fix(web): byte sizes just under the next unit no longer read "1024 KB"

apps/web/src/lib/formatBytes.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vite-plus/test";
+
+import { formatBytes } from "./formatBytes";
+
+describe("formatBytes", () => {
+  it.each([
+    [0, "0 B"],
+    [1_023, "1023 B"],
+    [1_024, "1.00 KB"],
+    [1_536, "1.50 KB"],
+    [1_047_552, "1023 KB"],
+    [1_048_576, "1.00 MB"],
+    [5 * 1_024 ** 4, "5.00 TB"],
+    [2_048 * 1_024 ** 4, "2048 TB"],
+  ])("formats %d bytes as %s", (value, label) => {
+    expect(formatBytes(value)).toBe(label);
+  });
+
+  it.each([
+    [1_023.6, "1.00 KB"],
+    [1_048_100, "1.00 MB"],
+    [1_073_217_536, "1.00 GB"],
+  ])("moves %d bytes to the next unit when rounding reaches 1024", (value, label) => {
+    expect(formatBytes(value)).toBe(label);
+  });
+});

apps/web/src/lib/formatBytes.ts

@@ -1,11 +1,16 @@
+function formatScaled(value: number): string {
+  return value.toFixed(value >= 100 ? 0 : value >= 10 ? 1 : 2);
+}
+
 export function formatBytes(value: number): string {
-  if (value < 1_024) return `${Math.round(value)} B`;
+  if (Math.round(value) < 1_024) return `${Math.round(value)} B`;
   const units = ["KB", "MB", "GB", "TB"] as const;
-  let next = value;
-  let unitIndex = -1;
-  do {
+  let next = value / 1_024;
+  let unitIndex = 0;
+  // Pick the unit after rounding, so 1023.6 KB reads "1.00 MB", not "1024 KB".
+  while (Number(formatScaled(next)) >= 1_024 && unitIndex < units.length - 1) {
     next /= 1_024;
     unitIndex += 1;
-  } while (next >= 1_024 && unitIndex < units.length - 1);
-  return `${next.toFixed(next >= 100 ? 0 : next >= 10 ? 1 : 2)} ${units[unitIndex]}`;
+  }
+  return `${formatScaled(next)} ${units[unitIndex]}`;
 }