feat: add usage stats parsing and fetching from /api/metrics/stats

tests/stats.test.ts

@@ -0,0 +1,52 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { fetchStats, parseStats, type UsageStats } from "../src/lib/stats";
+
+test("parseStats extracts totals and gen p95", () => {
+  const stats = parseStats({
+    total_requests: 1985,
+    total_input_tokens: 312327705,
+    total_output_tokens: 932710,
+    total_cache_tokens: 308144640,
+    gen_histogram: { p50: 341, p95: 378.86, p99: 392 },
+  });
+  assert.deepEqual(stats, { totalRequests: 1985, totalInputTokens: 312327705, totalOutputTokens: 932710, genP95: 378.86 });
+});
+
+test("parseStats defaults missing fields and rejects malformed input", () => {
+  assert.deepEqual(parseStats({}), { totalRequests: 0, totalInputTokens: 0, totalOutputTokens: 0, genP95: 0 });
+  assert.equal(parseStats({ total_requests: "nope" })!.totalRequests, 0);
+  assert.equal(parseStats(null), null);
+  assert.equal(parseStats("x"), null);
+});
+
+test("fetchStats calls /api/metrics/stats with a model query", async () => {
+  const calls: string[] = [];
+  const orig = globalThis.fetch;
+  globalThis.fetch = (async (url: RequestInfo | URL) => {
+    calls.push(String(url));
+    return { ok: true, json: async () => ({ total_requests: 7 }) } as unknown as Response;
+  }) as typeof fetch;
+  try {
+    await fetchStats({ baseUrl: "http://x" }, "DeepSeek-V4-Flash-0731");
+    assert.equal(calls[0], "http://x/api/metrics/stats?model=DeepSeek-V4-Flash-0731");
+  } finally {
+    globalThis.fetch = orig;
+  }
+});
+
+test("fetchStats omits the model query for 'all' and returns null on HTTP error", async () => {
+  const calls: string[] = [];
+  const orig = globalThis.fetch;
+  globalThis.fetch = (async (url: RequestInfo | URL) => {
+    calls.push(String(url));
+    return { ok: false, status: 500 } as unknown as Response;
+  }) as typeof fetch;
+  try {
+    const stats = await fetchStats({ baseUrl: "http://x" }, "all");
+    assert.equal(stats, null);
+    assert.equal(calls[0], "http://x/api/metrics/stats");
+  } finally {
+    globalThis.fetch = orig;
+  }
+});