const diameter = 451.0;
const dists = [7.13, 16.68, 97.06, 106.62, 159.66, 169.22];
const wire_width = 1.56;
const sectors = ['20', '1', '18', '4', '13', '6', '10', '15', '2', '17',
	'3', '19', '7', '16', '8', '11', '14', '9', '12', '5'];

const c_black = '#272b2c';
const c_white = '#fbe3ba';
const c_red = '#f6302f';
const c_green = '#22912d';
const c_wire = '#909ca0';
const c_wire_inner = '#d8e6ec';

const svgns = 'http://www.w3.org/2000/svg';

function p2c(a, r) {
	const t = a * Math.PI / 180;
	return [r * Math.cos(t), r * Math.sin(t)];
}

function gen_arc(a1, a2, r1, r2, c) {
	const [x1, y1] = p2c(a1 === a2 ? 1 : a2, r1);
	const [x2, y2] = p2c(a1 === a2 ? 0 : a1, r1);
	const [x3, y3] = p2c(a1 === a2 ? 0 : a1, r2);
	const [x4, y4] = p2c(a1 === a2 ? 1 : a2, r2);

	const elem = document.createElementNS(svgns, 'path');
	elem.setAttribute('d',
		`M${x1} ${y1}` +
			`A${r1} ${r1} 0 0 0 ${x2} ${y2}` +
			(a1 === a2 ? `A${r1} ${r1} 0 1 0 ${x1} ${y1}` : '') +
			`L${x3} ${y3}` +
			`A${r2} ${r2} 0 0 1 ${x4} ${y4}` +
			(a1 === a2 ? `A${r2} ${r2} 0 1 1 ${x3} ${y3}` : '') +
			'Z');
	elem.setAttribute('fill', c)
	return elem;
}

function gen_segment(a, r1, r2, c) {
	return gen_arc(a - 9, a + 9, r1, r2, c);
}

function gen_ring(r, w, c) {
	return gen_arc(0, 0, r - w/2, r + w/2, c);
}

function gen_circle(r, c) {
	const elem = document.createElementNS(svgns, 'circle');
	elem.setAttribute('r', r);
	elem.setAttribute('fill', c)
	return elem;
}

function gen_line(a, r1, r2, w, c) {
	const [x1, y1] = p2c(a, r1);
	const [x2, y2] = p2c(a, r2);

	const elem = document.createElementNS(svgns, 'line');
	elem.setAttribute('x1', x1);
	elem.setAttribute('y1', y1);
	elem.setAttribute('x2', x2);
	elem.setAttribute('y2', y2);
	elem.setAttribute('stroke', c);
	elem.setAttribute('stroke-width', w);
	return elem;
}

function draw_spider(board) {
	for (let i = 5; i > 1; --i) {
		board.appendChild(gen_ring(dists[i], wire_width, c_wire));
		board.appendChild(gen_ring(dists[i], wire_width/2, c_wire_inner));
	}

	for (let i = 20; i > 0; --i) {
		let a = 90 - (i * 18) - 9;
		if (a < 0) a += 360;
		board.appendChild(gen_line(a, dists[1], dists[5] + 10,
			wire_width, c_wire));
		board.appendChild(gen_line(a, dists[1], dists[5] + 10 - wire_width/4,
			wire_width/2, c_wire_inner));
	}

	for (let i = 1; i >= 0; --i) {
		board.appendChild(gen_ring(dists[i], wire_width, c_wire));
		board.appendChild(gen_ring(dists[i], wire_width/2, c_wire_inner));
	}
}

function draw_numbers(board) {
	board.appendChild(gen_ring(diameter/2 - wire_width*4, wire_width, '#ddd'));

	const r = diameter/2 - 33/2;
	for (let i = 0; i < 20; ++i) {
		let a = 90 - (i * 18);
		if (a < 0) a += 360;
		const [x, y] = p2c(a, r);

		const elem = document.createElementNS(svgns, 'text');
		elem.textContent = sectors[i];
		elem.setAttribute('font-size', '33');
		elem.setAttribute('fill',  '#fff');
		elem.setAttribute('transform',  `scale(1 -1) translate(${x} ${-y}) ` +
			`rotate(${a <= 180 ? 90 - a : 270 - a})`);
		elem.setAttribute('text-anchor',  'middle');
		elem.setAttribute('dominant-baseline',  'central');
		board.appendChild(elem);
	}
}

function draw_board() {
	const board = document.getElementById('dartboard');
	const points = document.getElementById('dartboard-points');

	const r = diameter/2;
	board.setAttribute('transform', `translate(${r} ${r}) scale(1 -1)`);
	points.setAttribute('transform', `translate(${r} ${r}) scale(1 -1)`);
	board.appendChild(gen_circle(r, c_black));

	for (let i = 5; i > 1; --i) {
		for (let j = 0; j < 20; ++j) {
			let a = 90 - (j * 18);
			if (a < 0) a += 360;

			const elem = gen_segment(a, dists[i-1], dists[i],
				i%2 ? (j%2 ? c_green : c_red) : (j%2 ? c_white : c_black));
			board.appendChild(elem);
		}
	}

	board.appendChild(gen_circle(dists[1], c_green));
	board.appendChild(gen_circle(dists[0], c_red));
	draw_spider(board);
	draw_numbers(board);
}

function draw_point(x, y) {
	const points = document.getElementById('dartboard-points');
	elem = gen_circle(8, '#33f');
	elem.setAttribute('cx', x);
	elem.setAttribute('cy', y);
	elem.setAttribute('stroke', '#ff0');
	elem.setAttribute('stroke-width', '2');
	points.appendChild(elem);
}

function clear_points() {
	document.getElementById('dartboard-points').textContent = '';
}

document.addEventListener('DOMContentLoaded', () => draw_board());