p-1): 0) + 
					(r<127 ? goL.get(p+1): 0)+ 
					(q<63 && r>0 ? goL.get(p+127): 0)+ 
					(q<63  ? goL.get(p+128): 0)+ 
					(q<63 && r<127 ? goL.get(p+129): 0);
					
			if(n<=1 || n>3) goL.put(p, 0, 1-i);
			else if(n==2) goL.put(p, goL.get(p), 1-i);
			else goL.put(p, 1, 1-i);
		}
		i=1-i;// switch current
		rects.style("fill",function(d){ return goL.get(d)==1? "steelblue":"white";});
		
		timeClr = setTimeout(function(){goL.update()},sp);
	}
	
	return goL;
}());