feat: add extensive test suite

app/api/health/handler.ts

@@ -0,0 +1,57 @@
+export type HealthCheck = () => Promise<Response | boolean>;
+
+type HealthRedis = {
+  ping(): Promise<unknown>;
+  exists(key: string): Promise<number | boolean>;
+  get(key: string): Promise<string | null>;
+  setex(key: string, ttl: number, value: string): Promise<unknown>;
+};
+
+const checkResult = async (check: HealthCheck) => {
+  try {
+    const result = await check();
+    return result instanceof Response ? result.ok : !!result;
+  } catch {
+    return false;
+  }
+};
+
+export function createHealthHandler({
+  redis,
+  checks,
+}: {
+  redis: HealthRedis;
+  checks: Record<string, HealthCheck>;
+}) {
+  return async function GET() {
+    const red = await redis
+      .ping()
+      .then(() => true)
+      .catch(() => false);
+
+    const entries = await Promise.all(
+      Object.entries(checks).map(async ([name, check]) => {
+        const key = `health:${name}`;
+        if (red) {
+          try {
+            if (await redis.exists(key))
+              return [name, (await redis.get(key)) === "ok"] as const;
+          } catch {}
+        }
+
+        const healthy = await checkResult(check);
+        if (red && healthy) {
+          try {
+            await redis.setex(key, 900, "ok");
+          } catch {}
+        }
+        return [name, healthy] as const;
+      }),
+    );
+    const results = Object.fromEntries(entries) as Record<string, boolean>;
+    return Response.json(
+      { red, ...results },
+      { status: red && results.database ? 200 : 503 },
+    );
+  };
+}