const tooltip = ((() => {
  const tip = d3.tip()
    .attr('class', 'd3-tip')
    .offset([50, 10]);
  return (svgSelection, state) => {
    tip.html(d => [
      `<div><strong>${state.radius}: </strong>`,
      `<span>${d[state.radius]}</span></div>`,
      `<div><strong>${state.x}: </strong>`,
      `<span>${d[state.x]}</span></div>`,
      `<div><strong>${state.y}: </strong>`,
      `<span>${d[state.y]}</span></div>`,
      `<div><strong>${state.color}: </strong>`,
      `<span>${d[state.color]}</span></div>`,
    ].join(''));
    svgSelection.call(tip);
    return {
      show: tip.show,
      hide: tip.hide,
    };
  };
})());