refactor(replay-ui): extract metrics formatters into lib module

replay-ui/src/lib/metrics-format.ts

@@ -0,0 +1,43 @@
+const MB = 1024 * 1024;
+
+export function formatHeap(bytes: number): string {
+  if (bytes <= 0) return "0B";
+  if (bytes < MB) return `${Math.round(bytes / 1024)}K`;
+  if (bytes < 1024 * MB) return `${Math.round(bytes / MB)}M`;
+  return `${(bytes / (1024 * MB)).toFixed(1)}G`;
+}
+
+export function formatTime(millis: number): string {
+  const safe = Math.max(0, Math.floor(millis));
+  const seconds = Math.floor(safe / 1000);
+  const mm = String(Math.floor(seconds / 60)).padStart(2, "0");
+  const ss = String(seconds % 60).padStart(2, "0");
+  return `${mm}:${ss}`;
+}
+
+export function fractionFor(index: number, count: number): number {
+  if (count <= 1) return 0.5;
+  return index / (count - 1);
+}
+
+export function buildPath<T>(
+  samples: T[],
+  getValue: (sample: T) => number | undefined,
+  ceiling: number,
+): string {
+  const segments: string[] = [];
+  let pendingCommand = "M";
+  samples.forEach((sample, index) => {
+    const value = getValue(sample);
+    if (value === undefined) {
+      pendingCommand = "M";
+      return;
+    }
+    const x = fractionFor(index, samples.length);
+    const ratio = ceiling === 0 ? 0 : Math.min(value / ceiling, 1);
+    const y = 1 - ratio;
+    segments.push(`${pendingCommand}${x.toFixed(4)},${y.toFixed(4)}`);
+    pendingCommand = "L";
+  });
+  return segments.join(" ");
+}

replay-ui/src/panels/MetricsChart.tsx

@@ -1,5 +1,11 @@
 import { useState } from "react";
 import type { Metrics } from "../types";
+import {
+  buildPath,
+  formatHeap,
+  formatTime,
+  fractionFor,
+} from "../lib/metrics-format";
 import "./MetricsChart.css";
 
 export interface MetricsSample {
@@ -15,50 +21,6 @@ export interface MetricsChartProps {
   runStartMillis?: number;
 }
 
-const MB = 1024 * 1024;
-
-function formatHeap(bytes: number): string {
-  if (bytes <= 0) return "0B";
-  if (bytes < MB) return `${Math.round(bytes / 1024)}K`;
-  if (bytes < 1024 * MB) return `${Math.round(bytes / MB)}M`;
-  return `${(bytes / (1024 * MB)).toFixed(1)}G`;
-}
-
-function formatTime(millis: number): string {
-  const safe = Math.max(0, Math.floor(millis));
-  const seconds = Math.floor(safe / 1000);
-  const mm = String(Math.floor(seconds / 60)).padStart(2, "0");
-  const ss = String(seconds % 60).padStart(2, "0");
-  return `${mm}:${ss}`;
-}
-
-function fractionFor(index: number, count: number): number {
-  if (count <= 1) return 0.5;
-  return index / (count - 1);
-}
-
-function buildPath(
-  samples: MetricsSample[],
-  getValue: (sample: MetricsSample) => number | undefined,
-  ceiling: number,
-): string {
-  const segments: string[] = [];
-  let pendingCommand = "M";
-  samples.forEach((sample, index) => {
-    const value = getValue(sample);
-    if (value === undefined) {
-      pendingCommand = "M";
-      return;
-    }
-    const x = fractionFor(index, samples.length);
-    const ratio = ceiling === 0 ? 0 : Math.min(value / ceiling, 1);
-    const y = 1 - ratio;
-    segments.push(`${pendingCommand}${x.toFixed(4)},${y.toFixed(4)}`);
-    pendingCommand = "L";
-  });
-  return segments.join(" ");
-}
-
 interface LaneDot {
   key: number | string;
   x: number;