Web vitals: prefer external RUM

lib/server/webVitals/localFileStore.ts

@@ -0,0 +1,115 @@
+import fs from "fs";
+import path from "path";
+import { logger } from "../../logger";
+
+const WEB_VITALS_DIR = path.join(process.cwd(), ".next", "web-vitals");
+
+export interface WebVitalData {
+  metric: string;
+  data: {
+    value: number;
+    rating: string;
+  };
+  url: string;
+  userAgent: string;
+  timestamp: string;
+  receivedAt: string;
+}
+
+export interface WebVitalMetrics {
+  [metric: string]: {
+    count: number;
+    average: number;
+    min: number;
+    max: number;
+    goodCount: number;
+    needsImprovementCount: number;
+    poorCount: number;
+    lastUpdated: string;
+  };
+}
+
+function ensureWebVitalsDir(): void {
+  if (!fs.existsSync(WEB_VITALS_DIR)) {
+    fs.mkdirSync(WEB_VITALS_DIR, { recursive: true });
+  }
+}
+
+export function appendLocalWebVital(vitalsData: WebVitalData): void {
+  ensureWebVitalsDir();
+  const filePath = path.join(WEB_VITALS_DIR, `${vitalsData.metric}.json`);
+  let existingData: WebVitalData[] = [];
+
+  if (fs.existsSync(filePath)) {
+    try {
+      const fileContent = fs.readFileSync(filePath, "utf8");
+      existingData = JSON.parse(fileContent) as WebVitalData[];
+    } catch (error) {
+      const err = error as Error;
+      logger.warn("Could not parse existing vitals data:", err.message);
+    }
+  }
+
+  existingData.push(vitalsData);
+
+  if (existingData.length > 100) {
+    existingData = existingData.slice(-100);
+  }
+
+  fs.writeFileSync(filePath, JSON.stringify(existingData, null, 2));
+}
+
+export function readLocalAggregatedMetrics(): WebVitalMetrics {
+  const metrics: WebVitalMetrics = {};
+
+  if (!fs.existsSync(WEB_VITALS_DIR)) {
+    return metrics;
+  }
+
+  const files = fs.readdirSync(WEB_VITALS_DIR);
+
+  files.forEach((file) => {
+    if (!file.endsWith(".json")) return;
+    const metric = file.replace(".json", "");
+    let data: WebVitalData[];
+    try {
+      const fileContent = fs.readFileSync(
+        path.join(WEB_VITALS_DIR, file),
+        "utf8",
+      );
+      data = JSON.parse(fileContent) as WebVitalData[];
+    } catch (error) {
+      logger.warn(
+        `Skipping corrupt web vitals file ${file}:`,
+        (error as Error).message,
+      );
+      return;
+    }
+
+    if (data.length === 0) return;
+
+    const values = data
+      .map((d) => d.data.value)
+      .filter((v) => v !== undefined);
+    const ratings = data
+      .map((d) => d.data.rating)
+      .filter((r) => r !== undefined);
+
+    metrics[metric] = {
+      count: data.length,
+      average:
+        values.length > 0
+          ? Math.round(values.reduce((a, b) => a + b, 0) / values.length)
+          : 0,
+      min: values.length > 0 ? Math.min(...values) : 0,
+      max: values.length > 0 ? Math.max(...values) : 0,
+      goodCount: ratings.filter((r) => r === "good").length,
+      needsImprovementCount: ratings.filter((r) => r === "needs-improvement")
+        .length,
+      poorCount: ratings.filter((r) => r === "poor").length,
+      lastUpdated: data[data.length - 1]?.receivedAt || "",
+    };
+  });
+
+  return metrics;
+}