Feat: tooltip improvement and line draw

web/global.d.ts

@@ -17,3 +17,9 @@ declare module "styled-components" {
   //eslint-disable-next-line @typescript-eslint/no-empty-interface
   export interface DefaultTheme extends Theme {}
 }
+
+declare module "chart.js" {
+  interface TooltipPositionerMap {
+    custom: TooltipPositionerFunction<ChartType>;
+  }
+}

web/src/pages/Home/CourtOverview/Chart.tsx

@@ -1,6 +1,7 @@
 import React, { useMemo, useState } from "react";
 import styled from "styled-components";
 
+import { Tooltip } from "chart.js";
 import { formatUnits } from "viem";
 
 import { DropdownSelect } from "@kleros/ui-components-library";
@@ -101,4 +102,23 @@ const Chart: React.FC = () => {
   );
 };
 
+// custom positioner for tooltip, we need dynamic top positioning, which is not available by default.
+Tooltip.positioners.custom = function (elements) {
+  const tooltip = this;
+  const height = tooltip.chart.chartArea.height;
+  const width = tooltip.chart.chartArea.width;
+
+  const x = elements[0]?.element.x;
+  const y = elements[0]?.element.y;
+  const isAtTop = height > y + tooltip.height;
+  const isAtEnd = width < x + tooltip.width;
+
+  return {
+    x: elements[0]?.element.x,
+    y: elements[0]?.element.y,
+    xAlign: isAtTop ? (isAtEnd ? "right" : "left") : "center",
+    yAlign: isAtTop ? "center" : "bottom",
+  };
+};
+
 export default Chart;

web/src/pages/Home/CourtOverview/TimeSeriesChart.tsx

@@ -1,7 +1,16 @@
 import React from "react";
 import styled, { useTheme } from "styled-components";
 
-import { Chart as ChartJS, CategoryScale, LinearScale, PointElement, LineElement, TimeScale, Tooltip } from "chart.js";
+import {
+  Chart as ChartJS,
+  CategoryScale,
+  LinearScale,
+  PointElement,
+  LineElement,
+  TimeScale,
+  Tooltip,
+  ScriptableContext,
+} from "chart.js";
 import { Line } from "react-chartjs-2";
 import "chartjs-adapter-moment";
 
@@ -51,6 +60,7 @@ const TimeSeriesChart: React.FC<ITimeSeriesChart> = ({ data }) => {
     },
     plugins: {
       tooltip: {
+        position: "custom",
         backgroundColor: theme.whiteBackground,
         titleColor: theme.primaryText,
         borderColor: theme.stroke,
@@ -74,18 +84,47 @@ const TimeSeriesChart: React.FC<ITimeSeriesChart> = ({ data }) => {
               datasets: [
                 {
                   data,
-                  borderColor: theme.primaryBlue,
+                  // borderColor: theme.primaryBlue,
                   stepped: true,
                   cubicInterpolationMode: "monotone",
+                  borderColor: (context: ScriptableContext<"line">) => {
+                    const ctx = context.chart.ctx;
+                    const gradient = ctx.createLinearGradient(0, 0, 0, 200);
+                    gradient.addColorStop(0, theme.primaryBlue);
+                    gradient.addColorStop(1, theme.secondaryPurple);
+                    return gradient;
+                  },
                 },
               ],
             },
             options,
           }}
+          plugins={[
+            {
+              id: "line-draw",
+              afterDatasetsDraw: (chart) => {
+                if (chart.tooltip?._active?.length) {
+                  const x = chart.tooltip._active[0].element.x;
+                  const y = chart.tooltip._active[0].element.y;
+                  const yAxis = chart.scales.y;
+
+                  const ctx = chart.ctx;
+                  ctx.save();
+                  ctx.beginPath();
+                  ctx.moveTo(x, y);
+                  ctx.lineTo(x, yAxis.bottom);
+                  ctx.lineWidth = 1;
+                  ctx.strokeStyle = theme.secondaryPurple;
+                  ctx.setLineDash([4, 4]);
+                  ctx.stroke();
+                  ctx.restore();
+                }
+              },
+            },
+          ]}
         />
       }
     </LineContainer>
   );
 };
-
 export default TimeSeriesChart;