Deduplicate duration and number formatting internals

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RaRBJFZKSTA7naHGuQHfnQ

tests/unit/module/formatDuration.test.js

@@ -0,0 +1,61 @@
+// The Lucia project.
+// Copyright 2026-2026 DSP, inc.  All rights reserved.
+// Authors:
+//   imacat.yang@dsp.im (imacat), 2026/7/5
+// AI assistance: Claude Code (Anthropic)
+
+import { describe, it, expect } from "vitest";
+import formatDuration, { pickDurationUnit } from "@/module/formatDuration.js";
+
+describe("formatDuration", () => {
+  it("formats a full cascade with the default separator", () => {
+    expect(formatDuration(93784)).toBe("1d 2h 3m 4s");
+  });
+
+  it("omits zero-valued units", () => {
+    expect(formatDuration(86400)).toBe("1d");
+    expect(formatDuration(3661)).toBe("1h 1m 1s");
+  });
+
+  it("returns an empty string when no unit qualifies", () => {
+    expect(formatDuration(0)).toBe("");
+    expect(formatDuration(NaN)).toBe("");
+  });
+
+  it("supports a custom separator", () => {
+    expect(formatDuration(90061, { separator: "" })).toBe("1d1h1m1s");
+  });
+
+  it("always appends seconds when alwaysSeconds is set", () => {
+    expect(formatDuration(0, { alwaysSeconds: true })).toBe("0s");
+    expect(formatDuration(60, { separator: "", alwaysSeconds: true })).toBe(
+      "1m0s",
+    );
+  });
+
+  it("truncates to maxUnits largest units", () => {
+    expect(formatDuration(93784, { maxUnits: 2 })).toBe("1d 2h");
+    expect(formatDuration(45, { maxUnits: 2 })).toBe("45s");
+  });
+});
+
+describe("pickDurationUnit", () => {
+  it("picks the largest unit reached by the value", () => {
+    expect(pickDurationUnit(86400).symbol).toBe("d");
+    expect(pickDurationUnit(3600).symbol).toBe("h");
+    expect(pickDurationUnit(60).symbol).toBe("m");
+    expect(pickDurationUnit(59).symbol).toBe("s");
+  });
+
+  it("requires strictly more than one unit when exclusive", () => {
+    expect(pickDurationUnit(86400, true).symbol).toBe("h");
+    expect(pickDurationUnit(86401, true).symbol).toBe("d");
+    expect(pickDurationUnit(60, true).symbol).toBe("s");
+    expect(pickDurationUnit(61, true).symbol).toBe("m");
+  });
+
+  it("falls back to seconds for zero and negative values", () => {
+    expect(pickDurationUnit(0).symbol).toBe("s");
+    expect(pickDurationUnit(-100).symbol).toBe("s");
+  });
+});