Add metrics, request logs, and graceful shutdown

src/services/metrics.ts

@@ -0,0 +1,57 @@
+import type { CountResult } from "../types.js";
+
+export class Metrics {
+  private readonly requestCounts = new Map<string, number>();
+  private requestDurationMs = 0;
+  private scanCount = 0;
+  private scanDurationMs = 0;
+  private cachedScanCount = 0;
+  private countedFiles = 0;
+  private countedLines = 0;
+
+  recordRequest(route: string, status: number, durationMs: number): void {
+    const key = `${route}\u0000${status}`;
+    this.requestCounts.set(key, (this.requestCounts.get(key) ?? 0) + 1);
+    this.requestDurationMs += durationMs;
+  }
+
+  recordScan(result: CountResult): void {
+    this.scanCount += 1;
+    this.scanDurationMs += result.durationMs;
+    this.cachedScanCount += Number(result.cached);
+    this.countedFiles += result.fileCount;
+    this.countedLines += result.lineCount;
+  }
+
+  renderPrometheus(): string {
+    const lines = [
+      "# HELP loc_via_git_http_requests_total HTTP responses by route and status.",
+      "# TYPE loc_via_git_http_requests_total counter"
+    ];
+    for (const [key, count] of this.requestCounts) {
+      const [route, status] = key.split("\u0000");
+      lines.push(`loc_via_git_http_requests_total{route="${route}",status="${status}"} ${count}`);
+    }
+    lines.push(
+      "# HELP loc_via_git_http_request_duration_ms_total Total HTTP request duration in milliseconds.",
+      "# TYPE loc_via_git_http_request_duration_ms_total counter",
+      `loc_via_git_http_request_duration_ms_total ${this.requestDurationMs}`,
+      "# HELP loc_via_git_scans_total Completed LOC scans.",
+      "# TYPE loc_via_git_scans_total counter",
+      `loc_via_git_scans_total ${this.scanCount}`,
+      "# HELP loc_via_git_cached_scans_total Completed scans served from cache.",
+      "# TYPE loc_via_git_cached_scans_total counter",
+      `loc_via_git_cached_scans_total ${this.cachedScanCount}`,
+      "# HELP loc_via_git_scan_duration_ms_total Total scan duration in milliseconds.",
+      "# TYPE loc_via_git_scan_duration_ms_total counter",
+      `loc_via_git_scan_duration_ms_total ${this.scanDurationMs}`,
+      "# HELP loc_via_git_counted_files_total Files included in completed scan results.",
+      "# TYPE loc_via_git_counted_files_total counter",
+      `loc_via_git_counted_files_total ${this.countedFiles}`,
+      "# HELP loc_via_git_counted_lines_total Non-empty lines included in completed scan results.",
+      "# TYPE loc_via_git_counted_lines_total counter",
+      `loc_via_git_counted_lines_total ${this.countedLines}`
+    );
+    return `${lines.join("\n")}\n`;
+  }
+}