1 files changed, 28 insertions, 0 deletions
diff --git a/packages/frontend/src/utility/chart-vline.ts b/packages/frontend/src/utility/chart-vline.ts
new file mode 100644
index 0000000000..465ca591c6
--- /dev/null
+++ b/packages/frontend/src/utility/chart-vline.ts
@@ -0,0 +1,28 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { Plugin } from 'chart.js';
+
+export const chartVLine = (vLineColor: string) => ({
+	id: 'vLine',
+	beforeDraw(chart, args, options) {
+		if (chart.tooltip?._active?.length) {
+			const ctx = chart.ctx;
+			const xs = chart.tooltip._active.map(a => a.element.x);
+			const x = xs.reduce((a, b) => a + b, 0) / xs.length;
+			const topY = chart.scales.y.top;
+			const bottomY = chart.scales.y.bottom;
+
+			ctx.save();
+			ctx.beginPath();
+			ctx.moveTo(x, bottomY);
+			ctx.lineTo(x, topY);
+			ctx.lineWidth = 1;
+			ctx.strokeStyle = vLineColor;
+			ctx.stroke();
+			ctx.restore();
+		}
+	},
+}) as Plugin;