#カスタムツールチップコンテンツ

const config = {
  type: 'line',
  data: data,
  options: {
    interaction: {
      intersect: false,
      mode: 'index',
    },
    plugins: {
      tooltip: {
        callbacks: {
          footer: footer,
        }
      }
    }
  }
};

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 footer = (tooltipItems) => {
  let sum = 0;
  tooltipItems.forEach(function(tooltipItem) {
    sum += tooltipItem.parsed.y;
  });
  return 'Sum: ' + sum;
};