tech-log-frontend/scripts/test-performance.ts

import { spawn } from "node:child_process";
import { mkdir, readFile } from "node:fs/promises";
import { performance } from "node:perf_hooks";
import process from "node:process";

import { chromium } from "@playwright/test";

import { evaluateLabBudget } from "../src/application/policies/performance-budgets.ts";
import { ROUTE_REGISTRY } from "../src/features/installed-feature-contracts.ts";
import { labPerformanceArtifactSchema } from "./contracts/release-artifacts.ts";
import { writeValidatedJsonArtifact } from "./lib/validated-json-artifact.ts";

type ContractPerformanceEvidence = {
  lcpMs: number;
  cls: number;
};

type ContractPerformanceWindow = Window & {
  __contractPerformance?: ContractPerformanceEvidence;
};

type LayoutShiftEntry = PerformanceEntry & {
  hadRecentInput: boolean;
  value: number;
};

const server = spawn(
  "corepack",
  ["pnpm", "preview", "--host", "127.0.0.1", "--port", "4173"],
  { stdio: "ignore" },
);
const baseUrl = "http://127.0.0.1:4173";

async function waitForServer() {
  for (let attempt = 0; attempt < 50; attempt += 1) {
    try {
      const response = await fetch(baseUrl);
      if (response.ok) return;
    } catch {
      // The bounded retry loop handles startup races.
    }
    await new Promise((resolve) => setTimeout(resolve, 100));
  }
  throw new Error("Preview server did not become ready.");
}

try {
  await waitForServer();
  const release = JSON.parse(
    await readFile("dist/release-manifest.json", "utf8"),
  );
  const thresholds = JSON.parse(
    await readFile("config/performance/budgets.json", "utf8"),
  ).lab;
  const browser = await chromium.launch();
  try {
    const context = await browser.newContext({
      viewport: { width: 1280, height: 720 },
    });
    const page = await context.newPage();
    const cdp = await context.newCDPSession(page);
    await cdp.send("Network.enable");
    await cdp.send("Network.emulateNetworkConditions", {
      offline: false,
      latency: 40,
      downloadThroughput: 200_000,
      uploadThroughput: 93_750,
      connectionType: "cellular4g",
    });
    await cdp.send("Emulation.setCPUThrottlingRate", { rate: 4 });
    await page.addInitScript(() => {
      const evidence = { lcpMs: 0, cls: 0 };
      (window as ContractPerformanceWindow).__contractPerformance = evidence;
      new PerformanceObserver((list) => {
        for (const entry of list.getEntries()) evidence.lcpMs = entry.startTime;
      }).observe({ type: "largest-contentful-paint", buffered: true });
      new PerformanceObserver((list) => {
        for (const entry of list.getEntries()) {
          const layoutShift = entry as LayoutShiftEntry;
          if (!layoutShift.hadRecentInput) {
            evidence.cls += layoutShift.value;
          }
        }
      }).observe({ type: "layout-shift", buffered: true });
    });
    await page.goto(baseUrl, { waitUntil: "networkidle" });
    const target = ROUTE_REGISTRY.TECH_LOG_HOME;
    const interactionStarted = performance.now();
    // Template merge. The template clicked a navigation link here; this
    // product measures its own landing route, which `goto` already reached, so
    // there is no click and no `targetLabel`. The template's lesson is kept
    // because it applies to whatever click lands here next: Playwright matches
    // accessible names by substring, so a nav entry can also match a call to
    // action and resolve to two links — a strict-mode violation before the
    // first measurement, which produces no performance evidence at all.
    await page.getByRole("heading", { name: target.title }).waitFor();
    const namedInteractionMs = performance.now() - interactionStarted;
    const paint = await page.evaluate(
      () => (window as ContractPerformanceWindow).__contractPerformance,
    );
    if (!paint) {
      throw new Error("Browser performance evidence was not initialized.");
    }
    const contextMetadata = {
      runner: {
        platform: process.platform,
        architecture: process.arch,
        nodeVersion: process.version,
      },
      browser: { name: "chromium", version: await browser.version() },
      viewport: { width: 1280, height: 720 },
      network: {
        profile: "contract-fast-4g",
        latencyMs: 40,
        downloadBytesPerSecond: 200_000,
        uploadBytesPerSecond: 93_750,
      },
      cpu: { throttlingRate: 4 },
      cache: { state: "cold", isolation: "new-browser-context" },
      build: { buildId: release.buildId, releaseId: release.releaseId },
    };
    const metrics = {
      lcpMs: Math.round(paint.lcpMs),
      cls: Number(paint.cls.toFixed(4)),
      namedInteractionMs: Math.round(namedInteractionMs),
    };
    const result = evaluateLabBudget(
      { context: contextMetadata, metrics },
      thresholds,
    );
    const fixtures = [
      {
        name: "missing-context",
        passed: !evaluateLabBudget({ metrics }, thresholds).passed,
      },
      {
        name: "lcp-over-threshold",
        passed: !evaluateLabBudget(
          {
            context: contextMetadata,
            metrics: { ...metrics, lcpMs: thresholds.lcpMs + 1 },
          },
          thresholds,
        ).passed,
      },
    ];
    const passed = result.passed && fixtures.every((fixture) => fixture.passed);
    await mkdir("artifacts/performance", { recursive: true });
    await writeValidatedJsonArtifact({
      path: "artifacts/performance/lab.json",
      schema: labPerformanceArtifactSchema,
      value: {
        schemaVersion: 1,
        generatedAt: new Date().toISOString(),
        context: contextMetadata,
        metrics,
        thresholds,
        fixtures,
        passed,
      },
    });
    if (!passed) {
      throw new Error(`Lab performance failed: ${JSON.stringify(metrics)}`);
    }
    process.stdout.write(
      `Lab performance: PASS (LCP ${metrics.lcpMs}ms, CLS ${metrics.cls}, interaction ${metrics.namedInteractionMs}ms)\n`,
    );
  } finally {
    await browser.close();
  }
} finally {
  server.kill("SIGTERM");
}