#外部 HTML ツールチップ

const config = {
  type: 'line',
  data: data,
  options: {
    interaction: {
      mode: 'index',
      intersect: false,
    },
    plugins: {
      title: {
        display: true,
        text: 'Chart.js Line Chart - External Tooltips'
      },
      tooltip: {
        enabled: false,
        position: 'nearest',
        external: externalTooltipHandler
      }
    }
  }
};

const DATA_COUNT = 7;
const NUMBER_CFG = {count: DATA_COUNT, min: -100, max: 100, decimals: 0};
const data = {
  labels: Utils.months({count: DATA_COUNT}),
  datasets: [
    {
      label: 'Dataset 1',
      data: Utils.numbers(NUMBER_CFG),
      fill: false,
      borderColor: Utils.CHART_COLORS.red,
      backgroundColor: Utils.transparentize(Utils.CHART_COLORS.red, 0.5),
    },
    {
      label: 'Dataset 2',
      data: Utils.numbers(NUMBER_CFG),
      fill: false,
      borderColor: Utils.CHART_COLORS.blue,
      backgroundColor: Utils.transparentize(Utils.CHART_COLORS.blue, 0.5),
    },
  ]
};

const getOrCreateTooltip = (chart) => {
  let tooltipEl = chart.canvas.parentNode.querySelector('div');
  if (!tooltipEl) {
    tooltipEl = document.createElement('div');
    tooltipEl.style.background = 'rgba(0, 0, 0, 0.7)';
    tooltipEl.style.borderRadius = '3px';
    tooltipEl.style.color = 'white';
    tooltipEl.style.opacity = 1;
    tooltipEl.style.pointerEvents = 'none';
    tooltipEl.style.position = 'absolute';
    tooltipEl.style.transform = 'translate(-50%, 0)';
    tooltipEl.style.transition = 'all .1s ease';
    const table = document.createElement('table');
    table.style.margin = '0px';
    tooltipEl.appendChild(table);
    chart.canvas.parentNode.appendChild(tooltipEl);
  }
  return tooltipEl;
};
const externalTooltipHandler = (context) => {
  // Tooltip Element
  const {chart, tooltip} = context;
  const tooltipEl = getOrCreateTooltip(chart);
  // Hide if no tooltip
  if (tooltip.opacity === 0) {
    tooltipEl.style.opacity = 0;
    return;
  }
  // Set Text
  if (tooltip.body) {
    const titleLines = tooltip.title || [];
    const bodyLines = tooltip.body.map(b => b.lines);
    const tableHead = document.createElement('thead');
    titleLines.forEach(title => {
      const tr = document.createElement('tr');
      tr.style.borderWidth = 0;
      const th = document.createElement('th');
      th.style.borderWidth = 0;
      const text = document.createTextNode(title);
      th.appendChild(text);
      tr.appendChild(th);
      tableHead.appendChild(tr);
    });
    const tableBody = document.createElement('tbody');
    bodyLines.forEach((body, i) => {
      const colors = tooltip.labelColors[i];
      const span = document.createElement('span');
      span.style.background = colors.backgroundColor;
      span.style.borderColor = colors.borderColor;
      span.style.borderWidth = '2px';
      span.style.marginRight = '10px';
      span.style.height = '10px';
      span.style.width = '10px';
      span.style.display = 'inline-block';
      const tr = document.createElement('tr');
      tr.style.backgroundColor = 'inherit';
      tr.style.borderWidth = 0;
      const td = document.createElement('td');
      td.style.borderWidth = 0;
      const text = document.createTextNode(body);
      td.appendChild(span);
      td.appendChild(text);
      tr.appendChild(td);
      tableBody.appendChild(tr);
    });
    const tableRoot = tooltipEl.querySelector('table');
    // Remove old children
    while (tableRoot.firstChild) {
      tableRoot.firstChild.remove();
    }
    // Add new children
    tableRoot.appendChild(tableHead);
    tableRoot.appendChild(tableBody);
  }
  const {offsetLeft: positionX, offsetTop: positionY} = chart.canvas;
  // Display, position, and set styles for font
  tooltipEl.style.opacity = 1;
  tooltipEl.style.left = positionX + tooltip.caretX + 'px';
  tooltipEl.style.top = positionY + tooltip.caretY + 'px';
  tooltipEl.style.font = tooltip.options.bodyFont.string;
  tooltipEl.style.padding = tooltip.options.padding + 'px ' + tooltip.options.padding + 'px';
};