// graph elements
function addAxis(element, scale, location) {
	var axis = d3.svg.axis().scale(scale).orient(location)
		.ticks(15, ",.1s")
    	.tickSize(3, 0);

	element.append("g").attr("class", "axis")
		.attr("transform", placeAxis(location))
		.call(axis);

};

function placeAxis(location){
	if(location == 'bottom'){
		return "translate("+ margin.left+"," + (height) + ")";
	} else if (location == 'left'){
		return "translate(" + margin.left + ",0)";
	}
}

function applyData(data){
	// initialize counter variables
	var maxValue = 0, maxWeight = 0, diff = 0, sizeSum = [0,0], comboSum = [0,0];

	// use data to define max value, weight, weight diffs, and sum size and combo
	data.forEach(function(d) {
		d.weightDiff = +d.endweight - +d.startweight;
		if (Math.abs(d.weightDiff) > diff) {
			diff = Math.abs(d.weightDiff)
		};
		maxValue = Math.max(maxValue, +d.startvalue, +d.endvalue);
		maxWeight = Math.max(maxWeight, +d.startweight, +d.endweight);

		// calculate for aggregate
		sizeSum = [sizeSum[0] + +d.startweight,
				   sizeSum[1] + +d.endweight];
		comboSum = [comboSum[0] + +d.startweight * +d.startvalue,
		  	        comboSum[1] + +d.endweight * +d.endvalue];
	})

	// calculate and append aggregate data
	// assumes same number of segments for start & end 
	// assumes no missing values
	var aggregate = {startvalue: comboSum[0] / sizeSum[0],
					 endvalue: comboSum[1] / sizeSum[1], 
					 startweight: sizeSum[0] / data.length,
					 endweight: sizeSum[1] / data.length, 
					};
	aggregate[segmentName] = 'aggregate';
	data.push(aggregate);

	// sets x and y scale to determine size of visible boxes
	var sizeScale = d3.scale.log().clamp(true)
		.domain([100, maxWeight])
		.range([0, width]);

	var valueScale = d3.scale.log().clamp(true)
		.domain([maxValue, .9])
		.range([0, height]);

	// color scale, based on data diffs
	var colorScale = d3.scale.linear()
		.domain([-diff, 0, diff])
		.range(['orange', 'grey', 'blue'])

	return {size: sizeScale, value: valueScale, color: colorScale}

};

// data to polygons
function valuesToPoints(startweight, endweight, startvalue, endvalue, halfWidth) {
	points = [[startweight, startvalue]];
	var a = startweight - endweight;
	var b = startvalue - endvalue;
	var dist = Math.sqrt(a * a + b * b);
	var newPoint1 = [halfWidth / dist * b + endweight, - halfWidth / dist * a + endvalue];
	var newPoint2 = [- halfWidth / dist * b + endweight, halfWidth / dist * a + endvalue];
	points.push(newPoint1, newPoint2);
	return points.join(" ")
};

// function to draw comets
function drawComets(element, data){
	element.selectAll("polygon")
		.data(data)
		.enter()
		.append("polygon")
		.attr("points", function(d) {
			return valuesToPoints(scales.size(+d.startweight),
								  scales.size(+d.endweight),
								  scales.value(+d.startvalue),
								  scales.value(+d.endvalue),
								  3);
		})
		.attr("fill", function(d) {
			if(d[segmentName] == 'aggregate'){
				//	
				return 'black';
			} else {
				return scales.color(d.weightDiff)
			};
		})
		.append("title")
			.text(function(d) {
				return d[filterName] + 
					   ', ' + segmentName +
					   d[segmentName] + 
					   ', value: ' + 
					   d.startvalue + ', ' + 
					   d.endvalue + 
					   ' weights ' + 
					   d.startweight + ' ' + 
					   d.endweight;
			});

};