(async () => {
	// Fetch graph data.
	const response = await fetch("/data/sunburst_data.min.json");
	if (!response.ok) throw new Error(response.statusText);
	const data = await response.json();

	// Specify the chart’s dimensions.
	const width = 928;
	const height = width;
	const radius = width / 6;

	// Create the color scale.
	const color = d3.scaleOrdinal(d3.quantize(d3.interpolateRainbow, data.children.length + 1));

	// Compute the layout.
	const hierarchy = d3.hierarchy(data)
			.sum(d => d.value)
			.sort((a, b) => b.value - a.value);
	const root = d3.partition()
			.size([2 * Math.PI, hierarchy.height + 1])
		(hierarchy);
	root.each(d => d.current = d);

	// Create the arc generator.
	const arc = d3.arc()
			.startAngle(d => d.x0)
			.endAngle(d => d.x1)
			.padAngle(d => Math.min((d.x1 - d.x0) / 2, 0.005))
			.padRadius(radius * 1.5)
			.innerRadius(d => d.y0 * radius)
			.outerRadius(d => Math.max(d.y0 * radius, d.y1 * radius - 1))

	// Select the SVG container.
	const svg = d3.select("#sunburst")
			.attr("viewBox", [-width / 2, -height / 2, width, width])
			.style("font", "10px sans-serif");

	// Append the arcs.
	const path = svg.append("g")
		.selectAll("path")
		.data(root.descendants().slice(1))
		.join("path")
			.attr("fill", d => { while (d.depth > 1) d = d.parent; return color(d.data.name); })
			.attr("fill-opacity", d => arcVisible(d.current) ? (d.children ? 0.6 : 0.4) : 0)
			.attr("pointer-events", d => arcVisible(d.current) ? "auto" : "none")

			.attr("d", d => arc(d.current));

	// Make them clickable if they have children.
	path.filter(d => d.children)
			.style("cursor", "pointer")
			.on("click", clicked);

	const format = d3.format(",d");
	path.append("title")
			.text(d => `${d.ancestors().map(d => d.data.name).reverse().join("/")}\n${format(d.value)}`);

	const label = svg.append("g")
			.attr("pointer-events", "none")
			.attr("text-anchor", "middle")
			.style("user-select", "none")
		.selectAll("text")
		.data(root.descendants().slice(1))
		.join("text")
			.attr("dy", "0.35em")
			.attr("fill-opacity", d => +labelVisible(d.current))
			.attr("transform", d => labelTransform(d.current))
			.attr("class", "sunburst-label")
			.text(d => d.data.name);

	const parent = svg.append("circle")
			.datum(root)
			.attr("r", radius)
			.attr("fill", "none")
			.attr("pointer-events", "all")
			.on("click", clicked);

	// Handle zoom on click.
	function clicked(event, p) {
		parent.datum(p.parent || root);

		root.each(d => d.target = {
			x0: Math.max(0, Math.min(1, (d.x0 - p.x0) / (p.x1 - p.x0))) * 2 * Math.PI,
			x1: Math.max(0, Math.min(1, (d.x1 - p.x0) / (p.x1 - p.x0))) * 2 * Math.PI,
			y0: Math.max(0, d.y0 - p.depth),
			y1: Math.max(0, d.y1 - p.depth)
		});

		const t = svg.transition().duration(event.altKey ? 7500 : 750);

		// Transition the data on all arcs, even the ones that aren’t visible,
		// so that if this transition is interrupted, entering arcs will start
		// the next transition from the desired position.
		path.transition(t)
				.tween("data", d => {
					const i = d3.interpolate(d.current, d.target);
					return t => d.current = i(t);
				})
			.filter(function(d) {
				return +this.getAttribute("fill-opacity") || arcVisible(d.target);
			})
				.attr("fill-opacity", d => arcVisible(d.target) ? (d.children ? 0.6 : 0.4) : 0)
				.attr("pointer-events", d => arcVisible(d.target) ? "auto" : "none") 

				.attrTween("d", d => () => arc(d.current));

		label.filter(function(d) {
				return +this.getAttribute("fill-opacity") || labelVisible(d.target);
			}).transition(t)
				.attr("fill-opacity", d => +labelVisible(d.target))
				.attrTween("transform", d => () => labelTransform(d.current));
	}

	function arcVisible(d) {
		return d.y1 <= 3 && d.y0 >= 1 && d.x1 > d.x0;
	}

	function labelVisible(d) {
		return d.y1 <= 3 && d.y0 >= 1 && (d.y1 - d.y0) * (d.x1 - d.x0) > 0.03;
	}

	function labelTransform(d) {
		const x = (d.x0 + d.x1) / 2 * 180 / Math.PI;
		const y = (d.y0 + d.y1) / 2 * radius;
		return `rotate(${x - 90}) translate(${y},0) rotate(${x < 180 ? 0 : 180})`;
	}

	// return svg.node();
})();